Sync to upstream/release/605 (#1118)

- Implemented [Require by String with Relative
Paths](https://github.com/luau-lang/rfcs/blob/master/docs/new-require-by-string-semantics.md)
RFC
- Implemented [Require by String with
Aliases](https://github.com/luau-lang/rfcs/blob/master/docs/require-by-string-aliases.md)
RFC with support for `paths` and `alias` arrays in .luarc
- Added SUBRK and DIVRK bytecode instructions to speed up
constant-number and constant/number operations
- Added `--vector-lib`, `--vector-ctor` and `--vector-type` options to
luau-compile to support code with vectors
 
New Solver
- Correctness fixes to subtyping
- Improvements to dataflow analysis

Native Code Generation
- Added bytecode analysis pass to predict type tags used in operations
- Fixed rare cases of numerical loops being generated without an
interrupt instruction
- Restored optimization data propagation into the linear block
- Duplicate buffer length checks are optimized away

Miscellaneous
- Small performance improvements to new non-strict mode
- Introduced more scripts for fuzzing Luau and processing the results,
including fuzzer build support for CMake

Co-authored-by: Alexander McCord <amccord@roblox.com>
Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: Aviral Goel <agoel@roblox.com>
Co-authored-by: David Cope <dcope@roblox.com>
Co-authored-by: Lily Brown <lbrown@roblox.com>
Co-authored-by: Vighnesh Vijay <vvijay@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

---------

Co-authored-by: Aaron Weiss <aaronweiss@roblox.com>
Co-authored-by: Alexander McCord <amccord@roblox.com>
Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: Aviral Goel <agoel@roblox.com>
Co-authored-by: David Cope <dcope@roblox.com>
Co-authored-by: Lily Brown <lbrown@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

Analysis/include/Luau/Constraint.h

@@ -49,8 +49,8 @@ struct InstantiationConstraint
     TypeId superType;
 };
 
-// iteratee is iterable
+// variables ~ iterate iterator
-// iterators is the iteration types.
+// Unpack the iterator, figure out what types it iterates over, and bind those types to variables.
 struct IterableConstraint
 {
     TypePackId iterator;

Analysis/include/Luau/ConstraintGenerator.h

@@ -225,6 +225,7 @@ private:
     Inference check(const ScopePtr& scope, AstExprConstantBool* bool_, std::optional<TypeId> expectedType, bool forceSingleton);
     Inference check(const ScopePtr& scope, AstExprLocal* local);
     Inference check(const ScopePtr& scope, AstExprGlobal* global);
+    Inference checkIndexName(const ScopePtr& scope, const RefinementKey* key, AstExpr* indexee, std::string index);
     Inference check(const ScopePtr& scope, AstExprIndexName* indexName);
     Inference check(const ScopePtr& scope, AstExprIndexExpr* indexExpr);
     Inference check(const ScopePtr& scope, AstExprFunction* func, std::optional<TypeId> expectedType, bool generalize);

Analysis/include/Luau/Error.h

@@ -372,13 +372,21 @@ struct CheckedFunctionCallError
     bool operator==(const CheckedFunctionCallError& rhs) const;
 };
 
+struct NonStrictFunctionDefinitionError
+{
+    std::string functionName;
+    std::string argument;
+    TypeId argumentType;
+    bool operator==(const NonStrictFunctionDefinitionError& rhs) const;
+};
+
 using TypeErrorData = Variant<TypeMismatch, UnknownSymbol, UnknownProperty, NotATable, CannotExtendTable, OnlyTablesCanHaveMethods,
     DuplicateTypeDefinition, CountMismatch, FunctionDoesNotTakeSelf, FunctionRequiresSelf, OccursCheckFailed, UnknownRequire,
     IncorrectGenericParameterCount, SyntaxError, CodeTooComplex, UnificationTooComplex, UnknownPropButFoundLikeProp, GenericError, InternalError,
     CannotCallNonFunction, ExtraInformation, DeprecatedApiUsed, ModuleHasCyclicDependency, IllegalRequire, FunctionExitsWithoutReturning,
     DuplicateGenericParameter, CannotInferBinaryOperation, MissingProperties, SwappedGenericTypeParameter, OptionalValueAccess, MissingUnionProperty,
     TypesAreUnrelated, NormalizationTooComplex, TypePackMismatch, DynamicPropertyLookupOnClassesUnsafe, UninhabitedTypeFamily,
-    UninhabitedTypePackFamily, WhereClauseNeeded, PackWhereClauseNeeded, CheckedFunctionCallError>;
+    UninhabitedTypePackFamily, WhereClauseNeeded, PackWhereClauseNeeded, CheckedFunctionCallError, NonStrictFunctionDefinitionError>;
 
 struct TypeErrorSummary
 {

Analysis/include/Luau/Subtyping.h

@@ -32,12 +32,17 @@ enum class SubtypingVariance
     // Used for an empty key. Should never appear in actual code.
     Invalid,
     Covariant,
+    // This is used to identify cases where we have a covariant + a
+    // contravariant reason and we need to merge them.
+    Contravariant,
     Invariant,
 };
 
 struct SubtypingReasoning
 {
+    // The path, relative to the _root subtype_, where subtyping failed.
     Path subPath;
+    // The path, relative to the _root supertype_, where subtyping failed.
     Path superPath;
     SubtypingVariance variance = SubtypingVariance::Covariant;
 
@@ -49,6 +54,9 @@ struct SubtypingReasoningHash
     size_t operator()(const SubtypingReasoning& r) const;
 };
 
+using SubtypingReasonings = DenseHashSet<SubtypingReasoning, SubtypingReasoningHash>;
+static const SubtypingReasoning kEmptyReasoning = SubtypingReasoning{TypePath::kEmpty, TypePath::kEmpty, SubtypingVariance::Invalid};
+
 struct SubtypingResult
 {
     bool isSubtype = false;
@@ -58,8 +66,7 @@ struct SubtypingResult
 
     /// The reason for isSubtype to be false. May not be present even if
     /// isSubtype is false, depending on the input types.
-    DenseHashSet<SubtypingReasoning, SubtypingReasoningHash> reasoning{
+    SubtypingReasonings reasoning{kEmptyReasoning};
-        SubtypingReasoning{TypePath::kEmpty, TypePath::kEmpty, SubtypingVariance::Invalid}};
 
     SubtypingResult& andAlso(const SubtypingResult& other);
     SubtypingResult& orElse(const SubtypingResult& other);
@@ -69,7 +76,6 @@ struct SubtypingResult
     SubtypingResult& withBothPath(TypePath::Path path);
     SubtypingResult& withSubPath(TypePath::Path path);
     SubtypingResult& withSuperPath(TypePath::Path path);
-    SubtypingResult& withVariance(SubtypingVariance variance);
 
     // Only negates the `isSubtype`.
     static SubtypingResult negate(const SubtypingResult& result);

Analysis/include/Luau/Unifier2.h

@@ -61,7 +61,7 @@ struct Unifier2
     bool unify(TypeId subTy, const UnionType* superUnion);
     bool unify(const IntersectionType* subIntersection, TypeId superTy);
     bool unify(TypeId subTy, const IntersectionType* superIntersection);
-    bool unify(const TableType* subTable, const TableType* superTable);
+    bool unify(TableType* subTable, const TableType* superTable);
     bool unify(const MetatableType* subMetatable, const MetatableType* superMetatable);
 
     // TODO think about this one carefully.  We don't do unions or intersections of type packs

Analysis/src/ConstraintGenerator.cpp

@@ -750,17 +750,18 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatForIn* forI
 
     for (AstLocal* var : forIn->vars)
     {
-        TypeId ty = nullptr;
-        if (var->annotation)
-            ty = resolveType(loopScope, var->annotation, /*inTypeArguments*/ false);
-        else
-            ty = freshType(loopScope);
-
-        loopScope->bindings[var] = Binding{ty, var->location};
-
         TypeId assignee = arena->addType(BlockedType{});
         variableTypes.push_back(assignee);
 
+        if (var->annotation)
+        {
+            TypeId annotationTy = resolveType(loopScope, var->annotation, /*inTypeArguments*/ false);
+            loopScope->bindings[var] = Binding{annotationTy, var->location};
+            addConstraint(scope, var->location, SubtypeConstraint{assignee, annotationTy});
+        }
+        else
+            loopScope->bindings[var] = Binding{assignee, var->location};
+
         DefId def = dfg->getDef(var);
         loopScope->lvalueTypes[def] = assignee;
     }
@@ -1439,9 +1440,6 @@ InferencePack ConstraintGenerator::checkPack(const ScopePtr& scope, AstExprCall*
     module->astOriginalCallTypes[call->func] = fnType;
     module->astOriginalCallTypes[call] = fnType;
 
-    TypeId instantiatedFnType = arena->addType(BlockedType{});
-    addConstraint(scope, call->location, InstantiationConstraint{instantiatedFnType, fnType});
-
     Checkpoint argBeginCheckpoint = checkpoint(this);
 
     std::vector<TypeId> args;
@@ -1740,12 +1738,11 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprGlobal* globa
     }
 }
 
-Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIndexName* indexName)
+Inference ConstraintGenerator::checkIndexName(const ScopePtr& scope, const RefinementKey* key, AstExpr* indexee, std::string index)
 {
-    TypeId obj = check(scope, indexName->expr).ty;
+    TypeId obj = check(scope, indexee).ty;
     TypeId result = arena->addType(BlockedType{});
 
-    const RefinementKey* key = dfg->getRefinementKey(indexName);
     if (key)
     {
         if (auto ty = lookup(scope.get(), key->def))
@@ -1754,7 +1751,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIndexName* in
         scope->rvalueRefinements[key->def] = result;
     }
 
-    addConstraint(scope, indexName->expr->location, HasPropConstraint{result, obj, indexName->index.value});
+    addConstraint(scope, indexee->location, HasPropConstraint{result, obj, std::move(index)});
 
     if (key)
         return Inference{result, refinementArena.proposition(key, builtinTypes->truthyType)};
@@ -1762,10 +1759,23 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIndexName* in
         return Inference{result};
 }
 
+Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIndexName* indexName)
+{
+    const RefinementKey* key = dfg->getRefinementKey(indexName);
+    return checkIndexName(scope, key, indexName->expr, indexName->index.value);
+}
+
 Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIndexExpr* indexExpr)
 {
+    if (auto constantString = indexExpr->index->as<AstExprConstantString>())
+    {
+        const RefinementKey* key = dfg->getRefinementKey(indexExpr);
+        return checkIndexName(scope, key, indexExpr->expr, constantString->value.data);
+    }
+
     TypeId obj = check(scope, indexExpr->expr).ty;
     TypeId indexType = check(scope, indexExpr->index).ty;
+
     TypeId result = freshType(scope);
 
     const RefinementKey* key = dfg->getRefinementKey(indexExpr);
@@ -3079,15 +3089,23 @@ struct GlobalPrepopulator : AstVisitor
     {
     }
 
+    bool visit(AstExprGlobal* global) override
+    {
+        if (auto ty = globalScope->lookup(global->name))
+        {
+            DefId def = dfg->getDef(global);
+            globalScope->lvalueTypes[def] = *ty;
+        }
+
+        return true;
+    }
+
     bool visit(AstStatFunction* function) override
     {
         if (AstExprGlobal* g = function->name->as<AstExprGlobal>())
         {
             TypeId bt = arena->addType(BlockedType{});
             globalScope->bindings[g->name] = Binding{bt};
-
-            DefId def = dfg->getDef(function->name);
-            globalScope->lvalueTypes[def] = bt;
         }
 
         return true;

Analysis/src/ConstraintSolver.cpp

@@ -1263,9 +1263,6 @@ bool ConstraintSolver::tryDispatch(const SetPropConstraint& c, NotNull<const Con
     if (isBlocked(subjectType))
         return block(subjectType, constraint);
 
-    if (!force && get<FreeType>(subjectType))
-        return block(subjectType, constraint);
-
     std::optional<TypeId> existingPropType = subjectType;
     for (const std::string& segment : c.path)
     {
@@ -1301,25 +1298,13 @@ bool ConstraintSolver::tryDispatch(const SetPropConstraint& c, NotNull<const Con
 
     if (get<FreeType>(subjectType))
     {
-        TypeId ty = freshType(arena, builtinTypes, constraint->scope);
+        /*
-
+         * This should never occur because lookupTableProp() will add bounds to
-        // Mint a chain of free tables per c.path
+         * any free types it encounters.  There will always be an
-        for (auto it = rbegin(c.path); it != rend(c.path); ++it)
+         * existingPropType if the subject is free.
-        {
+         */
-            TableType t{TableState::Free, TypeLevel{}, constraint->scope};
+        LUAU_ASSERT(false);
-            t.props[*it] = {ty};
+        return false;
-
-            ty = arena->addType(std::move(t));
-        }
-
-        LUAU_ASSERT(ty);
-
-        bind(subjectType, ty);
-        if (follow(c.resultType) != follow(ty))
-            bind(c.resultType, ty);
-        unblock(subjectType, constraint->location);
-        unblock(c.resultType, constraint->location);
-        return true;
     }
     else if (auto ttv = getMutable<TableType>(subjectType))
     {
@@ -1328,7 +1313,7 @@ bool ConstraintSolver::tryDispatch(const SetPropConstraint& c, NotNull<const Con
             LUAU_ASSERT(!subjectType->persistent);
 
             ttv->props[c.path[0]] = Property{c.propType};
-            bind(c.resultType, c.subjectType);
+            bind(c.resultType, subjectType);
             unblock(c.resultType, constraint->location);
             return true;
         }
@@ -1337,26 +1322,12 @@ bool ConstraintSolver::tryDispatch(const SetPropConstraint& c, NotNull<const Con
             LUAU_ASSERT(!subjectType->persistent);
 
             updateTheTableType(builtinTypes, NotNull{arena}, subjectType, c.path, c.propType);
-            bind(c.resultType, c.subjectType);
-            unblock(subjectType, constraint->location);
-            unblock(c.resultType, constraint->location);
-            return true;
-        }
-        else
-        {
-            bind(c.resultType, subjectType);
-            unblock(c.resultType, constraint->location);
-            return true;
         }
     }
-    else
+
-    {
+    bind(c.resultType, subjectType);
-        // Other kinds of types don't change shape when properties are assigned
+    unblock(c.resultType, constraint->location);
-        // to them. (if they allow properties at all!)
+    return true;
-        bind(c.resultType, subjectType);
-        unblock(c.resultType, constraint->location);
-        return true;
-    }
 }
 
 bool ConstraintSolver::tryDispatch(const SetIndexerConstraint& c, NotNull<const Constraint> constraint, bool force)
@@ -1908,6 +1879,7 @@ bool ConstraintSolver::tryDispatchIterableFunction(
     TypeId retIndex;
     if (isNil(firstIndexTy) || isOptional(firstIndexTy))
     {
+        // FIXME freshType is suspect here
         firstIndex = arena->addType(UnionType{{freshType(arena, builtinTypes, constraint->scope), builtinTypes->nilType}});
         retIndex = firstIndex;
     }
@@ -1949,7 +1921,7 @@ bool ConstraintSolver::tryDispatchIterableFunction(
         modifiedNextRetHead.push_back(*it);
 
     TypePackId modifiedNextRetPack = arena->addTypePack(std::move(modifiedNextRetHead), it.tail());
-    auto psc = pushConstraint(constraint->scope, constraint->location, PackSubtypeConstraint{c.variables, modifiedNextRetPack});
+    auto psc = pushConstraint(constraint->scope, constraint->location, UnpackConstraint{c.variables, modifiedNextRetPack});
     inheritBlocks(constraint, psc);
 
     return true;

Analysis/src/Error.cpp

@@ -533,6 +533,12 @@ struct ErrorConverter
         return "Function '" + e.checkedFunctionName + "' expects '" + toString(e.expected) + "' at argument #" + std::to_string(e.argumentIndex) +
                ", but got '" + Luau::toString(e.passed) + "'";
     }
+
+    std::string operator()(const NonStrictFunctionDefinitionError& e) const
+    {
+        return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' in function '" + e.functionName +
+               "' is used in a way that will run time error";
+    }
 };
 
 struct InvalidNameChecker
@@ -861,6 +867,11 @@ bool CheckedFunctionCallError::operator==(const CheckedFunctionCallError& rhs) c
            argumentIndex == rhs.argumentIndex;
 }
 
+bool NonStrictFunctionDefinitionError::operator==(const NonStrictFunctionDefinitionError& rhs) const
+{
+    return functionName == rhs.functionName && argument == rhs.argument && argumentType == rhs.argumentType;
+}
+
 std::string toString(const TypeError& error)
 {
     return toString(error, TypeErrorToStringOptions{});
@@ -1032,6 +1043,10 @@ void copyError(T& e, TypeArena& destArena, CloneState& cloneState)
         e.expected = clone(e.expected);
         e.passed = clone(e.passed);
     }
+    else if constexpr (std::is_same_v<T, NonStrictFunctionDefinitionError>)
+    {
+        e.argumentType = clone(e.argumentType);
+    }
     else
         static_assert(always_false_v<T>, "Non-exhaustive type switch");
 }

Analysis/src/IostreamHelpers.cpp

@@ -204,6 +204,9 @@ static void errorToString(std::ostream& stream, const T& err)
     else if constexpr (std::is_same_v<T, CheckedFunctionCallError>)
         stream << "CheckedFunctionCallError { expected = '" << toString(err.expected) << "', passed = '" << toString(err.passed)
                << "', checkedFunctionName = " << err.checkedFunctionName << ", argumentIndex = " << std::to_string(err.argumentIndex) << " }";
+    else if constexpr (std::is_same_v<T, NonStrictFunctionDefinitionError>)
+        stream << "NonStrictFunctionDefinitionError { functionName = '" + err.functionName + "', argument = '" + err.argument +
+                      "', argumentType = '" + toString(err.argumentType) + "' }";
     else
         static_assert(always_false_v<T>, "Non-exhaustive type switch");
 }

Analysis/src/NonStrictTypeChecker.cpp

@@ -14,6 +14,7 @@
 #include "Luau/Def.h"
 
 #include <iostream>
+#include <iterator>
 
 namespace Luau
 {
@@ -105,9 +106,10 @@ struct NonStrictContext
         return conj;
     }
 
-    void removeFromContext(const std::vector<DefId>& defs)
+    // Returns true if the removal was successful
+    bool remove(const DefId& def)
     {
-        // TODO: unimplemented
+        return context.erase(def.get()) == 1;
     }
 
     std::optional<TypeId> find(const DefId& def) const
@@ -138,6 +140,7 @@ struct NonStrictTypeChecker
     NotNull<const DataFlowGraph> dfg;
     DenseHashSet<TypeId> noTypeFamilyErrors{nullptr};
     std::vector<NotNull<Scope>> stack;
+    DenseHashMap<TypeId, TypeId> cachedNegations{nullptr};
 
     const NotNull<TypeCheckLimits> limits;
 
@@ -271,8 +274,22 @@ struct NonStrictTypeChecker
     {
         auto StackPusher = pushStack(block);
         NonStrictContext ctx;
-        for (AstStat* statement : block->body)
+
-            ctx = NonStrictContext::disjunction(builtinTypes, NotNull{&arena}, ctx, visit(statement));
+
+        for (auto it = block->body.rbegin(); it != block->body.rend(); it++)
+        {
+            AstStat* stat = *it;
+            if (AstStatLocal* local = stat->as<AstStatLocal>())
+            {
+                // Iterating in reverse order
+                // local x ; B generates the context of B without x
+                visit(local);
+                for (auto local : local->vars)
+                    ctx.remove(dfg->getDef(local));
+            }
+            else
+                ctx = NonStrictContext::disjunction(builtinTypes, NotNull{&arena}, visit(stat), ctx);
+        }
         return ctx;
     }
 
@@ -505,9 +522,7 @@ struct NonStrictTypeChecker
                     AstExpr* arg = call->args.data[i];
                     TypeId expectedArgType = argTypes[i];
                     DefId def = dfg->getDef(arg);
-                    // TODO: Cache negations created here!!!
+                    TypeId runTimeErrorTy = getOrCreateNegation(expectedArgType);
-                    // See Jira Ticket: https://roblox.atlassian.net/browse/CLI-87539
-                    TypeId runTimeErrorTy = arena.addType(NegationType{expectedArgType});
                     fresh.context[def.get()] = runTimeErrorTy;
                 }
 
@@ -537,8 +552,16 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstExprFunction* exprFn)
     {
+        // TODO: should a function being used as an expression generate a context without the arguments?
         auto pusher = pushStack(exprFn);
-        return visit(exprFn->body);
+        NonStrictContext remainder = visit(exprFn->body);
+        for (AstLocal* local : exprFn->args)
+        {
+            if (std::optional<TypeId> ty = willRunTimeErrorFunctionDefinition(local, remainder))
+                reportError(NonStrictFunctionDefinitionError{exprFn->debugname.value, local->name.value, *ty}, local->location);
+            remainder.remove(dfg->getDef(local));
+        }
+        return remainder;
     }
 
     NonStrictContext visit(AstExprTable* table)
@@ -603,6 +626,31 @@ struct NonStrictTypeChecker
 
         return {};
     }
+
+    std::optional<TypeId> willRunTimeErrorFunctionDefinition(AstLocal* fragment, const NonStrictContext& context)
+    {
+        DefId def = dfg->getDef(fragment);
+        if (std::optional<TypeId> contextTy = context.find(def))
+        {
+            SubtypingResult r1 = subtyping.isSubtype(builtinTypes->unknownType, *contextTy);
+            SubtypingResult r2 = subtyping.isSubtype(*contextTy, builtinTypes->unknownType);
+            if (r1.normalizationTooComplex || r2.normalizationTooComplex)
+                reportError(NormalizationTooComplex{}, fragment->location);
+            bool isUnknown = r1.isSubtype && r2.isSubtype;
+            if (isUnknown)
+                return {builtinTypes->unknownType};
+        }
+        return {};
+    }
+
+private:
+    TypeId getOrCreateNegation(TypeId baseType)
+    {
+        TypeId& cachedResult = cachedNegations[baseType];
+        if (!cachedResult)
+            cachedResult = arena.addType(NegationType{baseType});
+        return cachedResult;
+    };
 };
 
 void checkNonStrict(NotNull<BuiltinTypes> builtinTypes, NotNull<InternalErrorReporter> ice, NotNull<UnifierSharedState> unifierState,

Analysis/src/Normalize.cpp

@@ -2772,7 +2772,7 @@ bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there, Set<T
         return true;
     }
     else if (get<GenericType>(there) || get<FreeType>(there) || get<BlockedType>(there) || get<PendingExpansionType>(there) ||
-             get<TypeFamilyInstanceType>(there))
+             get<TypeFamilyInstanceType>(there) || get<LocalType>(there))
     {
         NormalizedType thereNorm{builtinTypes};
         NormalizedType topNorm{builtinTypes};
@@ -2780,6 +2780,10 @@ bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there, Set<T
         thereNorm.tyvars.insert_or_assign(there, std::make_unique<NormalizedType>(std::move(topNorm)));
         return intersectNormals(here, thereNorm);
     }
+    else if (auto lt = get<LocalType>(there))
+    {
+        return intersectNormalWithTy(here, lt->domain, seenSetTypes);
+    }
 
     NormalizedTyvars tyvars = std::move(here.tyvars);
 

Analysis/src/Subtyping.cpp

@@ -16,6 +16,8 @@
 
 #include <algorithm>
 
+LUAU_FASTFLAGVARIABLE(DebugLuauSubtypingCheckPathValidity, false);
+
 namespace Luau
 {
 
@@ -55,16 +57,69 @@ size_t SubtypingReasoningHash::operator()(const SubtypingReasoning& r) const
     return TypePath::PathHash()(r.subPath) ^ (TypePath::PathHash()(r.superPath) << 1) ^ (static_cast<size_t>(r.variance) << 1);
 }
 
+template<typename TID>
+static void assertReasoningValid(TID subTy, TID superTy, const SubtypingResult& result, NotNull<BuiltinTypes> builtinTypes)
+{
+    if (!FFlag::DebugLuauSubtypingCheckPathValidity)
+        return;
+
+    for (const SubtypingReasoning& reasoning : result.reasoning)
+    {
+        LUAU_ASSERT(traverse(subTy, reasoning.subPath, builtinTypes));
+        LUAU_ASSERT(traverse(superTy, reasoning.superPath, builtinTypes));
+    }
+}
+
+template<>
+void assertReasoningValid<TableIndexer>(TableIndexer subIdx, TableIndexer superIdx, const SubtypingResult& result, NotNull<BuiltinTypes> builtinTypes)
+{
+    // Empty method to satisfy the compiler.
+}
+
+static SubtypingReasonings mergeReasonings(const SubtypingReasonings& a, const SubtypingReasonings& b)
+{
+    SubtypingReasonings result{kEmptyReasoning};
+
+    for (const SubtypingReasoning& r : a)
+    {
+        if (r.variance == SubtypingVariance::Invariant)
+            result.insert(r);
+        else if (r.variance == SubtypingVariance::Covariant || r.variance == SubtypingVariance::Contravariant)
+        {
+            SubtypingReasoning inverseReasoning = SubtypingReasoning{
+                r.subPath, r.superPath, r.variance == SubtypingVariance::Covariant ? SubtypingVariance::Contravariant : SubtypingVariance::Covariant};
+            if (b.contains(inverseReasoning))
+                result.insert(SubtypingReasoning{r.subPath, r.superPath, SubtypingVariance::Invariant});
+            else
+                result.insert(r);
+        }
+    }
+
+    for (const SubtypingReasoning& r : b)
+    {
+        if (r.variance == SubtypingVariance::Invariant)
+            result.insert(r);
+        else if (r.variance == SubtypingVariance::Covariant || r.variance == SubtypingVariance::Contravariant)
+        {
+            SubtypingReasoning inverseReasoning = SubtypingReasoning{
+                r.subPath, r.superPath, r.variance == SubtypingVariance::Covariant ? SubtypingVariance::Contravariant : SubtypingVariance::Covariant};
+            if (a.contains(inverseReasoning))
+                result.insert(SubtypingReasoning{r.subPath, r.superPath, SubtypingVariance::Invariant});
+            else
+                result.insert(r);
+        }
+    }
+
+    return result;
+}
+
 SubtypingResult& SubtypingResult::andAlso(const SubtypingResult& other)
 {
     // If the other result is not a subtype, we want to join all of its
     // reasonings to this one. If this result already has reasonings of its own,
     // those need to be attributed here.
     if (!other.isSubtype)
-    {
+        reasoning = mergeReasonings(reasoning, other.reasoning);
-        for (const SubtypingReasoning& r : other.reasoning)
-            reasoning.insert(r);
-    }
 
     isSubtype &= other.isSubtype;
     // `|=` is intentional here, we want to preserve error related flags.
@@ -86,10 +141,7 @@ SubtypingResult& SubtypingResult::orElse(const SubtypingResult& other)
         if (other.isSubtype)
             reasoning.clear();
         else
-        {
+            reasoning = mergeReasonings(reasoning, other.reasoning);
-            for (const SubtypingReasoning& r : other.reasoning)
-                reasoning.insert(r);
-        }
     }
 
     isSubtype |= other.isSubtype;
@@ -162,19 +214,6 @@ SubtypingResult& SubtypingResult::withSuperPath(TypePath::Path path)
     return *this;
 }
 
-SubtypingResult& SubtypingResult::withVariance(SubtypingVariance variance)
-{
-    if (reasoning.empty())
-        reasoning.insert(SubtypingReasoning{TypePath::kEmpty, TypePath::kEmpty, variance});
-    else
-    {
-        for (auto& r : reasoning)
-            r.variance = variance;
-    }
-
-    return *this;
-}
-
 SubtypingResult SubtypingResult::negate(const SubtypingResult& result)
 {
     return SubtypingResult{
@@ -245,7 +284,10 @@ SubtypingResult Subtyping::isSubtype(TypeId subTy, TypeId superTy)
             result.isSubtype = false;
         }
 
-        result.andAlso(isCovariantWith(env, lowerBound, upperBound));
+        SubtypingResult boundsResult = isCovariantWith(env, lowerBound, upperBound);
+        boundsResult.reasoning.clear();
+
+        result.andAlso(boundsResult);
     }
 
     /* TODO: We presently don't store subtype test results in the persistent
@@ -370,7 +412,10 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         {
             SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy));
             if (semantic.isSubtype)
+            {
+                semantic.reasoning.clear();
                 result = semantic;
+            }
         }
     }
     else if (auto superIntersection = get<IntersectionType>(superTy))
@@ -382,7 +427,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         {
             SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy));
             if (semantic.isSubtype)
+            {
+                // Clear the semantic reasoning, as any reasonings within
+                // potentially contain invalid paths.
+                semantic.reasoning.clear();
                 result = semantic;
+            }
         }
     }
     else if (get<AnyType>(superTy))
@@ -411,9 +461,31 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     else if (auto p = get2<NegationType, NegationType>(subTy, superTy))
         result = isCovariantWith(env, p.first->ty, p.second->ty).withBothComponent(TypePath::TypeField::Negated);
     else if (auto subNegation = get<NegationType>(subTy))
+    {
         result = isCovariantWith(env, subNegation, superTy);
+        if (!result.isSubtype && !result.isErrorSuppressing && !result.normalizationTooComplex)
+        {
+            SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy));
+            if (semantic.isSubtype)
+            {
+                semantic.reasoning.clear();
+                result = semantic;
+            }
+        }
+    }
     else if (auto superNegation = get<NegationType>(superTy))
+    {
         result = isCovariantWith(env, subTy, superNegation);
+        if (!result.isSubtype && !result.isErrorSuppressing && !result.normalizationTooComplex)
+        {
+            SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy));
+            if (semantic.isSubtype)
+            {
+                semantic.reasoning.clear();
+                result = semantic;
+            }
+        }
+    }
     else if (auto subGeneric = get<GenericType>(subTy); subGeneric && variance == Variance::Covariant)
     {
         bool ok = bindGeneric(env, subTy, superTy);
@@ -449,6 +521,8 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     else if (auto p = get2<SingletonType, TableType>(subTy, superTy))
         result = isCovariantWith(env, p);
 
+    assertReasoningValid(subTy, superTy, result, builtinTypes);
+
     return cache(env, result, subTy, superTy);
 }
 
@@ -536,7 +610,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
                 for (size_t i = headSize; i < subHead.size(); ++i)
                     results.push_back(isCovariantWith(env, subHead[i], vt->ty)
                                           .withSubComponent(TypePath::Index{i})
-                                          .withSuperComponent(TypePath::TypeField::Variadic));
+                                          .withSuperPath(TypePath::PathBuilder().tail().variadic().build()));
             }
             else if (auto gt = get<GenericTypePack>(*superTail))
             {
@@ -664,19 +738,38 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
             iceReporter->ice("Subtyping test encountered the unexpected type pack: " + toString(*superTail));
     }
 
-    return SubtypingResult::all(results);
+    SubtypingResult result = SubtypingResult::all(results);
+    assertReasoningValid(subTp, superTp, result, builtinTypes);
+
+    return result;
 }
 
 template<typename SubTy, typename SuperTy>
 SubtypingResult Subtyping::isContravariantWith(SubtypingEnvironment& env, SubTy&& subTy, SuperTy&& superTy)
 {
     SubtypingResult result = isCovariantWith(env, superTy, subTy);
-    // If we don't swap the paths here, we will end up producing an invalid path
+    if (result.reasoning.empty())
-    // whenever we involve contravariance. We'll end up appending path
+        result.reasoning.insert(SubtypingReasoning{TypePath::kEmpty, TypePath::kEmpty, SubtypingVariance::Contravariant});
-    // components that should belong to the supertype to the subtype, and vice
+    else
-    // versa.
+    {
-    for (auto& reasoning : result.reasoning)
+        // If we don't swap the paths here, we will end up producing an invalid path
-        std::swap(reasoning.subPath, reasoning.superPath);
+        // whenever we involve contravariance. We'll end up appending path
+        // components that should belong to the supertype to the subtype, and vice
+        // versa.
+        for (auto& reasoning : result.reasoning)
+        {
+            std::swap(reasoning.subPath, reasoning.superPath);
+
+            // Also swap covariant/contravariant, since those are also the other way
+            // around.
+            if (reasoning.variance == SubtypingVariance::Covariant)
+                reasoning.variance = SubtypingVariance::Contravariant;
+            else if (reasoning.variance == SubtypingVariance::Contravariant)
+                reasoning.variance = SubtypingVariance::Covariant;
+        }
+    }
+
+    assertReasoningValid(subTy, superTy, result, builtinTypes);
 
     return result;
 }
@@ -684,7 +777,17 @@ SubtypingResult Subtyping::isContravariantWith(SubtypingEnvironment& env, SubTy&
 template<typename SubTy, typename SuperTy>
 SubtypingResult Subtyping::isInvariantWith(SubtypingEnvironment& env, SubTy&& subTy, SuperTy&& superTy)
 {
-    return isCovariantWith(env, subTy, superTy).andAlso(isContravariantWith(env, subTy, superTy)).withVariance(SubtypingVariance::Invariant);
+    SubtypingResult result = isCovariantWith(env, subTy, superTy).andAlso(isContravariantWith(env, subTy, superTy));
+    if (result.reasoning.empty())
+        result.reasoning.insert(SubtypingReasoning{TypePath::kEmpty, TypePath::kEmpty, SubtypingVariance::Invariant});
+    else
+    {
+        for (auto& reasoning : result.reasoning)
+            reasoning.variance = SubtypingVariance::Invariant;
+    }
+
+    assertReasoningValid(subTy, superTy, result, builtinTypes);
+    return result;
 }
 
 template<typename SubTy, typename SuperTy>
@@ -696,13 +799,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const TryP
 template<typename SubTy, typename SuperTy>
 SubtypingResult Subtyping::isContravariantWith(SubtypingEnvironment& env, const TryPair<const SubTy*, const SuperTy*>& pair)
 {
-    return isCovariantWith(env, pair.second, pair.first);
+    return isContravariantWith(env, pair.first, pair.second);
 }
 
 template<typename SubTy, typename SuperTy>
 SubtypingResult Subtyping::isInvariantWith(SubtypingEnvironment& env, const TryPair<const SubTy*, const SuperTy*>& pair)
 {
-    return isCovariantWith(env, pair).andAlso(isContravariantWith(pair)).withVariance(SubtypingVariance::Invariant);
+    return isInvariantWith(env, pair.first, pair.second);
 }
 
 /*
@@ -788,17 +891,17 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Nega
     if (is<NeverType>(negatedTy))
     {
         // ¬never ~ unknown
-        result = isCovariantWith(env, builtinTypes->unknownType, superTy);
+        result = isCovariantWith(env, builtinTypes->unknownType, superTy).withSubComponent(TypePath::TypeField::Negated);
     }
     else if (is<UnknownType>(negatedTy))
     {
         // ¬unknown ~ never
-        result = isCovariantWith(env, builtinTypes->neverType, superTy);
+        result = isCovariantWith(env, builtinTypes->neverType, superTy).withSubComponent(TypePath::TypeField::Negated);
     }
     else if (is<AnyType>(negatedTy))
     {
         // ¬any ~ any
-        result = isCovariantWith(env, negatedTy, superTy);
+        result = isCovariantWith(env, negatedTy, superTy).withSubComponent(TypePath::TypeField::Negated);
     }
     else if (auto u = get<UnionType>(negatedTy))
     {
@@ -808,8 +911,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Nega
 
         for (TypeId ty : u)
         {
-            NegationType negatedTmp{ty};
+            if (auto negatedPart = get<NegationType>(follow(ty)))
-            subtypings.push_back(isCovariantWith(env, &negatedTmp, superTy));
+                subtypings.push_back(isCovariantWith(env, negatedPart->ty, superTy).withSubComponent(TypePath::TypeField::Negated));
+            else
+            {
+                NegationType negatedTmp{ty};
+                subtypings.push_back(isCovariantWith(env, &negatedTmp, superTy));
+            }
         }
 
         result = SubtypingResult::all(subtypings);
@@ -823,7 +931,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Nega
         for (TypeId ty : i)
         {
             if (auto negatedPart = get<NegationType>(follow(ty)))
-                subtypings.push_back(isCovariantWith(env, negatedPart->ty, superTy));
+                subtypings.push_back(isCovariantWith(env, negatedPart->ty, superTy).withSubComponent(TypePath::TypeField::Negated));
             else
             {
                 NegationType negatedTmp{ty};
@@ -841,10 +949,10 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Nega
     // subtype of other stuff.
     else
     {
-        result = {false};
+        result = SubtypingResult{false}.withSubComponent(TypePath::TypeField::Negated);
     }
 
-    return result.withSubComponent(TypePath::TypeField::Negated);
+    return result;
 }
 
 SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const TypeId subTy, const NegationType* superNegation)
@@ -885,7 +993,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
             }
         }
 
-        result = SubtypingResult::all(subtypings);
+        return SubtypingResult::all(subtypings);
     }
     else if (auto i = get<IntersectionType>(negatedTy))
     {
@@ -904,7 +1012,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
             }
         }
 
-        result = SubtypingResult::any(subtypings);
+        return SubtypingResult::any(subtypings);
     }
     else if (auto p = get2<PrimitiveType, PrimitiveType>(subTy, negatedTy))
     {
@@ -986,8 +1094,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Tabl
     {
         std::vector<SubtypingResult> results;
         if (auto it = subTable->props.find(name); it != subTable->props.end())
-            results.push_back(isInvariantWith(env, it->second.type(), prop.type())
+            results.push_back(isInvariantWith(env, it->second.type(), prop.type()).withBothComponent(TypePath::Property(name)));
-                                  .withBothComponent(TypePath::Property(name)));
 
         if (subTable->indexer)
         {
@@ -1122,7 +1229,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Tabl
 {
     return isInvariantWith(env, subIndexer.indexType, superIndexer.indexType)
         .withBothComponent(TypePath::TypeField::IndexLookup)
-        .andAlso(isInvariantWith(env, superIndexer.indexResultType, subIndexer.indexResultType).withBothComponent(TypePath::TypeField::IndexResult));
+        .andAlso(isInvariantWith(env, subIndexer.indexResultType, superIndexer.indexResultType).withBothComponent(TypePath::TypeField::IndexResult));
 }
 
 SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const NormalizedType* subNorm, const NormalizedType* superNorm)
@@ -1249,12 +1356,11 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
 {
     std::vector<SubtypingResult> results;
 
-    size_t i = 0;
     for (TypeId subTy : subTypes)
     {
         results.emplace_back();
         for (TypeId superTy : superTypes)
-            results.back().orElse(isCovariantWith(env, subTy, superTy).withBothComponent(TypePath::Index{i++}));
+            results.back().orElse(isCovariantWith(env, subTy, superTy));
     }
 
     return SubtypingResult::all(results);

Analysis/src/ToString.cpp

@@ -1721,7 +1721,7 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
             std::string iteratorStr = tos(c.iterator);
             std::string variableStr = tos(c.variables);
 
-            return variableStr + " ~ Iterate<" + iteratorStr + ">";
+            return variableStr + " ~ iterate " + iteratorStr;
         }
         else if constexpr (std::is_same_v<T, NameConstraint>)
         {

Analysis/src/TypeChecker2.cpp

@@ -2467,6 +2467,8 @@ struct TypeChecker2
             std::string relation = "a subtype of";
             if (reasoning.variance == SubtypingVariance::Invariant)
                 relation = "exactly";
+            else if (reasoning.variance == SubtypingVariance::Contravariant)
+                relation = "a supertype of";
 
             std::string reason;
             if (reasoning.subPath == reasoning.superPath)

Analysis/src/TypePath.cpp

@@ -12,7 +12,6 @@
 #include <optional>
 #include <sstream>
 #include <type_traits>
-#include <unordered_set>
 
 LUAU_FASTFLAG(DebugLuauReadWriteProperties);
 
@@ -252,8 +251,6 @@ struct TraversalState
 
     TypeOrPack current;
     NotNull<BuiltinTypes> builtinTypes;
-
-    DenseHashSet<const void*> seen{nullptr};
     int steps = 0;
 
     void updateCurrent(TypeId ty)
@@ -268,18 +265,6 @@ struct TraversalState
         current = follow(tp);
     }
 
-    bool haveCycle()
-    {
-        const void* currentPtr = ptr(current);
-
-        if (seen.contains(currentPtr))
-            return true;
-        else
-            seen.insert(currentPtr);
-
-        return false;
-    }
-
     bool tooLong()
     {
         return ++steps > DFInt::LuauTypePathMaximumTraverseSteps;
@@ -287,7 +272,7 @@ struct TraversalState
 
     bool checkInvariants()
     {
-        return haveCycle() || tooLong();
+        return tooLong();
     }
 
     bool traverse(const TypePath::Property& property)
@@ -313,18 +298,36 @@ struct TraversalState
         {
             prop = lookupClassProp(c, property.name);
         }
-        else if (auto m = getMetatable(*currentType, builtinTypes))
+        // For a metatable type, the table takes priority; check that before
+        // falling through to the metatable entry below.
+        else if (auto m = get<MetatableType>(*currentType))
         {
-            // Weird: rather than use findMetatableEntry, which requires a lot
+            TypeOrPack pinned = current;
-            // of stuff that we don't have and don't want to pull in, we use the
+            updateCurrent(m->table);
-            // path traversal logic to grab __index and then re-enter the lookup
-            // logic there.
-            updateCurrent(*m);
 
-            if (!traverse(TypePath::Property{"__index"}))
+            if (traverse(property))
-                return false;
+                return true;
 
-            return traverse(property);
+            // Restore the old current type if we didn't traverse the metatable
+            // successfully; we'll use the next branch to address this.
+            current = pinned;
+        }
+
+        if (!prop)
+        {
+            if (auto m = getMetatable(*currentType, builtinTypes))
+            {
+                // Weird: rather than use findMetatableEntry, which requires a lot
+                // of stuff that we don't have and don't want to pull in, we use the
+                // path traversal logic to grab __index and then re-enter the lookup
+                // logic there.
+                updateCurrent(*m);
+
+                if (!traverse(TypePath::Property{"__index"}))
+                    return false;
+
+                return traverse(property);
+            }
         }
 
         if (prop)

Analysis/src/Unifier2.cpp

@@ -113,7 +113,7 @@ bool Unifier2::unify(TypeId subTy, TypeId superTy)
         return argResult && retResult;
     }
 
-    auto subTable = get<TableType>(subTy);
+    auto subTable = getMutable<TableType>(subTy);
     auto superTable = get<TableType>(superTy);
     if (subTable && superTable)
     {
@@ -210,7 +210,7 @@ bool Unifier2::unify(TypeId subTy, const IntersectionType* superIntersection)
     return result;
 }
 
-bool Unifier2::unify(const TableType* subTable, const TableType* superTable)
+bool Unifier2::unify(TableType* subTable, const TableType* superTable)
 {
     bool result = true;
 
@@ -256,6 +256,21 @@ bool Unifier2::unify(const TableType* subTable, const TableType* superTable)
         result &= unify(subTable->indexer->indexResultType, superTable->indexer->indexResultType);
     }
 
+    if (!subTable->indexer && subTable->state == TableState::Unsealed && superTable->indexer)
+    {
+        /*
+         * Unsealed tables are always created from literal table expressions. We
+         * can't be completely certain whether such a table has an indexer just
+         * by the content of the expression itself, so we need to be a bit more
+         * flexible here.
+         *
+         * If we are trying to reconcile an unsealed table with a table that has
+         * an indexer, we therefore conclude that the unsealed table has the
+         * same indexer.
+         */
+        subTable->indexer = *superTable->indexer;
+    }
+
     return result;
 }
 

Ast/include/Luau/Ast.h

@@ -3,6 +3,7 @@
 
 #include "Luau/Location.h"
 
+#include <iterator>
 #include <optional>
 #include <functional>
 #include <string>
@@ -91,10 +92,21 @@ struct AstArray
     {
         return data;
     }
+
     const T* end() const
     {
         return data + size;
     }
+
+    std::reverse_iterator<const T*> rbegin() const
+    {
+        return std::make_reverse_iterator(end());
+    }
+
+    std::reverse_iterator<const T*> rend() const
+    {
+        return std::make_reverse_iterator(begin());
+    }
 };
 
 struct AstTypeList

Ast/src/Parser.cpp

@@ -19,8 +19,6 @@ LUAU_FASTINTVARIABLE(LuauParseErrorLimit, 100)
 LUAU_FASTFLAGVARIABLE(LuauClipExtraHasEndProps, false)
 LUAU_FASTFLAG(LuauCheckedFunctionSyntax)
 
-LUAU_FASTFLAGVARIABLE(LuauParseImpreciseNumber, false)
-
 namespace Luau
 {
 
@@ -2168,11 +2166,8 @@ static ConstantNumberParseResult parseInteger(double& result, const char* data,
             return base == 2 ? ConstantNumberParseResult::BinOverflow : ConstantNumberParseResult::HexOverflow;
     }
 
-    if (FFlag::LuauParseImpreciseNumber)
+    if (value >= (1ull << 53) && static_cast<unsigned long long>(result) != value)
-    {
+        return ConstantNumberParseResult::Imprecise;
-        if (value >= (1ull << 53) && static_cast<unsigned long long>(result) != value)
-            return ConstantNumberParseResult::Imprecise;
-    }
 
     return ConstantNumberParseResult::Ok;
 }
@@ -2190,32 +2185,24 @@ static ConstantNumberParseResult parseDouble(double& result, const char* data)
     char* end = nullptr;
     double value = strtod(data, &end);
 
-    if (FFlag::LuauParseImpreciseNumber)
+    // trailing non-numeric characters
+    if (*end != 0)
+        return ConstantNumberParseResult::Malformed;
+
+    result = value;
+
+    // for linting, we detect integer constants that are parsed imprecisely
+    // since the check is expensive we only perform it when the number is larger than the precise integer range
+    if (value >= double(1ull << 53) && strspn(data, "0123456789") == strlen(data))
     {
-        // trailing non-numeric characters
+        char repr[512];
-        if (*end != 0)
+        snprintf(repr, sizeof(repr), "%.0f", value);
-            return ConstantNumberParseResult::Malformed;
 
-        result = value;
+        if (strcmp(repr, data) != 0)
-
+            return ConstantNumberParseResult::Imprecise;
-        // for linting, we detect integer constants that are parsed imprecisely
-        // since the check is expensive we only perform it when the number is larger than the precise integer range
-        if (value >= double(1ull << 53) && strspn(data, "0123456789") == strlen(data))
-        {
-            char repr[512];
-            snprintf(repr, sizeof(repr), "%.0f", value);
-
-            if (strcmp(repr, data) != 0)
-                return ConstantNumberParseResult::Imprecise;
-        }
-
-        return ConstantNumberParseResult::Ok;
-    }
-    else
-    {
-        result = value;
-        return *end == 0 ? ConstantNumberParseResult::Ok : ConstantNumberParseResult::Malformed;
     }
+
+    return ConstantNumberParseResult::Ok;
 }
 
 // simpleexp -> NUMBER | STRING | NIL | true | false | ... | constructor | FUNCTION body | primaryexp

CLI/Compile.cpp

@@ -37,13 +37,19 @@ enum class RecordStats
 {
     None,
     Total,
-    Split
+    File,
+    Function
 };
 
 struct GlobalOptions
 {
     int optimizationLevel = 1;
     int debugLevel = 1;
+
+    std::string vectorLib;
+    std::string vectorCtor;
+    std::string vectorType;
+
 } globalOptions;
 
 static Luau::CompileOptions copts()
@@ -52,6 +58,11 @@ static Luau::CompileOptions copts()
     result.optimizationLevel = globalOptions.optimizationLevel;
     result.debugLevel = globalOptions.debugLevel;
 
+    // globalOptions outlive the CompileOptions, so it's safe to use string data pointers here
+    result.vectorLib = globalOptions.vectorLib.c_str();
+    result.vectorCtor = globalOptions.vectorCtor.c_str();
+    result.vectorType = globalOptions.vectorType.c_str();
+
     return result;
 }
 
@@ -159,11 +170,26 @@ struct CompileStats
 \"blockLinearizationStats\": {\
 \"constPropInstructionCount\": %u, \
 \"timeSeconds\": %f\
-}}",
+}",
             lines, bytecode, bytecodeInstructionCount, codegen, readTime, miscTime, parseTime, compileTime, codegenTime, lowerStats.totalFunctions,
             lowerStats.skippedFunctions, lowerStats.spillsToSlot, lowerStats.spillsToRestore, lowerStats.maxSpillSlotsUsed, lowerStats.blocksPreOpt,
             lowerStats.blocksPostOpt, lowerStats.maxBlockInstructions, lowerStats.regAllocErrors, lowerStats.loweringErrors,
             lowerStats.blockLinearizationStats.constPropInstructionCount, lowerStats.blockLinearizationStats.timeSeconds);
+        if (lowerStats.collectFunctionStats)
+        {
+            fprintf(fp, ", \"functions\": [");
+            auto functionCount = lowerStats.functions.size();
+            for (size_t i = 0; i < functionCount; ++i)
+            {
+                const Luau::CodeGen::FunctionStats& fstat = lowerStats.functions[i];
+                fprintf(fp, "{\"name\": \"%s\", \"line\": %d, \"bcodeCount\": %u, \"irCount\": %u, \"asmCount\": %u}", fstat.name.c_str(), fstat.line,
+                    fstat.bcodeCount, fstat.irCount, fstat.asmCount);
+                if (i < functionCount - 1)
+                    fprintf(fp, ", ");
+            }
+            fprintf(fp, "]");
+        }
+        fprintf(fp, "}");
     }
 
     CompileStats& operator+=(const CompileStats& that)
@@ -321,7 +347,11 @@ static void displayHelp(const char* argv0)
     printf("  -g<n>: compile with debug level n (default 1, n should be between 0 and 2).\n");
     printf("  --target=<target>: compile code for specific architecture (a64, x64, a64_nf, x64_ms).\n");
     printf("  --timetrace: record compiler time tracing information into trace.json\n");
-    printf("  --record-stats=<style>: records compilation stats in stats.json (total, split).\n");
+    printf("  --stats-file=<filename>: file in which compilation stats will be recored (default 'stats.json').\n");
+    printf("  --record-stats=<granularity>: granularity of compilation stats recorded in stats.json (total, file, function).\n");
+    printf("  --vector-lib=<name>: name of the library providing vector type operations.\n");
+    printf("  --vector-ctor=<name>: name of the function constructing a vector value.\n");
+    printf("  --vector-type=<name>: name of the vector type.\n");
 }
 
 static int assertionHandler(const char* expr, const char* file, int line, const char* function)
@@ -420,11 +450,13 @@ int main(int argc, char** argv)
 
             if (strcmp(value, "total") == 0)
                 recordStats = RecordStats::Total;
-            else if (strcmp(value, "split") == 0)
+            else if (strcmp(value, "file") == 0)
-                recordStats = RecordStats::Split;
+                recordStats = RecordStats::File;
+            else if (strcmp(value, "function") == 0)
+                recordStats = RecordStats::Function;
             else
             {
-                fprintf(stderr, "Error: unknown 'style' for '--record-stats'\n");
+                fprintf(stderr, "Error: unknown 'granularity' for '--record-stats'\n");
                 return 1;
             }
         }
@@ -442,6 +474,18 @@ int main(int argc, char** argv)
         {
             setLuauFlags(argv[i] + 9);
         }
+        else if (strncmp(argv[i], "--vector-lib=", 13) == 0)
+        {
+            globalOptions.vectorLib = argv[i] + 13;
+        }
+        else if (strncmp(argv[i], "--vector-ctor=", 14) == 0)
+        {
+            globalOptions.vectorCtor = argv[i] + 14;
+        }
+        else if (strncmp(argv[i], "--vector-type=", 14) == 0)
+        {
+            globalOptions.vectorType = argv[i] + 14;
+        }
         else if (argv[i][0] == '-' && argv[i][1] == '-' && getCompileFormat(argv[i] + 2))
         {
             compileFormat = *getCompileFormat(argv[i] + 2);
@@ -473,7 +517,7 @@ int main(int argc, char** argv)
     CompileStats stats = {};
 
     std::vector<CompileStats> fileStats;
-    if (recordStats == RecordStats::Split)
+    if (recordStats == RecordStats::File || recordStats == RecordStats::Function)
         fileStats.reserve(fileCount);
 
     int failed = 0;
@@ -481,9 +525,10 @@ int main(int argc, char** argv)
     for (const std::string& path : files)
     {
         CompileStats fileStat = {};
+        fileStat.lowerStats.collectFunctionStats = (recordStats == RecordStats::Function);
         failed += !compileFile(path.c_str(), compileFormat, assemblyTarget, fileStat);
         stats += fileStat;
-        if (recordStats == RecordStats::Split)
+        if (recordStats == RecordStats::File || recordStats == RecordStats::Function)
             fileStats.push_back(fileStat);
     }
 
@@ -506,7 +551,6 @@ int main(int argc, char** argv)
 
     if (recordStats != RecordStats::None)
     {
-
         FILE* fp = fopen(statsFile.c_str(), "w");
 
         if (!fp)
@@ -519,7 +563,7 @@ int main(int argc, char** argv)
         {
             stats.serializeToJson(fp);
         }
-        else if (recordStats == RecordStats::Split)
+        else if (recordStats == RecordStats::File || recordStats == RecordStats::Function)
         {
             fprintf(fp, "{\n");
             for (size_t i = 0; i < fileCount; ++i)

CLI/FileUtils.cpp

@@ -10,6 +10,7 @@
 #ifndef NOMINMAX
 #define NOMINMAX
 #endif
+#include <direct.h>
 #include <windows.h>
 #else
 #include <dirent.h>
@@ -44,6 +45,148 @@ static std::string toUtf8(const std::wstring& path)
 }
 #endif
 
+bool isAbsolutePath(std::string_view path)
+{
+#ifdef _WIN32
+    // Must either begin with "X:/", "X:\", "/", or "\", where X is a drive letter
+    return (path.size() >= 3 && isalpha(path[0]) && path[1] == ':' && (path[2] == '/' || path[2] == '\\')) ||
+           (path.size() >= 1 && (path[0] == '/' || path[0] == '\\'));
+#else
+    // Must begin with '/'
+    return path.size() >= 1 && path[0] == '/';
+#endif
+}
+
+bool isExplicitlyRelative(std::string_view path)
+{
+    return (path == ".") || (path == "..") || (path.size() >= 2 && path[0] == '.' && path[1] == '/') ||
+           (path.size() >= 3 && path[0] == '.' && path[1] == '.' && path[2] == '/');
+}
+
+std::optional<std::string> getCurrentWorkingDirectory()
+{
+    // 2^17 - derived from the Windows path length limit
+    constexpr size_t maxPathLength = 131072;
+    constexpr size_t initialPathLength = 260;
+
+    std::string directory(initialPathLength, '\0');
+    char* cstr = nullptr;
+
+    while (!cstr && directory.size() <= maxPathLength)
+    {
+#ifdef _WIN32
+        cstr = _getcwd(directory.data(), static_cast<int>(directory.size()));
+#else
+        cstr = getcwd(directory.data(), directory.size());
+#endif
+        if (cstr)
+        {
+            directory.resize(strlen(cstr));
+            return directory;
+        }
+        else if (errno != ERANGE || directory.size() * 2 > maxPathLength)
+        {
+            return std::nullopt;
+        }
+        else
+        {
+            directory.resize(directory.size() * 2);
+        }
+    }
+    return std::nullopt;
+}
+
+// Returns the normal/canonical form of a path (e.g. "../subfolder/../module.luau" -> "../module.luau")
+std::string normalizePath(std::string_view path)
+{
+    return resolvePath(path, "");
+}
+
+// Takes a path that is relative to the file at baseFilePath and returns the path explicitly rebased onto baseFilePath.
+// For absolute paths, baseFilePath will be ignored, and this function will resolve the path to a canonical path:
+// (e.g. "/Users/.././Users/johndoe" -> "/Users/johndoe").
+std::string resolvePath(std::string_view path, std::string_view baseFilePath)
+{
+    std::vector<std::string_view> pathComponents;
+    std::vector<std::string_view> baseFilePathComponents;
+
+    // Dependent on whether the final resolved path is absolute or relative
+    // - if relative (when path and baseFilePath are both relative), resolvedPathPrefix remains empty
+    // - if absolute (if either path or baseFilePath are absolute), resolvedPathPrefix is "C:\", "/", etc.
+    std::string resolvedPathPrefix;
+
+    if (isAbsolutePath(path))
+    {
+        // path is absolute, we use path's prefix and ignore baseFilePath
+        size_t afterPrefix = path.find_first_of("\\/") + 1;
+        resolvedPathPrefix = path.substr(0, afterPrefix);
+        pathComponents = splitPath(path.substr(afterPrefix));
+    }
+    else
+    {
+        pathComponents = splitPath(path);
+        if (isAbsolutePath(baseFilePath))
+        {
+            // path is relative and baseFilePath is absolute, we use baseFilePath's prefix
+            size_t afterPrefix = baseFilePath.find_first_of("\\/") + 1;
+            resolvedPathPrefix = baseFilePath.substr(0, afterPrefix);
+            baseFilePathComponents = splitPath(baseFilePath.substr(afterPrefix));
+        }
+        else
+        {
+            // path and baseFilePath are both relative, we do not set a prefix (resolved path will be relative)
+            baseFilePathComponents = splitPath(baseFilePath);
+        }
+    }
+
+    // Remove filename from components
+    if (!baseFilePathComponents.empty())
+        baseFilePathComponents.pop_back();
+
+    // Resolve the path by applying pathComponents to baseFilePathComponents
+    int numPrependedParents = 0;
+    for (std::string_view component : pathComponents)
+    {
+        if (component == "..")
+        {
+            if (baseFilePathComponents.empty())
+            {
+                if (resolvedPathPrefix.empty()) // only when final resolved path will be relative
+                    numPrependedParents++;      // "../" will later be added to the beginning of the resolved path
+            }
+            else if (baseFilePathComponents.back() != "..")
+            {
+                baseFilePathComponents.pop_back(); // Resolve cases like "folder/subfolder/../../file" to "file"
+            }
+        }
+        else if (component != "." && !component.empty())
+        {
+            baseFilePathComponents.push_back(component);
+        }
+    }
+
+    // Join baseFilePathComponents to form the resolved path
+    std::string resolvedPath = resolvedPathPrefix;
+    // Only when resolvedPath will be relative
+    for (int i = 0; i < numPrependedParents; i++)
+    {
+        resolvedPath += "../";
+    }
+    for (auto iter = baseFilePathComponents.begin(); iter != baseFilePathComponents.end(); ++iter)
+    {
+        if (iter != baseFilePathComponents.begin())
+            resolvedPath += "/";
+
+        resolvedPath += *iter;
+    }
+    if (resolvedPath.size() > resolvedPathPrefix.size() && resolvedPath.back() == '/')
+    {
+        // Remove trailing '/' if present
+        resolvedPath.pop_back();
+    }
+    return resolvedPath;
+}
+
 std::optional<std::string> readFile(const std::string& name)
 {
 #ifdef _WIN32
@@ -224,6 +367,24 @@ bool isDirectory(const std::string& path)
 #endif
 }
 
+std::vector<std::string_view> splitPath(std::string_view path)
+{
+    std::vector<std::string_view> components;
+
+    size_t pos = 0;
+    size_t nextPos = path.find_first_of("\\/", pos);
+
+    while (nextPos != std::string::npos)
+    {
+        components.push_back(path.substr(pos, nextPos - pos));
+        pos = nextPos + 1;
+        nextPos = path.find_first_of("\\/", pos);
+    }
+    components.push_back(path.substr(pos));
+
+    return components;
+}
+
 std::string joinPaths(const std::string& lhs, const std::string& rhs)
 {
     std::string result = lhs;

CLI/FileUtils.h

@@ -3,15 +3,24 @@
 
 #include <optional>
 #include <string>
+#include <string_view>
 #include <functional>
 #include <vector>
 
+std::optional<std::string> getCurrentWorkingDirectory();
+
+std::string normalizePath(std::string_view path);
+std::string resolvePath(std::string_view relativePath, std::string_view baseFilePath);
+
 std::optional<std::string> readFile(const std::string& name);
 std::optional<std::string> readStdin();
 
+bool isAbsolutePath(std::string_view path);
+bool isExplicitlyRelative(std::string_view path);
 bool isDirectory(const std::string& path);
 bool traverseDirectory(const std::string& path, const std::function<void(const std::string& name)>& callback);
 
+std::vector<std::string_view> splitPath(std::string_view path);
 std::string joinPaths(const std::string& lhs, const std::string& rhs);
 std::optional<std::string> getParentPath(const std::string& path);
 

CLI/Repl.cpp

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Repl.h"
 
+#include "Luau/Common.h"
 #include "lua.h"
 #include "lualib.h"
 
@@ -13,6 +14,7 @@
 #include "FileUtils.h"
 #include "Flags.h"
 #include "Profiler.h"
+#include "Require.h"
 
 #include "isocline.h"
 
@@ -39,6 +41,8 @@
 
 LUAU_FASTFLAG(DebugLuauTimeTracing)
 
+LUAU_FASTFLAGVARIABLE(LuauUpdatedRequireByStringSemantics, false)
+
 constexpr int MaxTraversalLimit = 50;
 
 static bool codegen = false;
@@ -115,74 +119,129 @@ static int finishrequire(lua_State* L)
 
 static int lua_require(lua_State* L)
 {
-    std::string name = luaL_checkstring(L, 1);
+    if (FFlag::LuauUpdatedRequireByStringSemantics)
-    std::string chunkname = "=" + name;
-
-    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
-
-    // return the module from the cache
-    lua_getfield(L, -1, name.c_str());
-    if (!lua_isnil(L, -1))
     {
-        // L stack: _MODULES result
+        std::string name = luaL_checkstring(L, 1);
+
+        RequireResolver::ResolvedRequire resolvedRequire = RequireResolver::resolveRequire(L, std::move(name));
+
+        if (resolvedRequire.status == RequireResolver::ModuleStatus::Cached)
+            return finishrequire(L);
+        else if (resolvedRequire.status == RequireResolver::ModuleStatus::NotFound)
+            luaL_errorL(L, "error requiring module");
+
+        // module needs to run in a new thread, isolated from the rest
+        // note: we create ML on main thread so that it doesn't inherit environment of L
+        lua_State* GL = lua_mainthread(L);
+        lua_State* ML = lua_newthread(GL);
+        lua_xmove(GL, L, 1);
+
+        // new thread needs to have the globals sandboxed
+        luaL_sandboxthread(ML);
+
+        // now we can compile & run module on the new thread
+        std::string bytecode = Luau::compile(resolvedRequire.sourceCode, copts());
+        if (luau_load(ML, resolvedRequire.chunkName.c_str(), bytecode.data(), bytecode.size(), 0) == 0)
+        {
+            if (codegen)
+                Luau::CodeGen::compile(ML, -1);
+
+            if (coverageActive())
+                coverageTrack(ML, -1);
+
+            int status = lua_resume(ML, L, 0);
+
+            if (status == 0)
+            {
+                if (lua_gettop(ML) == 0)
+                    lua_pushstring(ML, "module must return a value");
+                else if (!lua_istable(ML, -1) && !lua_isfunction(ML, -1))
+                    lua_pushstring(ML, "module must return a table or function");
+            }
+            else if (status == LUA_YIELD)
+            {
+                lua_pushstring(ML, "module can not yield");
+            }
+            else if (!lua_isstring(ML, -1))
+            {
+                lua_pushstring(ML, "unknown error while running module");
+            }
+        }
+
+        // there's now a return value on top of ML; L stack: _MODULES ML
+        lua_xmove(ML, L, 1);
+        lua_pushvalue(L, -1);
+        lua_setfield(L, -4, resolvedRequire.absolutePath.c_str());
+
+        // L stack: _MODULES ML result
         return finishrequire(L);
     }
-
+    else
-    lua_pop(L, 1);
-
-    std::optional<std::string> source = readFile(name + ".luau");
-    if (!source)
     {
-        source = readFile(name + ".lua"); // try .lua if .luau doesn't exist
+        std::string name = luaL_checkstring(L, 1);
+        std::string chunkname = "=" + name;
+
+        luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+
+        // return the module from the cache
+        lua_getfield(L, -1, name.c_str());
+        if (!lua_isnil(L, -1))
+        {
+            // L stack: _MODULES result
+            return finishrequire(L);
+        }
+
+        lua_pop(L, 1);
+
+        std::optional<std::string> source = readFile(name + ".luau");
         if (!source)
-            luaL_argerrorL(L, 1, ("error loading " + name).c_str()); // if neither .luau nor .lua exist, we have an error
+        {
+            source = readFile(name + ".lua"); // try .lua if .luau doesn't exist
+            if (!source)
+                luaL_argerrorL(L, 1, ("error loading " + name).c_str()); // if neither .luau nor .lua exist, we have an error
+        }
+
+        // module needs to run in a new thread, isolated from the rest
+        // note: we create ML on main thread so that it doesn't inherit environment of L
+        lua_State* GL = lua_mainthread(L);
+        lua_State* ML = lua_newthread(GL);
+        lua_xmove(GL, L, 1);
+        // new thread needs to have the globals sandboxed
+        luaL_sandboxthread(ML);
+
+        // now we can compile & run module on the new thread
+        std::string bytecode = Luau::compile(*source, copts());
+        if (luau_load(ML, chunkname.c_str(), bytecode.data(), bytecode.size(), 0) == 0)
+        {
+            if (codegen)
+                Luau::CodeGen::compile(ML, -1);
+            if (coverageActive())
+                coverageTrack(ML, -1);
+            int status = lua_resume(ML, L, 0);
+            if (status == 0)
+            {
+                if (lua_gettop(ML) == 0)
+                    lua_pushstring(ML, "module must return a value");
+                else if (!lua_istable(ML, -1) && !lua_isfunction(ML, -1))
+                    lua_pushstring(ML, "module must return a table or function");
+            }
+            else if (status == LUA_YIELD)
+            {
+                lua_pushstring(ML, "module can not yield");
+            }
+            else if (!lua_isstring(ML, -1))
+            {
+                lua_pushstring(ML, "unknown error while running module");
+            }
+        }
+        // there's now a return value on top of ML; L stack: _MODULES ML
+        lua_xmove(ML, L, 1);
+        lua_pushvalue(L, -1);
+        lua_setfield(L, -4, name.c_str());
+
+        // L stack: _MODULES ML result
+        return finishrequire(L);
     }
-
-    // module needs to run in a new thread, isolated from the rest
-    // note: we create ML on main thread so that it doesn't inherit environment of L
-    lua_State* GL = lua_mainthread(L);
-    lua_State* ML = lua_newthread(GL);
-    lua_xmove(GL, L, 1);
-
-    // new thread needs to have the globals sandboxed
-    luaL_sandboxthread(ML);
-
-    // now we can compile & run module on the new thread
-    std::string bytecode = Luau::compile(*source, copts());
-    if (luau_load(ML, chunkname.c_str(), bytecode.data(), bytecode.size(), 0) == 0)
-    {
-        if (codegen)
-            Luau::CodeGen::compile(ML, -1);
-
-        if (coverageActive())
-            coverageTrack(ML, -1);
-
-        int status = lua_resume(ML, L, 0);
-
-        if (status == 0)
-        {
-            if (lua_gettop(ML) == 0)
-                lua_pushstring(ML, "module must return a value");
-            else if (!lua_istable(ML, -1) && !lua_isfunction(ML, -1))
-                lua_pushstring(ML, "module must return a table or function");
-        }
-        else if (status == LUA_YIELD)
-        {
-            lua_pushstring(ML, "module can not yield");
-        }
-        else if (!lua_isstring(ML, -1))
-        {
-            lua_pushstring(ML, "unknown error while running module");
-        }
-    }
-
-    // there's now a return value on top of ML; L stack: _MODULES ML
-    lua_xmove(ML, L, 1);
-    lua_pushvalue(L, -1);
-    lua_setfield(L, -4, name.c_str());
-
-    // L stack: _MODULES ML result
-    return finishrequire(L);
 }
 
 static int lua_collectgarbage(lua_State* L)

CLI/Require.cpp

@@ -0,0 +1,290 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#include "Require.h"
+
+#include "FileUtils.h"
+#include "Luau/Common.h"
+
+#include <algorithm>
+#include <array>
+#include <utility>
+
+RequireResolver::RequireResolver(lua_State* L, std::string path)
+    : pathToResolve(std::move(path))
+    , L(L)
+{
+    lua_Debug ar;
+    lua_getinfo(L, 1, "s", &ar);
+    sourceChunkname = ar.source;
+
+    if (!isRequireAllowed(sourceChunkname))
+        luaL_errorL(L, "require is not supported in this context");
+
+    if (isAbsolutePath(pathToResolve))
+        luaL_argerrorL(L, 1, "cannot require an absolute path");
+
+    bool isAlias = !pathToResolve.empty() && pathToResolve[0] == '@';
+    if (!isAlias && !isExplicitlyRelative(pathToResolve))
+        luaL_argerrorL(L, 1, "must require an alias prepended with '@' or an explicitly relative path");
+
+    std::replace(pathToResolve.begin(), pathToResolve.end(), '\\', '/');
+    if (isAlias)
+    {
+        pathToResolve = pathToResolve.substr(1);
+        substituteAliasIfPresent(pathToResolve);
+    }
+}
+
+[[nodiscard]] RequireResolver::ResolvedRequire RequireResolver::resolveRequire(lua_State* L, std::string path)
+{
+    RequireResolver resolver(L, std::move(path));
+    ModuleStatus status = resolver.findModule();
+    if (status != ModuleStatus::FileRead)
+        return ResolvedRequire{status};
+    else
+        return ResolvedRequire{status, std::move(resolver.chunkname), std::move(resolver.absolutePath), std::move(resolver.sourceCode)};
+}
+
+RequireResolver::ModuleStatus RequireResolver::findModule()
+{
+    resolveAndStoreDefaultPaths();
+
+    // Put _MODULES table on stack for checking and saving to the cache
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+
+    RequireResolver::ModuleStatus moduleStatus = findModuleImpl();
+
+    if (moduleStatus != RequireResolver::ModuleStatus::NotFound)
+        return moduleStatus;
+
+    if (!shouldSearchPathsArray())
+        return moduleStatus;
+
+    if (!isConfigFullyResolved)
+        parseNextConfig();
+
+    // Index-based iteration because std::iterator may be invalidated if config.paths is reallocated
+    for (size_t i = 0; i < config.paths.size(); ++i)
+    {
+        // "placeholder" acts as a requiring file in the relevant directory
+        std::optional<std::string> absolutePathOpt = resolvePath(pathToResolve, joinPaths(config.paths[i], "placeholder"));
+
+        if (!absolutePathOpt)
+            luaL_errorL(L, "error requiring module");
+
+        chunkname = *absolutePathOpt;
+        absolutePath = *absolutePathOpt;
+
+        moduleStatus = findModuleImpl();
+
+        if (moduleStatus != RequireResolver::ModuleStatus::NotFound)
+            return moduleStatus;
+
+        // Before finishing the loop, parse more config files if there are any
+        if (i == config.paths.size() - 1 && !isConfigFullyResolved)
+            parseNextConfig(); // could reallocate config.paths when paths are parsed and added
+    }
+
+    return RequireResolver::ModuleStatus::NotFound;
+}
+
+RequireResolver::ModuleStatus RequireResolver::findModuleImpl()
+{
+    static const std::array<const char*, 4> possibleSuffixes = {".luau", ".lua", "/init.luau", "/init.lua"};
+
+    size_t unsuffixedAbsolutePathSize = absolutePath.size();
+
+    for (const char* possibleSuffix : possibleSuffixes)
+    {
+        absolutePath += possibleSuffix;
+
+        // Check cache for module
+        lua_getfield(L, -1, absolutePath.c_str());
+        if (!lua_isnil(L, -1))
+        {
+            return ModuleStatus::Cached;
+        }
+        lua_pop(L, 1);
+
+        // Try to read the matching file
+        std::optional<std::string> source = readFile(absolutePath);
+        if (source)
+        {
+            chunkname = "=" + chunkname + possibleSuffix;
+            sourceCode = *source;
+            return ModuleStatus::FileRead;
+        }
+
+        absolutePath.resize(unsuffixedAbsolutePathSize); // truncate to remove suffix
+    }
+
+    return ModuleStatus::NotFound;
+}
+
+bool RequireResolver::isRequireAllowed(std::string_view sourceChunkname)
+{
+    LUAU_ASSERT(!sourceChunkname.empty());
+    return (sourceChunkname[0] == '=' || sourceChunkname[0] == '@');
+}
+
+bool RequireResolver::shouldSearchPathsArray()
+{
+    return !isAbsolutePath(pathToResolve) && !isExplicitlyRelative(pathToResolve);
+}
+
+void RequireResolver::resolveAndStoreDefaultPaths()
+{
+    if (!isAbsolutePath(pathToResolve))
+    {
+        std::string chunknameContext = getRequiringContextRelative();
+        std::optional<std::string> absolutePathContext = getRequiringContextAbsolute();
+
+        if (!absolutePathContext)
+            luaL_errorL(L, "error requiring module");
+
+        // resolvePath automatically sanitizes/normalizes the paths
+        std::optional<std::string> chunknameOpt = resolvePath(pathToResolve, chunknameContext);
+        std::optional<std::string> absolutePathOpt = resolvePath(pathToResolve, *absolutePathContext);
+
+        if (!chunknameOpt || !absolutePathOpt)
+            luaL_errorL(L, "error requiring module");
+
+        chunkname = std::move(*chunknameOpt);
+        absolutePath = std::move(*absolutePathOpt);
+    }
+    else
+    {
+        // Here we must explicitly sanitize, as the path is taken as is
+        std::optional<std::string> sanitizedPath = normalizePath(pathToResolve);
+        if (!sanitizedPath)
+            luaL_errorL(L, "error requiring module");
+
+        chunkname = *sanitizedPath;
+        absolutePath = std::move(*sanitizedPath);
+    }
+}
+
+std::optional<std::string> RequireResolver::getRequiringContextAbsolute()
+{
+    std::string requiringFile;
+    if (isAbsolutePath(sourceChunkname.substr(1)))
+    {
+        // We already have an absolute path for the requiring file
+        requiringFile = sourceChunkname.substr(1);
+    }
+    else
+    {
+        // Requiring file's stored path is relative to the CWD, must make absolute
+        std::optional<std::string> cwd = getCurrentWorkingDirectory();
+        if (!cwd)
+            return std::nullopt;
+
+        if (sourceChunkname.substr(1) == "stdin")
+        {
+            // Require statement is being executed from REPL input prompt
+            // The requiring context is the pseudo-file "stdin" in the CWD
+            requiringFile = joinPaths(*cwd, "stdin");
+        }
+        else
+        {
+            // Require statement is being executed in a file, must resolve relative to CWD
+            std::optional<std::string> requiringFileOpt = resolvePath(sourceChunkname.substr(1), joinPaths(*cwd, "stdin"));
+            if (!requiringFileOpt)
+                return std::nullopt;
+
+            requiringFile = *requiringFileOpt;
+        }
+    }
+    std::replace(requiringFile.begin(), requiringFile.end(), '\\', '/');
+    return requiringFile;
+}
+
+std::string RequireResolver::getRequiringContextRelative()
+{
+    std::string baseFilePath;
+    if (sourceChunkname.substr(1) != "stdin")
+        baseFilePath = sourceChunkname.substr(1);
+
+    return baseFilePath;
+}
+
+void RequireResolver::substituteAliasIfPresent(std::string& path)
+{
+    std::string potentialAlias = path.substr(0, path.find_first_of("\\/"));
+
+    // Not worth searching when potentialAlias cannot be an alias
+    if (!Luau::isValidAlias(potentialAlias))
+        return;
+
+    std::optional<std::string> alias = getAlias(potentialAlias);
+    if (alias)
+    {
+        path = *alias + path.substr(potentialAlias.size());
+    }
+}
+
+std::optional<std::string> RequireResolver::getAlias(std::string alias)
+{
+    std::transform(alias.begin(), alias.end(), alias.begin(), [](unsigned char c) {
+        return ('A' <= c && c <= 'Z') ? (c + ('a' - 'A')) : c;
+    });
+    while (!config.aliases.count(alias) && !isConfigFullyResolved)
+    {
+        parseNextConfig();
+    }
+    if (!config.aliases.count(alias) && isConfigFullyResolved)
+        return std::nullopt; // could not find alias
+
+    return resolvePath(config.aliases[alias], joinPaths(lastSearchedDir, Luau::kConfigName));
+}
+
+void RequireResolver::parseNextConfig()
+{
+    if (isConfigFullyResolved)
+        return; // no config files left to parse
+
+    std::optional<std::string> directory;
+    if (lastSearchedDir.empty())
+    {
+        std::optional<std::string> requiringFile = getRequiringContextAbsolute();
+        if (!requiringFile)
+            luaL_errorL(L, "error requiring module");
+
+        directory = getParentPath(*requiringFile);
+    }
+    else
+        directory = getParentPath(lastSearchedDir);
+
+    if (directory)
+    {
+        lastSearchedDir = *directory;
+        parseConfigInDirectory(*directory);
+    }
+    else
+        isConfigFullyResolved = true;
+}
+
+void RequireResolver::parseConfigInDirectory(const std::string& directory)
+{
+    std::string configPath = joinPaths(directory, Luau::kConfigName);
+
+    size_t numPaths = config.paths.size();
+
+    if (std::optional<std::string> contents = readFile(configPath))
+    {
+        std::optional<std::string> error = Luau::parseConfig(*contents, config);
+        if (error)
+            luaL_errorL(L, "error parsing %s (%s)", configPath.c_str(), (*error).c_str());
+    }
+
+    // Resolve any newly obtained relative paths in "paths" in relation to configPath
+    for (auto it = config.paths.begin() + numPaths; it != config.paths.end(); ++it)
+    {
+        if (!isAbsolutePath(*it))
+        {
+            if (std::optional<std::string> resolvedPath = resolvePath(*it, configPath))
+                *it = std::move(*resolvedPath);
+            else
+                luaL_errorL(L, "error requiring module");
+        }
+    }
+}

CLI/Require.h

@@ -0,0 +1,62 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "lua.h"
+#include "lualib.h"
+
+#include "Luau/Config.h"
+
+#include <string>
+#include <string_view>
+
+class RequireResolver
+{
+public:
+    std::string chunkname;
+    std::string absolutePath;
+    std::string sourceCode;
+
+    enum class ModuleStatus
+    {
+        Cached,
+        FileRead,
+        NotFound
+    };
+
+    struct ResolvedRequire
+    {
+        ModuleStatus status;
+        std::string chunkName;
+        std::string absolutePath;
+        std::string sourceCode;
+    };
+
+    [[nodiscard]] ResolvedRequire static resolveRequire(lua_State* L, std::string path);
+
+private:
+    std::string pathToResolve;
+    std::string_view sourceChunkname;
+
+    RequireResolver(lua_State* L, std::string path);
+
+    ModuleStatus findModule();
+    lua_State* L;
+    Luau::Config config;
+    std::string lastSearchedDir;
+    bool isConfigFullyResolved = false;
+
+    bool isRequireAllowed(std::string_view sourceChunkname);
+    bool shouldSearchPathsArray();
+
+    void resolveAndStoreDefaultPaths();
+    ModuleStatus findModuleImpl();
+
+    std::optional<std::string> getRequiringContextAbsolute();
+    std::string getRequiringContextRelative();
+
+    void substituteAliasIfPresent(std::string& path);
+    std::optional<std::string> getAlias(std::string alias);
+
+    void parseNextConfig();
+    void parseConfigInDirectory(const std::string& path);
+};

CMakeLists.txt

@@ -193,7 +193,7 @@ if(LUAU_BUILD_CLI)
 
     target_include_directories(Luau.Repl.CLI PRIVATE extern extern/isocline/include)
 
-    target_link_libraries(Luau.Repl.CLI PRIVATE Luau.Compiler Luau.CodeGen Luau.VM isocline)
+    target_link_libraries(Luau.Repl.CLI PRIVATE Luau.Compiler Luau.Config Luau.CodeGen Luau.VM isocline)
 
     if(UNIX)
         find_library(LIBPTHREAD pthread)
@@ -230,7 +230,7 @@ if(LUAU_BUILD_TESTS)
 
     target_compile_options(Luau.CLI.Test PRIVATE ${LUAU_OPTIONS})
     target_include_directories(Luau.CLI.Test PRIVATE extern CLI)
-    target_link_libraries(Luau.CLI.Test PRIVATE Luau.Compiler Luau.CodeGen Luau.VM isocline)
+    target_link_libraries(Luau.CLI.Test PRIVATE Luau.Compiler Luau.Config Luau.CodeGen Luau.VM isocline)
     if(UNIX)
         find_library(LIBPTHREAD pthread)
         if (LIBPTHREAD)
@@ -254,6 +254,8 @@ if(LUAU_BUILD_WEB)
     target_link_options(Luau.Web PRIVATE -sSINGLE_FILE=1)
 endif()
 
+add_subdirectory(fuzz)
+
 # validate dependencies for internal libraries
 foreach(LIB Luau.Ast Luau.Compiler Luau.Config Luau.Analysis Luau.CodeGen Luau.VM)
     if(TARGET ${LIB})

CMakePresets.json

@@ -0,0 +1,47 @@
+{
+    "version": 6,
+    "configurePresets": [
+        {
+            "name": "fuzz",
+            "displayName": "Fuzz",
+            "description": "Configures required fuzzer settings.",
+            "binaryDir": "build",
+            "condition": {
+                "type": "anyOf",
+                "conditions": [
+                    {
+                        "type": "equals",
+                        "lhs": "${hostSystemName}",
+                        "rhs": "Darwin"
+                    },
+                    {
+                        "type": "equals",
+                        "lhs": "${hostSystemName}",
+                        "rhs": "Linux"
+                    }
+                ]
+            },
+            "cacheVariables": {
+                "CMAKE_OSX_ARCHITECTURES": "x86_64",
+                "CMAKE_BUILD_TYPE": "Release",
+                "CMAKE_CXX_STANDARD": "17",
+                "CMAKE_CXX_EXTENSIONS": false
+            },
+            "warnings": {
+                "dev": false
+            }
+        }
+    ],
+    "buildPresets": [
+        {
+            "name": "fuzz-proto",
+            "displayName": "Protobuf Fuzzer",
+            "description": "Builds the protobuf-based fuzzer and transpiler tools.",
+            "configurePreset": "fuzz",
+            "targets": [
+                "Luau.Fuzz.Proto",
+                "Luau.Fuzz.ProtoTest"
+            ]
+        }
+    ]
+}

CodeGen/include/Luau/BytecodeAnalysis.h

@@ -0,0 +1,21 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/Common.h"
+
+#include <vector>
+
+#include <stdint.h>
+
+namespace Luau
+{
+namespace CodeGen
+{
+
+struct IrFunction;
+
+void buildBytecodeBlocks(IrFunction& function, const std::vector<uint8_t>& jumpTargets);
+void analyzeBytecodeTypes(IrFunction& function);
+
+} // namespace CodeGen
+} // namespace Luau

CodeGen/include/Luau/CodeGen.h

@@ -3,6 +3,7 @@
 
 #include <algorithm>
 #include <string>
+#include <vector>
 
 #include <stddef.h>
 #include <stdint.h>
@@ -101,6 +102,15 @@ struct BlockLinearizationStats
     }
 };
 
+struct FunctionStats
+{
+    std::string name;
+    int line = -1;
+    unsigned bcodeCount = 0;
+    unsigned irCount = 0;
+    unsigned asmCount = 0;
+};
+
 struct LoweringStats
 {
     unsigned totalFunctions = 0;
@@ -117,6 +127,9 @@ struct LoweringStats
 
     BlockLinearizationStats blockLinearizationStats;
 
+    bool collectFunctionStats = false;
+    std::vector<FunctionStats> functions;
+
     LoweringStats operator+(const LoweringStats& other) const
     {
         LoweringStats result(*this);
@@ -137,6 +150,8 @@ struct LoweringStats
         this->regAllocErrors += that.regAllocErrors;
         this->loweringErrors += that.loweringErrors;
         this->blockLinearizationStats += that.blockLinearizationStats;
+        if (this->collectFunctionStats)
+            this->functions.insert(this->functions.end(), that.functions.begin(), that.functions.end());
         return *this;
     }
 };

CodeGen/include/Luau/IrBuilder.h

@@ -78,7 +78,13 @@ struct IrBuilder
 
     std::vector<uint32_t> instIndexToBlock; // Block index at the bytecode instruction
 
-    std::vector<IrOp> loopStepStack;
+    struct LoopInfo
+    {
+        IrOp step;
+        int startpc = 0;
+    };
+
+    std::vector<LoopInfo> numericLoopStack;
 
     // Similar to BytecodeBuilder, duplicate constants are removed used the same method
     struct ConstantKey

CodeGen/include/Luau/IrData.h

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/Bytecode.h"
 #include "Luau/IrAnalysis.h"
 #include "Luau/Label.h"
 #include "Luau/RegisterX64.h"
@@ -12,6 +13,8 @@
 #include <stdint.h>
 #include <string.h>
 
+LUAU_FASTFLAG(LuauKeepVmapLinear2)
+
 struct Proto;
 
 namespace Luau
@@ -930,18 +933,37 @@ struct BytecodeMapping
     uint32_t asmLocation;
 };
 
+struct BytecodeBlock
+{
+    // 'start' and 'finish' define an inclusive range of instructions which belong to the block
+    int startpc = -1;
+    int finishpc = -1;
+};
+
+struct BytecodeTypes
+{
+    uint8_t result = LBC_TYPE_ANY;
+    uint8_t a = LBC_TYPE_ANY;
+    uint8_t b = LBC_TYPE_ANY;
+    uint8_t c = LBC_TYPE_ANY;
+};
+
 struct IrFunction
 {
     std::vector<IrBlock> blocks;
     std::vector<IrInst> instructions;
     std::vector<IrConst> constants;
 
+    std::vector<BytecodeBlock> bcBlocks;
+    std::vector<BytecodeTypes> bcTypes;
+
     std::vector<BytecodeMapping> bcMapping;
     uint32_t entryBlock = 0;
     uint32_t entryLocation = 0;
 
     // For each instruction, an operand that can be used to recompute the value
     std::vector<IrOp> valueRestoreOps;
+    std::vector<uint32_t> validRestoreOpBlocks;
     uint32_t validRestoreOpBlockIdx = 0;
 
     Proto* proto = nullptr;
@@ -1086,22 +1108,53 @@ struct IrFunction
         if (instIdx >= valueRestoreOps.size())
             return {};
 
-        const IrBlock& block = blocks[validRestoreOpBlockIdx];
+        if (FFlag::LuauKeepVmapLinear2)
-
-        // When spilled, values can only reference restore operands in the current block
-        if (limitToCurrentBlock)
         {
-            if (instIdx < block.start || instIdx > block.finish)
+            // When spilled, values can only reference restore operands in the current block chain
-                return {};
+            if (limitToCurrentBlock)
-        }
+            {
+                for (uint32_t blockIdx : validRestoreOpBlocks)
+                {
+                    const IrBlock& block = blocks[blockIdx];
 
-        return valueRestoreOps[instIdx];
+                    if (instIdx >= block.start && instIdx <= block.finish)
+                        return valueRestoreOps[instIdx];
+                }
+
+                return {};
+            }
+
+            return valueRestoreOps[instIdx];
+        }
+        else
+        {
+            const IrBlock& block = blocks[validRestoreOpBlockIdx];
+
+            // When spilled, values can only reference restore operands in the current block
+            if (limitToCurrentBlock)
+            {
+                if (instIdx < block.start || instIdx > block.finish)
+                    return {};
+            }
+
+            return valueRestoreOps[instIdx];
+        }
     }
 
     IrOp findRestoreOp(const IrInst& inst, bool limitToCurrentBlock) const
     {
         return findRestoreOp(getInstIndex(inst), limitToCurrentBlock);
     }
+
+    BytecodeTypes getBytecodeTypesAt(int pcpos) const
+    {
+        LUAU_ASSERT(pcpos >= 0);
+
+        if (size_t(pcpos) < bcTypes.size())
+            return bcTypes[pcpos];
+
+        return BytecodeTypes();
+    }
 };
 
 inline IrCondition conditionOp(IrOp op)

CodeGen/include/Luau/IrDump.h

@@ -29,6 +29,7 @@ void toString(IrToStringContext& ctx, const IrBlock& block, uint32_t index); //
 void toString(IrToStringContext& ctx, IrOp op);
 
 void toString(std::string& result, IrConst constant);
+void toString(std::string& result, const BytecodeTypes& bcTypes);
 
 void toStringDetailed(IrToStringContext& ctx, const IrBlock& block, uint32_t blockIdx, const IrInst& inst, uint32_t instIdx, bool includeUseInfo);
 void toStringDetailed(IrToStringContext& ctx, const IrBlock& block, uint32_t index, bool includeUseInfo); // Block title

CodeGen/src/BytecodeAnalysis.cpp

@@ -0,0 +1,884 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#include "Luau/BytecodeAnalysis.h"
+
+#include "Luau/BytecodeUtils.h"
+#include "Luau/IrData.h"
+#include "Luau/IrUtils.h"
+
+#include "lobject.h"
+
+namespace Luau
+{
+namespace CodeGen
+{
+
+static bool hasTypedParameters(Proto* proto)
+{
+    return proto->typeinfo && proto->numparams != 0;
+}
+
+static uint8_t getBytecodeConstantTag(Proto* proto, unsigned ki)
+{
+    TValue protok = proto->k[ki];
+
+    switch (protok.tt)
+    {
+    case LUA_TNIL:
+        return LBC_TYPE_NIL;
+    case LUA_TBOOLEAN:
+        return LBC_TYPE_BOOLEAN;
+    case LUA_TLIGHTUSERDATA:
+        return LBC_TYPE_USERDATA;
+    case LUA_TNUMBER:
+        return LBC_TYPE_NUMBER;
+    case LUA_TVECTOR:
+        return LBC_TYPE_VECTOR;
+    case LUA_TSTRING:
+        return LBC_TYPE_STRING;
+    case LUA_TTABLE:
+        return LBC_TYPE_TABLE;
+    case LUA_TFUNCTION:
+        return LBC_TYPE_FUNCTION;
+    case LUA_TUSERDATA:
+        return LBC_TYPE_USERDATA;
+    case LUA_TTHREAD:
+        return LBC_TYPE_THREAD;
+    case LUA_TBUFFER:
+        return LBC_TYPE_BUFFER;
+    }
+
+    return LBC_TYPE_ANY;
+}
+
+static void applyBuiltinCall(int bfid, BytecodeTypes& types)
+{
+    switch (bfid)
+    {
+    case LBF_NONE:
+    case LBF_ASSERT:
+        types.result = LBC_TYPE_ANY;
+        break;
+    case LBF_MATH_ABS:
+    case LBF_MATH_ACOS:
+    case LBF_MATH_ASIN:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_ATAN2:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_ATAN:
+    case LBF_MATH_CEIL:
+    case LBF_MATH_COSH:
+    case LBF_MATH_COS:
+    case LBF_MATH_DEG:
+    case LBF_MATH_EXP:
+    case LBF_MATH_FLOOR:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_FMOD:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_FREXP:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_LDEXP:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_LOG10:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_LOG:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER; // We can mark optional arguments
+        break;
+    case LBF_MATH_MAX:
+    case LBF_MATH_MIN:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER; // We can mark optional arguments
+        break;
+    case LBF_MATH_MODF:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_POW:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_RAD:
+    case LBF_MATH_SINH:
+    case LBF_MATH_SIN:
+    case LBF_MATH_SQRT:
+    case LBF_MATH_TANH:
+    case LBF_MATH_TAN:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BIT32_ARSHIFT:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BIT32_BAND:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER; // We can mark optional arguments
+        break;
+    case LBF_BIT32_BNOT:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BIT32_BOR:
+    case LBF_BIT32_BXOR:
+    case LBF_BIT32_BTEST:
+    case LBF_BIT32_EXTRACT:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER; // We can mark optional arguments
+        break;
+    case LBF_BIT32_LROTATE:
+    case LBF_BIT32_LSHIFT:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BIT32_REPLACE:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER; // We can mark optional arguments
+        break;
+    case LBF_BIT32_RROTATE:
+    case LBF_BIT32_RSHIFT:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_TYPE:
+        types.result = LBC_TYPE_STRING;
+        break;
+    case LBF_STRING_BYTE:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_STRING;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_STRING_CHAR:
+        types.result = LBC_TYPE_STRING;
+
+        // We can mark optional arguments
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_STRING_LEN:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_STRING;
+        break;
+    case LBF_TYPEOF:
+        types.result = LBC_TYPE_STRING;
+        break;
+    case LBF_STRING_SUB:
+        types.result = LBC_TYPE_STRING;
+        types.a = LBC_TYPE_STRING;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_CLAMP:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_SIGN:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_MATH_ROUND:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_RAWGET:
+        types.result = LBC_TYPE_ANY;
+        types.a = LBC_TYPE_TABLE;
+        break;
+    case LBF_RAWEQUAL:
+        types.result = LBC_TYPE_BOOLEAN;
+        break;
+    case LBF_TABLE_UNPACK:
+        types.result = LBC_TYPE_ANY;
+        types.a = LBC_TYPE_TABLE;
+        types.b = LBC_TYPE_NUMBER; // We can mark optional arguments
+        break;
+    case LBF_VECTOR:
+        types.result = LBC_TYPE_VECTOR;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BIT32_COUNTLZ:
+    case LBF_BIT32_COUNTRZ:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_SELECT_VARARG:
+        types.result = LBC_TYPE_ANY;
+        break;
+    case LBF_RAWLEN:
+        types.result = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BIT32_EXTRACTK:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_GETMETATABLE:
+        types.result = LBC_TYPE_TABLE;
+        break;
+    case LBF_TONUMBER:
+        types.result = LBC_TYPE_NUMBER;
+        break;
+    case LBF_TOSTRING:
+        types.result = LBC_TYPE_STRING;
+        break;
+    case LBF_BIT32_BYTESWAP:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_READI8:
+    case LBF_BUFFER_READU8:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_WRITEU8:
+        types.result = LBC_TYPE_NIL;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_READI16:
+    case LBF_BUFFER_READU16:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_WRITEU16:
+        types.result = LBC_TYPE_NIL;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_READI32:
+    case LBF_BUFFER_READU32:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_WRITEU32:
+        types.result = LBC_TYPE_NIL;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_READF32:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_WRITEF32:
+        types.result = LBC_TYPE_NIL;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_READF64:
+        types.result = LBC_TYPE_NUMBER;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        break;
+    case LBF_BUFFER_WRITEF64:
+        types.result = LBC_TYPE_NIL;
+        types.a = LBC_TYPE_BUFFER;
+        types.b = LBC_TYPE_NUMBER;
+        types.c = LBC_TYPE_NUMBER;
+        break;
+    case LBF_TABLE_INSERT:
+        types.result = LBC_TYPE_NIL;
+        types.a = LBC_TYPE_TABLE;
+        break;
+    case LBF_RAWSET:
+        types.result = LBC_TYPE_ANY;
+        types.a = LBC_TYPE_TABLE;
+        break;
+    case LBF_SETMETATABLE:
+        types.result = LBC_TYPE_TABLE;
+        types.a = LBC_TYPE_TABLE;
+        types.b = LBC_TYPE_TABLE;
+        break;
+    }
+}
+
+void buildBytecodeBlocks(IrFunction& function, const std::vector<uint8_t>& jumpTargets)
+{
+    Proto* proto = function.proto;
+    LUAU_ASSERT(proto);
+
+    std::vector<BytecodeBlock>& bcBlocks = function.bcBlocks;
+
+    // Using the same jump targets, create VM bytecode basic blocks
+    bcBlocks.push_back(BytecodeBlock{0, -1});
+
+    int previ = 0;
+
+    for (int i = 0; i < proto->sizecode;)
+    {
+        const Instruction* pc = &proto->code[i];
+        LuauOpcode op = LuauOpcode(LUAU_INSN_OP(*pc));
+
+        int nexti = i + getOpLength(op);
+
+        // If instruction is a jump target, begin new block starting from it
+        if (i != 0 && jumpTargets[i])
+        {
+            bcBlocks.back().finishpc = previ;
+            bcBlocks.push_back(BytecodeBlock{i, -1});
+        }
+
+        int target = getJumpTarget(*pc, uint32_t(i));
+
+        // Implicit fallthroughs terminate the block and might start a new one
+        if (target >= 0 && !isFastCall(op))
+        {
+            bcBlocks.back().finishpc = i;
+
+            // Start a new block if there was no explicit jump for the fallthrough
+            if (!jumpTargets[nexti])
+                bcBlocks.push_back(BytecodeBlock{nexti, -1});
+        }
+        // Returns just terminate the block
+        else if (op == LOP_RETURN)
+        {
+            bcBlocks.back().finishpc = i;
+        }
+
+        previ = i;
+        i = nexti;
+        LUAU_ASSERT(i <= proto->sizecode);
+    }
+}
+
+void analyzeBytecodeTypes(IrFunction& function)
+{
+    Proto* proto = function.proto;
+    LUAU_ASSERT(proto);
+
+    // Setup our current knowledge of type tags based on arguments
+    uint8_t regTags[256];
+    memset(regTags, LBC_TYPE_ANY, 256);
+
+    function.bcTypes.resize(proto->sizecode);
+
+    // Now that we have VM basic blocks, we can attempt to track register type tags locally
+    for (const BytecodeBlock& block : function.bcBlocks)
+    {
+        LUAU_ASSERT(block.startpc != -1);
+        LUAU_ASSERT(block.finishpc != -1);
+
+        // At the block start, reset or knowledge to the starting state
+        // In the future we might be able to propagate some info between the blocks as well
+        if (hasTypedParameters(proto))
+        {
+            for (int i = 0; i < proto->numparams; ++i)
+            {
+                uint8_t et = proto->typeinfo[2 + i];
+
+                // TODO: if argument is optional, this might force a VM exit unnecessarily
+                regTags[i] = et & ~LBC_TYPE_OPTIONAL_BIT;
+            }
+        }
+
+        for (int i = proto->numparams; i < proto->maxstacksize; ++i)
+            regTags[i] = LBC_TYPE_ANY;
+
+        for (int i = block.startpc; i <= block.finishpc;)
+        {
+            const Instruction* pc = &proto->code[i];
+            LuauOpcode op = LuauOpcode(LUAU_INSN_OP(*pc));
+
+            BytecodeTypes& bcType = function.bcTypes[i];
+
+            switch (op)
+            {
+            case LOP_NOP:
+                break;
+            case LOP_LOADNIL:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                regTags[ra] = LBC_TYPE_NIL;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_LOADB:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                regTags[ra] = LBC_TYPE_BOOLEAN;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_LOADN:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                regTags[ra] = LBC_TYPE_NUMBER;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_LOADK:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int kb = LUAU_INSN_D(*pc);
+                bcType.a = getBytecodeConstantTag(proto, kb);
+                regTags[ra] = bcType.a;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_LOADKX:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int kb = int(pc[1]);
+                bcType.a = getBytecodeConstantTag(proto, kb);
+                regTags[ra] = bcType.a;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_MOVE:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                bcType.a = regTags[rb];
+                regTags[ra] = regTags[rb];
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_GETTABLE:
+            {
+                int rb = LUAU_INSN_B(*pc);
+                int rc = LUAU_INSN_C(*pc);
+                bcType.a = regTags[rb];
+                bcType.b = regTags[rc];
+                break;
+            }
+            case LOP_SETTABLE:
+            {
+                int rb = LUAU_INSN_B(*pc);
+                int rc = LUAU_INSN_C(*pc);
+                bcType.a = regTags[rb];
+                bcType.b = regTags[rc];
+                break;
+            }
+            case LOP_GETTABLEKS:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                uint32_t kc = pc[1];
+
+                bcType.a = regTags[rb];
+                bcType.b = getBytecodeConstantTag(proto, kc);
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                // Assuming that vector component is being indexed
+                // TODO: check what key is used
+                if (bcType.a == LBC_TYPE_VECTOR)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_SETTABLEKS:
+            {
+                int rb = LUAU_INSN_B(*pc);
+                bcType.a = regTags[rb];
+                bcType.b = LBC_TYPE_STRING;
+                break;
+            }
+            case LOP_GETTABLEN:
+            case LOP_SETTABLEN:
+            {
+                int rb = LUAU_INSN_B(*pc);
+                bcType.a = regTags[rb];
+                bcType.b = LBC_TYPE_NUMBER;
+                break;
+            }
+            case LOP_ADD:
+            case LOP_SUB:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int rc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = regTags[rc];
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER && bcType.b == LBC_TYPE_NUMBER)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+                else if (bcType.a == LBC_TYPE_VECTOR && bcType.b == LBC_TYPE_VECTOR)
+                    regTags[ra] = LBC_TYPE_VECTOR;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_MUL:
+            case LOP_DIV:
+            case LOP_IDIV:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int rc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = regTags[rc];
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER)
+                {
+                    if (bcType.b == LBC_TYPE_NUMBER)
+                        regTags[ra] = LBC_TYPE_NUMBER;
+                    else if (bcType.b == LBC_TYPE_VECTOR)
+                        regTags[ra] = LBC_TYPE_VECTOR;
+                }
+                else if (bcType.a == LBC_TYPE_VECTOR)
+                {
+                    if (bcType.b == LBC_TYPE_NUMBER || bcType.b == LBC_TYPE_VECTOR)
+                        regTags[ra] = LBC_TYPE_VECTOR;
+                }
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_MOD:
+            case LOP_POW:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int rc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = regTags[rc];
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER && bcType.b == LBC_TYPE_NUMBER)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_ADDK:
+            case LOP_SUBK:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int kc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = getBytecodeConstantTag(proto, kc);
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER && bcType.b == LBC_TYPE_NUMBER)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+                else if (bcType.a == LBC_TYPE_VECTOR && bcType.b == LBC_TYPE_VECTOR)
+                    regTags[ra] = LBC_TYPE_VECTOR;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_MULK:
+            case LOP_DIVK:
+            case LOP_IDIVK:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int kc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = getBytecodeConstantTag(proto, kc);
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER)
+                {
+                    if (bcType.b == LBC_TYPE_NUMBER)
+                        regTags[ra] = LBC_TYPE_NUMBER;
+                    else if (bcType.b == LBC_TYPE_VECTOR)
+                        regTags[ra] = LBC_TYPE_VECTOR;
+                }
+                else if (bcType.a == LBC_TYPE_VECTOR)
+                {
+                    if (bcType.b == LBC_TYPE_NUMBER || bcType.b == LBC_TYPE_VECTOR)
+                        regTags[ra] = LBC_TYPE_VECTOR;
+                }
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_MODK:
+            case LOP_POWK:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int kc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = getBytecodeConstantTag(proto, kc);
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER && bcType.b == LBC_TYPE_NUMBER)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_SUBRK:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int kb = LUAU_INSN_B(*pc);
+                int rc = LUAU_INSN_C(*pc);
+
+                bcType.a = getBytecodeConstantTag(proto, kb);
+                bcType.b = regTags[rc];
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER && bcType.b == LBC_TYPE_NUMBER)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+                else if (bcType.a == LBC_TYPE_VECTOR && bcType.b == LBC_TYPE_VECTOR)
+                    regTags[ra] = LBC_TYPE_VECTOR;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_DIVRK:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+                int kc = LUAU_INSN_C(*pc);
+
+                bcType.a = regTags[rb];
+                bcType.b = getBytecodeConstantTag(proto, kc);
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER)
+                {
+                    if (bcType.b == LBC_TYPE_NUMBER)
+                        regTags[ra] = LBC_TYPE_NUMBER;
+                    else if (bcType.b == LBC_TYPE_VECTOR)
+                        regTags[ra] = LBC_TYPE_VECTOR;
+                }
+                else if (bcType.a == LBC_TYPE_VECTOR)
+                {
+                    if (bcType.b == LBC_TYPE_NUMBER || bcType.b == LBC_TYPE_VECTOR)
+                        regTags[ra] = LBC_TYPE_VECTOR;
+                }
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_NOT:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+
+                bcType.a = regTags[rb];
+
+                regTags[ra] = LBC_TYPE_BOOLEAN;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_MINUS:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+
+                bcType.a = regTags[rb];
+
+                regTags[ra] = LBC_TYPE_ANY;
+
+                if (bcType.a == LBC_TYPE_NUMBER)
+                    regTags[ra] = LBC_TYPE_NUMBER;
+                else if (bcType.a == LBC_TYPE_VECTOR)
+                    regTags[ra] = LBC_TYPE_VECTOR;
+
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_LENGTH:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                int rb = LUAU_INSN_B(*pc);
+
+                bcType.a = regTags[rb];
+
+                regTags[ra] = LBC_TYPE_NUMBER; // Even if it's a custom __len, it's ok to assume a sane result
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_NEWTABLE:
+            case LOP_DUPTABLE:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                regTags[ra] = LBC_TYPE_TABLE;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_FASTCALL:
+            {
+                int bfid = LUAU_INSN_A(*pc);
+                int skip = LUAU_INSN_C(*pc);
+
+                Instruction call = pc[skip + 1];
+                LUAU_ASSERT(LUAU_INSN_OP(call) == LOP_CALL);
+                int ra = LUAU_INSN_A(call);
+
+                applyBuiltinCall(bfid, bcType);
+                regTags[ra + 1] = bcType.a;
+                regTags[ra + 2] = bcType.b;
+                regTags[ra + 3] = bcType.c;
+                regTags[ra] = bcType.result;
+                break;
+            }
+            case LOP_FASTCALL1:
+            case LOP_FASTCALL2K:
+            {
+                int bfid = LUAU_INSN_A(*pc);
+                int skip = LUAU_INSN_C(*pc);
+
+                Instruction call = pc[skip + 1];
+                LUAU_ASSERT(LUAU_INSN_OP(call) == LOP_CALL);
+                int ra = LUAU_INSN_A(call);
+
+                applyBuiltinCall(bfid, bcType);
+
+                regTags[LUAU_INSN_B(*pc)] = bcType.a;
+                regTags[ra] = bcType.result;
+                break;
+            }
+            case LOP_FASTCALL2:
+            {
+                int bfid = LUAU_INSN_A(*pc);
+                int skip = LUAU_INSN_C(*pc);
+
+                Instruction call = pc[skip + 1];
+                LUAU_ASSERT(LUAU_INSN_OP(call) == LOP_CALL);
+                int ra = LUAU_INSN_A(call);
+
+                applyBuiltinCall(bfid, bcType);
+
+                regTags[LUAU_INSN_B(*pc)] = bcType.a;
+                regTags[int(pc[1])] = bcType.b;
+                regTags[ra] = bcType.result;
+                break;
+            }
+            case LOP_FORNPREP:
+            {
+                int ra = LUAU_INSN_A(*pc);
+
+                regTags[ra] = LBC_TYPE_NUMBER;
+                regTags[ra + 1] = LBC_TYPE_NUMBER;
+                regTags[ra + 2] = LBC_TYPE_NUMBER;
+                break;
+            }
+            case LOP_FORNLOOP:
+            {
+                int ra = LUAU_INSN_A(*pc);
+
+                // These types are established by LOP_FORNPREP and we reinforce that here
+                regTags[ra] = LBC_TYPE_NUMBER;
+                regTags[ra + 1] = LBC_TYPE_NUMBER;
+                regTags[ra + 2] = LBC_TYPE_NUMBER;
+                break;
+            }
+            case LOP_CONCAT:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                regTags[ra] = LBC_TYPE_STRING;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_NEWCLOSURE:
+            case LOP_DUPCLOSURE:
+            {
+                int ra = LUAU_INSN_A(*pc);
+                regTags[ra] = LBC_TYPE_FUNCTION;
+                bcType.result = regTags[ra];
+                break;
+            }
+            case LOP_GETGLOBAL:
+            case LOP_SETGLOBAL:
+            case LOP_CALL:
+            case LOP_RETURN:
+            case LOP_JUMP:
+            case LOP_JUMPBACK:
+            case LOP_JUMPIF:
+            case LOP_JUMPIFNOT:
+            case LOP_JUMPIFEQ:
+            case LOP_JUMPIFLE:
+            case LOP_JUMPIFLT:
+            case LOP_JUMPIFNOTEQ:
+            case LOP_JUMPIFNOTLE:
+            case LOP_JUMPIFNOTLT:
+            case LOP_JUMPX:
+            case LOP_JUMPXEQKNIL:
+            case LOP_JUMPXEQKB:
+            case LOP_JUMPXEQKN:
+            case LOP_JUMPXEQKS:
+            case LOP_SETLIST:
+            case LOP_GETUPVAL:
+            case LOP_SETUPVAL:
+            case LOP_CLOSEUPVALS:
+            case LOP_FORGLOOP:
+            case LOP_FORGPREP_NEXT:
+            case LOP_FORGPREP_INEXT:
+            case LOP_AND:
+            case LOP_ANDK:
+            case LOP_OR:
+            case LOP_ORK:
+            case LOP_COVERAGE:
+            case LOP_GETIMPORT:
+            case LOP_CAPTURE:
+            case LOP_NAMECALL:
+            case LOP_PREPVARARGS:
+            case LOP_GETVARARGS:
+            case LOP_FORGPREP:
+                break;
+            default:
+                LUAU_ASSERT(!"Unknown instruction");
+            }
+
+            i += getOpLength(op);
+        }
+    }
+}
+
+} // namespace CodeGen
+} // namespace Luau

CodeGen/src/CodeGenAssembly.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/CodeGen.h"
+#include "Luau/BytecodeUtils.h"
 
 #include "CodeGenLower.h"
 
@@ -42,6 +43,17 @@ static void logFunctionHeader(AssemblyBuilder& build, Proto* proto)
         build.logAppend("\n");
 }
 
+unsigned getInstructionCount(const Instruction* insns, const unsigned size)
+{
+    unsigned count = 0;
+    for (unsigned i = 0; i < size;)
+    {
+        ++count;
+        i += Luau::getOpLength(LuauOpcode(LUAU_INSN_OP(insns[i])));
+    }
+    return count;
+}
+
 template<typename AssemblyBuilder>
 static std::string getAssemblyImpl(AssemblyBuilder& build, const TValue* func, AssemblyOptions options, LoweringStats* stats)
 {
@@ -53,7 +65,11 @@ static std::string getAssemblyImpl(AssemblyBuilder& build, const TValue* func, A
     std::vector<Proto*> protos;
     gatherFunctions(protos, root, options.flags);
 
-    protos.erase(std::remove_if(protos.begin(), protos.end(), [](Proto* p) { return p == nullptr; }), protos.end());
+    protos.erase(std::remove_if(protos.begin(), protos.end(),
+                     [](Proto* p) {
+                         return p == nullptr;
+                     }),
+        protos.end());
 
     if (stats)
         stats->totalFunctions += unsigned(protos.size());
@@ -77,6 +93,7 @@ static std::string getAssemblyImpl(AssemblyBuilder& build, const TValue* func, A
     {
         IrBuilder ir;
         ir.buildFunctionIr(p);
+        unsigned asmCount = build.getCodeSize();
 
         if (options.includeAssembly || options.includeIr)
             logFunctionHeader(build, p);
@@ -86,9 +103,24 @@ static std::string getAssemblyImpl(AssemblyBuilder& build, const TValue* func, A
             if (build.logText)
                 build.logAppend("; skipping (can't lower)\n");
 
+            asmCount = 0;
+
             if (stats)
                 stats->skippedFunctions += 1;
         }
+        else
+        {
+            asmCount = build.getCodeSize() - asmCount;
+        }
+
+        if (stats && stats->collectFunctionStats)
+        {
+            const char* name = p->debugname ? getstr(p->debugname) : "";
+            int line = p->linedefined;
+            unsigned bcodeCount = getInstructionCount(p->code, p->sizecode);
+            unsigned irCount = unsigned(ir.function.instructions.size());
+            stats->functions.push_back({name, line, bcodeCount, irCount, asmCount});
+        }
 
         if (build.logText)
             build.logAppend("\n");

CodeGen/src/CodeGenLower.h

@@ -26,6 +26,7 @@ LUAU_FASTFLAG(DebugCodegenSkipNumbering)
 LUAU_FASTINT(CodegenHeuristicsInstructionLimit)
 LUAU_FASTINT(CodegenHeuristicsBlockLimit)
 LUAU_FASTINT(CodegenHeuristicsBlockInstructionLimit)
+LUAU_FASTFLAG(LuauKeepVmapLinear2)
 
 namespace Luau
 {
@@ -112,8 +113,16 @@ inline bool lowerImpl(AssemblyBuilder& build, IrLowering& lowering, IrFunction&
             toStringDetailed(ctx, block, blockIndex, /* includeUseInfo */ true);
         }
 
-        // Values can only reference restore operands in the current block
+        if (FFlag::LuauKeepVmapLinear2)
-        function.validRestoreOpBlockIdx = blockIndex;
+        {
+            // Values can only reference restore operands in the current block chain
+            function.validRestoreOpBlocks.push_back(blockIndex);
+        }
+        else
+        {
+            // Values can only reference restore operands in the current block
+            function.validRestoreOpBlockIdx = blockIndex;
+        }
 
         build.setLabel(block.label);
 
@@ -139,6 +148,15 @@ inline bool lowerImpl(AssemblyBuilder& build, IrLowering& lowering, IrFunction&
             if (outputEnabled && options.annotator && bcLocation != ~0u)
             {
                 options.annotator(options.annotatorContext, build.text, bytecodeid, bcLocation);
+
+                // If available, report inferred register tags
+                BytecodeTypes bcTypes = function.getBytecodeTypesAt(bcLocation);
+
+                if (bcTypes.result != LBC_TYPE_ANY || bcTypes.a != LBC_TYPE_ANY || bcTypes.b != LBC_TYPE_ANY || bcTypes.c != LBC_TYPE_ANY)
+                {
+                    toString(ctx.result, bcTypes);
+                    build.logAppend("\n");
+                }
             }
 
             // If bytecode needs the location of this instruction for jumps, record it
@@ -190,6 +208,9 @@ inline bool lowerImpl(AssemblyBuilder& build, IrLowering& lowering, IrFunction&
 
         if (options.includeIr)
             build.logAppend("#\n");
+
+        if (FFlag::LuauKeepVmapLinear2 && block.expectedNextBlock == ~0u)
+            function.validRestoreOpBlocks.clear();
     }
 
     if (!seenFallback)

CodeGen/src/CodeGenUtils.cpp

@@ -426,7 +426,7 @@ const Instruction* executeGETTABLEKS(lua_State* L, const Instruction* pc, StkId
 
             if (unsigned(ic) < LUA_VECTOR_SIZE && name[1] == '\0')
             {
-                const float* v = rb->value.v; // silences ubsan when indexing v[]
+                const float* v = vvalue(rb); // silences ubsan when indexing v[]
                 setnvalue(ra, v[ic]);
                 return pc;
             }

CodeGen/src/IrBuilder.cpp

@@ -2,6 +2,7 @@
 #include "Luau/IrBuilder.h"
 
 #include "Luau/Bytecode.h"
+#include "Luau/BytecodeAnalysis.h"
 #include "Luau/BytecodeUtils.h"
 #include "Luau/IrData.h"
 #include "Luau/IrUtils.h"
@@ -12,6 +13,8 @@
 
 #include <string.h>
 
+LUAU_FASTFLAGVARIABLE(LuauCodegenBytecodeInfer, false)
+
 namespace Luau
 {
 namespace CodeGen
@@ -119,6 +122,10 @@ void IrBuilder::buildFunctionIr(Proto* proto)
     // Rebuild original control flow blocks
     rebuildBytecodeBasicBlocks(proto);
 
+    // Infer register tags in bytecode
+    if (FFlag::LuauCodegenBytecodeInfer)
+        analyzeBytecodeTypes(function);
+
     function.bcMapping.resize(proto->sizecode, {~0u, ~0u});
 
     if (generateTypeChecks)
@@ -152,7 +159,7 @@ void IrBuilder::buildFunctionIr(Proto* proto)
         // Numeric for loops require additional processing to maintain loop stack
         // Notably, this must be performed even when the block is dead so that we maintain the pairing FORNPREP-FORNLOOP
         if (op == LOP_FORNPREP)
-            beforeInstForNPrep(*this, pc);
+            beforeInstForNPrep(*this, pc, i);
 
         // We skip dead bytecode instructions when they appear after block was already terminated
         if (!inTerminatedBlock)
@@ -212,7 +219,6 @@ void IrBuilder::rebuildBytecodeBasicBlocks(Proto* proto)
         LUAU_ASSERT(i <= proto->sizecode);
     }
 
-
     // Bytecode blocks are created at bytecode jump targets and the start of a function
     jumpTargets[0] = true;
 
@@ -224,6 +230,9 @@ void IrBuilder::rebuildBytecodeBasicBlocks(Proto* proto)
             instIndexToBlock[i] = b.index;
         }
     }
+
+    if (FFlag::LuauCodegenBytecodeInfer)
+        buildBytecodeBlocks(function, jumpTargets);
 }
 
 void IrBuilder::translateInst(LuauOpcode op, const Instruction* pc, int i)

CodeGen/src/IrDump.cpp

@@ -432,7 +432,10 @@ void toString(IrToStringContext& ctx, IrOp op)
         append(ctx.result, "U%d", vmUpvalueOp(op));
         break;
     case IrOpKind::VmExit:
-        append(ctx.result, "exit(%d)", vmExitOp(op));
+        if (vmExitOp(op) == kVmExitEntryGuardPc)
+            append(ctx.result, "exit(entry)");
+        else
+            append(ctx.result, "exit(%d)", vmExitOp(op));
         break;
     }
 }
@@ -459,6 +462,47 @@ void toString(std::string& result, IrConst constant)
     }
 }
 
+const char* getBytecodeTypeName(uint8_t type)
+{
+    switch (type)
+    {
+    case LBC_TYPE_NIL:
+        return "nil";
+    case LBC_TYPE_BOOLEAN:
+        return "boolean";
+    case LBC_TYPE_NUMBER:
+        return "number";
+    case LBC_TYPE_STRING:
+        return "string";
+    case LBC_TYPE_TABLE:
+        return "table";
+    case LBC_TYPE_FUNCTION:
+        return "function";
+    case LBC_TYPE_THREAD:
+        return "thread";
+    case LBC_TYPE_USERDATA:
+        return "userdata";
+    case LBC_TYPE_VECTOR:
+        return "vector";
+    case LBC_TYPE_BUFFER:
+        return "buffer";
+    case LBC_TYPE_ANY:
+        return "any";
+    }
+
+    LUAU_ASSERT(!"Unhandled type in getBytecodeTypeName");
+    return nullptr;
+}
+
+void toString(std::string& result, const BytecodeTypes& bcTypes)
+{
+    if (bcTypes.c != LBC_TYPE_ANY)
+        append(result, "%s <- %s, %s, %s", getBytecodeTypeName(bcTypes.result), getBytecodeTypeName(bcTypes.a), getBytecodeTypeName(bcTypes.b),
+            getBytecodeTypeName(bcTypes.c));
+    else
+        append(result, "%s <- %s, %s", getBytecodeTypeName(bcTypes.result), getBytecodeTypeName(bcTypes.a), getBytecodeTypeName(bcTypes.b));
+}
+
 static void appendBlockSet(IrToStringContext& ctx, BlockIteratorWrapper blocks)
 {
     bool comma = false;

CodeGen/src/IrLoweringX64.cpp

@@ -1912,7 +1912,7 @@ void IrLoweringX64::finishBlock(const IrBlock& curr, const IrBlock& next)
     {
         // If we have spills remaining, we have to immediately lower the successor block
         for (uint32_t predIdx : predecessors(function.cfg, function.getBlockIndex(next)))
-            LUAU_ASSERT(predIdx == function.getBlockIndex(curr));
+            LUAU_ASSERT(predIdx == function.getBlockIndex(curr) || function.blocks[predIdx].kind == IrBlockKind::Dead);
 
         // And the next block cannot be a join block in cfg
         LUAU_ASSERT(next.useCount == 1);

CodeGen/src/IrTranslateBuiltins.cpp

@@ -9,7 +9,6 @@
 #include <math.h>
 
 LUAU_FASTFLAGVARIABLE(LuauBufferTranslateIr, false)
-LUAU_FASTFLAGVARIABLE(LuauImproveInsertIr, false)
 
 // TODO: when nresults is less than our actual result count, we can skip computing/writing unused results
 
@@ -691,34 +690,24 @@ static BuiltinImplResult translateBuiltinTableInsert(IrBuilder& build, int npara
 
     IrOp setnum = build.inst(IrCmd::TABLE_SETNUM, table, pos);
 
-    if (FFlag::LuauImproveInsertIr)
+    if (args.kind == IrOpKind::Constant)
     {
-        if (args.kind == IrOpKind::Constant)
+        LUAU_ASSERT(build.function.constOp(args).kind == IrConstKind::Double);
-        {
-            LUAU_ASSERT(build.function.constOp(args).kind == IrConstKind::Double);
 
-            // No barrier necessary since numbers aren't collectable
+        // No barrier necessary since numbers aren't collectable
-            build.inst(IrCmd::STORE_DOUBLE, setnum, args);
+        build.inst(IrCmd::STORE_DOUBLE, setnum, args);
-            build.inst(IrCmd::STORE_TAG, setnum, build.constTag(LUA_TNUMBER));
+        build.inst(IrCmd::STORE_TAG, setnum, build.constTag(LUA_TNUMBER));
-        }
-        else
-        {
-            IrOp va = build.inst(IrCmd::LOAD_TVALUE, args);
-            build.inst(IrCmd::STORE_TVALUE, setnum, va);
-
-            // Compiler only generates FASTCALL*K for source-level constants, so dynamic imports are not affected
-            LUAU_ASSERT(build.function.proto);
-            IrOp argstag = args.kind == IrOpKind::VmConst ? build.constTag(build.function.proto->k[vmConstOp(args)].tt) : build.undef();
-
-            build.inst(IrCmd::BARRIER_TABLE_FORWARD, table, args, argstag);
-        }
     }
     else
     {
         IrOp va = build.inst(IrCmd::LOAD_TVALUE, args);
         build.inst(IrCmd::STORE_TVALUE, setnum, va);
 
-        build.inst(IrCmd::BARRIER_TABLE_FORWARD, table, args, build.undef());
+        // Compiler only generates FASTCALL*K for source-level constants, so dynamic imports are not affected
+        LUAU_ASSERT(build.function.proto);
+        IrOp argstag = args.kind == IrOpKind::VmConst ? build.constTag(build.function.proto->k[vmConstOp(args)].tt) : build.undef();
+
+        build.inst(IrCmd::BARRIER_TABLE_FORWARD, table, args, argstag);
     }
 
     return {BuiltinImplType::Full, 0};

CodeGen/src/IrTranslation.cpp

@@ -12,9 +12,8 @@
 #include "lstate.h"
 #include "ltm.h"
 
-LUAU_FASTFLAGVARIABLE(LuauLowerAltLoopForn, false)
-LUAU_FASTFLAG(LuauImproveInsertIr)
 LUAU_FASTFLAGVARIABLE(LuauFullLoopLuserdata, false)
+LUAU_FASTFLAGVARIABLE(LuauLoopInterruptFix, false)
 
 namespace Luau
 {
@@ -44,6 +43,14 @@ struct FallbackStreamScope
     IrOp next;
 };
 
+static IrOp getInitializedFallback(IrBuilder& build, IrOp& fallback)
+{
+    if (fallback.kind == IrOpKind::None)
+        fallback = build.block(IrBlockKind::Fallback);
+
+    return fallback;
+}
+
 void translateInstLoadNil(IrBuilder& build, const Instruction* pc)
 {
     int ra = LUAU_INSN_A(*pc);
@@ -329,19 +336,22 @@ void translateInstJumpxEqS(IrBuilder& build, const Instruction* pc, int pcpos)
 
 static void translateInstBinaryNumeric(IrBuilder& build, int ra, int rb, int rc, IrOp opb, IrOp opc, int pcpos, TMS tm)
 {
-    IrOp fallback = build.block(IrBlockKind::Fallback);
+    IrOp fallback;
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     // fast-path: number
     if (rb != -1)
     {
         IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-        build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TNUMBER), fallback);
+        build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TNUMBER),
+            bcTypes.a == LBC_TYPE_NUMBER ? build.vmExit(pcpos) : getInitializedFallback(build, fallback));
     }
 
-    if (rc != -1 && rc != rb) // TODO: optimization should handle second check, but we'll test it later
+    if (rc != -1 && rc != rb)
     {
         IrOp tc = build.inst(IrCmd::LOAD_TAG, build.vmReg(rc));
-        build.inst(IrCmd::CHECK_TAG, tc, build.constTag(LUA_TNUMBER), fallback);
+        build.inst(IrCmd::CHECK_TAG, tc, build.constTag(LUA_TNUMBER),
+            bcTypes.b == LBC_TYPE_NUMBER ? build.vmExit(pcpos) : getInitializedFallback(build, fallback));
     }
 
     IrOp vb, vc;
@@ -420,12 +430,15 @@ static void translateInstBinaryNumeric(IrBuilder& build, int ra, int rb, int rc,
     if (ra != rb && ra != rc) // TODO: optimization should handle second check, but we'll test this later
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    IrOp next = build.blockAtInst(pcpos + 1);
+    if (fallback.kind != IrOpKind::None)
-    FallbackStreamScope scope(build, fallback, next);
+    {
+        IrOp next = build.blockAtInst(pcpos + 1);
+        FallbackStreamScope scope(build, fallback, next);
 
-    build.inst(IrCmd::SET_SAVEDPC, build.constUint(pcpos + 1));
+        build.inst(IrCmd::SET_SAVEDPC, build.constUint(pcpos + 1));
-    build.inst(IrCmd::DO_ARITH, build.vmReg(ra), opb, opc, build.constInt(tm));
+        build.inst(IrCmd::DO_ARITH, build.vmReg(ra), opb, opc, build.constInt(tm));
-    build.inst(IrCmd::JUMP, next);
+        build.inst(IrCmd::JUMP, next);
+    }
 }
 
 void translateInstBinary(IrBuilder& build, const Instruction* pc, int pcpos, TMS tm)
@@ -462,13 +475,15 @@ void translateInstNot(IrBuilder& build, const Instruction* pc)
 
 void translateInstMinus(IrBuilder& build, const Instruction* pc, int pcpos)
 {
+    IrOp fallback;
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
+
     int ra = LUAU_INSN_A(*pc);
     int rb = LUAU_INSN_B(*pc);
 
-    IrOp fallback = build.block(IrBlockKind::Fallback);
-
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TNUMBER), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TNUMBER),
+        bcTypes.a == LBC_TYPE_NUMBER ? build.vmExit(pcpos) : getInitializedFallback(build, fallback));
 
     // fast-path: number
     IrOp vb = build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(rb));
@@ -479,23 +494,29 @@ void translateInstMinus(IrBuilder& build, const Instruction* pc, int pcpos)
     if (ra != rb)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    IrOp next = build.blockAtInst(pcpos + 1);
+    if (fallback.kind != IrOpKind::None)
-    FallbackStreamScope scope(build, fallback, next);
+    {
+        IrOp next = build.blockAtInst(pcpos + 1);
+        FallbackStreamScope scope(build, fallback, next);
 
-    build.inst(IrCmd::SET_SAVEDPC, build.constUint(pcpos + 1));
+        build.inst(IrCmd::SET_SAVEDPC, build.constUint(pcpos + 1));
-    build.inst(IrCmd::DO_ARITH, build.vmReg(LUAU_INSN_A(*pc)), build.vmReg(LUAU_INSN_B(*pc)), build.vmReg(LUAU_INSN_B(*pc)), build.constInt(TM_UNM));
+        build.inst(
-    build.inst(IrCmd::JUMP, next);
+            IrCmd::DO_ARITH, build.vmReg(LUAU_INSN_A(*pc)), build.vmReg(LUAU_INSN_B(*pc)), build.vmReg(LUAU_INSN_B(*pc)), build.constInt(TM_UNM));
+        build.inst(IrCmd::JUMP, next);
+    }
 }
 
 void translateInstLength(IrBuilder& build, const Instruction* pc, int pcpos)
 {
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
+
     int ra = LUAU_INSN_A(*pc);
     int rb = LUAU_INSN_B(*pc);
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
 
     // fast-path: table without __len
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
@@ -585,7 +606,7 @@ IrOp translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool
 
     IrOp builtinArgs = args;
 
-    if (customArgs.kind == IrOpKind::VmConst && (FFlag::LuauImproveInsertIr || bfid != LBF_TABLE_INSERT))
+    if (customArgs.kind == IrOpKind::VmConst)
     {
         LUAU_ASSERT(build.function.proto);
         TValue protok = build.function.proto->k[vmConstOp(customArgs)];
@@ -656,18 +677,18 @@ static IrOp getLoopStepK(IrBuilder& build, int ra)
     return build.undef();
 }
 
-void beforeInstForNPrep(IrBuilder& build, const Instruction* pc)
+void beforeInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos)
 {
     int ra = LUAU_INSN_A(*pc);
 
     IrOp stepK = getLoopStepK(build, ra);
-    build.loopStepStack.push_back(stepK);
+    build.numericLoopStack.push_back({stepK, pcpos + 1});
 }
 
 void afterInstForNLoop(IrBuilder& build, const Instruction* pc)
 {
-    LUAU_ASSERT(!build.loopStepStack.empty());
+    LUAU_ASSERT(!build.numericLoopStack.empty());
-    build.loopStepStack.pop_back();
+    build.numericLoopStack.pop_back();
 }
 
 void translateInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos)
@@ -677,8 +698,8 @@ void translateInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos)
     IrOp loopStart = build.blockAtInst(pcpos + getOpLength(LuauOpcode(LUAU_INSN_OP(*pc))));
     IrOp loopExit = build.blockAtInst(getJumpTarget(*pc, pcpos));
 
-    LUAU_ASSERT(!build.loopStepStack.empty());
+    LUAU_ASSERT(!build.numericLoopStack.empty());
-    IrOp stepK = build.loopStepStack.back();
+    IrOp stepK = build.numericLoopStack.back().step;
 
     // When loop parameters are not numbers, VM tries to perform type coercion from string and raises an exception if that fails
     // Performing that fallback in native code increases code size and complicates CFG, obscuring the values when they are constant
@@ -696,35 +717,9 @@ void translateInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos)
         IrOp tagStep = build.inst(IrCmd::LOAD_TAG, build.vmReg(ra + 1));
         build.inst(IrCmd::CHECK_TAG, tagStep, build.constTag(LUA_TNUMBER), build.vmExit(pcpos));
 
-        if (FFlag::LuauLowerAltLoopForn)
+        IrOp step = build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(ra + 1));
-        {
-            IrOp step = build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(ra + 1));
 
-            build.inst(IrCmd::JUMP_FORN_LOOP_COND, idx, limit, step, loopStart, loopExit);
+        build.inst(IrCmd::JUMP_FORN_LOOP_COND, idx, limit, step, loopStart, loopExit);
-        }
-        else
-        {
-            IrOp direct = build.block(IrBlockKind::Internal);
-            IrOp reverse = build.block(IrBlockKind::Internal);
-
-            IrOp zero = build.constDouble(0.0);
-            IrOp step = build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(ra + 1));
-
-            // step > 0
-            // note: equivalent to 0 < step, but lowers into one instruction on both X64 and A64
-            build.inst(IrCmd::JUMP_CMP_NUM, step, zero, build.cond(IrCondition::Greater), direct, reverse);
-
-            // Condition to start the loop: step > 0 ? idx <= limit : limit <= idx
-            // We invert the condition so that loopStart is the fallthrough (false) label
-
-            // step > 0 is false, check limit <= idx
-            build.beginBlock(reverse);
-            build.inst(IrCmd::JUMP_CMP_NUM, limit, idx, build.cond(IrCondition::NotLessEqual), loopExit, loopStart);
-
-            // step > 0 is true, check idx <= limit
-            build.beginBlock(direct);
-            build.inst(IrCmd::JUMP_CMP_NUM, idx, limit, build.cond(IrCondition::NotLessEqual), loopExit, loopStart);
-        }
     }
     else
     {
@@ -752,17 +747,32 @@ void translateInstForNLoop(IrBuilder& build, const Instruction* pc, int pcpos)
 {
     int ra = LUAU_INSN_A(*pc);
 
-    IrOp loopRepeat = build.blockAtInst(getJumpTarget(*pc, pcpos));
+    int repeatJumpTarget = getJumpTarget(*pc, pcpos);
+    IrOp loopRepeat = build.blockAtInst(repeatJumpTarget);
     IrOp loopExit = build.blockAtInst(pcpos + getOpLength(LuauOpcode(LUAU_INSN_OP(*pc))));
 
-    // normally, the interrupt is placed at the beginning of the loop body by FORNPREP translation
+    LUAU_ASSERT(!build.numericLoopStack.empty());
-    // however, there are rare contrived cases where FORNLOOP ends up jumping to itself without an interrupt placed
+    IrBuilder::LoopInfo loopInfo = build.numericLoopStack.back();
-    // we detect this by checking if loopRepeat has any instructions (it should normally start with INTERRUPT) and emit a failsafe INTERRUPT if not
-    if (build.function.blockOp(loopRepeat).start == build.function.instructions.size())
-        build.inst(IrCmd::INTERRUPT, build.constUint(pcpos));
 
-    LUAU_ASSERT(!build.loopStepStack.empty());
+    if (FFlag::LuauLoopInterruptFix)
-    IrOp stepK = build.loopStepStack.back();
+    {
+        // normally, the interrupt is placed at the beginning of the loop body by FORNPREP translation
+        // however, there are rare cases where FORNLOOP might not jump directly to the first loop instruction
+        // we detect this by checking the starting instruction of the loop body from loop information stack
+        if (repeatJumpTarget != loopInfo.startpc)
+            build.inst(IrCmd::INTERRUPT, build.constUint(pcpos));
+    }
+    else
+    {
+        // normally, the interrupt is placed at the beginning of the loop body by FORNPREP translation
+        // however, there are rare contrived cases where FORNLOOP ends up jumping to itself without an interrupt placed
+        // we detect this by checking if loopRepeat has any instructions (it should normally start with INTERRUPT) and emit a failsafe INTERRUPT if
+        // not
+        if (build.function.blockOp(loopRepeat).start == build.function.instructions.size())
+            build.inst(IrCmd::INTERRUPT, build.constUint(pcpos));
+    }
+
+    IrOp stepK = loopInfo.step;
 
     IrOp limit = build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(ra + 0));
     IrOp step = stepK.kind == IrOpKind::Undef ? build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(ra + 1)) : stepK;
@@ -773,31 +783,7 @@ void translateInstForNLoop(IrBuilder& build, const Instruction* pc, int pcpos)
 
     if (stepK.kind == IrOpKind::Undef)
     {
-        if (FFlag::LuauLowerAltLoopForn)
+        build.inst(IrCmd::JUMP_FORN_LOOP_COND, idx, limit, step, loopRepeat, loopExit);
-        {
-            build.inst(IrCmd::JUMP_FORN_LOOP_COND, idx, limit, step, loopRepeat, loopExit);
-        }
-        else
-        {
-            IrOp direct = build.block(IrBlockKind::Internal);
-            IrOp reverse = build.block(IrBlockKind::Internal);
-
-            IrOp zero = build.constDouble(0.0);
-
-            // step > 0
-            // note: equivalent to 0 < step, but lowers into one instruction on both X64 and A64
-            build.inst(IrCmd::JUMP_CMP_NUM, step, zero, build.cond(IrCondition::Greater), direct, reverse);
-
-            // Condition to continue the loop: step > 0 ? idx <= limit : limit <= idx
-
-            // step > 0 is false, check limit <= idx
-            build.beginBlock(reverse);
-            build.inst(IrCmd::JUMP_CMP_NUM, limit, idx, build.cond(IrCondition::LessEqual), loopRepeat, loopExit);
-
-            // step > 0 is true, check idx <= limit
-            build.beginBlock(direct);
-            build.inst(IrCmd::JUMP_CMP_NUM, idx, limit, build.cond(IrCondition::LessEqual), loopRepeat, loopExit);
-        }
     }
     else
     {
@@ -936,9 +922,10 @@ void translateInstGetTableN(IrBuilder& build, const Instruction* pc, int pcpos)
     int c = LUAU_INSN_C(*pc);
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
 
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
 
@@ -965,9 +952,10 @@ void translateInstSetTableN(IrBuilder& build, const Instruction* pc, int pcpos)
     int c = LUAU_INSN_C(*pc);
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
 
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
 
@@ -997,11 +985,12 @@ void translateInstGetTable(IrBuilder& build, const Instruction* pc, int pcpos)
     int rc = LUAU_INSN_C(*pc);
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
     IrOp tc = build.inst(IrCmd::LOAD_TAG, build.vmReg(rc));
-    build.inst(IrCmd::CHECK_TAG, tc, build.constTag(LUA_TNUMBER), fallback);
+    build.inst(IrCmd::CHECK_TAG, tc, build.constTag(LUA_TNUMBER), bcTypes.b == LBC_TYPE_NUMBER ? build.vmExit(pcpos) : fallback);
 
     // fast-path: table with a number index
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
@@ -1034,11 +1023,12 @@ void translateInstSetTable(IrBuilder& build, const Instruction* pc, int pcpos)
     int rc = LUAU_INSN_C(*pc);
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
     IrOp tc = build.inst(IrCmd::LOAD_TAG, build.vmReg(rc));
-    build.inst(IrCmd::CHECK_TAG, tc, build.constTag(LUA_TNUMBER), fallback);
+    build.inst(IrCmd::CHECK_TAG, tc, build.constTag(LUA_TNUMBER), bcTypes.b == LBC_TYPE_NUMBER ? build.vmExit(pcpos) : fallback);
 
     // fast-path: table with a number index
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
@@ -1103,9 +1093,10 @@ void translateInstGetTableKS(IrBuilder& build, const Instruction* pc, int pcpos)
     uint32_t aux = pc[1];
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
 
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
 
@@ -1130,9 +1121,10 @@ void translateInstSetTableKS(IrBuilder& build, const Instruction* pc, int pcpos)
     uint32_t aux = pc[1];
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
-    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), fallback);
+    build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
 
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
 

CodeGen/src/IrTranslation.h

@@ -66,7 +66,7 @@ void translateInstAndX(IrBuilder& build, const Instruction* pc, int pcpos, IrOp
 void translateInstOrX(IrBuilder& build, const Instruction* pc, int pcpos, IrOp c);
 void translateInstNewClosure(IrBuilder& build, const Instruction* pc, int pcpos);
 
-void beforeInstForNPrep(IrBuilder& build, const Instruction* pc);
+void beforeInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos);
 void afterInstForNLoop(IrBuilder& build, const Instruction* pc);
 
 } // namespace CodeGen

CodeGen/src/OptimizeConstProp.cpp

@@ -8,6 +8,8 @@
 
 #include "lua.h"
 
+#include <limits.h>
+
 #include <array>
 #include <utility>
 #include <vector>
@@ -15,9 +17,9 @@
 LUAU_FASTINTVARIABLE(LuauCodeGenMinLinearBlockPath, 3)
 LUAU_FASTINTVARIABLE(LuauCodeGenReuseSlotLimit, 64)
 LUAU_FASTFLAGVARIABLE(DebugLuauAbortingChecks, false)
-LUAU_FASTFLAGVARIABLE(LuauReuseArrSlots2, false)
-LUAU_FASTFLAG(LuauLowerAltLoopForn)
 LUAU_FASTFLAGVARIABLE(LuauCodeGenFixByteLower, false)
+LUAU_FASTFLAGVARIABLE(LuauKeepVmapLinear2, false)
+LUAU_FASTFLAGVARIABLE(LuauReuseBufferChecks, false)
 
 namespace Luau
 {
@@ -194,12 +196,19 @@ struct ConstPropState
         checkArraySizeCache.clear();
     }
 
+    void invalidateHeapBufferData()
+    {
+        checkBufferLenCache.clear();
+    }
+
     void invalidateHeap()
     {
         for (int i = 0; i <= maxReg; ++i)
             invalidateHeap(regs[i]);
 
         invalidateHeapTableData();
+
+        // Buffer length checks are not invalidated since buffer size is immutable
     }
 
     void invalidateHeap(RegisterInfo& reg)
@@ -408,6 +417,7 @@ struct ConstPropState
 
         invalidateValuePropagation();
         invalidateHeapTableData();
+        invalidateHeapBufferData();
     }
 
     IrFunction& function;
@@ -435,6 +445,8 @@ struct ConstPropState
 
     std::vector<uint32_t> getArrAddrCache;
     std::vector<uint32_t> checkArraySizeCache; // Additionally, fallback block argument might be different
+
+    std::vector<uint32_t> checkBufferLenCache; // Additionally, fallback block argument might be different
 };
 
 static void handleBuiltinEffects(ConstPropState& state, LuauBuiltinFunction bfid, uint32_t firstReturnReg, int nresults)
@@ -677,7 +689,21 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
         if (inst.a.kind == IrOpKind::VmReg || inst.a.kind == IrOpKind::Inst)
         {
             if (inst.a.kind == IrOpKind::VmReg)
+            {
+                if (FFlag::LuauReuseBufferChecks && inst.b.kind == IrOpKind::Inst)
+                {
+                    if (uint32_t* prevIdx = state.getPreviousVersionedLoadIndex(IrCmd::LOAD_TVALUE, inst.a))
+                    {
+                        if (*prevIdx == inst.b.index)
+                        {
+                            kill(function, inst);
+                            break;
+                        }
+                    }
+                }
+
                 state.invalidate(inst.a);
+            }
 
             uint8_t tag = state.tryGetTag(inst.b);
             IrOp value = state.tryGetValue(inst.b);
@@ -921,8 +947,65 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
         }
         break;
     case IrCmd::CHECK_BUFFER_LEN:
-        // TODO: remove duplicate checks and extend earlier check bound when possible
+    {
+        if (!FFlag::LuauReuseBufferChecks)
+            break;
+
+        std::optional<int> bufferOffset = function.asIntOp(inst.b.kind == IrOpKind::Constant ? inst.b : state.tryGetValue(inst.b));
+        int accessSize = function.intOp(inst.c);
+        LUAU_ASSERT(accessSize > 0);
+
+        if (bufferOffset)
+        {
+            // Negative offsets and offsets overflowing signed integer will jump to fallback, no need to keep the check
+            if (*bufferOffset < 0 || unsigned(*bufferOffset) + unsigned(accessSize) >= unsigned(INT_MAX))
+            {
+                replace(function, block, index, {IrCmd::JUMP, inst.d});
+                break;
+            }
+        }
+
+        for (uint32_t prevIdx : state.checkBufferLenCache)
+        {
+            IrInst& prev = function.instructions[prevIdx];
+
+            if (prev.a != inst.a || prev.c != inst.c)
+                continue;
+
+            if (prev.b == inst.b)
+            {
+                if (FFlag::DebugLuauAbortingChecks)
+                    replace(function, inst.d, build.undef());
+                else
+                    kill(function, inst);
+                return; // Break out from both the loop and the switch
+            }
+            else if (inst.b.kind == IrOpKind::Constant && prev.b.kind == IrOpKind::Constant)
+            {
+                // If arguments are different constants, we can check if a larger bound was already tested or if the previous bound can be raised
+                int currBound = function.intOp(inst.b);
+                int prevBound = function.intOp(prev.b);
+
+                // Negative and overflowing constant offsets should already be replaced with unconditional jumps to a fallback
+                LUAU_ASSERT(currBound >= 0);
+                LUAU_ASSERT(prevBound >= 0);
+
+                if (unsigned(currBound) >= unsigned(prevBound))
+                    replace(function, prev.b, inst.b);
+
+                if (FFlag::DebugLuauAbortingChecks)
+                    replace(function, inst.d, build.undef());
+                else
+                    kill(function, inst);
+
+                return; // Break out from both the loop and the switch
+            }
+        }
+
+        if (int(state.checkBufferLenCache.size()) < FInt::LuauCodeGenReuseSlotLimit)
+            state.checkBufferLenCache.push_back(index);
         break;
+    }
     case IrCmd::BUFFER_READI8:
     case IrCmd::BUFFER_READU8:
     case IrCmd::BUFFER_WRITEI8:
@@ -969,9 +1052,6 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
     case IrCmd::LOAD_ENV:
         break;
     case IrCmd::GET_ARR_ADDR:
-        if (!FFlag::LuauReuseArrSlots2)
-            break;
-
         for (uint32_t prevIdx : state.getArrAddrCache)
         {
             const IrInst& prev = function.instructions[prevIdx];
@@ -1039,9 +1119,6 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
     case IrCmd::DUP_TABLE:
         break;
     case IrCmd::TRY_NUM_TO_INDEX:
-        if (!FFlag::LuauReuseArrSlots2)
-            break;
-
         for (uint32_t prevIdx : state.tryNumToIndexCache)
         {
             const IrInst& prev = function.instructions[prevIdx];
@@ -1079,7 +1156,7 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
         std::optional<int> arrayIndex = function.asIntOp(inst.b.kind == IrOpKind::Constant ? inst.b : state.tryGetValue(inst.b));
 
         // Negative offsets will jump to fallback, no need to keep the check
-        if (FFlag::LuauReuseArrSlots2 && arrayIndex && *arrayIndex < 0)
+        if (arrayIndex && *arrayIndex < 0)
         {
             replace(function, block, index, {IrCmd::JUMP, inst.c});
             break;
@@ -1105,9 +1182,6 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
             }
         }
 
-        if (!FFlag::LuauReuseArrSlots2)
-            break;
-
         for (uint32_t prevIdx : state.checkArraySizeCache)
         {
             const IrInst& prev = function.instructions[prevIdx];
@@ -1220,6 +1294,7 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
         // TODO: this can be relaxed when x64 emitInstSetList becomes aware of register allocator
         state.invalidateValuePropagation();
         state.invalidateHeapTableData();
+        state.invalidateHeapBufferData();
         break;
     case IrCmd::CALL:
         state.invalidateRegistersFrom(vmRegOp(inst.a));
@@ -1236,6 +1311,7 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
         // TODO: this can be relaxed when x64 emitInstForGLoop becomes aware of register allocator
         state.invalidateValuePropagation();
         state.invalidateHeapTableData();
+        state.invalidateHeapBufferData();
         break;
     case IrCmd::FORGLOOP_FALLBACK:
         state.invalidateRegistersFrom(vmRegOp(inst.a) + 2); // Rn and Rn+1 are not modified
@@ -1299,11 +1375,15 @@ static void constPropInBlock(IrBuilder& build, IrBlock& block, ConstPropState& s
         constPropInInst(state, build, function, block, inst, index);
     }
 
-    // Value numbering and load/store propagation is not performed between blocks
+    if (!FFlag::LuauKeepVmapLinear2)
-    state.invalidateValuePropagation();
+    {
+        // Value numbering and load/store propagation is not performed between blocks
+        state.invalidateValuePropagation();
 
-    // Same for table slot data propagation
+        // Same for table and buffer data propagation
-    state.invalidateHeapTableData();
+        state.invalidateHeapTableData();
+        state.invalidateHeapBufferData();
+    }
 }
 
 static void constPropInBlockChain(IrBuilder& build, std::vector<uint8_t>& visited, IrBlock* block, ConstPropState& state)
@@ -1323,6 +1403,16 @@ static void constPropInBlockChain(IrBuilder& build, std::vector<uint8_t>& visite
 
         constPropInBlock(build, *block, state);
 
+        if (FFlag::LuauKeepVmapLinear2)
+        {
+            // Value numbering and load/store propagation is not performed between blocks
+            state.invalidateValuePropagation();
+
+            // Same for table and buffer data propagation
+            state.invalidateHeapTableData();
+            state.invalidateHeapBufferData();
+        }
+
         // Blocks in a chain are guaranteed to follow each other
         // We force that by giving all blocks the same sorting key, but consecutive chain keys
         block->sortkey = startSortkey;
@@ -1341,7 +1431,7 @@ static void constPropInBlockChain(IrBuilder& build, std::vector<uint8_t>& visite
 
             if (target.useCount == 1 && !visited[targetIdx] && target.kind != IrBlockKind::Fallback)
             {
-                if (FFlag::LuauLowerAltLoopForn && getLiveOutValueCount(function, target) != 0)
+                if (getLiveOutValueCount(function, target) != 0)
                     break;
 
                 // Make sure block ordering guarantee is checked at lowering time

Compiler/src/BuiltinFolding.cpp

@@ -473,9 +473,7 @@ Constant foldBuiltin(int bfid, const Constant* args, size_t count)
         break;
 
     case LBF_VECTOR:
-        if (FFlag::LuauVectorLiterals && count >= 3 &&
+        if (FFlag::LuauVectorLiterals && count >= 3 && args[0].type == Constant::Type_Number && args[1].type == Constant::Type_Number &&
-            args[0].type == Constant::Type_Number &&
-            args[1].type == Constant::Type_Number &&
             args[2].type == Constant::Type_Number)
         {
             if (count == 3)

Compiler/src/BytecodeBuilder.cpp

@@ -366,7 +366,8 @@ int32_t BytecodeBuilder::addConstantVector(float x, float y, float z, float w)
     c.valueVector[3] = w;
 
     ConstantKey k = {Constant::Type_Vector};
-    static_assert(sizeof(k.value) == sizeof(x) + sizeof(y) && sizeof(k.extra) == sizeof(z) + sizeof(w), "Expecting vector to have four 32-bit components");
+    static_assert(
+        sizeof(k.value) == sizeof(x) + sizeof(y) && sizeof(k.extra) == sizeof(z) + sizeof(w), "Expecting vector to have four 32-bit components");
     memcpy(&k.value, &x, sizeof(x));
     memcpy((char*)&k.value + sizeof(x), &y, sizeof(y));
     memcpy(&k.extra, &z, sizeof(z));

Compiler/src/Compiler.cpp

@@ -26,9 +26,6 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineThreshold, 25)
 LUAU_FASTINTVARIABLE(LuauCompileInlineThresholdMaxBoost, 300)
 LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
-LUAU_FASTFLAGVARIABLE(LuauCompileSideEffects, false)
-LUAU_FASTFLAGVARIABLE(LuauCompileDeadIf, false)
-
 LUAU_FASTFLAGVARIABLE(LuauCompileRevK, false)
 
 namespace Luau
@@ -2245,16 +2242,13 @@ struct Compiler
 
     void compileExprSide(AstExpr* node)
     {
-        if (FFlag::LuauCompileSideEffects)
+        // Optimization: some expressions never carry side effects so we don't need to emit any code
-        {
+        if (node->is<AstExprLocal>() || node->is<AstExprGlobal>() || node->is<AstExprVarargs>() || node->is<AstExprFunction>() || isConstant(node))
-            // Optimization: some expressions never carry side effects so we don't need to emit any code
+            return;
-            if (node->is<AstExprLocal>() || node->is<AstExprGlobal>() || node->is<AstExprVarargs>() || node->is<AstExprFunction>() || isConstant(node))
-                return;
 
-            // note: the remark is omitted for calls as it's fairly noisy due to inlining
+        // note: the remark is omitted for calls as it's fairly noisy due to inlining
-            if (!node->is<AstExprCall>())
+        if (!node->is<AstExprCall>())
-                bytecode.addDebugRemark("expression only compiled for side effects");
+            bytecode.addDebugRemark("expression only compiled for side effects");
-        }
 
         RegScope rsi(this);
         compileExprAuto(node, rsi);
@@ -2544,15 +2538,12 @@ struct Compiler
         }
 
         // Optimization: condition is always false but isn't a constant => we only need the else body and condition's side effects
-        if (FFlag::LuauCompileDeadIf)
+        if (AstExprBinary* cand = stat->condition->as<AstExprBinary>(); cand && cand->op == AstExprBinary::And && isConstantFalse(cand->right))
         {
-            if (AstExprBinary* cand = stat->condition->as<AstExprBinary>(); cand && cand->op == AstExprBinary::And && isConstantFalse(cand->right))
+            compileExprSide(cand->left);
-            {
+            if (stat->elsebody)
-                compileExprSide(cand->left);
+                compileStat(stat->elsebody);
-                if (stat->elsebody)
+            return;
-                    compileStat(stat->elsebody);
-                return;
-            }
         }
 
         // Optimization: body is a "break" statement with no "else" => we can directly break out of the loop in "then" case

Compiler/src/ConstantFolding.cpp

@@ -27,11 +27,8 @@ static bool constantsEqual(const Constant& la, const Constant& ra)
         return ra.type == Constant::Type_Number && la.valueNumber == ra.valueNumber;
 
     case Constant::Type_Vector:
-        return ra.type == Constant::Type_Vector &&
+        return ra.type == Constant::Type_Vector && la.valueVector[0] == ra.valueVector[0] && la.valueVector[1] == ra.valueVector[1] &&
-            la.valueVector[0] == ra.valueVector[0] &&
+               la.valueVector[2] == ra.valueVector[2] && la.valueVector[3] == ra.valueVector[3];
-            la.valueVector[1] == ra.valueVector[1] &&
-            la.valueVector[2] == ra.valueVector[2] &&
-            la.valueVector[3] == ra.valueVector[3];
 
     case Constant::Type_String:
         return ra.type == Constant::Type_String && la.stringLength == ra.stringLength && memcmp(la.valueString, ra.valueString, la.stringLength) == 0;

Config/include/Luau/Config.h

@@ -4,8 +4,9 @@
 #include "Luau/LinterConfig.h"
 #include "Luau/ParseOptions.h"
 
-#include <string>
 #include <optional>
+#include <string>
+#include <unordered_map>
 #include <vector>
 
 namespace Luau
@@ -30,6 +31,9 @@ struct Config
     bool typeErrors = true;
 
     std::vector<std::string> globals;
+
+    std::vector<std::string> paths;
+    std::unordered_map<std::string, std::string> aliases;
 };
 
 struct ConfigResolver
@@ -50,6 +54,8 @@ std::optional<std::string> parseModeString(Mode& mode, const std::string& modeSt
 std::optional<std::string> parseLintRuleString(
     LintOptions& enabledLints, LintOptions& fatalLints, const std::string& warningName, const std::string& value, bool compat = false);
 
+bool isValidAlias(const std::string& alias);
+
 std::optional<std::string> parseConfig(const std::string& contents, Config& config, bool compat = false);
 
 } // namespace Luau

Config/src/Config.cpp

@@ -3,6 +3,8 @@
 
 #include "Luau/Lexer.h"
 #include "Luau/StringUtils.h"
+#include <algorithm>
+#include <unordered_map>
 
 namespace Luau
 {
@@ -107,6 +109,42 @@ Error parseLintRuleString(LintOptions& enabledLints, LintOptions& fatalLints, co
     return std::nullopt;
 }
 
+bool isValidAlias(const std::string& alias)
+{
+    if (alias.empty())
+        return false;
+
+    bool aliasIsNotAPath = alias != "." && alias != ".." && alias.find_first_of("\\/") == std::string::npos;
+
+    if (!aliasIsNotAPath)
+        return false;
+
+    for (char ch : alias)
+    {
+        bool isupper = 'A' <= ch && ch <= 'Z';
+        bool islower = 'a' <= ch && ch <= 'z';
+        bool isdigit = '0' <= ch && ch <= '9';
+        if (!isupper && !islower && !isdigit && ch != '-' && ch != '_' && ch != '.')
+            return false;
+    }
+
+    return true;
+}
+
+Error parseAlias(std::unordered_map<std::string, std::string>& aliases, std::string aliasKey, const std::string& aliasValue)
+{
+    if (!isValidAlias(aliasKey))
+        return Error{"Invalid alias " + aliasKey};
+
+    std::transform(aliasKey.begin(), aliasKey.end(), aliasKey.begin(), [](unsigned char c) {
+        return ('A' <= c && c <= 'Z') ? (c + ('a' - 'A')) : c;
+    });
+    if (!aliases.count(aliasKey))
+        aliases[std::move(aliasKey)] = aliasValue;
+
+    return std::nullopt;
+}
+
 static void next(Lexer& lexer)
 {
     lexer.next();
@@ -253,6 +291,13 @@ Error parseConfig(const std::string& contents, Config& config, bool compat)
             config.globals.push_back(value);
             return std::nullopt;
         }
+        else if (keys.size() == 1 && keys[0] == "paths")
+        {
+            config.paths.push_back(value);
+            return std::nullopt;
+        }
+        else if (keys.size() == 2 && keys[0] == "aliases")
+            return parseAlias(config.aliases, keys[1], value);
         else if (compat && keys.size() == 2 && keys[0] == "language" && keys[1] == "mode")
             return parseModeString(config.mode, value, compat);
         else

Makefile

@@ -38,11 +38,11 @@ ISOCLINE_SOURCES=extern/isocline/src/isocline.c
 ISOCLINE_OBJECTS=$(ISOCLINE_SOURCES:%=$(BUILD)/%.o)
 ISOCLINE_TARGET=$(BUILD)/libisocline.a
 
-TESTS_SOURCES=$(wildcard tests/*.cpp) CLI/FileUtils.cpp CLI/Flags.cpp CLI/Profiler.cpp CLI/Coverage.cpp CLI/Repl.cpp
+TESTS_SOURCES=$(wildcard tests/*.cpp) CLI/FileUtils.cpp CLI/Flags.cpp CLI/Profiler.cpp CLI/Coverage.cpp CLI/Repl.cpp CLI/Require.cpp
 TESTS_OBJECTS=$(TESTS_SOURCES:%=$(BUILD)/%.o)
 TESTS_TARGET=$(BUILD)/luau-tests
 
-REPL_CLI_SOURCES=CLI/FileUtils.cpp CLI/Flags.cpp CLI/Profiler.cpp CLI/Coverage.cpp CLI/Repl.cpp CLI/ReplEntry.cpp
+REPL_CLI_SOURCES=CLI/FileUtils.cpp CLI/Flags.cpp CLI/Profiler.cpp CLI/Coverage.cpp CLI/Repl.cpp CLI/ReplEntry.cpp CLI/Require.cpp
 REPL_CLI_OBJECTS=$(REPL_CLI_SOURCES:%=$(BUILD)/%.o)
 REPL_CLI_TARGET=$(BUILD)/luau
 
@@ -219,7 +219,7 @@ luau-tests: $(TESTS_TARGET)
 
 # executable targets
 $(TESTS_TARGET): $(TESTS_OBJECTS) $(ANALYSIS_TARGET) $(COMPILER_TARGET) $(CONFIG_TARGET) $(AST_TARGET) $(CODEGEN_TARGET) $(VM_TARGET) $(ISOCLINE_TARGET)
-$(REPL_CLI_TARGET): $(REPL_CLI_OBJECTS) $(COMPILER_TARGET) $(AST_TARGET) $(CODEGEN_TARGET) $(VM_TARGET) $(ISOCLINE_TARGET)
+$(REPL_CLI_TARGET): $(REPL_CLI_OBJECTS) $(COMPILER_TARGET) $(CONFIG_TARGET) $(AST_TARGET) $(CODEGEN_TARGET) $(VM_TARGET) $(ISOCLINE_TARGET)
 $(ANALYZE_CLI_TARGET): $(ANALYZE_CLI_OBJECTS) $(ANALYSIS_TARGET) $(AST_TARGET) $(CONFIG_TARGET)
 $(COMPILE_CLI_TARGET): $(COMPILE_CLI_OBJECTS) $(COMPILER_TARGET) $(AST_TARGET) $(CODEGEN_TARGET) $(VM_TARGET)
 $(BYTECODE_CLI_TARGET): $(BYTECODE_CLI_OBJECTS) $(COMPILER_TARGET) $(AST_TARGET) $(CODEGEN_TARGET) $(VM_TARGET)

Sources.cmake

@@ -92,6 +92,7 @@ target_sources(Luau.CodeGen PRIVATE
     CodeGen/include/Luau/UnwindBuilder.h
     CodeGen/include/Luau/UnwindBuilderDwarf2.h
     CodeGen/include/Luau/UnwindBuilderWin.h
+    CodeGen/include/Luau/BytecodeAnalysis.h
     CodeGen/include/Luau/BytecodeSummary.h
     CodeGen/include/luacodegen.h
 
@@ -125,6 +126,7 @@ target_sources(Luau.CodeGen PRIVATE
     CodeGen/src/OptimizeFinalX64.cpp
     CodeGen/src/UnwindBuilderDwarf2.cpp
     CodeGen/src/UnwindBuilderWin.cpp
+    CodeGen/src/BytecodeAnalysis.cpp
     CodeGen/src/BytecodeSummary.cpp
 
     CodeGen/src/BitUtils.h
@@ -349,7 +351,8 @@ if(TARGET Luau.Repl.CLI)
         CLI/Profiler.h
         CLI/Profiler.cpp
         CLI/Repl.cpp
-        CLI/ReplEntry.cpp)
+        CLI/ReplEntry.cpp
+        CLI/Require.cpp)
 endif()
 
 if(TARGET Luau.Analyze.CLI)
@@ -455,7 +458,7 @@ if(TARGET Luau.UnitTest)
         tests/TypeInfer.tables.test.cpp
         tests/TypeInfer.test.cpp
         tests/TypeInfer.tryUnify.test.cpp
-        tests/TypeInfer.typePacks.cpp
+        tests/TypeInfer.typePacks.test.cpp
         tests/TypeInfer.typestates.test.cpp
         tests/TypeInfer.unionTypes.test.cpp
         tests/TypeInfer.unknownnever.test.cpp
@@ -489,10 +492,12 @@ if(TARGET Luau.CLI.Test)
         CLI/Profiler.h
         CLI/Profiler.cpp
         CLI/Repl.cpp
+        CLI/Require.cpp
 
         tests/RegisterCallbacks.h
         tests/RegisterCallbacks.cpp
         tests/Repl.test.cpp
+        tests/RequireByString.test.cpp
         tests/main.cpp)
 endif()
 

VM/src/lvmexecute.cpp

@@ -521,7 +521,7 @@ reentry:
 
                         if (unsigned(ic) < LUA_VECTOR_SIZE && name[1] == '\0')
                         {
-                            const float* v = rb->value.v; // silences ubsan when indexing v[]
+                            const float* v = vvalue(rb); // silences ubsan when indexing v[]
                             setnvalue(ra, v[ic]);
                             VM_NEXT();
                         }
@@ -1464,8 +1464,8 @@ reentry:
                 }
                 else if (ttisvector(rb) && ttisvector(rc))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
-                    const float* vc = rc->value.v;
+                    const float* vc = vvalue(rc);
                     setvvalue(ra, vb[0] + vc[0], vb[1] + vc[1], vb[2] + vc[2], vb[3] + vc[3]);
                     VM_NEXT();
                 }
@@ -1510,8 +1510,8 @@ reentry:
                 }
                 else if (ttisvector(rb) && ttisvector(rc))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
-                    const float* vc = rc->value.v;
+                    const float* vc = vvalue(rc);
                     setvvalue(ra, vb[0] - vc[0], vb[1] - vc[1], vb[2] - vc[2], vb[3] - vc[3]);
                     VM_NEXT();
                 }
@@ -1556,22 +1556,22 @@ reentry:
                 }
                 else if (ttisvector(rb) && ttisnumber(rc))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
                     float vc = cast_to(float, nvalue(rc));
                     setvvalue(ra, vb[0] * vc, vb[1] * vc, vb[2] * vc, vb[3] * vc);
                     VM_NEXT();
                 }
                 else if (ttisvector(rb) && ttisvector(rc))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
-                    const float* vc = rc->value.v;
+                    const float* vc = vvalue(rc);
                     setvvalue(ra, vb[0] * vc[0], vb[1] * vc[1], vb[2] * vc[2], vb[3] * vc[3]);
                     VM_NEXT();
                 }
                 else if (ttisnumber(rb) && ttisvector(rc))
                 {
                     float vb = cast_to(float, nvalue(rb));
-                    const float* vc = rc->value.v;
+                    const float* vc = vvalue(rc);
                     setvvalue(ra, vb * vc[0], vb * vc[1], vb * vc[2], vb * vc[3]);
                     VM_NEXT();
                 }
@@ -1617,22 +1617,22 @@ reentry:
                 }
                 else if (ttisvector(rb) && ttisnumber(rc))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
                     float vc = cast_to(float, nvalue(rc));
                     setvvalue(ra, vb[0] / vc, vb[1] / vc, vb[2] / vc, vb[3] / vc);
                     VM_NEXT();
                 }
                 else if (ttisvector(rb) && ttisvector(rc))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
-                    const float* vc = rc->value.v;
+                    const float* vc = vvalue(rc);
                     setvvalue(ra, vb[0] / vc[0], vb[1] / vc[1], vb[2] / vc[2], vb[3] / vc[3]);
                     VM_NEXT();
                 }
                 else if (ttisnumber(rb) && ttisvector(rc))
                 {
                     float vb = cast_to(float, nvalue(rb));
-                    const float* vc = rc->value.v;
+                    const float* vc = vvalue(rc);
                     setvvalue(ra, vb / vc[0], vb / vc[1], vb / vc[2], vb / vc[3]);
                     VM_NEXT();
                 }
@@ -1812,7 +1812,7 @@ reentry:
                 }
                 else if (ttisvector(rb))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
                     float vc = cast_to(float, nvalue(kv));
                     setvvalue(ra, vb[0] * vc, vb[1] * vc, vb[2] * vc, vb[3] * vc);
                     VM_NEXT();
@@ -2071,7 +2071,7 @@ reentry:
                 }
                 else if (ttisvector(rb))
                 {
-                    const float* vb = rb->value.v;
+                    const float* vb = vvalue(rb);
                     setvvalue(ra, -vb[0], -vb[1], -vb[2], -vb[3]);
                     VM_NEXT();
                 }

VM/src/lvmutils.cpp

@@ -46,7 +46,7 @@ int luaV_tostring(lua_State* L, StkId obj)
 const float* luaV_tovector(const TValue* obj)
 {
     if (ttisvector(obj))
-        return obj->value.v;
+        return vvalue(obj);
 
     return nullptr;
 }

fuzz/CMakeLists.txt

@@ -0,0 +1,105 @@
+# This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+cmake_minimum_required(VERSION 3.26)
+
+include(FetchContent)
+
+cmake_policy(SET CMP0054 NEW)
+cmake_policy(SET CMP0058 NEW)
+cmake_policy(SET CMP0074 NEW)
+cmake_policy(SET CMP0077 NEW)
+cmake_policy(SET CMP0091 NEW)
+
+if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    message(WARNING "Building the Luau fuzzer requires Clang to be used. AppleClang is not sufficient.")
+    return()
+endif()
+
+if(NOT CMAKE_OSX_ARCHITECTURES STREQUAL "x86_64")
+    message(WARNING "Building the Luau fuzzer for ARM64 is currently unsupported.")
+    return()
+endif()
+
+# protobuf / std integer types vary based on platform; disable sign-compare
+# warnings for portability.
+set(FUZZ_COMPILE_OPTIONS ${LUAU_OPTIONS} -fsanitize=address,fuzzer -g2 -Wno-sign-compare)
+set(FUZZ_LINK_OPTIONS ${LUAU_OPTIONS} -fsanitize=address,fuzzer)
+
+FetchContent_Declare(
+    ProtobufMutator
+    GIT_REPOSITORY https://github.com/google/libprotobuf-mutator
+    GIT_TAG 212a7be1eb08e7f9c79732d2aab9b2097085d936
+    # libprotobuf-mutator unconditionally configures its examples, but this
+    # doesn't actually work with how we're building Protobuf from source. This
+    # patch disables configuration of the examples.
+    PATCH_COMMAND
+    git apply
+    --reverse
+    --check
+    --ignore-space-change
+    --ignore-whitespace
+    "${CMAKE_CURRENT_SOURCE_DIR}/libprotobuf-mutator-patch.patch"
+    ||
+    git apply
+    --ignore-space-change
+    --ignore-whitespace
+    "${CMAKE_CURRENT_SOURCE_DIR}/libprotobuf-mutator-patch.patch"
+)
+
+FetchContent_Declare(
+    Protobuf
+    GIT_REPOSITORY https://github.com/protocolbuffers/protobuf.git
+    # Needs to match the Protobuf version that libprotobuf-mutator is written for, roughly.
+    GIT_TAG v22.3
+    GIT_SHALLOW ON
+
+    # libprotobuf-mutator will need to be able to find this at configuration
+    # time.
+    OVERRIDE_FIND_PACKAGE
+)
+
+set(protobuf_BUILD_TESTS OFF)
+set(protobuf_BUILD_SHARED_LIBS OFF)
+# libprotobuf-mutator relies on older module support.
+set(protobuf_MODULE_COMPATIBLE ON)
+
+find_package(Protobuf CONFIG REQUIRED)
+
+# libprotobuf-mutator happily ignores CMP0077 because of its minimum version
+# requirement. To override that, we set the policy default here.
+set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
+set(LIB_PROTO_MUTATOR_TESTING OFF)
+
+FetchContent_MakeAvailable(ProtobufMutator)
+
+# This patches around the fact that find_package isn't going to set the right
+# values for libprotobuf-mutator to link against protobuf libraries.
+target_link_libraries(protobuf-mutator-libfuzzer protobuf::libprotobuf)
+target_link_libraries(protobuf-mutator protobuf::libprotobuf)
+
+set(LUAU_PB_DIR ${CMAKE_CURRENT_BINARY_DIR}/protobuf)
+set(LUAU_PB_SOURCES ${LUAU_PB_DIR}/luau.pb.cc ${LUAU_PB_DIR}/luau.pb.h)
+
+add_custom_command(
+    OUTPUT ${LUAU_PB_SOURCES}
+    COMMAND ${CMAKE_COMMAND} -E make_directory ${LUAU_PB_DIR}
+    COMMAND $<TARGET_FILE:protobuf::protoc> ${CMAKE_CURRENT_SOURCE_DIR}/luau.proto --proto_path=${CMAKE_CURRENT_SOURCE_DIR} --cpp_out=${LUAU_PB_DIR}
+    DEPENDS protobuf::protoc ${CMAKE_CURRENT_SOURCE_DIR}/luau.proto
+)
+
+add_executable(Luau.Fuzz.Proto)
+target_compile_options(Luau.Fuzz.Proto PRIVATE ${FUZZ_COMPILE_OPTIONS})
+target_link_options(Luau.Fuzz.Proto PRIVATE ${FUZZ_LINK_OPTIONS})
+target_compile_features(Luau.Fuzz.Proto PRIVATE cxx_std_17)
+target_include_directories(Luau.Fuzz.Proto PRIVATE ${LUAU_PB_DIR} ${protobufmutator_SOURCE_DIR})
+target_sources(Luau.Fuzz.Proto PRIVATE ${LUAU_PB_SOURCES} proto.cpp protoprint.cpp)
+target_link_libraries(Luau.Fuzz.Proto PRIVATE protobuf::libprotobuf protobuf-mutator-libfuzzer protobuf-mutator Luau.Analysis Luau.Compiler Luau.Ast Luau.Config Luau.VM Luau.CodeGen)
+set_target_properties(Luau.Fuzz.Proto PROPERTIES CXX_STANDARD_REQUIRED ON CXX_EXTENSIONS OFF OUTPUT_NAME fuzz-proto)
+
+add_executable(Luau.Fuzz.ProtoTest)
+target_compile_options(Luau.Fuzz.ProtoTest PRIVATE ${FUZZ_COMPILE_OPTIONS})
+target_link_options(Luau.Fuzz.ProtoTest PRIVATE ${FUZZ_LINK_OPTIONS})
+target_compile_features(Luau.Fuzz.ProtoTest PRIVATE cxx_std_17)
+target_include_directories(Luau.Fuzz.ProtoTest PRIVATE ${LUAU_PB_DIR} ${protobufmutator_SOURCE_DIR})
+target_sources(Luau.Fuzz.ProtoTest PRIVATE ${LUAU_PB_SOURCES} prototest.cpp protoprint.cpp)
+target_link_libraries(Luau.Fuzz.ProtoTest PRIVATE protobuf::libprotobuf protobuf-mutator-libfuzzer protobuf-mutator)
+set_target_properties(Luau.Fuzz.ProtoTest PROPERTIES CXX_STANDARD_REQUIRED ON CXX_EXTENSIONS OFF OUTPUT_NAME fuzz-prototest)

fuzz/libprotobuf-mutator-patch.patch

@@ -0,0 +1,12 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 4805c82..9f0df5c 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -149,7 +149,6 @@ add_subdirectory(src)
+ 
+ if (NOT "${LIB_PROTO_MUTATOR_FUZZER_LIBRARIES}" STREQUAL "" OR
+     NOT "${FUZZING_FLAGS}" STREQUAL "")
+-  add_subdirectory(examples EXCLUDE_FROM_ALL)
+ endif()
+ 
+ install(EXPORT libprotobuf-mutatorTargets FILE libprotobuf-mutatorTargets.cmake

tests/AstJsonEncoder.test.cpp

@@ -11,12 +11,14 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(LuauClipExtraHasEndProps);
+
 struct JsonEncoderFixture
 {
     Allocator allocator;
     AstNameTable names{allocator};
 
-    ScopedFastFlag sff{"LuauClipExtraHasEndProps", true};
+    ScopedFastFlag sff{FFlag::LuauClipExtraHasEndProps, true};
 
     ParseResult parse(std::string_view src)
     {
@@ -93,7 +95,7 @@ TEST_CASE("basic_escaping")
 
 TEST_CASE("encode_AstStatBlock")
 {
-    ScopedFastFlag sff{"LuauClipExtraHasEndProps", true};
+    ScopedFastFlag sff{FFlag::LuauClipExtraHasEndProps, true};
 
     AstLocal astlocal{AstName{"a_local"}, Location(), nullptr, 0, 0, nullptr};
     AstLocal* astlocalarray[] = {&astlocal};

tests/Autocomplete.test.cpp

@@ -15,6 +15,8 @@
 
 LUAU_FASTFLAG(LuauTraceTypesInNonstrictMode2)
 LUAU_FASTFLAG(LuauSetMetatableDoesNotTimeTravel)
+LUAU_FASTFLAG(LuauAutocompleteStringLiteralBounds);
+LUAU_FASTFLAG(LuauAutocompleteDoEnd);
 
 using namespace Luau;
 
@@ -978,7 +980,7 @@ TEST_CASE_FIXTURE(ACFixture, "autocomplete_end_with_lambda")
 
 TEST_CASE_FIXTURE(ACFixture, "autocomplete_end_of_do_block")
 {
-    ScopedFastFlag sff{"LuauAutocompleteDoEnd", true};
+    ScopedFastFlag sff{FFlag::LuauAutocompleteDoEnd, true};
 
     check("do @1");
 
@@ -3105,7 +3107,7 @@ TEST_CASE_FIXTURE(ACFixture, "string_singleton_as_table_key")
 // https://github.com/Roblox/luau/issues/858
 TEST_CASE_FIXTURE(ACFixture, "string_singleton_in_if_statement")
 {
-    ScopedFastFlag sff{"LuauAutocompleteStringLiteralBounds", true};
+    ScopedFastFlag sff{FFlag::LuauAutocompleteStringLiteralBounds, true};
 
     check(R"(
         --!strict

tests/Compiler.test.cpp

@@ -15,6 +15,15 @@ namespace Luau
 std::string rep(const std::string& s, size_t n);
 }
 
+LUAU_FASTFLAG(LuauVectorLiterals)
+LUAU_FASTFLAG(LuauCompileRevK)
+LUAU_FASTINT(LuauCompileInlineDepth)
+LUAU_FASTINT(LuauCompileInlineThreshold)
+LUAU_FASTINT(LuauCompileInlineThresholdMaxBoost)
+LUAU_FASTINT(LuauCompileLoopUnrollThreshold)
+LUAU_FASTINT(LuauCompileLoopUnrollThresholdMaxBoost)
+LUAU_FASTINT(LuauRecursionLimit)
+
 using namespace Luau;
 
 static std::string compileFunction(const char* source, uint32_t id, int optimizationLevel = 1, bool enableVectors = false)
@@ -1173,7 +1182,7 @@ RETURN R0 1
 
 TEST_CASE("AndOrChainCodegen")
 {
-    ScopedFastFlag sff("LuauCompileRevK", true);
+    ScopedFastFlag sff(FFlag::LuauCompileRevK, true);
 
     const char* source = R"(
     return
@@ -1986,7 +1995,7 @@ RETURN R0 0
 
 TEST_CASE("LoopContinueCorrectlyHandlesImplicitConstantAfterUnroll")
 {
-    ScopedFastInt sfi("LuauCompileLoopUnrollThreshold", 200);
+    ScopedFastInt sfi(FInt::LuauCompileLoopUnrollThreshold, 200);
 
     // access to implicit constant that depends on the unrolled loop constant is still invalid even though we can constant-propagate it
     try
@@ -2097,7 +2106,7 @@ RETURN R0 0
 
 TEST_CASE("AndOrOptimizations")
 {
-    ScopedFastFlag sff("LuauCompileRevK", true);
+    ScopedFastFlag sff(FFlag::LuauCompileRevK, true);
 
     // the OR/ORK optimization triggers for cutoff since lhs is simple
     CHECK_EQ("\n" + compileFunction(R"(
@@ -2297,9 +2306,9 @@ TEST_CASE("RecursionParse")
     // The test forcibly pushes the stack limit during compilation; in NoOpt, the stack consumption is much larger so we need to reduce the limit to
     // not overflow the C stack. When ASAN is enabled, stack consumption increases even more.
 #if defined(LUAU_ENABLE_ASAN)
-    ScopedFastInt flag("LuauRecursionLimit", 200);
+    ScopedFastInt flag(FInt::LuauRecursionLimit, 200);
 #elif defined(_NOOPT) || defined(_DEBUG)
-    ScopedFastInt flag("LuauRecursionLimit", 300);
+    ScopedFastInt flag(FInt::LuauRecursionLimit, 300);
 #endif
 
     Luau::BytecodeBuilder bcb;
@@ -4481,7 +4490,7 @@ L0: RETURN R0 -1
 
 TEST_CASE("VectorLiterals")
 {
-    ScopedFastFlag sff("LuauVectorLiterals", true);
+    ScopedFastFlag sff(FFlag::LuauVectorLiterals, true);
 
     CHECK_EQ("\n" + compileFunction("return Vector3.new(1, 2, 3)", 0, 2, /*enableVectors*/ true), R"(
 LOADK R0 K0 [1, 2, 3]
@@ -4793,8 +4802,8 @@ L1: RETURN R0 0
 TEST_CASE("LoopUnrollControlFlow")
 {
     ScopedFastInt sfis[] = {
-        {"LuauCompileLoopUnrollThreshold", 50},
+        {FInt::LuauCompileLoopUnrollThreshold, 50},
-        {"LuauCompileLoopUnrollThresholdMaxBoost", 300},
+        {FInt::LuauCompileLoopUnrollThresholdMaxBoost, 300},
     };
 
     // break jumps to the end
@@ -4930,8 +4939,8 @@ RETURN R0 0
 TEST_CASE("LoopUnrollCost")
 {
     ScopedFastInt sfis[] = {
-        {"LuauCompileLoopUnrollThreshold", 25},
+        {FInt::LuauCompileLoopUnrollThreshold, 25},
-        {"LuauCompileLoopUnrollThresholdMaxBoost", 300},
+        {FInt::LuauCompileLoopUnrollThresholdMaxBoost, 300},
     };
 
     // loops with short body
@@ -5108,8 +5117,8 @@ L1: RETURN R0 0
 TEST_CASE("LoopUnrollCostBuiltins")
 {
     ScopedFastInt sfis[] = {
-        {"LuauCompileLoopUnrollThreshold", 25},
+        {FInt::LuauCompileLoopUnrollThreshold, 25},
-        {"LuauCompileLoopUnrollThresholdMaxBoost", 300},
+        {FInt::LuauCompileLoopUnrollThresholdMaxBoost, 300},
     };
 
     // this loop uses builtins and is close to the cost budget so it's important that we model builtins as cheaper than regular calls
@@ -5986,9 +5995,9 @@ RETURN R3 1
 TEST_CASE("InlineThresholds")
 {
     ScopedFastInt sfis[] = {
-        {"LuauCompileInlineThreshold", 25},
+        {FInt::LuauCompileInlineThreshold, 25},
-        {"LuauCompileInlineThresholdMaxBoost", 300},
+        {FInt::LuauCompileInlineThresholdMaxBoost, 300},
-        {"LuauCompileInlineDepth", 2},
+        {FInt::LuauCompileInlineDepth, 2},
     };
 
     // this function has enormous register pressure (50 regs) so we choose not to inline it
@@ -7725,8 +7734,6 @@ RETURN R1 1
 
 TEST_CASE("SideEffects")
 {
-    ScopedFastFlag sff("LuauCompileSideEffects", true);
-
     // we do not evaluate expressions in some cases when we know they can't carry side effects
     CHECK_EQ("\n" + compileFunction0(R"(
 local x = 5, print
@@ -7778,9 +7785,6 @@ RETURN R0 0
 
 TEST_CASE("IfElimination")
 {
-    ScopedFastFlag sff1("LuauCompileDeadIf", true);
-    ScopedFastFlag sff2("LuauCompileSideEffects", true);
-
     // if the left hand side of a condition is constant, it constant folds and we don't emit the branch
     CHECK_EQ("\n" + compileFunction0("local a = false if a and b then b() end"), R"(
 RETURN R0 0
@@ -7848,7 +7852,7 @@ RETURN R0 1
 
 TEST_CASE("ArithRevK")
 {
-    ScopedFastFlag sff("LuauCompileRevK", true);
+    ScopedFastFlag sff(FFlag::LuauCompileRevK, true);
 
     // - and / have special optimized form for reverse constants; in the future, + and * will likely get compiled to ADDK/MULK
     // other operators are not important enough to optimize reverse constant forms for

tests/Conformance.test.cpp

@@ -26,6 +26,14 @@ extern bool verbose;
 extern bool codegen;
 extern int optimizationLevel;
 
+LUAU_FASTFLAG(LuauBit32Byteswap);
+LUAU_FASTFLAG(LuauBufferBetterMsg);
+LUAU_FASTFLAG(LuauBufferDefinitions);
+LUAU_FASTFLAG(LuauCodeGenFixByteLower);
+LUAU_FASTFLAG(LuauCompileBufferAnnotation);
+LUAU_FASTFLAG(LuauLoopInterruptFix);
+LUAU_DYNAMIC_FASTFLAG(LuauStricterUtf8);
+
 static lua_CompileOptions defaultOptions()
 {
     lua_CompileOptions copts = {};
@@ -288,7 +296,9 @@ static std::vector<Luau::CodeGen::FunctionBytecodeSummary> analyzeFile(const cha
     std::unique_ptr<lua_State, void (*)(lua_State*)> globalState(luaL_newstate(), lua_close);
     lua_State* L = globalState.get();
 
-    LUAU_ASSERT(luau_load(L, "source", bytecode.data(), bytecode.size(), 0) == 0);
+    int result = luau_load(L, "source", bytecode.data(), bytecode.size(), 0);
+    REQUIRE(result == 0);
+
     return Luau::CodeGen::summarizeBytecode(L, -1, nestingLimit);
 }
 
@@ -312,8 +322,8 @@ TEST_CASE("Basic")
 
 TEST_CASE("Buffers")
 {
-    ScopedFastFlag luauBufferBetterMsg{"LuauBufferBetterMsg", true};
+    ScopedFastFlag luauBufferBetterMsg{FFlag::LuauBufferBetterMsg, true};
-    ScopedFastFlag luauCodeGenFixByteLower{"LuauCodeGenFixByteLower", true};
+    ScopedFastFlag luauCodeGenFixByteLower{FFlag::LuauCodeGenFixByteLower, true};
 
     runConformance("buffers.lua");
 }
@@ -429,13 +439,13 @@ TEST_CASE("GC")
 
 TEST_CASE("Bitwise")
 {
-    ScopedFastFlag sffs{"LuauBit32Byteswap", true};
+    ScopedFastFlag sffs{FFlag::LuauBit32Byteswap, true};
     runConformance("bitwise.lua");
 }
 
 TEST_CASE("UTF8")
 {
-    ScopedFastFlag sff("LuauStricterUtf8", true);
+    ScopedFastFlag sff(DFFlag::LuauStricterUtf8, true);
     runConformance("utf8.lua");
 }
 
@@ -580,7 +590,7 @@ static void populateRTTI(lua_State* L, Luau::TypeId type)
 
 TEST_CASE("Types")
 {
-    ScopedFastFlag luauBufferDefinitions{"LuauBufferDefinitions", true};
+    ScopedFastFlag luauBufferDefinitions{FFlag::LuauBufferDefinitions, true};
 
     runConformance("types.lua", [](lua_State* L) {
         Luau::NullModuleResolver moduleResolver;
@@ -1528,6 +1538,8 @@ TEST_CASE("GCDump")
 
 TEST_CASE("Interrupt")
 {
+    ScopedFastFlag luauLoopInterruptFix{FFlag::LuauLoopInterruptFix, true};
+
     lua_CompileOptions copts = defaultOptions();
     copts.optimizationLevel = 1; // disable loop unrolling to get fixed expected hit results
 
@@ -1586,12 +1598,12 @@ TEST_CASE("Interrupt")
         if (gc >= 0)
             return;
 
-        CHECK(index < 10);
+        CHECK(index < 11);
-        if (++index == 10)
+        if (++index == 11)
             lua_yield(L, 0);
     };
 
-    for (int test = 1; test <= 9; ++test)
+    for (int test = 1; test <= 10; ++test)
     {
         lua_State* T = lua_newthread(L);
 
@@ -1601,7 +1613,7 @@ TEST_CASE("Interrupt")
         index = 0;
         int status = lua_resume(T, nullptr, 0);
         CHECK(status == LUA_YIELD);
-        CHECK(index == 10);
+        CHECK(index == 11);
 
         // abandon the thread
         lua_pop(L, 1);
@@ -1913,8 +1925,6 @@ TEST_CASE("SafeEnv")
 
 TEST_CASE("Native")
 {
-    ScopedFastFlag luauLowerAltLoopForn{"LuauLowerAltLoopForn", true};
-
     runConformance("native.lua");
 }
 
@@ -1924,7 +1934,7 @@ TEST_CASE("NativeTypeAnnotations")
     if (!codegen || !luau_codegen_supported())
         return;
 
-    ScopedFastFlag luauCompileBufferAnnotation{"LuauCompileBufferAnnotation", true};
+    ScopedFastFlag luauCompileBufferAnnotation{FFlag::LuauCompileBufferAnnotation, true};
 
     lua_CompileOptions copts = defaultOptions();
     copts.vectorCtor = "vector";

tests/ConstraintGeneratorFixture.cpp

@@ -1,5 +1,8 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "ConstraintGeneratorFixture.h"
+#include "ScopedFlags.h"
+
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 
 namespace Luau
 {
@@ -7,7 +10,7 @@ namespace Luau
 ConstraintGeneratorFixture::ConstraintGeneratorFixture()
     : Fixture()
     , mainModule(new Module)
-    , forceTheFlag{"DebugLuauDeferredConstraintResolution", true}
+    , forceTheFlag{FFlag::DebugLuauDeferredConstraintResolution, true}
 {
     mainModule->name = "MainModule";
     mainModule->humanReadableName = "MainModule";

tests/DataFlowGraph.test.cpp

@@ -10,10 +10,12 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+
 struct DataFlowGraphFixture
 {
     // Only needed to fix the operator== reflexivity of an empty Symbol.
-    ScopedFastFlag dcr{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag dcr{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     InternalErrorReporter handle;
 

tests/Differ.test.cpp

@@ -590,7 +590,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_table_cyclic_diamonds_unraveled")
 TEST_CASE_FIXTURE(DifferFixture, "equal_function_cyclic")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         function foo()
@@ -611,7 +611,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_function_cyclic")
 TEST_CASE_FIXTURE(DifferFixture, "equal_function_table_cyclic")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         function foo()
@@ -638,7 +638,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_function_table_cyclic")
 TEST_CASE_FIXTURE(DifferFixture, "function_table_self_referential_cyclic")
 {
     // Old solver does not correctly infer function typepacks
-    // ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    // ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         function foo()
@@ -685,7 +685,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_union_cyclic")
 TEST_CASE_FIXTURE(DifferFixture, "equal_intersection_cyclic")
 {
     // Old solver does not correctly refine test types
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo1(x: number)
@@ -883,7 +883,7 @@ TEST_CASE_FIXTURE(DifferFixture, "intersection_tables_missing_left")
 TEST_CASE_FIXTURE(DifferFixture, "equal_function")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number)
@@ -901,7 +901,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_function")
 TEST_CASE_FIXTURE(DifferFixture, "equal_function_inferred_ret_length")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function bar(x: number, y: string)
@@ -925,7 +925,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_function_inferred_ret_length")
 TEST_CASE_FIXTURE(DifferFixture, "equal_function_inferred_ret_length_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function bar(x: number, y: string)
@@ -946,7 +946,7 @@ TEST_CASE_FIXTURE(DifferFixture, "equal_function_inferred_ret_length_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_arg_normal")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: number, z: number)
@@ -965,7 +965,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_arg_normal")
 TEST_CASE_FIXTURE(DifferFixture, "function_arg_normal_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: number, z: string)
@@ -984,7 +984,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_arg_normal_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_ret_normal")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: number, z: string)
@@ -1003,7 +1003,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_ret_normal")
 TEST_CASE_FIXTURE(DifferFixture, "function_arg_length")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: number)
@@ -1022,7 +1022,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_arg_length")
 TEST_CASE_FIXTURE(DifferFixture, "function_arg_length_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: string, z: number)
@@ -1041,7 +1041,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_arg_length_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_arg_length_none")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo()
@@ -1060,7 +1060,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_arg_length_none")
 TEST_CASE_FIXTURE(DifferFixture, "function_arg_length_none_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number)
@@ -1079,7 +1079,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_arg_length_none_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_ret_length")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: number)
@@ -1098,7 +1098,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_ret_length")
 TEST_CASE_FIXTURE(DifferFixture, "function_ret_length_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: string, z: number)
@@ -1117,7 +1117,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_ret_length_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_ret_length_none")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: string)
@@ -1136,7 +1136,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_ret_length_none")
 TEST_CASE_FIXTURE(DifferFixture, "function_ret_length_none_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo()
@@ -1155,7 +1155,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_ret_length_none_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_variadic_arg_normal")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: string, ...: number)
@@ -1174,7 +1174,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_variadic_arg_normal")
 TEST_CASE_FIXTURE(DifferFixture, "function_variadic_arg_missing")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: string, ...: number)
@@ -1193,7 +1193,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_variadic_arg_missing")
 TEST_CASE_FIXTURE(DifferFixture, "function_variadic_arg_missing_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x: number, y: string)
@@ -1212,7 +1212,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_variadic_arg_missing_2")
 TEST_CASE_FIXTURE(DifferFixture, "function_variadic_oversaturation")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     -- allowed to be oversaturated
@@ -1231,7 +1231,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_variadic_oversaturation")
 TEST_CASE_FIXTURE(DifferFixture, "function_variadic_oversaturation_2")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     -- must not be oversaturated
@@ -1250,7 +1250,7 @@ TEST_CASE_FIXTURE(DifferFixture, "function_variadic_oversaturation_2")
 TEST_CASE_FIXTURE(DifferFixture, "generic")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo(x, y)
@@ -1269,7 +1269,7 @@ TEST_CASE_FIXTURE(DifferFixture, "generic")
 TEST_CASE_FIXTURE(DifferFixture, "generic_one_vs_two")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo<X>(x: X, y: X)
@@ -1288,7 +1288,7 @@ TEST_CASE_FIXTURE(DifferFixture, "generic_one_vs_two")
 TEST_CASE_FIXTURE(DifferFixture, "generic_three_or_three")
 {
     // Old solver does not correctly infer function typepacks
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
     function foo<X, Y>(x: X, y: X, z: Y)
@@ -1329,7 +1329,7 @@ TEST_CASE_FIXTURE(DifferFixtureWithBuiltins, "equal_metatable")
 
 TEST_CASE_FIXTURE(DifferFixtureWithBuiltins, "metatable_normal")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", false};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, false};
 
     CheckResult result = check(R"(
     local metaFoo = {

tests/Error.test.cpp

@@ -6,6 +6,8 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(LuauStacklessTypeClone3);
+
 TEST_SUITE_BEGIN("ErrorTests");
 
 TEST_CASE("TypeError_code_should_return_nonzero_code")
@@ -17,7 +19,7 @@ TEST_CASE("TypeError_code_should_return_nonzero_code")
 TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_names_show_instead_of_tables")
 {
     frontend.options.retainFullTypeGraphs = false;
-    ScopedFastFlag sff{"LuauStacklessTypeClone3", true};
+    ScopedFastFlag sff{FFlag::LuauStacklessTypeClone3, true};
     CheckResult result = check(R"(
 --!strict
 local Account = {}

tests/Fixture.cpp

@@ -22,6 +22,7 @@
 static const char* mainModuleName = "MainModule";
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(DebugLuauFreezeArena);
 
 extern std::optional<unsigned> randomSeed; // tests/main.cpp
 
@@ -136,7 +137,7 @@ const Config& TestConfigResolver::getConfig(const ModuleName& name) const
 }
 
 Fixture::Fixture(bool freeze, bool prepareAutocomplete)
-    : sff_DebugLuauFreezeArena("DebugLuauFreezeArena", freeze)
+    : sff_DebugLuauFreezeArena(FFlag::DebugLuauFreezeArena, freeze)
     , frontend(&fileResolver, &configResolver,
           {/* retainFullTypeGraphs= */ true, /* forAutocomplete */ false, /* runLintChecks */ false, /* randomConstraintResolutionSeed */ randomSeed})
     , builtinTypes(frontend.builtinTypes)

tests/Fixture.h

@@ -22,6 +22,8 @@
 #include <unordered_map>
 #include <optional>
 
+LUAU_FASTFLAG(LuauBufferTypeck);
+
 namespace Luau
 {
 
@@ -99,7 +101,7 @@ struct Fixture
 
     ScopedFastFlag sff_DebugLuauFreezeArena;
 
-    ScopedFastFlag luauBufferTypeck{"LuauBufferTypeck", true};
+    ScopedFastFlag luauBufferTypeck{FFlag::LuauBufferTypeck, true};
 
     TestFileResolver fileResolver;
     TestConfigResolver configResolver;

tests/Frontend.test.cpp

@@ -13,6 +13,8 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAG(DebugLuauFreezeArena);
+LUAU_FASTFLAG(CorrectEarlyReturnInMarkDirty);
 
 namespace
 {
@@ -1112,7 +1114,7 @@ a:b() -- this should error, since A doesn't define a:b()
 TEST_CASE("no_use_after_free_with_type_fun_instantiation")
 {
     // This flag forces this test to crash if there's a UAF in this code.
-    ScopedFastFlag sff_DebugLuauFreezeArena("DebugLuauFreezeArena", true);
+    ScopedFastFlag sff_DebugLuauFreezeArena(FFlag::DebugLuauFreezeArena, true);
 
     FrontendFixture fix;
 
@@ -1252,7 +1254,7 @@ TEST_CASE_FIXTURE(FrontendFixture, "parse_only")
 
 TEST_CASE_FIXTURE(FrontendFixture, "markdirty_early_return")
 {
-    ScopedFastFlag fflag("CorrectEarlyReturnInMarkDirty", true);
+    ScopedFastFlag fflag(FFlag::CorrectEarlyReturnInMarkDirty, true);
 
     constexpr char moduleName[] = "game/Gui/Modules/A";
     fileResolver.source[moduleName] = R"(

tests/IrBuilder.test.cpp

@@ -13,6 +13,8 @@
 
 using namespace Luau::CodeGen;
 
+LUAU_FASTFLAG(LuauReuseBufferChecks);
+
 class IrBuilderFixture
 {
 public:
@@ -2058,8 +2060,6 @@ bb_fallback_1:
 
 TEST_CASE_FIXTURE(IrBuilderFixture, "DuplicateArrayElemChecksSameIndex")
 {
-    ScopedFastFlag luauReuseHashSlots{"LuauReuseArrSlots2", true};
-
     IrOp block = build.block(IrBlockKind::Internal);
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
@@ -2115,8 +2115,6 @@ bb_fallback_1:
 
 TEST_CASE_FIXTURE(IrBuilderFixture, "DuplicateArrayElemChecksSameValue")
 {
-    ScopedFastFlag luauReuseHashSlots{"LuauReuseArrSlots2", true};
-
     IrOp block = build.block(IrBlockKind::Internal);
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
@@ -2180,8 +2178,6 @@ bb_fallback_1:
 
 TEST_CASE_FIXTURE(IrBuilderFixture, "DuplicateArrayElemChecksLowerIndex")
 {
-    ScopedFastFlag luauReuseHashSlots{"LuauReuseArrSlots2", true};
-
     IrOp block = build.block(IrBlockKind::Internal);
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
@@ -2236,8 +2232,6 @@ bb_fallback_1:
 
 TEST_CASE_FIXTURE(IrBuilderFixture, "DuplicateArrayElemChecksInvalidations")
 {
-    ScopedFastFlag luauReuseHashSlots{"LuauReuseArrSlots2", true};
-
     IrOp block = build.block(IrBlockKind::Internal);
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
@@ -2296,8 +2290,6 @@ bb_fallback_1:
 
 TEST_CASE_FIXTURE(IrBuilderFixture, "ArrayElemChecksNegativeIndex")
 {
-    ScopedFastFlag luauReuseHashSlots{"LuauReuseArrSlots2", true};
-
     IrOp block = build.block(IrBlockKind::Internal);
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
@@ -2343,6 +2335,111 @@ bb_fallback_1:
 )");
 }
 
+TEST_CASE_FIXTURE(IrBuilderFixture, "DuplicateBufferLengthChecks")
+{
+    ScopedFastFlag luauReuseBufferChecks{FFlag::LuauReuseBufferChecks, true};
+
+    IrOp block = build.block(IrBlockKind::Internal);
+    IrOp fallback = build.block(IrBlockKind::Fallback);
+
+    build.beginBlock(block);
+
+    IrOp sourceBuf = build.inst(IrCmd::LOAD_TVALUE, build.vmReg(0));
+
+    build.inst(IrCmd::STORE_TVALUE, build.vmReg(2), sourceBuf);
+    IrOp buffer1 = build.inst(IrCmd::LOAD_POINTER, build.vmReg(2));
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer1, build.constInt(12), build.constInt(4), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI32, buffer1, build.constInt(12), build.constInt(32));
+
+    // Now with lower index, should be removed
+    build.inst(IrCmd::STORE_TVALUE, build.vmReg(2), sourceBuf);
+    IrOp buffer2 = build.inst(IrCmd::LOAD_POINTER, build.vmReg(2));
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer2, build.constInt(8), build.constInt(4), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI32, buffer2, build.constInt(8), build.constInt(30));
+
+    // Now with higher index, should raise the initial check bound
+    build.inst(IrCmd::STORE_TVALUE, build.vmReg(2), sourceBuf);
+    IrOp buffer3 = build.inst(IrCmd::LOAD_POINTER, build.vmReg(2));
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer3, build.constInt(16), build.constInt(4), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI32, buffer3, build.constInt(16), build.constInt(60));
+
+    // Now with different access size, should not reuse previous checks (can be improved in the future)
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer3, build.constInt(16), build.constInt(2), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI16, buffer3, build.constInt(16), build.constInt(55));
+
+    // Now with same, but unknown index value
+    IrOp index = build.inst(IrCmd::LOAD_INT, build.vmReg(1));
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer3, index, build.constInt(2), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI16, buffer3, index, build.constInt(1));
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer3, index, build.constInt(2), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI16, buffer3, index, build.constInt(2));
+
+    build.inst(IrCmd::RETURN, build.vmReg(1), build.constUint(1));
+
+    build.beginBlock(fallback);
+    build.inst(IrCmd::RETURN, build.vmReg(0), build.constUint(1));
+
+    updateUseCounts(build.function);
+    constPropInBlockChains(build, true);
+
+    CHECK("\n" + toString(build.function, /* includeUseInfo */ false) == R"(
+bb_0:
+   %0 = LOAD_TVALUE R0
+   STORE_TVALUE R2, %0
+   %2 = LOAD_POINTER R2
+   CHECK_BUFFER_LEN %2, 16i, 4i, bb_fallback_1
+   BUFFER_WRITEI32 %2, 12i, 32i
+   BUFFER_WRITEI32 %2, 8i, 30i
+   BUFFER_WRITEI32 %2, 16i, 60i
+   CHECK_BUFFER_LEN %2, 16i, 2i, bb_fallback_1
+   BUFFER_WRITEI16 %2, 16i, 55i
+   %15 = LOAD_INT R1
+   CHECK_BUFFER_LEN %2, %15, 2i, bb_fallback_1
+   BUFFER_WRITEI16 %2, %15, 1i
+   BUFFER_WRITEI16 %2, %15, 2i
+   RETURN R1, 1u
+
+bb_fallback_1:
+   RETURN R0, 1u
+
+)");
+}
+
+TEST_CASE_FIXTURE(IrBuilderFixture, "BufferLenghtChecksNegativeIndex")
+{
+    ScopedFastFlag luauReuseBufferChecks{FFlag::LuauReuseBufferChecks, true};
+
+    IrOp block = build.block(IrBlockKind::Internal);
+    IrOp fallback = build.block(IrBlockKind::Fallback);
+
+    build.beginBlock(block);
+
+    IrOp sourceBuf = build.inst(IrCmd::LOAD_TVALUE, build.vmReg(0));
+
+    build.inst(IrCmd::STORE_TVALUE, build.vmReg(2), sourceBuf);
+    IrOp buffer1 = build.inst(IrCmd::LOAD_POINTER, build.vmReg(2));
+    build.inst(IrCmd::CHECK_BUFFER_LEN, buffer1, build.constInt(-4), build.constInt(4), fallback);
+    build.inst(IrCmd::BUFFER_WRITEI32, buffer1, build.constInt(-4), build.constInt(32));
+    build.inst(IrCmd::RETURN, build.vmReg(1), build.constUint(1));
+
+    build.beginBlock(fallback);
+    build.inst(IrCmd::RETURN, build.vmReg(0), build.constUint(1));
+
+    updateUseCounts(build.function);
+    constPropInBlockChains(build, true);
+
+    CHECK("\n" + toString(build.function, /* includeUseInfo */ false) == R"(
+bb_0:
+   %0 = LOAD_TVALUE R0
+   STORE_TVALUE R2, %0
+   JUMP bb_fallback_1
+
+bb_fallback_1:
+   RETURN R0, 1u
+
+)");
+}
+
 TEST_SUITE_END();
 
 TEST_SUITE_BEGIN("Analysis");

tests/Linter.test.cpp

@@ -1829,8 +1829,6 @@ local _ = 0x10000000000000000
 
 TEST_CASE_FIXTURE(Fixture, "IntegerParsingDecimalImprecise")
 {
-    ScopedFastFlag sff("LuauParseImpreciseNumber", true);
-
     LintResult result = lint(R"(
 local _ = 10000000000000000000000000000000000000000000000000000000000000000
 local _ = 10000000000000001
@@ -1867,8 +1865,6 @@ local _ = -9223372036854775808
 
 TEST_CASE_FIXTURE(Fixture, "IntegerParsingHexImprecise")
 {
-    ScopedFastFlag sff("LuauParseImpreciseNumber", true);
-
     LintResult result = lint(R"(
 local _ = 0x1234567812345678
 

tests/Module.test.cpp

@@ -15,6 +15,9 @@ using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauStacklessTypeClone3)
+LUAU_FASTFLAG(DebugLuauFreezeArena);
+LUAU_FASTINT(LuauTypeCloneIterationLimit);
+LUAU_FASTINT(LuauTypeCloneRecursionLimit);
 
 TEST_SUITE_BEGIN("ModuleTests");
 
@@ -112,7 +115,7 @@ TEST_CASE_FIXTURE(Fixture, "deepClone_cyclic_table")
     // not, but it's tangental to the core purpose of this test.
 
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     CheckResult result = check(R"(
@@ -270,7 +273,7 @@ TEST_CASE_FIXTURE(Fixture, "clone_class")
 
 TEST_CASE_FIXTURE(Fixture, "clone_free_types")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", false};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, false};
 
     TypeArena arena;
     TypeId freeTy = freshType(NotNull{&arena}, builtinTypes, nullptr);
@@ -336,8 +339,8 @@ TEST_CASE_FIXTURE(Fixture, "clone_recursion_limit")
     int limit = 400;
 #endif
 
-    ScopedFastFlag sff{"LuauStacklessTypeClone3", false};
+    ScopedFastFlag sff{FFlag::LuauStacklessTypeClone3, false};
-    ScopedFastInt luauTypeCloneRecursionLimit{"LuauTypeCloneRecursionLimit", limit};
+    ScopedFastInt luauTypeCloneRecursionLimit{FInt::LuauTypeCloneRecursionLimit, limit};
 
     TypeArena src;
 
@@ -360,8 +363,8 @@ TEST_CASE_FIXTURE(Fixture, "clone_recursion_limit")
 
 TEST_CASE_FIXTURE(Fixture, "clone_iteration_limit")
 {
-    ScopedFastFlag sff{"LuauStacklessTypeClone3", true};
+    ScopedFastFlag sff{FFlag::LuauStacklessTypeClone3, true};
-    ScopedFastInt sfi{"LuauTypeCloneIterationLimit", 500};
+    ScopedFastInt sfi{FInt::LuauTypeCloneIterationLimit, 500};
 
     TypeArena src;
 
@@ -530,7 +533,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "clone_table_bound_to_table_bound_to_table")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "clone_a_bound_type_to_a_persistent_type")
 {
-    ScopedFastFlag sff{"LuauStacklessTypeClone3", true};
+    ScopedFastFlag sff{FFlag::LuauStacklessTypeClone3, true};
 
     TypeArena arena;
 
@@ -546,7 +549,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "clone_a_bound_type_to_a_persistent_type")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "clone_a_bound_typepack_to_a_persistent_typepack")
 {
-    ScopedFastFlag sff{"LuauStacklessTypeClone3", true};
+    ScopedFastFlag sff{FFlag::LuauStacklessTypeClone3, true};
 
     TypeArena arena;
 

tests/NonStrictTypeChecker.test.cpp

@@ -3,33 +3,73 @@
 
 #include "Fixture.h"
 
-#include "Luau/Common.h"
 #include "Luau/Ast.h"
+#include "Luau/Common.h"
+#include "Luau/IostreamHelpers.h"
 #include "Luau/ModuleResolver.h"
 #include "Luau/VisitType.h"
+
 #include "ScopedFlags.h"
 #include "doctest.h"
 #include <iostream>
 
 using namespace Luau;
 
-#define NONSTRICT_REQUIRE_CHECKED_ERR(index, name, result) \
+LUAU_FASTFLAG(LuauCheckedFunctionSyntax);
+
+#define NONSTRICT_REQUIRE_ERR_AT_POS(pos, result, idx) \
     do \
     { \
-        REQUIRE(index < result.errors.size()); \
+        auto pos_ = (pos); \
-        auto err##index = get<CheckedFunctionCallError>(result.errors[index]); \
+        bool foundErr = false; \
-        REQUIRE(err##index != nullptr); \
+        int index = 0; \
-        CHECK_EQ((err##index)->checkedFunctionName, name); \
+        for (const auto& err : result.errors) \
+        { \
+            if (err.location.begin == pos_) \
+            { \
+                foundErr = true; \
+                break; \
+            } \
+            index++; \
+        } \
+        REQUIRE_MESSAGE(foundErr, "Expected error at " << pos_); \
+        idx = index; \
     } while (false)
 
+#define NONSTRICT_REQUIRE_CHECKED_ERR(pos, name, result) \
+    do \
+    { \
+        int errIndex; \
+        NONSTRICT_REQUIRE_ERR_AT_POS(pos, result, errIndex); \
+        auto err = get<CheckedFunctionCallError>(result.errors[errIndex]); \
+        REQUIRE(err != nullptr); \
+        CHECK_EQ(err->checkedFunctionName, name); \
+    } while (false)
+
+#define NONSTRICT_REQUIRE_FUNC_DEFINITION_ERR(pos, argname, result) \
+    do \
+    { \
+        int errIndex; \
+        NONSTRICT_REQUIRE_ERR_AT_POS(pos, result, errIndex); \
+        auto err = get<NonStrictFunctionDefinitionError>(result.errors[errIndex]); \
+        REQUIRE(err != nullptr); \
+        CHECK_EQ(err->argument, argname); \
+    } while (false)
+
+
 struct NonStrictTypeCheckerFixture : Fixture
 {
 
+    NonStrictTypeCheckerFixture()
+    {
+        registerHiddenTypes(&frontend);
+    }
+
     CheckResult checkNonStrict(const std::string& code)
     {
         ScopedFastFlag flags[] = {
-            {"LuauCheckedFunctionSyntax", true},
+            {FFlag::LuauCheckedFunctionSyntax, true},
-            {"DebugLuauDeferredConstraintResolution", true},
+            {FFlag::DebugLuauDeferredConstraintResolution, true},
         };
         LoadDefinitionFileResult res = loadDefinition(definitions);
         LUAU_ASSERT(res.success);
@@ -40,19 +80,41 @@ struct NonStrictTypeCheckerFixture : Fixture
 declare function @checked abs(n: number): number
 declare function @checked lower(s: string): string
 declare function cond() : boolean
+declare function @checked contrived(n : Not<number>) : number
 )BUILTIN_SRC";
 };
 
 
 TEST_SUITE_BEGIN("NonStrictTypeCheckerTest");
 
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "simple_negation_caching_example")
+{
+    CheckResult result = checkNonStrict(R"(
+local x = 3
+abs(x)
+abs(x)
+)");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    result = checkNonStrict(R"(
+local x = 3
+contrived(x)
+contrived(x)
+			      )");
+
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 10), "contrived", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 10), "contrived", result);
+}
+
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "simple_non_strict_failure")
 {
     CheckResult result = checkNonStrict(R"BUILTIN_SRC(
 abs("hi")
 )BUILTIN_SRC");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(1, 4), "abs", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "nested_function_calls_constant")
@@ -63,7 +125,7 @@ abs(lower(x))
 )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 4), "abs", result);
 }
 
 
@@ -79,8 +141,8 @@ end
 )");
 
     LUAU_REQUIRE_ERROR_COUNT(2, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 8), "abs", result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(1, "lower", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(5, 10), "lower", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "if_then_else_warns_nil_branches")
@@ -95,8 +157,8 @@ end
 )");
 
     LUAU_REQUIRE_ERROR_COUNT(2, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 8), "abs", result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(1, "lower", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(5, 10), "lower", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "if_then_else_doesnt_warn_else_branch")
@@ -111,7 +173,7 @@ end
 )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 8), "abs", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "if_then_no_else")
@@ -129,13 +191,13 @@ end
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "if_then_no_else_err_in_cond")
 {
     CheckResult result = checkNonStrict(R"(
-local x : string
+local x : string = ""
 if abs(x) then
     lower(x)
 end
 )");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 7), "abs", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "if_then_else_expr_should_warn")
@@ -145,8 +207,8 @@ local x : never
 local y = if cond() then abs(x) else lower(x)
 )");
     LUAU_REQUIRE_ERROR_COUNT(2, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 29), "abs", result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(1, "lower", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 43), "lower", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "if_then_else_expr_doesnt_warn_else_branch")
@@ -156,21 +218,7 @@ local x : string = "hi"
 local y = if cond() then abs(x) else lower(x)
 )");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 29), "abs", result);
-}
-
-
-TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "sequencing_errors")
-{
-    CheckResult result = checkNonStrict(R"(
-function f(x)
-    abs(x)
-    lower(x)
-end
-)");
-    LUAU_REQUIRE_ERROR_COUNT(2, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "abs", result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(1, "lower", result);
 }
 
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "sequencing_if_checked_call")
@@ -185,10 +233,10 @@ end
 lower(x)
 )");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    NONSTRICT_REQUIRE_CHECKED_ERR(0, "lower", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(7, 6), "lower", result);
 }
 
-TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "sequencing_unrelated_checked_calls")
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_unrelated_checked_calls")
 {
     CheckResult result = checkNonStrict(R"(
 function h(x, y)
@@ -200,5 +248,143 @@ end
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_basic_no_errors")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x)
+    abs(x)
+end
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_basic_errors")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x : string)
+    abs(x)
+end
+)");
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 8), "abs", result);
+}
+
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_failure")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x)
+    abs(lower(x))
+end
+)");
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 8), "abs", result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_sequencing_errors")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x)
+    abs(x)
+    lower(x)
+end
+)");
+    LUAU_REQUIRE_ERROR_COUNT(3, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 8), "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 10), "lower", result);
+    NONSTRICT_REQUIRE_FUNC_DEFINITION_ERR(Position(1, 11), "x", result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "local_fn_produces_error")
+{
+    CheckResult result = checkNonStrict(R"(
+local x = 5
+local function y() lower(x) end
+)");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 25), "lower", result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "fn_expr_produces_error")
+{
+    CheckResult result = checkNonStrict(R"(
+local x = 5
+local y = function() lower(x) end
+)");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 27), "lower", result);
+}
+
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_if_warns_never")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x)
+    if cond() then
+        abs(x)
+    else
+        lower(x)
+    end
+end
+)");
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 12), "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(5, 14), "lower", result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_if_no_else")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x)
+    if cond() then
+        abs(x)
+    end
+end
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_if_assignment_errors")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x)
+    if cond() then
+        x = 5
+    else
+        x = nil
+    end
+    lower(x)
+end
+)");
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(7, 10), "lower", result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_if_assignment_no_errors")
+{
+    CheckResult result = checkNonStrict(R"(
+function f(x : string | number)
+    if cond() then
+        x = 5
+    else
+        x = "hi"
+    end
+    abs(x)
+end
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "local_only_one_warning")
+{
+    CheckResult result = checkNonStrict(R"(
+local x = 5
+lower(x)
+)");
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 6), "lower", result);
+}
 
 TEST_SUITE_END();

tests/Normalize.test.cpp

@@ -11,6 +11,7 @@
 #include "Luau/BuiltinDefinitions.h"
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAG(LuauTransitiveSubtyping);
 
 using namespace Luau;
 
@@ -32,7 +33,7 @@ struct IsSubtypeFixture : Fixture
     bool isConsistentSubtype(TypeId a, TypeId b)
     {
         // any test that is testing isConsistentSubtype is testing the old solver exclusively!
-        ScopedFastFlag noDcr{"DebugLuauDeferredConstraintResolution", false};
+        ScopedFastFlag noDcr{FFlag::DebugLuauDeferredConstraintResolution, false};
 
         Location location;
         ModulePtr module = getMainModule();
@@ -182,7 +183,7 @@ TEST_CASE_FIXTURE(IsSubtypeFixture, "table_with_union_prop")
 TEST_CASE_FIXTURE(IsSubtypeFixture, "table_with_any_prop")
 {
     ScopedFastFlag sffs[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     check(R"(
@@ -243,7 +244,7 @@ TEST_CASE_FIXTURE(IsSubtypeFixture, "union_and_intersection")
 TEST_CASE_FIXTURE(IsSubtypeFixture, "tables")
 {
     ScopedFastFlag sffs[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     check(R"(
@@ -398,7 +399,7 @@ TEST_CASE_FIXTURE(IsSubtypeFixture, "metatable" * doctest::expected_failures{1})
 TEST_CASE_FIXTURE(IsSubtypeFixture, "any_is_unknown_union_error")
 {
     ScopedFastFlag sffs[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     check(R"(
@@ -418,7 +419,7 @@ TEST_CASE_FIXTURE(IsSubtypeFixture, "any_is_unknown_union_error")
 TEST_CASE_FIXTURE(IsSubtypeFixture, "any_intersect_T_is_T")
 {
     ScopedFastFlag sffs[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     check(R"(
@@ -440,7 +441,7 @@ TEST_CASE_FIXTURE(IsSubtypeFixture, "any_intersect_T_is_T")
 TEST_CASE_FIXTURE(IsSubtypeFixture, "error_suppression")
 {
     ScopedFastFlag sffs[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     check("");

tests/Parser.test.cpp

@@ -11,6 +11,13 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(LuauCheckedFunctionSyntax);
+LUAU_FASTFLAG(LuauLexerLookaheadRemembersBraceType);
+LUAU_FASTINT(LuauRecursionLimit);
+LUAU_FASTINT(LuauTypeLengthLimit);
+LUAU_FASTINT(LuauParseErrorLimit);
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+
 namespace
 {
 
@@ -1156,7 +1163,7 @@ until false
 TEST_CASE_FIXTURE(Fixture, "parse_nesting_based_end_detection_local_function")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     try
@@ -1192,7 +1199,7 @@ end
 TEST_CASE_FIXTURE(Fixture, "parse_nesting_based_end_detection_failsafe_earlier")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     try
@@ -1317,7 +1324,7 @@ end
 
 TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_type_group")
 {
-    ScopedFastInt sfis{"LuauRecursionLimit", 10};
+    ScopedFastInt sfis{FInt::LuauRecursionLimit, 10};
 
     matchParseError(
         "function f(): ((((((((((Fail)))))))))) end", "Exceeded allowed recursion depth; simplify your type annotation to make the code compile");
@@ -1336,7 +1343,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_type_group")
 
 TEST_CASE_FIXTURE(Fixture, "can_parse_complex_unions_successfully")
 {
-    ScopedFastInt sfis[] = {{"LuauRecursionLimit", 10}, {"LuauTypeLengthLimit", 10}};
+    ScopedFastInt sfis[] = {{FInt::LuauRecursionLimit, 10}, {FInt::LuauTypeLengthLimit, 10}};
 
     parse(R"(
 local f:
@@ -1367,7 +1374,7 @@ local f: a? | b? | c? | d? | e? | f? | g? | h?
 
 TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_if_statements")
 {
-    ScopedFastInt sfis{"LuauRecursionLimit", 10};
+    ScopedFastInt sfis{FInt::LuauRecursionLimit, 10};
 
     matchParseErrorPrefix(
         "function f() if true then if true then if true then if true then if true then if true then if true then if true then if true "
@@ -1377,7 +1384,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_if_statements")
 
 TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_changed_elseif_statements")
 {
-    ScopedFastInt sfis{"LuauRecursionLimit", 10};
+    ScopedFastInt sfis{FInt::LuauRecursionLimit, 10};
 
     matchParseErrorPrefix(
         "function f() if false then elseif false then elseif false then elseif false then elseif false then elseif false then elseif "
@@ -1387,7 +1394,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_changed_elseif_statements"
 
 TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_ifelse_expressions1")
 {
-    ScopedFastInt sfis{"LuauRecursionLimit", 10};
+    ScopedFastInt sfis{FInt::LuauRecursionLimit, 10};
 
     matchParseError("function f() return if true then 1 elseif true then 2 elseif true then 3 elseif true then 4 elseif true then 5 elseif true then "
                     "6 elseif true then 7 elseif true then 8 elseif true then 9 elseif true then 10 else 11 end",
@@ -1396,7 +1403,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_ifelse_expressions1
 
 TEST_CASE_FIXTURE(Fixture, "parse_error_with_too_many_nested_ifelse_expressions2")
 {
-    ScopedFastInt sfis{"LuauRecursionLimit", 10};
+    ScopedFastInt sfis{FInt::LuauRecursionLimit, 10};
 
     matchParseError(
         "function f() return if if if if if if if if if if true then false else true then false else true then false else true then false else true "
@@ -2411,7 +2418,7 @@ local a : { [string] : number, [number] : string, count: number }
 
 TEST_CASE_FIXTURE(Fixture, "recovery_error_limit_1")
 {
-    ScopedFastInt luauParseErrorLimit("LuauParseErrorLimit", 1);
+    ScopedFastInt luauParseErrorLimit(FInt::LuauParseErrorLimit, 1);
 
     try
     {
@@ -2427,7 +2434,7 @@ TEST_CASE_FIXTURE(Fixture, "recovery_error_limit_1")
 
 TEST_CASE_FIXTURE(Fixture, "recovery_error_limit_2")
 {
-    ScopedFastInt luauParseErrorLimit("LuauParseErrorLimit", 2);
+    ScopedFastInt luauParseErrorLimit(FInt::LuauParseErrorLimit, 2);
 
     try
     {
@@ -2491,7 +2498,7 @@ TEST_CASE_FIXTURE(Fixture, "recovery_of_parenthesized_expressions")
     };
 
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     checkRecovery("function foo(a, b. c) return a + b end", "function foo(a, b) return a + b end", 1);
@@ -2725,7 +2732,7 @@ TEST_CASE_FIXTURE(Fixture, "AstName_comparison")
 TEST_CASE_FIXTURE(Fixture, "generic_type_list_recovery")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     try
@@ -3020,7 +3027,7 @@ TEST_CASE_FIXTURE(Fixture, "do_block_with_no_end")
 
 TEST_CASE_FIXTURE(Fixture, "parse_interpolated_string_with_lookahead_involved")
 {
-    ScopedFastFlag sff{"LuauLexerLookaheadRemembersBraceType", true};
+    ScopedFastFlag sff{FFlag::LuauLexerLookaheadRemembersBraceType, true};
 
     ParseResult result = tryParse(R"(
         local x = `{ {y} }`
@@ -3031,7 +3038,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_interpolated_string_with_lookahead_involved")
 
 TEST_CASE_FIXTURE(Fixture, "parse_interpolated_string_with_lookahead_involved2")
 {
-    ScopedFastFlag sff{"LuauLexerLookaheadRemembersBraceType", true};
+    ScopedFastFlag sff{FFlag::LuauLexerLookaheadRemembersBraceType, true};
 
     ParseResult result = tryParse(R"(
         local x = `{ { y{} } }`
@@ -3044,7 +3051,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_top_level_checked_fn")
 {
     ParseOptions opts;
     opts.allowDeclarationSyntax = true;
-    ScopedFastFlag sff{"LuauCheckedFunctionSyntax", true};
+    ScopedFastFlag sff{FFlag::LuauCheckedFunctionSyntax, true};
 
     std::string src = R"BUILTIN_SRC(
 declare function @checked abs(n: number): number
@@ -3064,7 +3071,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_declared_table_checked_member")
 {
     ParseOptions opts;
     opts.allowDeclarationSyntax = true;
-    ScopedFastFlag sff{"LuauCheckedFunctionSyntax", true};
+    ScopedFastFlag sff{FFlag::LuauCheckedFunctionSyntax, true};
 
     const std::string src = R"BUILTIN_SRC(
     declare math : {
@@ -3092,7 +3099,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_checked_outside_decl_fails")
 {
     ParseOptions opts;
     opts.allowDeclarationSyntax = true;
-    ScopedFastFlag sff{"LuauCheckedFunctionSyntax", true};
+    ScopedFastFlag sff{FFlag::LuauCheckedFunctionSyntax, true};
 
     ParseResult pr = tryParse(R"(
     local @checked = 3
@@ -3106,7 +3113,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_checked_in_and_out_of_decl_fails")
 {
     ParseOptions opts;
     opts.allowDeclarationSyntax = true;
-    ScopedFastFlag sff{"LuauCheckedFunctionSyntax", true};
+    ScopedFastFlag sff{FFlag::LuauCheckedFunctionSyntax, true};
 
     auto pr = tryParse(R"(
     local @checked = 3
@@ -3122,7 +3129,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_checked_as_function_name_fails")
 {
     ParseOptions opts;
     opts.allowDeclarationSyntax = true;
-    ScopedFastFlag sff{"LuauCheckedFunctionSyntax", true};
+    ScopedFastFlag sff{FFlag::LuauCheckedFunctionSyntax, true};
 
     auto pr = tryParse(R"(
     function @checked(x: number) : number
@@ -3136,7 +3143,7 @@ TEST_CASE_FIXTURE(Fixture, "cannot_use_@_as_variable_name")
 {
     ParseOptions opts;
     opts.allowDeclarationSyntax = true;
-    ScopedFastFlag sff{"LuauCheckedFunctionSyntax", true};
+    ScopedFastFlag sff{FFlag::LuauCheckedFunctionSyntax, true};
 
     auto pr = tryParse(R"(
     local @blah = 3

tests/RequireByString.test.cpp

@@ -0,0 +1,395 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#include "Luau/Common.h"
+#include "ScopedFlags.h"
+#include "lua.h"
+#include "lualib.h"
+
+#include "Repl.h"
+#include "FileUtils.h"
+
+#include "doctest.h"
+
+#include <algorithm>
+#include <initializer_list>
+#include <memory>
+
+LUAU_FASTFLAG(LuauUpdatedRequireByStringSemantics)
+
+class ReplWithPathFixture
+{
+public:
+    ReplWithPathFixture()
+        : luaState(luaL_newstate(), lua_close)
+    {
+        L = luaState.get();
+        setupState(L);
+        luaL_sandboxthread(L);
+
+        runCode(L, prettyPrintSource);
+    }
+
+    // Returns all of the output captured from the pretty printer
+    std::string getCapturedOutput()
+    {
+        lua_getglobal(L, "capturedoutput");
+        const char* str = lua_tolstring(L, -1, nullptr);
+        std::string result(str);
+        lua_pop(L, 1);
+        return result;
+    }
+
+    enum class PathType
+    {
+        Absolute,
+        Relative
+    };
+
+    std::string getLuauDirectory(PathType type)
+    {
+        std::string luauDirRel = ".";
+        std::string luauDirAbs;
+
+        std::optional<std::string> cwd = getCurrentWorkingDirectory();
+        REQUIRE_MESSAGE(cwd, "Error getting Luau path");
+        std::replace((*cwd).begin(), (*cwd).end(), '\\', '/');
+        luauDirAbs = *cwd;
+
+        for (int i = 0; i < 20; ++i)
+        {
+            if (isDirectory(luauDirAbs + "/Luau/tests") || isDirectory(luauDirAbs + "/Client/Luau/tests"))
+            {
+                if (isDirectory(luauDirAbs + "/Client/Luau/tests"))
+                {
+                    luauDirRel += "/Client";
+                    luauDirAbs += "/Client";
+                }
+                luauDirRel += "/Luau";
+                luauDirAbs += "/Luau";
+
+                if (type == PathType::Relative)
+                    return luauDirRel;
+                if (type == PathType::Absolute)
+                    return luauDirAbs;
+            }
+
+            luauDirRel += "/..";
+            std::optional<std::string> parentPath = getParentPath(luauDirAbs);
+            REQUIRE_MESSAGE(parentPath, "Error getting Luau path");
+            luauDirAbs = *parentPath;
+        }
+
+        // Could not find the directory
+        REQUIRE_MESSAGE(false, "Error getting Luau path");
+        return {};
+    }
+
+    void runProtectedRequire(const std::string& path)
+    {
+        runCode(L, "return pcall(function() return require(\"" + path + "\") end)");
+    }
+
+    void assertOutputContainsAll(const std::initializer_list<std::string>& list)
+    {
+        const std::string capturedOutput = getCapturedOutput();
+        for (const std::string& elem : list)
+        {
+            CHECK_MESSAGE(capturedOutput.find(elem) != std::string::npos, "Captured output: ", capturedOutput);
+        }
+    }
+
+    lua_State* L;
+
+private:
+    std::unique_ptr<lua_State, void (*)(lua_State*)> luaState;
+
+    // This is a simplistic and incomplete pretty printer.
+    // It is included here to test that the pretty printer hook is being called.
+    // More elaborate tests to ensure correct output can be added if we introduce
+    // a more feature rich pretty printer.
+    std::string prettyPrintSource = R"(
+-- Accumulate pretty printer output in `capturedoutput`
+capturedoutput = ""
+
+function arraytostring(arr)
+    local strings = {}
+    table.foreachi(arr, function(k,v) table.insert(strings, pptostring(v)) end )
+    return "{" .. table.concat(strings, ", ") .. "}"
+end
+
+function pptostring(x)
+    if type(x) == "table" then
+        -- Just assume array-like tables for now.
+        return arraytostring(x)
+    elseif type(x) == "string" then
+        return '"' .. x .. '"'
+    else
+        return tostring(x)
+    end
+end
+
+-- Note: Instead of calling print, the pretty printer just stores the output
+-- in `capturedoutput` so we can check for the correct results.
+function _PRETTYPRINT(...)
+    local args = table.pack(...)
+    local strings = {}
+    for i=1, args.n do
+        local item = args[i]
+        local str = pptostring(item, customoptions)
+        if i == 1 then
+            capturedoutput = capturedoutput .. str
+        else
+            capturedoutput = capturedoutput .. "\t" .. str
+        end
+    end
+end
+)";
+};
+
+TEST_SUITE_BEGIN("RequireByStringTests");
+
+TEST_CASE("PathResolution")
+{
+#ifdef _WIN32
+    std::string prefix = "C:/";
+#else
+    std::string prefix = "/";
+#endif
+
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    CHECK(resolvePath(prefix + "Users/modules/module.luau", "") == prefix + "Users/modules/module.luau");
+    CHECK(resolvePath(prefix + "Users/modules/module.luau", "a/string/that/should/be/ignored") == prefix + "Users/modules/module.luau");
+    CHECK(resolvePath(prefix + "Users/modules/module.luau", "./a/string/that/should/be/ignored") == prefix + "Users/modules/module.luau");
+    CHECK(resolvePath(prefix + "Users/modules/module.luau", "/a/string/that/should/be/ignored") == prefix + "Users/modules/module.luau");
+    CHECK(resolvePath(prefix + "Users/modules/module.luau", "/Users/modules") == prefix + "Users/modules/module.luau");
+
+    CHECK(resolvePath("../module", "") == "../module");
+    CHECK(resolvePath("../../module", "") == "../../module");
+    CHECK(resolvePath("../module/..", "") == "..");
+    CHECK(resolvePath("../module/../..", "") == "../..");
+
+    CHECK(resolvePath("../dependency", prefix + "Users/modules/module.luau") == prefix + "Users/dependency");
+    CHECK(resolvePath("../dependency/", prefix + "Users/modules/module.luau") == prefix + "Users/dependency");
+    CHECK(resolvePath("../../../../../Users/dependency", prefix + "Users/modules/module.luau") == prefix + "Users/dependency");
+    CHECK(resolvePath("../..", prefix + "Users/modules/module.luau") == prefix);
+}
+
+TEST_CASE("PathNormalization")
+{
+#ifdef _WIN32
+    std::string prefix = "C:/";
+#else
+    std::string prefix = "/";
+#endif
+
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    // Relative path
+    std::optional<std::string> result = normalizePath("../../modules/module");
+    CHECK(result);
+    std::string normalized = *result;
+    std::vector<std::string> variants = {
+        "./.././.././modules/./module/", "placeholder/../../../modules/module", "../placeholder/placeholder2/../../../modules/module"};
+    for (const std::string& variant : variants)
+    {
+        result = normalizePath(variant);
+        CHECK(result);
+        CHECK(normalized == *result);
+    }
+
+    // Absolute path
+    result = normalizePath(prefix + "Users/modules/module");
+    CHECK(result);
+    normalized = *result;
+    variants = {"Users/Users/Users/.././.././modules/./module/", "placeholder/../Users/..//Users/modules/module",
+        "Users/../placeholder/placeholder2/../../Users/modules/module"};
+    for (const std::string& variant : variants)
+    {
+        result = normalizePath(prefix + variant);
+        CHECK(result);
+        CHECK(normalized == *result);
+    }
+}
+
+#if 0
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireSimpleRelativePath")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/dependency";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from dependency"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireRelativeToRequiringFile")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/module";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from dependency", "required into module"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireLua")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/lua_dependency";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from lua_dependency"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireInitLuau")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/luau";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from init.luau"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireInitLua")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/lua";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from init.lua"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "CheckCacheAfterRequireLuau")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string relativePath = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/module";
+    std::string absolutePath = getLuauDirectory(PathType::Absolute) + "/tests/require/without_config/module";
+
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + ".luau").c_str());
+    REQUIRE_MESSAGE(lua_isnil(L, -1), "Cache already contained module result");
+
+    runProtectedRequire(relativePath);
+
+    assertOutputContainsAll({"true", "result from dependency", "required into module"});
+
+    // Check cache for the absolute path as a cache key
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + ".luau").c_str());
+    REQUIRE_FALSE_MESSAGE(lua_isnil(L, -1), "Cache did not contain module result");
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "CheckCacheAfterRequireLua")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string relativePath = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/lua_dependency";
+    std::string absolutePath = getLuauDirectory(PathType::Absolute) + "/tests/require/without_config/lua_dependency";
+
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + ".luau").c_str());
+    REQUIRE_MESSAGE(lua_isnil(L, -1), "Cache already contained module result");
+
+    runProtectedRequire(relativePath);
+
+    assertOutputContainsAll({"true", "result from lua_dependency"});
+
+    // Check cache for the absolute path as a cache key
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + ".lua").c_str());
+    REQUIRE_FALSE_MESSAGE(lua_isnil(L, -1), "Cache did not contain module result");
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "CheckCacheAfterRequireInitLuau")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string relativePath = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/luau";
+    std::string absolutePath = getLuauDirectory(PathType::Absolute) + "/tests/require/without_config/luau";
+
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + "/init.luau").c_str());
+    REQUIRE_MESSAGE(lua_isnil(L, -1), "Cache already contained module result");
+
+    runProtectedRequire(relativePath);
+
+    assertOutputContainsAll({"true", "result from init.luau"});
+
+    // Check cache for the absolute path as a cache key
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + "/init.luau").c_str());
+    REQUIRE_FALSE_MESSAGE(lua_isnil(L, -1), "Cache did not contain module result");
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "CheckCacheAfterRequireInitLua")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string relativePath = getLuauDirectory(PathType::Relative) + "/tests/require/without_config/lua";
+    std::string absolutePath = getLuauDirectory(PathType::Absolute) + "/tests/require/without_config/lua";
+
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + "/init.lua").c_str());
+    REQUIRE_MESSAGE(lua_isnil(L, -1), "Cache already contained module result");
+
+    runProtectedRequire(relativePath);
+
+    assertOutputContainsAll({"true", "result from init.lua"});
+
+    // Check cache for the absolute path as a cache key
+    luaL_findtable(L, LUA_REGISTRYINDEX, "_MODULES", 1);
+    lua_getfield(L, -1, (absolutePath + "/init.lua").c_str());
+    REQUIRE_FALSE_MESSAGE(lua_isnil(L, -1), "Cache did not contain module result");
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "LoadStringRelative")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    runCode(L, "return pcall(function() return loadstring(\"require('a/relative/path')\")() end)");
+    assertOutputContainsAll({"false", "require is not supported in this context"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireAbsolutePath")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+#ifdef _WIN32
+    std::string absolutePath = "C:/an/absolute/path";
+#else
+    std::string absolutePath = "/an/absolute/path";
+#endif
+    runProtectedRequire(absolutePath);
+    assertOutputContainsAll({"false", "cannot require an absolute path"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "PathsArrayRelativePath")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/with_config/src/requirer";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from library"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "PathsArrayExplicitlyRelativePath")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/with_config/src/fail_requirer";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"false", "error requiring module"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "PathsArrayFromParent")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/with_config/src/global_library_requirer";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from global_library"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequirePathWithAlias")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/with_config/src/alias_requirer";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from dependency"});
+}
+
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequirePathWithParentAlias")
+{
+    ScopedFastFlag sff{FFlag::LuauUpdatedRequireByStringSemantics, true};
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/with_config/src/parent_alias_requirer";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from other_dependency"});
+}
+
+#endif
+
+TEST_SUITE_END();

tests/RuntimeLimits.test.cpp

@@ -17,10 +17,13 @@
 
 using namespace Luau;
 
+LUAU_FASTINT(LuauTypeInferRecursionLimit)
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+
 struct LimitFixture : BuiltinsFixture
 {
 #if defined(_NOOPT) || defined(_DEBUG)
-    ScopedFastInt LuauTypeInferRecursionLimit{"LuauTypeInferRecursionLimit", 90};
+    ScopedFastInt LuauTypeInferRecursionLimit{FInt::LuauTypeInferRecursionLimit, 100};
 #endif
 };
 
@@ -38,7 +41,7 @@ TEST_SUITE_BEGIN("RuntimeLimits");
 TEST_CASE_FIXTURE(LimitFixture, "typescript_port_of_Result_type")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     constexpr const char* src = R"LUA(

tests/ScopedFlags.h

@@ -13,18 +13,11 @@ private:
     T oldValue = T();
 
 public:
-    ScopedFValue(const char* name, T newValue)
+    ScopedFValue(Luau::FValue<T>& fvalue, T newValue)
     {
-        for (Luau::FValue<T>* v = Luau::FValue<T>::list; v; v = v->next)
+        value = &fvalue;
-            if (strcmp(v->name, name) == 0)
+        oldValue = fvalue.value;
-            {
+        fvalue.value = newValue;
-                value = v;
-                oldValue = v->value;
-                v->value = newValue;
-                break;
-            }
-
-        LUAU_ASSERT(value);
     }
 
     ScopedFValue(const ScopedFValue&) = delete;

tests/Simplify.test.cpp

@@ -8,6 +8,8 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+
 namespace
 {
 
@@ -59,7 +61,7 @@ struct SimplifyFixture : Fixture
     TypeId anotherChildClassTy = nullptr;
     TypeId unrelatedClassTy = nullptr;
 
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     SimplifyFixture()
     {

tests/Subtyping.test.cpp

@@ -24,6 +24,8 @@ std::ostream& operator<<(std::ostream& lhs, const SubtypingVariance& variance)
     {
     case SubtypingVariance::Covariant:
         return lhs << "covariant";
+    case SubtypingVariance::Contravariant:
+        return lhs << "contravariant";
     case SubtypingVariance::Invariant:
         return lhs << "invariant";
     case SubtypingVariance::Invalid:
@@ -643,12 +645,7 @@ TEST_CASE_FIXTURE(SubtypeFixture, "(number) -> () <!: <T>(T) -> ()")
 
 TEST_CASE_FIXTURE(SubtypeFixture, "<T>() -> (T, T) <!: () -> (string, number)")
 {
-    TypeId nothingToTwoTs = arena.addType(FunctionType{
+    TypeId nothingToTwoTs = arena.addType(FunctionType{{genericT}, {}, builtinTypes->emptyTypePack, arena.addTypePack({genericT, genericT})});
-        {genericT},
-        {},
-        builtinTypes->emptyTypePack,
-        arena.addTypePack({genericT, genericT})
-    });
 
     TypeId nothingToStringAndNumber = fn({}, {builtinTypes->stringType, builtinTypes->numberType});
 
@@ -790,7 +787,7 @@ TEST_IS_NOT_SUBTYPE(negate(builtinTypes->neverType), builtinTypes->stringType);
 TEST_IS_SUBTYPE(negate(builtinTypes->unknownType), builtinTypes->stringType);
 TEST_IS_NOT_SUBTYPE(negate(builtinTypes->anyType), builtinTypes->stringType);
 TEST_IS_SUBTYPE(negate(meet(builtinTypes->neverType, builtinTypes->unknownType)), builtinTypes->stringType);
-TEST_IS_NOT_SUBTYPE(negate(join(builtinTypes->neverType, builtinTypes->unknownType)), builtinTypes->stringType);
+TEST_IS_SUBTYPE(negate(join(builtinTypes->neverType, builtinTypes->unknownType)), builtinTypes->stringType);
 
 // Negated supertypes: never/unknown/any/error
 TEST_IS_SUBTYPE(builtinTypes->stringType, negate(builtinTypes->neverType));
@@ -812,7 +809,7 @@ TEST_IS_SUBTYPE(builtinTypes->booleanType, negate(meet(builtinTypes->stringType,
 TEST_IS_SUBTYPE(builtinTypes->trueType, negate(meet(builtinTypes->booleanType, builtinTypes->numberType)));
 TEST_IS_SUBTYPE(rootClass, negate(meet(builtinTypes->classType, childClass)));
 TEST_IS_SUBTYPE(childClass, negate(meet(builtinTypes->classType, builtinTypes->numberType)));
-TEST_IS_NOT_SUBTYPE(builtinTypes->unknownType, negate(meet(builtinTypes->classType, builtinTypes->numberType)));
+TEST_IS_SUBTYPE(builtinTypes->unknownType, negate(meet(builtinTypes->classType, builtinTypes->numberType)));
 TEST_IS_NOT_SUBTYPE(str("foo"), negate(meet(builtinTypes->stringType, negate(str("bar")))));
 
 // Negated supertypes: tables and metatables
@@ -1041,6 +1038,16 @@ TEST_CASE_FIXTURE(SubtypeFixture, "(string | number) & (\"a\" | true) <: { lower
     CHECK_IS_SUBTYPE(base, tableWithLower);
 }
 
+TEST_CASE_FIXTURE(SubtypeFixture, "number <: ~~number")
+{
+    CHECK_IS_SUBTYPE(builtinTypes->numberType, negate(negate(builtinTypes->numberType)));
+}
+
+TEST_CASE_FIXTURE(SubtypeFixture, "~~number <: number")
+{
+    CHECK_IS_SUBTYPE(negate(negate(builtinTypes->numberType)), builtinTypes->numberType);
+}
+
 /*
  * Within the scope to which a generic belongs, that generic ought to be treated
  * as its bounds.
@@ -1075,11 +1082,15 @@ TEST_IS_NOT_SUBTYPE(tbl({}), idx(builtinTypes->numberType, builtinTypes->numberT
 TEST_IS_NOT_SUBTYPE(tbl({{"X", builtinTypes->numberType}}), idx(builtinTypes->numberType, builtinTypes->numberType));
 TEST_IS_NOT_SUBTYPE(idx(builtinTypes->numberType, builtinTypes->numberType), tbl({{"X", builtinTypes->numberType}}));
 
-TEST_IS_NOT_SUBTYPE(idx(join(builtinTypes->numberType, builtinTypes->stringType), builtinTypes->numberType), idx(builtinTypes->numberType, builtinTypes->numberType));
+TEST_IS_NOT_SUBTYPE(
-TEST_IS_NOT_SUBTYPE(idx(builtinTypes->numberType, builtinTypes->numberType), idx(join(builtinTypes->numberType, builtinTypes->stringType), builtinTypes->numberType));
+    idx(join(builtinTypes->numberType, builtinTypes->stringType), builtinTypes->numberType), idx(builtinTypes->numberType, builtinTypes->numberType));
+TEST_IS_NOT_SUBTYPE(
+    idx(builtinTypes->numberType, builtinTypes->numberType), idx(join(builtinTypes->numberType, builtinTypes->stringType), builtinTypes->numberType));
 
-TEST_IS_NOT_SUBTYPE(idx(builtinTypes->numberType, join(builtinTypes->stringType, builtinTypes->numberType)), idx(builtinTypes->numberType, builtinTypes->numberType));
+TEST_IS_NOT_SUBTYPE(
-TEST_IS_NOT_SUBTYPE(idx(builtinTypes->numberType, builtinTypes->numberType), idx(builtinTypes->numberType, join(builtinTypes->stringType, builtinTypes->numberType)));
+    idx(builtinTypes->numberType, join(builtinTypes->stringType, builtinTypes->numberType)), idx(builtinTypes->numberType, builtinTypes->numberType));
+TEST_IS_NOT_SUBTYPE(
+    idx(builtinTypes->numberType, builtinTypes->numberType), idx(builtinTypes->numberType, join(builtinTypes->stringType, builtinTypes->numberType)));
 
 TEST_IS_NOT_SUBTYPE(tbl({{"X", builtinTypes->numberType}}), idx(builtinTypes->stringType, builtinTypes->numberType));
 TEST_IS_SUBTYPE(idx(builtinTypes->stringType, builtinTypes->numberType), tbl({{"X", builtinTypes->numberType}}));
@@ -1176,6 +1187,7 @@ TEST_CASE_FIXTURE(SubtypeFixture, "fn_arguments")
     CHECK(result.reasoning == std::vector{SubtypingReasoning{
                                   /* subPath */ TypePath::PathBuilder().args().index(0).build(),
                                   /* superPath */ TypePath::PathBuilder().args().index(0).build(),
+                                  /* variance */ SubtypingVariance::Contravariant,
                               }});
 }
 
@@ -1189,6 +1201,7 @@ TEST_CASE_FIXTURE(SubtypeFixture, "fn_arguments_tail")
     CHECK(result.reasoning == std::vector{SubtypingReasoning{
                                   /* subPath */ TypePath::PathBuilder().args().tail().variadic().build(),
                                   /* superPath */ TypePath::PathBuilder().args().tail().variadic().build(),
+                                  /* variance */ SubtypingVariance::Contravariant,
                               }});
 }
 

tests/Symbol.test.cpp

@@ -8,6 +8,8 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+
 TEST_SUITE_BEGIN("SymbolTests");
 
 TEST_CASE("equality_and_hashing_of_globals")
@@ -66,7 +68,7 @@ TEST_CASE("equality_and_hashing_of_locals")
 
 TEST_CASE("equality_of_empty_symbols")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     std::string s1 = "name";
     std::string s2 = "name";

tests/ToDot.test.cpp

@@ -289,7 +289,7 @@ n3 [label="TableType 3"];
 TEST_CASE_FIXTURE(Fixture, "free")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     Type type{TypeVariant{FreeType{TypeLevel{0, 0}}}};
@@ -305,7 +305,7 @@ n1 [label="FreeType 1"];
 TEST_CASE_FIXTURE(Fixture, "free_with_constraints")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
 
     Type type{TypeVariant{FreeType{nullptr, builtinTypes->numberType, builtinTypes->optionalNumberType}}};

tests/ToString.test.cpp

@@ -12,6 +12,8 @@ using namespace Luau;
 
 LUAU_FASTFLAG(LuauRecursiveTypeParameterRestriction);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauCheckedFunctionSyntax);
+LUAU_FASTFLAG(DebugLuauSharedSelf);
 
 TEST_SUITE_BEGIN("ToString");
 
@@ -236,7 +238,7 @@ TEST_CASE_FIXTURE(Fixture, "functions_are_always_parenthesized_in_unions_or_inte
 
 TEST_CASE_FIXTURE(Fixture, "simple_intersections_printed_on_one_line")
 {
-    ScopedFastFlag sff{"LuauToStringSimpleCompositeTypesSingleLine", true};
+    ScopedFastFlag sff{FFlag::LuauToStringSimpleCompositeTypesSingleLine, true};
     CheckResult result = check(R"(
         local a: string & number
     )");
@@ -249,7 +251,7 @@ TEST_CASE_FIXTURE(Fixture, "simple_intersections_printed_on_one_line")
 
 TEST_CASE_FIXTURE(Fixture, "complex_intersections_printed_on_multiple_lines")
 {
-    ScopedFastFlag sff{"LuauToStringSimpleCompositeTypesSingleLine", true};
+    ScopedFastFlag sff{FFlag::LuauToStringSimpleCompositeTypesSingleLine, true};
     CheckResult result = check(R"(
         local a: string & number & boolean
     )");
@@ -268,7 +270,7 @@ TEST_CASE_FIXTURE(Fixture, "complex_intersections_printed_on_multiple_lines")
 
 TEST_CASE_FIXTURE(Fixture, "overloaded_functions_always_printed_on_multiple_lines")
 {
-    ScopedFastFlag sff{"LuauToStringSimpleCompositeTypesSingleLine", true};
+    ScopedFastFlag sff{FFlag::LuauToStringSimpleCompositeTypesSingleLine, true};
     CheckResult result = check(R"(
         local a: ((string) -> string) & ((number) -> number)
     )");
@@ -285,7 +287,7 @@ TEST_CASE_FIXTURE(Fixture, "overloaded_functions_always_printed_on_multiple_line
 
 TEST_CASE_FIXTURE(Fixture, "simple_unions_printed_on_one_line")
 {
-    ScopedFastFlag sff{"LuauToStringSimpleCompositeTypesSingleLine", true};
+    ScopedFastFlag sff{FFlag::LuauToStringSimpleCompositeTypesSingleLine, true};
     CheckResult result = check(R"(
         local a: number | boolean
     )");
@@ -298,7 +300,7 @@ TEST_CASE_FIXTURE(Fixture, "simple_unions_printed_on_one_line")
 
 TEST_CASE_FIXTURE(Fixture, "complex_unions_printed_on_multiple_lines")
 {
-    ScopedFastFlag sff{"LuauToStringSimpleCompositeTypesSingleLine", true};
+    ScopedFastFlag sff{FFlag::LuauToStringSimpleCompositeTypesSingleLine, true};
     CheckResult result = check(R"(
         local a: string | number | boolean
     )");
@@ -565,7 +567,7 @@ TEST_CASE_FIXTURE(Fixture, "toStringDetailed")
 TEST_CASE_FIXTURE(BuiltinsFixture, "toStringDetailed2")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauSharedSelf", true},
+        {FFlag::DebugLuauSharedSelf, true},
     };
 
     CheckResult result = check(R"(
@@ -865,7 +867,7 @@ TEST_CASE_FIXTURE(Fixture, "pick_distinct_names_for_mixed_explicit_and_implicit_
 TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_include_self_param")
 {
     ScopedFastFlag sff[]{
-        {"DebugLuauSharedSelf", true},
+        {FFlag::DebugLuauSharedSelf, true},
     };
 
     CheckResult result = check(R"(
@@ -887,7 +889,7 @@ TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_include_self_param")
 TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_hide_self_param")
 {
     ScopedFastFlag sff[]{
-        {"DebugLuauSharedSelf", true},
+        {FFlag::DebugLuauSharedSelf, true},
     };
 
     CheckResult result = check(R"(
@@ -965,8 +967,8 @@ Type 'string' could not be converted into 'number' in an invariant context)";
 TEST_CASE_FIXTURE(Fixture, "checked_fn_toString")
 {
     ScopedFastFlag flags[] = {
-        {"LuauCheckedFunctionSyntax", true},
+        {FFlag::LuauCheckedFunctionSyntax, true},
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
 
     auto _result = loadDefinition(R"(

tests/TxnLog.test.cpp

@@ -12,6 +12,8 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+
 struct TxnLogFixture
 {
     TxnLog log{/*useScopes*/ true};
@@ -33,7 +35,7 @@ TEST_SUITE_BEGIN("TxnLog");
 
 TEST_CASE_FIXTURE(TxnLogFixture, "colliding_union_incoming_type_has_greater_scope")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     log.replace(c, BoundType{a});
     log2.replace(a, BoundType{c});
@@ -66,7 +68,7 @@ TEST_CASE_FIXTURE(TxnLogFixture, "colliding_union_incoming_type_has_greater_scop
 
 TEST_CASE_FIXTURE(TxnLogFixture, "colliding_union_incoming_type_has_lesser_scope")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     log.replace(a, BoundType{c});
     log2.replace(c, BoundType{a});
@@ -99,7 +101,7 @@ TEST_CASE_FIXTURE(TxnLogFixture, "colliding_union_incoming_type_has_lesser_scope
 
 TEST_CASE_FIXTURE(TxnLogFixture, "colliding_coincident_logs_do_not_create_degenerate_unions")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     log.replace(a, BoundType{b});
     log2.replace(a, BoundType{b});

tests/TypeInfer.aliases.test.cpp

@@ -8,6 +8,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAG(DebugLuauSharedSelf);
 
 TEST_SUITE_BEGIN("TypeAliases");
 
@@ -188,7 +189,7 @@ TEST_CASE_FIXTURE(Fixture, "mutually_recursive_aliases")
 TEST_CASE_FIXTURE(Fixture, "generic_aliases")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
     CheckResult result = check(R"(
         type T<a> = { v: a }
@@ -206,7 +207,7 @@ TEST_CASE_FIXTURE(Fixture, "generic_aliases")
 TEST_CASE_FIXTURE(Fixture, "dependent_generic_aliases")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
 
     CheckResult result = check(R"(
@@ -334,7 +335,7 @@ TEST_CASE_FIXTURE(Fixture, "stringify_type_alias_of_recursive_template_table_typ
 TEST_CASE_FIXTURE(Fixture, "cli_38393_recursive_intersection_oom")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     }; // FIXME
 
     CheckResult result = check(R"(
@@ -820,7 +821,7 @@ TEST_CASE_FIXTURE(Fixture, "forward_declared_alias_is_not_clobbered_by_prior_uni
 TEST_CASE_FIXTURE(Fixture, "forward_declared_alias_is_not_clobbered_by_prior_unification_with_any_2")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauSharedSelf", true},
+        {FFlag::DebugLuauSharedSelf, true},
     };
 
     CheckResult result = check(R"(

tests/TypeInfer.annotations.test.cpp

@@ -8,6 +8,7 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(DebugLuauMagicTypes);
 
 using namespace Luau;
 
@@ -77,7 +78,7 @@ TEST_CASE_FIXTURE(Fixture, "assignment_cannot_transform_a_table_property_type")
 
 TEST_CASE_FIXTURE(Fixture, "assignments_to_unannotated_parameters_can_transform_the_type")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         function f(x)
@@ -93,7 +94,7 @@ TEST_CASE_FIXTURE(Fixture, "assignments_to_unannotated_parameters_can_transform_
 
 TEST_CASE_FIXTURE(Fixture, "assignments_to_annotated_parameters_are_checked")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         function f(x: string)
@@ -768,7 +769,7 @@ int AssertionCatcher::tripped;
 
 TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_exception_with_flag")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
+    ScopedFastFlag sffs{FFlag::DebugLuauMagicTypes, true};
 
     AssertionCatcher ac;
 
@@ -782,7 +783,7 @@ TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_exception_with_flag")
 
 TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_exception_with_flag_handler")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
+    ScopedFastFlag sffs{FFlag::DebugLuauMagicTypes, true};
 
     bool caught = false;
 
@@ -800,7 +801,7 @@ TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_exception_with_flag_handler
 
 TEST_CASE_FIXTURE(Fixture, "luau_ice_is_not_special_without_the_flag")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", false};
+    ScopedFastFlag sffs{FFlag::DebugLuauMagicTypes, false};
 
     // We only care that this does not throw
     check(R"(
@@ -816,7 +817,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "luau_print_is_magic_if_the_flag_is_set")
         output.push_back(s);
     });
 
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
+    ScopedFastFlag sffs{FFlag::DebugLuauMagicTypes, true};
 
     CheckResult result = check(R"(
         local a: _luau_print<typeof(math.abs)>
@@ -829,7 +830,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "luau_print_is_magic_if_the_flag_is_set")
 
 TEST_CASE_FIXTURE(Fixture, "luau_print_is_not_special_without_the_flag")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", false};
+    ScopedFastFlag sffs{FFlag::DebugLuauMagicTypes, false};
 
     CheckResult result = check(R"(
         local a: _luau_print<number>
@@ -840,7 +841,7 @@ TEST_CASE_FIXTURE(Fixture, "luau_print_is_not_special_without_the_flag")
 
 TEST_CASE_FIXTURE(Fixture, "luau_print_incomplete")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
+    ScopedFastFlag sffs{FFlag::DebugLuauMagicTypes, true};
 
     CheckResult result = check(R"(
         local a: _luau_print

tests/TypeInfer.builtins.test.cpp

@@ -9,6 +9,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
 
 TEST_SUITE_BEGIN("BuiltinTests");
 
@@ -133,7 +134,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "sort_with_predicate")
 TEST_CASE_FIXTURE(BuiltinsFixture, "sort_with_bad_predicate")
 {
     ScopedFastFlag sff[] = {
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
 
     CheckResult result = check(R"(

tests/TypeInfer.cfa.test.cpp

@@ -6,11 +6,14 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(LuauTinyControlFlowAnalysis);
+LUAU_FASTFLAG(LuauLoopControlFlowAnalysis);
+
 TEST_SUITE_BEGIN("ControlFlowAnalysis");
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -28,10 +31,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -51,10 +51,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -74,7 +71,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_return")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?, y: string?)
@@ -96,10 +93,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_return")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_not_y_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -124,10 +118,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_not_y_break")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_not_y_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -152,10 +143,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_not_y_continue")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -180,10 +168,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_break")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_not_y_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -208,7 +193,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_not_y_continue")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_rand_return_elif_not_y_return")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?, y: string?)
@@ -232,10 +217,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_rand_return_elif_not_y_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_rand_break_elif_not_y_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -262,10 +244,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_rand_break_elif_not_y_br
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_rand_continue_elif_not_y_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -292,7 +271,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_rand_continue_elif_no
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_rand_return_elif_not_y_fallthrough")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?, y: string?)
@@ -316,10 +295,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_rand_return_elif_no
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_rand_break_elif_not_y_fallthrough")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -346,10 +322,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_rand_break_elif_not_y_fa
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_rand_continue_elif_not_y_fallthrough")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -376,7 +349,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_rand_continue_elif_no
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_fallthrough_elif_not_z_return")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?, y: string?, z: string?)
@@ -402,10 +375,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_fallthrough_elif_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_not_y_fallthrough_elif_not_z_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}}, z: {{value: string?}})
@@ -435,10 +405,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_elif_not_y_fallthrough_elif_n
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_not_y_fallthrough_elif_not_z_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}}, z: {{value: string?}})
@@ -468,10 +435,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_not_y_fallthrough_eli
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_not_y_throw_elif_not_z_fallthrough")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}}, z: {{value: string?}})
@@ -501,10 +465,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_elif_not_y_throw_elif_not_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_fallthrough_elif_not_z_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}}, z: {{value: string?}})
@@ -534,7 +495,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_elif_not_y_fallthrough_elif_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "do_if_not_x_return")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -554,10 +515,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "do_if_not_x_return")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "for_record_do_if_not_x_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -579,10 +537,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "for_record_do_if_not_x_break")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "for_record_do_if_not_x_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -604,7 +559,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "for_record_do_if_not_x_continue")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "early_return_in_a_loop_which_isnt_guaranteed_to_run_first")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -627,7 +582,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "early_return_in_a_loop_which_isnt_guaranteed
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "early_return_in_a_loop_which_is_guaranteed_to_run_first")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -650,7 +605,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "early_return_in_a_loop_which_is_guaranteed_t
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "early_return_in_a_loop_which_is_guaranteed_to_run_first_2")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -673,7 +628,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "early_return_in_a_loop_which_is_guaranteed_t
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_then_error")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -691,7 +646,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_then_error")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_then_assert_false")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -709,7 +664,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_then_assert_false")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_if_not_y_return")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?, y: string?)
@@ -733,10 +688,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_return_if_not_y_return")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_if_not_y_break")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -763,10 +715,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_if_not_y_break")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_if_not_y_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -793,10 +742,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_if_not_y_continue")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_if_not_y_throw")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -823,10 +769,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_continue_if_not_y_throw")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_if_not_y_continue")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}}, y: {{value: string?}})
@@ -853,7 +796,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "if_not_x_break_if_not_y_continue")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_does_not_leak_out")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)
@@ -876,10 +819,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_does_not_leak_out")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_does_not_leak_out_breaking")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -904,10 +844,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_does_not_leak_out_breaking")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_does_not_leak_out_continuing")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -932,7 +869,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_does_not_leak_out_continuing")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "prototyping_and_visiting_alias_has_the_same_scope")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     // In CG, we walk the block to prototype aliases. We then visit the block in-order, which will resolve the prototype to a real type.
     // That second walk assumes that the name occurs in the same `Scope` that the prototype walk had. If we arbitrarily change scope midway
@@ -958,10 +895,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "prototyping_and_visiting_alias_has_the_same_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "prototyping_and_visiting_alias_has_the_same_scope_breaking")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -986,10 +920,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "prototyping_and_visiting_alias_has_the_same_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "prototyping_and_visiting_alias_has_the_same_scope_continuing")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         local function f(x: {{value: string?}})
@@ -1014,7 +945,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "prototyping_and_visiting_alias_has_the_same_
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "tagged_unions")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         type Ok<T> = { tag: "ok", value: T }
@@ -1049,10 +980,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "tagged_unions")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "tagged_unions_breaking")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         type Ok<T> = { tag: "ok", value: T }
@@ -1085,10 +1013,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "tagged_unions_breaking")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "tagged_unions_continuing")
 {
-    ScopedFastFlag flags[] = {
+    ScopedFastFlag flags[] = {{FFlag::LuauTinyControlFlowAnalysis, true}, {FFlag::LuauLoopControlFlowAnalysis, true}};
-        {"LuauTinyControlFlowAnalysis", true},
-        {"LuauLoopControlFlowAnalysis", true}
-    };
 
     CheckResult result = check(R"(
         type Ok<T> = { tag: "ok", value: T }
@@ -1121,7 +1046,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "tagged_unions_continuing")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "do_assert_x")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     CheckResult result = check(R"(
         local function f(x: string?)

tests/TypeInfer.classes.test.cpp

@@ -13,6 +13,7 @@ using namespace Luau;
 using std::nullopt;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
 
 TEST_SUITE_BEGIN("TypeInferClasses");
 
@@ -368,7 +369,7 @@ b.X = 2 -- real Vector2.X is also read-only
 TEST_CASE_FIXTURE(ClassFixture, "detailed_class_unification_error")
 {
     ScopedFastFlag sff[] = {
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
     CheckResult result = check(R"(
 local function foo(v)

tests/TypeInfer.definitions.test.cpp

@@ -7,6 +7,8 @@
 
 #include "doctest.h"
 
+LUAU_FASTFLAG(LuauDefinitionFileSetModuleName)
+
 using namespace Luau;
 
 TEST_SUITE_BEGIN("DefinitionTests");
@@ -443,7 +445,7 @@ TEST_CASE_FIXTURE(Fixture, "class_definitions_reference_other_classes")
 
 TEST_CASE_FIXTURE(Fixture, "definition_file_has_source_module_name_set")
 {
-    ScopedFastFlag sff{"LuauDefinitionFileSetModuleName", true};
+    ScopedFastFlag sff{FFlag::LuauDefinitionFileSetModuleName, true};
 
     LoadDefinitionFileResult result = loadDefinition(R"(
         declare class Foo

tests/TypeInfer.functions.test.cpp

@@ -16,6 +16,8 @@ using namespace Luau;
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
+LUAU_FASTINT(LuauTarjanChildLimit);
 
 TEST_SUITE_BEGIN("TypeInferFunctions");
 
@@ -1911,7 +1913,7 @@ end
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "dont_assert_when_the_tarjan_limit_is_exceeded_during_generalization")
 {
-    ScopedFastInt sfi{"LuauTarjanChildLimit", 2};
+    ScopedFastInt sfi{FInt::LuauTarjanChildLimit, 2};
     if (!FFlag::DebugLuauDeferredConstraintResolution)
         return;
 
@@ -1995,7 +1997,7 @@ TEST_CASE_FIXTURE(Fixture, "function_exprs_are_generalized_at_signature_scope_no
 TEST_CASE_FIXTURE(BuiltinsFixture, "param_1_and_2_both_takes_the_same_generic_but_their_arguments_are_incompatible")
 {
     ScopedFastFlag sff[] = {
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
 
     CheckResult result = check(R"(
@@ -2050,7 +2052,7 @@ Table type '{ x: number }' not compatible with type 'vec2' because the former is
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "param_1_and_2_both_takes_the_same_generic_but_their_arguments_are_incompatible_2")
 {
-    ScopedFastFlag sff{"LuauAlwaysCommitInferencesOfFunctionCalls", true};
+    ScopedFastFlag sff{FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true};
 
     CheckResult result = check(R"(
         local function f<a>(x: a, y: a): a
@@ -2103,7 +2105,7 @@ TEST_CASE_FIXTURE(Fixture, "generic_packs_are_not_variadic")
     if (!FFlag::DebugLuauDeferredConstraintResolution)
         return;
 
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         local function apply<a, b..., c...>(f: (a, b...) -> c..., x: a)

tests/TypeInfer.generics.test.cpp

@@ -11,6 +11,7 @@
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(DebugLuauSharedSelf);
 
 using namespace Luau;
 
@@ -274,7 +275,7 @@ TEST_CASE_FIXTURE(Fixture, "infer_nested_generic_function")
 
 TEST_CASE_FIXTURE(Fixture, "infer_generic_methods")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         local x = {}
@@ -1260,7 +1261,7 @@ end
 TEST_CASE_FIXTURE(BuiltinsFixture, "higher_rank_polymorphism_should_not_accept_instantiated_arguments")
 {
     ScopedFastFlag sffs[] = {
-        {"LuauInstantiateInSubtyping", true},
+        {FFlag::LuauInstantiateInSubtyping, true},
     };
 
     CheckResult result = check(R"(

tests/TypeInfer.intersectionTypes.test.cpp

@@ -965,12 +965,12 @@ local y = x.Bar
 TEST_CASE_FIXTURE(BuiltinsFixture, "index_property_table_intersection_2")
 {
     CheckResult result = check(R"(
-type Foo = {
+        type Foo = {
-	Bar: string,
+            Bar: string,
-} & { Baz: number }
+        } & { Baz: number }
 
-local x: Foo = { Bar = "1", Baz = 2 }
+        local x: Foo = { Bar = "1", Baz = 2 }
-local y = x["Bar"]
+        local y = x["Bar"]
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
@@ -978,7 +978,7 @@ local y = x["Bar"]
 
 TEST_CASE_FIXTURE(Fixture, "cli_80596_simplify_degenerate_intersections")
 {
-    ScopedFastFlag dcr{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag dcr{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         type A = {
@@ -1002,7 +1002,7 @@ TEST_CASE_FIXTURE(Fixture, "cli_80596_simplify_degenerate_intersections")
 
 TEST_CASE_FIXTURE(Fixture, "cli_80596_simplify_more_realistic_intersections")
 {
-    ScopedFastFlag dcr{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag dcr{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         type A = {

tests/TypeInfer.loops.test.cpp

@@ -38,7 +38,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "iteration_no_table_passed")
     if (!FFlag::DebugLuauDeferredConstraintResolution)
         return;
 
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
     CheckResult result = check(R"(
 
 type Iterable = typeof(setmetatable(
@@ -188,7 +188,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_with_just_one_iterator_is_ok")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_loop_with_zero_iterators_dcr")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         function no_iter() end

tests/TypeInfer.modules.test.cpp

@@ -12,6 +12,7 @@
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAG(LuauTinyControlFlowAnalysis);
 
 using namespace Luau;
 
@@ -491,7 +492,7 @@ return unpack(l0[_])
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "check_imported_module_names")
 {
-    ScopedFastFlag sff{"LuauTinyControlFlowAnalysis", true};
+    ScopedFastFlag sff{FFlag::LuauTinyControlFlowAnalysis, true};
 
     fileResolver.source["game/A"] = R"(
 return function(...) end

tests/TypeInfer.oop.test.cpp

@@ -15,6 +15,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauStacklessTypeClone3);
 
 TEST_SUITE_BEGIN("TypeInferOOP");
 
@@ -415,7 +416,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "promise_type_error_too_complex" * doctest::t
     // TODO: LTI changes to function call resolution have rendered this test impossibly slow
     // shared self should fix it, but there may be other mitigations possible as well
     REQUIRE(!FFlag::DebugLuauDeferredConstraintResolution);
-    ScopedFastFlag sff{"LuauStacklessTypeClone3", true};
+    ScopedFastFlag sff{FFlag::LuauStacklessTypeClone3, true};
 
     frontend.options.retainFullTypeGraphs = false;
 

tests/TypeInfer.provisional.test.cpp

@@ -11,6 +11,13 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(DebugLuauSharedSelf);
+LUAU_FASTFLAG(LuauTransitiveSubtyping);
+LUAU_FASTINT(LuauNormalizeCacheLimit);
+LUAU_FASTINT(LuauTarjanChildLimit);
+LUAU_FASTINT(LuauTypeInferIterationLimit);
+LUAU_FASTINT(LuauTypeInferRecursionLimit);
+LUAU_FASTINT(LuauTypeInferTypePackLoopLimit);
 
 TEST_SUITE_BEGIN("ProvisionalTests");
 
@@ -119,7 +126,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "xpcall_returns_what_f_returns")
 TEST_CASE_FIXTURE(Fixture, "weirditer_should_not_loop_forever")
 {
     // this flag is intentionally here doing nothing to demonstrate that we exit early via case detection
-    ScopedFastInt sfis{"LuauTypeInferTypePackLoopLimit", 50};
+    ScopedFastInt sfis{FInt::LuauTypeInferTypePackLoopLimit, 50};
 
     CheckResult result = check(R"(
         local function toVertexList(vertices, x, y, ...)
@@ -271,8 +278,8 @@ TEST_CASE_FIXTURE(Fixture, "discriminate_from_x_not_equal_to_nil")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "bail_early_if_unification_is_too_complicated" * doctest::timeout(0.5))
 {
-    ScopedFastInt sffi{"LuauTarjanChildLimit", 1};
+    ScopedFastInt sffi{FInt::LuauTarjanChildLimit, 1};
-    ScopedFastInt sffi2{"LuauTypeInferIterationLimit", 1};
+    ScopedFastInt sffi2{FInt::LuauTypeInferIterationLimit, 1};
 
     CheckResult result = check(R"LUA(
         local Result
@@ -355,7 +362,7 @@ TEST_CASE_FIXTURE(Fixture, "weird_fail_to_unify_type_pack")
     ScopedFastFlag sff[] = {
         // I'm not sure why this is broken without DCR, but it seems to be fixed
         // when DCR is enabled.
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     CheckResult result = check(R"(
@@ -438,7 +445,7 @@ TEST_CASE_FIXTURE(Fixture, "free_is_not_bound_to_any")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "greedy_inference_with_shared_self_triggers_function_with_no_returns")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         local T = {}
@@ -461,7 +468,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "greedy_inference_with_shared_self_triggers_f
 TEST_CASE_FIXTURE(Fixture, "dcr_can_partially_dispatch_a_constraint")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
 
     CheckResult result = check(R"(
@@ -502,7 +509,7 @@ TEST_CASE_FIXTURE(Fixture, "dcr_can_partially_dispatch_a_constraint")
 TEST_CASE_FIXTURE(Fixture, "free_options_cannot_be_unified_together")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     TypeArena arena;
@@ -539,7 +546,7 @@ TEST_CASE_FIXTURE(Fixture, "free_options_cannot_be_unified_together")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_loop_with_zero_iterators")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", false};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, false};
 
     CheckResult result = check(R"(
         function no_iter() end
@@ -911,7 +918,7 @@ TEST_CASE_FIXTURE(Fixture, "floating_generics_should_not_be_allowed")
 TEST_CASE_FIXTURE(Fixture, "free_options_can_be_unified_together")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     TypeArena arena;
@@ -1023,7 +1030,7 @@ end
 TEST_CASE_FIXTURE(BuiltinsFixture, "table_unification_infinite_recursion")
 {
 #if defined(_NOOPT) || defined(_DEBUG)
-    ScopedFastInt LuauTypeInferRecursionLimit{"LuauTypeInferRecursionLimit", 100};
+    ScopedFastInt LuauTypeInferRecursionLimit{FInt::LuauTypeInferRecursionLimit, 100};
 #endif
 
     fileResolver.source["game/A"] = R"(
@@ -1065,12 +1072,12 @@ tbl:f3()
 TEST_CASE_FIXTURE(BuiltinsFixture, "normalization_limit_in_unify_with_any")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
 
     // With default limit, this test will take 10 seconds in NoOpt
-    ScopedFastInt luauNormalizeCacheLimit{"LuauNormalizeCacheLimit", 1000};
+    ScopedFastInt luauNormalizeCacheLimit{FInt::LuauNormalizeCacheLimit, 1000};
 
     // Build a function type with a large overload set
     const int parts = 100;

tests/TypeInfer.refinements.test.cpp

@@ -1855,7 +1855,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_annotations_arent_relevant_when_doing_d
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "function_call_with_colon_after_refining_not_to_be_nil")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         --!strict
@@ -1921,7 +1921,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "many_refinements_on_val")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "refine_unknown_to_table")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
     // this test is DCR-only as an instance of DCR fixing a bug in the old solver
 
     CheckResult result = check(R"(
@@ -1954,7 +1954,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "refine_unknown_to_table")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "conditional_refinement_should_stay_error_suppressing")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
     // this test is DCR-only as an instance of DCR fixing a bug in the old solver
 
     CheckResult result = check(R"(

tests/TypeInfer.rwprops.test.cpp

@@ -4,6 +4,7 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(DebugLuauReadWriteProperties)
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 
 using namespace Luau;
 
@@ -12,7 +13,7 @@ namespace
 
 struct ReadWriteFixture : Fixture
 {
-    ScopedFastFlag dcr{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag dcr{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     ReadWriteFixture()
         : Fixture()

tests/TypeInfer.singletons.test.cpp

@@ -353,7 +353,7 @@ Table type 'a' not compatible with type 'Bad' because the former is missing fiel
 TEST_CASE_FIXTURE(Fixture, "parametric_tagged_union_alias")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
     };
     CheckResult result = check(R"(
         type Ok<T> = {success: true, result: T}

tests/TypeInfer.tables.test.cpp

@@ -18,6 +18,9 @@ using namespace Luau;
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
+LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls)
+LUAU_FASTFLAG(LuauFixIndexerSubtypingOrdering)
+LUAU_FASTFLAG(DebugLuauSharedSelf)
 
 TEST_SUITE_BEGIN("TableTests");
 
@@ -321,34 +324,6 @@ TEST_CASE_FIXTURE(Fixture, "used_colon_instead_of_dot")
     REQUIRE(it != result.errors.end());
 }
 
-#if 0
-TEST_CASE_FIXTURE(Fixture, "open_table_unification")
-{
-    CheckResult result = check(R"(
-        function foo(o)
-            print(o.foo)
-            print(o.bar)
-        end
-
-        local a = {}
-        a.foo = 9
-
-        local b = {}
-        b.foo = 0
-
-        if random() then
-            b = a
-        end
-
-        b.bar = '99'
-
-        foo(a)
-        foo(b)
-    )");
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-#endif
-
 TEST_CASE_FIXTURE(Fixture, "open_table_unification_2")
 {
     CheckResult result = check(R"(
@@ -1577,7 +1552,7 @@ TEST_CASE_FIXTURE(Fixture, "right_table_missing_key2")
 
 TEST_CASE_FIXTURE(Fixture, "casting_unsealed_tables_with_props_into_table_with_indexer")
 {
-    ScopedFastFlag sff{"LuauAlwaysCommitInferencesOfFunctionCalls", true};
+    ScopedFastFlag sff{FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true};
 
     CheckResult result = check(R"(
         type StringToStringMap = { [string]: string }
@@ -1632,7 +1607,7 @@ TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer2")
 
 TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer3")
 {
-    ScopedFastFlag sff{"LuauAlwaysCommitInferencesOfFunctionCalls", true};
+    ScopedFastFlag sff{FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true};
 
     CheckResult result = check(R"(
         local function foo(a: {[string]: number, a: string}) end
@@ -1740,7 +1715,7 @@ TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_extra_props_is_ok")
 
 TEST_CASE_FIXTURE(Fixture, "type_mismatch_on_massive_table_is_cut_short")
 {
-    ScopedFastInt sfis{"LuauTableTypeMaximumStringifierLength", 40};
+    ScopedFastInt sfis{FInt::LuauTableTypeMaximumStringifierLength, 40};
 
     CheckResult result = check(R"(
         local t
@@ -2019,7 +1994,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "quantifying_a_bound_var_works")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "less_exponential_blowup_please")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         --!strict
@@ -2492,7 +2467,7 @@ TEST_CASE_FIXTURE(Fixture, "confusing_indexing")
 
 TEST_CASE_FIXTURE(Fixture, "pass_a_union_of_tables_to_a_function_that_requires_a_table")
 {
-    ScopedFastFlag sff{"LuauAlwaysCommitInferencesOfFunctionCalls", true};
+    ScopedFastFlag sff{FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true};
 
     CheckResult result = check(R"(
         local a: {x: number, y: number, [any]: any} | {y: number}
@@ -2515,7 +2490,7 @@ TEST_CASE_FIXTURE(Fixture, "pass_a_union_of_tables_to_a_function_that_requires_a
 
 TEST_CASE_FIXTURE(Fixture, "pass_a_union_of_tables_to_a_function_that_requires_a_table_2")
 {
-    ScopedFastFlag sff{"LuauAlwaysCommitInferencesOfFunctionCalls", true};
+    ScopedFastFlag sff{FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true};
 
     CheckResult result = check(R"(
         local a: {y: number} | {x: number, y: number, [any]: any}
@@ -3194,8 +3169,8 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "dont_leak_free_table_props")
 TEST_CASE_FIXTURE(Fixture, "inferred_return_type_of_free_table")
 {
     ScopedFastFlag sff[] = {
-        // {"LuauLowerBoundsCalculation", true},
+        // {FFlag::LuauLowerBoundsCalculation, true},
-        {"DebugLuauSharedSelf", true},
+        {FFlag::DebugLuauSharedSelf, true},
     };
 
     check(R"(
@@ -3234,7 +3209,7 @@ TEST_CASE_FIXTURE(Fixture, "mixed_tables_with_implicit_numbered_keys")
 
 TEST_CASE_FIXTURE(Fixture, "shared_selfs")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         local t = {}
@@ -3255,7 +3230,7 @@ TEST_CASE_FIXTURE(Fixture, "shared_selfs")
 
 TEST_CASE_FIXTURE(Fixture, "shared_selfs_from_free_param")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         local function f(t)
@@ -3271,7 +3246,7 @@ TEST_CASE_FIXTURE(Fixture, "shared_selfs_from_free_param")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "shared_selfs_through_metatables")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         local t = {}
@@ -3350,7 +3325,7 @@ TEST_CASE_FIXTURE(Fixture, "prop_access_on_unions_of_indexers_where_key_whose_ty
 TEST_CASE_FIXTURE(BuiltinsFixture, "quantify_metatables_of_metatables_of_table")
 {
     ScopedFastFlag sff[]{
-        {"DebugLuauSharedSelf", true},
+        {FFlag::DebugLuauSharedSelf, true},
     };
 
     CheckResult result = check(R"(
@@ -3380,7 +3355,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "quantify_metatables_of_metatables_of_table")
 
 TEST_CASE_FIXTURE(Fixture, "quantify_even_that_table_was_never_exported_at_all")
 {
-    ScopedFastFlag sff{"DebugLuauSharedSelf", true};
+    ScopedFastFlag sff{FFlag::DebugLuauSharedSelf, true};
 
     CheckResult result = check(R"(
         local T = {}
@@ -3431,7 +3406,7 @@ TEST_CASE_FIXTURE(Fixture, "scalar_is_a_subtype_of_a_compatible_polymorphic_shap
 TEST_CASE_FIXTURE(Fixture, "scalar_is_not_a_subtype_of_a_compatible_polymorphic_shape_type")
 {
     ScopedFastFlag sff[] = {
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
 
     CheckResult result = check(R"(
@@ -3536,7 +3511,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "a_free_shape_can_turn_into_a_scalar_directly
 TEST_CASE_FIXTURE(Fixture, "invariant_table_properties_means_instantiating_tables_in_call_is_unsound")
 {
     ScopedFastFlag sff[]{
-        {"LuauInstantiateInSubtyping", true},
+        {FFlag::LuauInstantiateInSubtyping, true},
     };
 
     CheckResult result = check(R"(
@@ -3657,7 +3632,7 @@ _ = _._
 TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_table_unify_instantiated_table")
 {
     ScopedFastFlag sff[]{
-        {"LuauInstantiateInSubtyping", true},
+        {FFlag::LuauInstantiateInSubtyping, true},
     };
 
     CheckResult result = check(R"(
@@ -3674,7 +3649,7 @@ return _[_()()[_]] <= _
 TEST_CASE_FIXTURE(Fixture, "fuzz_table_unify_instantiated_table_with_prop_realloc")
 {
     ScopedFastFlag sff[]{
-        {"LuauInstantiateInSubtyping", true},
+        {FFlag::LuauInstantiateInSubtyping, true},
     };
 
     CheckResult result = check(R"(
@@ -3884,7 +3859,7 @@ TEST_CASE_FIXTURE(Fixture, "cyclic_shifted_tables")
 
 TEST_CASE_FIXTURE(Fixture, "cli_84607_missing_prop_in_array_or_dict")
 {
-    ScopedFastFlag sff{"LuauFixIndexerSubtypingOrdering", true};
+    ScopedFastFlag sff{FFlag::LuauFixIndexerSubtypingOrdering, true};
 
     CheckResult result = check(R"(
         type Thing = { name: string, prop: boolean }
@@ -3939,7 +3914,7 @@ TEST_CASE_FIXTURE(Fixture, "simple_method_definition")
 
 TEST_CASE_FIXTURE(Fixture, "identify_all_problematic_table_fields")
 {
-    ScopedFastFlag sff_DebugLuauDeferredConstraintResolution{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff_DebugLuauDeferredConstraintResolution{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         type T = {

tests/TypeInfer.test.cpp

@@ -18,6 +18,11 @@
 LUAU_FASTFLAG(LuauFixLocationSpanTableIndexExpr);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauInstantiateInSubtyping);
+LUAU_FASTFLAG(LuauTransitiveSubtyping);
+LUAU_FASTINT(LuauCheckRecursionLimit);
+LUAU_FASTINT(LuauNormalizeCacheLimit);
+LUAU_FASTINT(LuauRecursionLimit);
+LUAU_FASTINT(LuauTypeInferRecursionLimit);
 
 using namespace Luau;
 
@@ -133,7 +138,7 @@ TEST_CASE_FIXTURE(Fixture, "infer_locals_via_assignment_from_its_call_site")
 TEST_CASE_FIXTURE(Fixture, "infer_in_nocheck_mode")
 {
     ScopedFastFlag sff[]{
-        {"DebugLuauDeferredConstraintResolution", false},
+        {FFlag::DebugLuauDeferredConstraintResolution, false},
     };
 
     CheckResult result = check(R"(
@@ -375,7 +380,7 @@ TEST_CASE_FIXTURE(Fixture, "check_type_infer_recursion_count")
     int limit = 600;
 #endif
 
-    ScopedFastInt sfi{"LuauCheckRecursionLimit", limit};
+    ScopedFastInt sfi{FInt::LuauCheckRecursionLimit, limit};
 
     CheckResult result = check("function f() return " + rep("{a=", limit) + "'a'" + rep("}", limit) + " end");
 
@@ -393,8 +398,8 @@ TEST_CASE_FIXTURE(Fixture, "check_block_recursion_limit")
     int limit = 600;
 #endif
 
-    ScopedFastInt luauRecursionLimit{"LuauRecursionLimit", limit + 100};
+    ScopedFastInt luauRecursionLimit{FInt::LuauRecursionLimit, limit + 100};
-    ScopedFastInt luauCheckRecursionLimit{"LuauCheckRecursionLimit", limit - 100};
+    ScopedFastInt luauCheckRecursionLimit{FInt::LuauCheckRecursionLimit, limit - 100};
 
     CheckResult result = check(rep("do ", limit) + "local a = 1" + rep(" end", limit));
 
@@ -411,8 +416,8 @@ TEST_CASE_FIXTURE(Fixture, "check_expr_recursion_limit")
 #else
     int limit = 600;
 #endif
-    ScopedFastInt luauRecursionLimit{"LuauRecursionLimit", limit + 100};
+    ScopedFastInt luauRecursionLimit{FInt::LuauRecursionLimit, limit + 100};
-    ScopedFastInt luauCheckRecursionLimit{"LuauCheckRecursionLimit", limit - 100};
+    ScopedFastInt luauCheckRecursionLimit{FInt::LuauCheckRecursionLimit, limit - 100};
 
     CheckResult result = check(R"(("foo"))" + rep(":lower()", limit));
 
@@ -1081,7 +1086,7 @@ Table type 'FieldSpecifier' not compatible with type '{| from: number? |}' becau
 
 TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_no_ice")
 {
-    ScopedFastInt sfi("LuauTypeInferRecursionLimit", 2);
+    ScopedFastInt sfi(FInt::LuauTypeInferRecursionLimit, 2);
 
     CheckResult result = check(R"(
         function complex()
@@ -1099,7 +1104,7 @@ TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_no_ice")
 
 TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_normalizer")
 {
-    ScopedFastInt sfi("LuauTypeInferRecursionLimit", 10);
+    ScopedFastInt sfi(FInt::LuauTypeInferRecursionLimit, 10);
 
     CheckResult result = check(R"(
         function f<a,b,c,d,e,f,g,h,i,j>()
@@ -1118,7 +1123,7 @@ TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_normalizer")
 
 TEST_CASE_FIXTURE(Fixture, "type_infer_cache_limit_normalizer")
 {
-    ScopedFastInt sfi("LuauNormalizeCacheLimit", 10);
+    ScopedFastInt sfi(FInt::LuauNormalizeCacheLimit, 10);
 
     CheckResult result = check(R"(
         local x : ((number) -> number) & ((string) -> string) & ((nil) -> nil) & (({}) -> {})
@@ -1287,10 +1292,10 @@ end
 TEST_CASE_FIXTURE(Fixture, "dcr_delays_expansion_of_function_containing_blocked_parameter_type")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
         // If we run this with error-suppression, it triggers an assertion.
         // FATAL ERROR: Assertion failed: !"Internal error: Trying to normalize a BlockedType"
-        {"LuauTransitiveSubtyping", false},
+        {FFlag::LuauTransitiveSubtyping, false},
     };
 
     CheckResult result = check(R"(
@@ -1453,7 +1458,7 @@ TEST_CASE_FIXTURE(Fixture, "promote_tail_type_packs")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "lti_must_record_contributing_locations")
 {
-    ScopedFastFlag sff_DebugLuauDeferredConstraintResolution{"DebugLuauDeferredConstraintResolution", true};
+    ScopedFastFlag sff_DebugLuauDeferredConstraintResolution{FFlag::DebugLuauDeferredConstraintResolution, true};
 
     CheckResult result = check(R"(
         local function f(a)

tests/TypeInfer.tryUnify.test.cpp

@@ -11,12 +11,14 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
+LUAU_FASTFLAG(LuauTransitiveSubtyping);
 
 struct TryUnifyFixture : Fixture
 {
     // Cannot use `TryUnifyFixture` under DCR.
-    ScopedFastFlag noDcr{"DebugLuauDeferredConstraintResolution", false};
+    ScopedFastFlag noDcr{FFlag::DebugLuauDeferredConstraintResolution, false};
 
     TypeArena arena;
     ScopePtr globalScope{new Scope{arena.addTypePack({TypeId{}})}};
@@ -31,7 +33,7 @@ TEST_SUITE_BEGIN("TryUnifyTests");
 TEST_CASE_FIXTURE(TryUnifyFixture, "primitives_unify")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     Type numberOne{TypeVariant{PrimitiveType{PrimitiveType::Number}}};
@@ -46,7 +48,7 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "primitives_unify")
 TEST_CASE_FIXTURE(TryUnifyFixture, "compatible_functions_are_unified")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     Type functionOne{
@@ -67,7 +69,7 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "compatible_functions_are_unified")
 TEST_CASE_FIXTURE(TryUnifyFixture, "incompatible_functions_are_preserved")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     TypePackVar argPackOne{TypePack{{arena.freshType(globalScope->level)}, std::nullopt}};
@@ -93,7 +95,7 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "incompatible_functions_are_preserved")
 TEST_CASE_FIXTURE(TryUnifyFixture, "tables_can_be_unified")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     Type tableOne{TypeVariant{
@@ -119,7 +121,7 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "tables_can_be_unified")
 TEST_CASE_FIXTURE(TryUnifyFixture, "incompatible_tables_are_preserved")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     Type tableOne{TypeVariant{
@@ -185,7 +187,7 @@ TEST_CASE_FIXTURE(Fixture, "uninhabited_table_sub_anything")
 TEST_CASE_FIXTURE(Fixture, "members_of_failed_typepack_unification_are_unified_with_errorType")
 {
     ScopedFastFlag sff[] = {
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
 
     CheckResult result = check(R"(
@@ -204,7 +206,7 @@ TEST_CASE_FIXTURE(Fixture, "members_of_failed_typepack_unification_are_unified_w
 TEST_CASE_FIXTURE(Fixture, "result_of_failed_typepack_unification_is_constrained")
 {
     ScopedFastFlag sff[] = {
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
 
     CheckResult result = check(R"(
@@ -351,7 +353,7 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "txnlog_preserves_pack_owner")
 TEST_CASE_FIXTURE(TryUnifyFixture, "metatables_unify_against_shape_of_free_table")
 {
     ScopedFastFlag sff[] = {
-        {"LuauTransitiveSubtyping", true},
+        {FFlag::LuauTransitiveSubtyping, true},
     };
 
     TableType::Props freeProps{
@@ -448,7 +450,7 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "unifying_two_unions_under_dcr_does_not_creat
     const TypeId innerType = arena.freshType(nestedScope.get());
 
     ScopedFastFlag sffs[]{
-        {"LuauAlwaysCommitInferencesOfFunctionCalls", true},
+        {FFlag::LuauAlwaysCommitInferencesOfFunctionCalls, true},
     };
 
     state.enableNewSolver();

tests/TypeInfer.typePacks.test.cpp

@@ -10,6 +10,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauInstantiateInSubtyping);
 
 TEST_SUITE_BEGIN("TypePackTests");
 
@@ -1057,7 +1058,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_packs_with_tails_in_vararg_adjustment")
 {
     std::optional<ScopedFastFlag> sff;
     if (FFlag::DebugLuauDeferredConstraintResolution)
-        sff = {"LuauInstantiateInSubtyping", true};
+        sff = {FFlag::LuauInstantiateInSubtyping, true};
 
     CheckResult result = check(R"(
         local function wrapReject<TArg, TResult>(fn: (self: any, ...TArg) -> ...TResult): (self: any, ...TArg) -> ...TResult
@@ -1077,8 +1078,8 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_packs_with_tails_in_vararg_adjustment")
 TEST_CASE_FIXTURE(BuiltinsFixture, "generalize_expectedTypes_with_proper_scope")
 {
     ScopedFastFlag sff[] = {
-        {"DebugLuauDeferredConstraintResolution", true},
+        {FFlag::DebugLuauDeferredConstraintResolution, true},
-        {"LuauInstantiateInSubtyping", true},
+        {FFlag::LuauInstantiateInSubtyping, true},
     };
 
     CheckResult result = check(R"(