Sync to upstream/release/555 (#768)

* Type mismatch errors now mention if unification failed in covariant or
invariant context, to explain why sometimes derived class can't be
converted to base class or why `T` can't be converted into `T?` and so
on
* Class type indexing is no longer an error in non-strict mode (still an
error in strict mode)
* Fixed cyclic type packs not being displayed in the type
* Added an error when unrelated types are compared with `==`/`~=`
* Fixed false positive errors involving sub-type tests an `never` type
* Fixed miscompilation of multiple assignment statements (Fixes
https://github.com/Roblox/luau/issues/754)
* Type inference stability improvements

Analysis/include/Luau/BuiltinDefinitions.h

@@ -40,6 +40,7 @@ TypeId makeFunction( // Polymorphic
 
 void attachMagicFunction(TypeId ty, MagicFunction fn);
 void attachDcrMagicFunction(TypeId ty, DcrMagicFunction fn);
+void attachDcrMagicRefinement(TypeId ty, DcrMagicRefinement fn);
 
 Property makeProperty(TypeId ty, std::optional<std::string> documentationSymbol = std::nullopt);
 void assignPropDocumentationSymbols(TableTypeVar::Props& props, const std::string& baseName);

Analysis/include/Luau/Connective.h

@@ -3,7 +3,6 @@
 
 #include "Luau/Def.h"
 #include "Luau/TypedAllocator.h"
-#include "Luau/TypeVar.h"
 #include "Luau/Variant.h"
 
 #include <memory>
@@ -11,6 +10,9 @@
 namespace Luau
 {
 
+struct TypeVar;
+using TypeId = const TypeVar*;
+
 struct Negation;
 struct Conjunction;
 struct Disjunction;

Analysis/include/Luau/Constraint.h

@@ -149,11 +149,15 @@ struct SetPropConstraint
     TypeId propType;
 };
 
-// result ~ if isSingleton D then ~D else unknown where D = discriminantType
+// if negation:
+//   result ~ if isSingleton D then ~D else unknown where D = discriminantType
+// if not negation:
+//   result ~ if isSingleton D then D else unknown where D = discriminantType
 struct SingletonOrTopTypeConstraint
 {
     TypeId resultType;
     TypeId discriminantType;
+    bool negated;
 };
 
 using ConstraintV = Variant<SubtypeConstraint, PackSubtypeConstraint, GeneralizationConstraint, InstantiationConstraint, UnaryConstraint,

Analysis/include/Luau/ConstraintGraphBuilder.h

@@ -4,7 +4,7 @@
 #include "Luau/Ast.h"
 #include "Luau/Connective.h"
 #include "Luau/Constraint.h"
-#include "Luau/DataFlowGraphBuilder.h"
+#include "Luau/DataFlowGraph.h"
 #include "Luau/Module.h"
 #include "Luau/ModuleResolver.h"
 #include "Luau/NotNull.h"
@@ -215,7 +215,7 @@ struct ConstraintGraphBuilder
         ScopePtr bodyScope;
     };
 
-    FunctionSignature checkFunctionSignature(const ScopePtr& parent, AstExprFunction* fn);
+    FunctionSignature checkFunctionSignature(const ScopePtr& parent, AstExprFunction* fn, std::optional<TypeId> expectedType = {});
 
     /**
      * Checks the body of a function expression.

Analysis/include/Luau/DataFlowGraph.h

@@ -69,9 +69,14 @@ private:
     struct InternalErrorReporter* handle;
     std::vector<std::unique_ptr<DfgScope>> scopes;
 
+    // Does not belong in DataFlowGraphBuilder, but the old solver allows properties to escape the scope they were defined in,
+    // so we will need to be able to emulate this same behavior here too. We can kill this once we have better flow sensitivity.
+    DenseHashMap<const Def*, std::unordered_map<std::string, const Def*>> props{nullptr};
+
     DfgScope* childScope(DfgScope* scope);
 
     std::optional<DefId> use(DfgScope* scope, Symbol symbol, AstExpr* e);
+    DefId use(DefId def, AstExprIndexName* e);
 
     void visit(DfgScope* scope, AstStatBlock* b);
     void visitBlockWithoutChildScope(DfgScope* scope, AstStatBlock* b);

Analysis/include/Luau/Def.h

@@ -5,37 +5,38 @@
 #include "Luau/TypedAllocator.h"
 #include "Luau/Variant.h"
 
+#include <string>
+#include <optional>
+
 namespace Luau
 {
 
-using Def = Variant<struct Undefined, struct Phi>;
+struct Def;
-
-/**
- * We statically approximate a value at runtime using a symbolic value, which we call a Def.
- *
- * DataFlowGraphBuilder will allocate these defs as a stand-in for some Luau values, and bind them to places that
- * can hold a Luau value, and then observes how those defs will commute as it statically evaluate the program.
- *
- * It must also be noted that defs are a cyclic graph, so it is not safe to recursively traverse into it expecting it to terminate.
- */
 using DefId = NotNull<const Def>;
 
+struct FieldMetadata
+{
+    DefId parent;
+    std::string propName;
+};
+
 /**
- * A "single-object" value.
+ * A cell is a "single-object" value.
  *
  * Leaky implementation note: sometimes "multiple-object" values, but none of which were interesting enough to warrant creating a phi node instead.
  * That can happen because there's no point in creating a phi node that points to either resultant in `if math.random() > 0.5 then 5 else "hello"`.
  * This might become of utmost importance if we wanted to do some backward reasoning, e.g. if `5` is taken, then `cond` must be `truthy`.
  */
-struct Undefined
+struct Cell
 {
+    std::optional<struct FieldMetadata> field;
 };
 
 /**
- * A phi node is a union of defs.
+ * A phi node is a union of cells.
  *
  * We need this because we're statically evaluating a program, and sometimes a place may be assigned with
- * different defs, and when that happens, we need a special data type that merges in all the defs
+ * different cells, and when that happens, we need a special data type that merges in all the cells
  * that will flow into that specific place. For example, consider this simple program:
  *
  * ```
@@ -56,23 +57,35 @@ struct Phi
     std::vector<DefId> operands;
 };
 
-template<typename T>
+/**
-T* getMutable(DefId def)
+ * We statically approximate a value at runtime using a symbolic value, which we call a Def.
+ *
+ * DataFlowGraphBuilder will allocate these defs as a stand-in for some Luau values, and bind them to places that
+ * can hold a Luau value, and then observes how those defs will commute as it statically evaluate the program.
+ *
+ * It must also be noted that defs are a cyclic graph, so it is not safe to recursively traverse into it expecting it to terminate.
+ */
+struct Def
 {
-    return get_if<T>(def.get());
+    using V = Variant<struct Cell, struct Phi>;
-}
+
+    V v;
+};
 
 template<typename T>
 const T* get(DefId def)
 {
-    return getMutable<T>(def);
+    return get_if<T>(&def->v);
 }
 
 struct DefArena
 {
     TypedAllocator<Def> allocator;
 
-    DefId freshDef();
+    DefId freshCell();
+    DefId freshCell(DefId parent, const std::string& prop);
+    // TODO: implement once we have cases where we need to merge in definitions
+    // DefId phi(const std::vector<DefId>& defs);
 };
 
 } // namespace Luau

Analysis/include/Luau/Error.h

@@ -7,21 +7,31 @@
 #include "Luau/Variant.h"
 #include "Luau/TypeArena.h"
 
-LUAU_FASTFLAG(LuauIceExceptionInheritanceChange)
-
 namespace Luau
 {
 struct TypeError;
 
+
 struct TypeMismatch
 {
+    enum Context
+    {
+        CovariantContext,
+        InvariantContext
+    };
+
     TypeMismatch() = default;
     TypeMismatch(TypeId wantedType, TypeId givenType);
     TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason);
     TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, std::optional<TypeError> error);
 
+    TypeMismatch(TypeId wantedType, TypeId givenType, Context context);
+    TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, Context context);
+    TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, std::optional<TypeError> error, Context context);
+
     TypeId wantedType = nullptr;
     TypeId givenType = nullptr;
+    Context context = CovariantContext;
 
     std::string reason;
     std::shared_ptr<TypeError> error;
@@ -312,12 +322,33 @@ struct TypePackMismatch
     bool operator==(const TypePackMismatch& rhs) const;
 };
 
+struct DynamicPropertyLookupOnClassesUnsafe
+{
+    TypeId ty;
+
+    bool operator==(const DynamicPropertyLookupOnClassesUnsafe& 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>;
+    TypesAreUnrelated, NormalizationTooComplex, TypePackMismatch, DynamicPropertyLookupOnClassesUnsafe>;
+
+struct TypeErrorSummary
+{
+    Location location;
+    ModuleName moduleName;
+    int code;
+
+    TypeErrorSummary(const Location& location, const ModuleName& moduleName, int code)
+        : location(location)
+        , moduleName(moduleName)
+        , code(code)
+    {
+    }
+};
 
 struct TypeError
 {
@@ -325,6 +356,7 @@ struct TypeError
     ModuleName moduleName;
     TypeErrorData data;
 
+    static int minCode();
     int code() const;
 
     TypeError() = default;
@@ -342,6 +374,8 @@ struct TypeError
     }
 
     bool operator==(const TypeError& rhs) const;
+
+    TypeErrorSummary summary() const;
 };
 
 template<typename T>
@@ -406,10 +440,4 @@ public:
     const std::optional<Location> location;
 };
 
-// These two function overloads only exist to facilitate fast flagging a change to InternalCompilerError
-// Both functions can be removed when FFlagLuauIceExceptionInheritanceChange is removed and calling code
-// can directly throw InternalCompilerError.
-[[noreturn]] void throwRuntimeError(const std::string& message);
-[[noreturn]] void throwRuntimeError(const std::string& message, const std::string& moduleName);
-
 } // namespace Luau

Analysis/include/Luau/Normalize.h

@@ -194,6 +194,8 @@ struct NormalizedFunctionType
 struct NormalizedType;
 using NormalizedTyvars = std::unordered_map<TypeId, std::unique_ptr<NormalizedType>>;
 
+bool isInhabited_DEPRECATED(const NormalizedType& norm);
+
 // A normalized type is either any, unknown, or one of the form P | T | F | G where
 // * P is a union of primitive types (including singletons, classes and the error type)
 // * T is a union of table types
@@ -328,6 +330,10 @@ public:
     bool intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
     bool intersectNormalWithTy(NormalizedType& here, TypeId there);
 
+    // Check for inhabitance
+    bool isInhabited(TypeId ty, std::unordered_set<TypeId> seen = {});
+    bool isInhabited(const NormalizedType* norm, std::unordered_set<TypeId> seen = {});
+
     // -------- Convert back from a normalized type to a type
     TypeId typeFromNormal(const NormalizedType& norm);
 };

Analysis/include/Luau/NotNull.h

@@ -59,6 +59,20 @@ struct NotNull
         return ptr;
     }
 
+    template<typename U>
+    bool operator==(NotNull<U> other) const noexcept
+    {
+        return get() == other.get();
+    }
+
+    template<typename U>
+    bool operator!=(NotNull<U> other) const noexcept
+    {
+        return get() != other.get();
+    }
+
+    operator bool() const noexcept = delete;
+
     T& operator[](int) = delete;
 
     T& operator+(int) = delete;

Analysis/include/Luau/RecursionCounter.h

@@ -15,16 +15,6 @@ struct RecursionLimitException : public InternalCompilerError
     RecursionLimitException()
         : InternalCompilerError("Internal recursion counter limit exceeded")
     {
-        LUAU_ASSERT(FFlag::LuauIceExceptionInheritanceChange);
-    }
-};
-
-struct RecursionLimitException_DEPRECATED : public std::exception
-{
-    const char* what() const noexcept
-    {
-        LUAU_ASSERT(!FFlag::LuauIceExceptionInheritanceChange);
-        return "Internal recursion counter limit exceeded";
     }
 };
 
@@ -53,14 +43,7 @@ struct RecursionLimiter : RecursionCounter
     {
         if (limit > 0 && *count > limit)
         {
-            if (FFlag::LuauIceExceptionInheritanceChange)
+            throw RecursionLimitException();
-            {
-                throw RecursionLimitException();
-            }
-            else
-            {
-                throw RecursionLimitException_DEPRECATED();
-            }
         }
     }
 };

Analysis/include/Luau/ToString.h

@@ -30,7 +30,7 @@ struct ToStringOptions
     bool hideTableKind = false;                   // If true, all tables will be surrounded with plain '{}'
     bool hideNamedFunctionTypeParameters = false; // If true, type parameters of functions will be hidden at top-level.
     bool hideFunctionSelfArgument = false;        // If true, `self: X` will be omitted from the function signature if the function has self
-    bool indent = false;
+    bool DEPRECATED_indent = false;               // TODO Deprecated field, prune when clipping flag FFlagLuauLineBreaksDeterminIndents
     size_t maxTableLength = size_t(FInt::LuauTableTypeMaximumStringifierLength); // Only applied to TableTypeVars
     size_t maxTypeLength = size_t(FInt::LuauTypeMaximumStringifierLength);
     ToStringNameMap nameMap;
@@ -90,8 +90,6 @@ inline std::string toString(const Constraint& c)
     return toString(c, ToStringOptions{});
 }
 
-std::string toString(const LValue& lvalue);
-
 std::string toString(const TypeVar& tv, ToStringOptions& opts);
 std::string toString(const TypePackVar& tp, ToStringOptions& opts);
 

Analysis/include/Luau/TxnLog.h

@@ -108,6 +108,8 @@ struct TxnLog
     // If both logs talk about the same type, pack, or table, the rhs takes
     // priority.
     void concat(TxnLog rhs);
+    void concatAsIntersections(TxnLog rhs, NotNull<TypeArena> arena);
+    void concatAsUnion(TxnLog rhs, NotNull<TypeArena> arena);
 
     // Commits the TxnLog, rebinding all type pointers to their pending states.
     // Clears the TxnLog afterwards.

Analysis/include/Luau/TypeInfer.h

@@ -54,16 +54,9 @@ public:
     explicit TimeLimitError(const std::string& moduleName)
         : InternalCompilerError("Typeinfer failed to complete in allotted time", moduleName)
     {
-        LUAU_ASSERT(FFlag::LuauIceExceptionInheritanceChange);
     }
 };
 
-class TimeLimitError_DEPRECATED : public std::exception
-{
-public:
-    virtual const char* what() const throw();
-};
-
 // All TypeVars are retained via Environment::typeVars.  All TypeIds
 // within a program are borrowed pointers into this set.
 struct TypeChecker

Analysis/include/Luau/TypeUtils.h

@@ -25,9 +25,9 @@ std::optional<TypeId> getIndexTypeFromType(const ScopePtr& scope, ErrorVec& erro
 // Returns the minimum and maximum number of types the argument list can accept.
 std::pair<size_t, std::optional<size_t>> getParameterExtents(const TxnLog* log, TypePackId tp, bool includeHiddenVariadics = false);
 
-// "Render" a type pack out to an array of a given length. Expands variadics and
+// Extend the provided pack to at least `length` types.
-// various other things to get there.
+// Returns a temporary TypePack that contains those types plus a tail.
-std::vector<TypeId> flatten(TypeArena& arena, NotNull<SingletonTypes> singletonTypes, TypePackId pack, size_t length);
+TypePack extendTypePack(TypeArena& arena, NotNull<SingletonTypes> singletonTypes, TypePackId pack, size_t length);
 
 /**
  * Reduces a union by decomposing to the any/error type if it appears in the

Analysis/include/Luau/TypeVar.h

@@ -3,6 +3,8 @@
 
 #include "Luau/Ast.h"
 #include "Luau/Common.h"
+#include "Luau/Connective.h"
+#include "Luau/DataFlowGraph.h"
 #include "Luau/DenseHash.h"
 #include "Luau/Def.h"
 #include "Luau/NotNull.h"
@@ -257,7 +259,17 @@ struct MagicFunctionCallContext
     TypePackId result;
 };
 
-using DcrMagicFunction = std::function<bool(MagicFunctionCallContext)>;
+using DcrMagicFunction = bool (*)(MagicFunctionCallContext);
+
+struct MagicRefinementContext
+{
+    ScopePtr scope;
+    NotNull<const DataFlowGraph> dfg;
+    NotNull<ConnectiveArena> connectiveArena;
+    const class AstExprCall* callSite;
+};
+
+using DcrMagicRefinement = std::vector<ConnectiveId> (*)(MagicRefinementContext);
 
 struct FunctionTypeVar
 {
@@ -279,19 +291,20 @@ struct FunctionTypeVar
     FunctionTypeVar(TypeLevel level, Scope* scope, std::vector<TypeId> generics, std::vector<TypePackId> genericPacks, TypePackId argTypes,
         TypePackId retTypes, std::optional<FunctionDefinition> defn = {}, bool hasSelf = false);
 
-    TypeLevel level;
+    std::optional<FunctionDefinition> definition;
-    Scope* scope = nullptr;
     /// These should all be generic
     std::vector<TypeId> generics;
     std::vector<TypePackId> genericPacks;
-    TypePackId argTypes;
     std::vector<std::optional<FunctionArgument>> argNames;
-    TypePackId retTypes;
-    std::optional<FunctionDefinition> definition;
-    MagicFunction magicFunction = nullptr;       // Function pointer, can be nullptr.
-    DcrMagicFunction dcrMagicFunction = nullptr; // can be nullptr
-    bool hasSelf;
     Tags tags;
+    TypeLevel level;
+    Scope* scope = nullptr;
+    TypePackId argTypes;
+    TypePackId retTypes;
+    MagicFunction magicFunction = nullptr;
+    DcrMagicFunction dcrMagicFunction = nullptr;     // Fired only while solving constraints
+    DcrMagicRefinement dcrMagicRefinement = nullptr; // Fired only while generating constraints
+    bool hasSelf;
     bool hasNoGenerics = false;
 };
 

Analysis/include/Luau/Unifier.h

@@ -120,6 +120,9 @@ private:
 
     std::optional<TypeId> findTablePropertyRespectingMeta(TypeId lhsType, Name name);
 
+    TxnLog combineLogsIntoIntersection(std::vector<TxnLog> logs);
+    TxnLog combineLogsIntoUnion(std::vector<TxnLog> logs);
+
 public:
     // Returns true if the type "needle" already occurs within "haystack" and reports an "infinite type error"
     bool occursCheck(TypeId needle, TypeId haystack);
@@ -134,6 +137,7 @@ public:
 
 private:
     bool isNonstrictMode() const;
+    TypeMismatch::Context mismatchContext();
 
     void checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, TypeId wantedType, TypeId givenType);
     void checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, const std::string& prop, TypeId wantedType, TypeId givenType);

Analysis/src/AstQuery.cpp

@@ -11,15 +11,12 @@
 
 #include <algorithm>
 
-LUAU_FASTFLAGVARIABLE(LuauCheckOverloadedDocSymbol, false)
-
 namespace Luau
 {
 
 namespace
 {
 
-
 struct AutocompleteNodeFinder : public AstVisitor
 {
     const Position pos;
@@ -432,8 +429,6 @@ ExprOrLocal findExprOrLocalAtPosition(const SourceModule& source, Position pos)
 static std::optional<DocumentationSymbol> checkOverloadedDocumentationSymbol(
     const Module& module, const TypeId ty, const AstExpr* parentExpr, const std::optional<DocumentationSymbol> documentationSymbol)
 {
-    LUAU_ASSERT(FFlag::LuauCheckOverloadedDocSymbol);
-
     if (!documentationSymbol)
         return std::nullopt;
 
@@ -469,40 +464,7 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
     AstExpr* parentExpr = ancestry.size() >= 2 ? ancestry[ancestry.size() - 2]->asExpr() : nullptr;
 
     if (std::optional<Binding> binding = findBindingAtPosition(module, source, position))
-    {
+        return checkOverloadedDocumentationSymbol(module, binding->typeId, parentExpr, binding->documentationSymbol);
-        if (FFlag::LuauCheckOverloadedDocSymbol)
-        {
-            return checkOverloadedDocumentationSymbol(module, binding->typeId, parentExpr, binding->documentationSymbol);
-        }
-        else
-        {
-            if (binding->documentationSymbol)
-            {
-                // This might be an overloaded function binding.
-                if (get<IntersectionTypeVar>(follow(binding->typeId)))
-                {
-                    TypeId matchingOverload = nullptr;
-                    if (parentExpr && parentExpr->is<AstExprCall>())
-                    {
-                        if (auto it = module.astOverloadResolvedTypes.find(parentExpr))
-                        {
-                            matchingOverload = *it;
-                        }
-                    }
-
-                    if (matchingOverload)
-                    {
-                        std::string overloadSymbol = *binding->documentationSymbol + "/overload/";
-                        // Default toString options are fine for this purpose.
-                        overloadSymbol += toString(matchingOverload);
-                        return overloadSymbol;
-                    }
-                }
-            }
-
-            return binding->documentationSymbol;
-        }
-    }
 
     if (targetExpr)
     {
@@ -514,22 +476,12 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                 if (const TableTypeVar* ttv = get<TableTypeVar>(parentTy))
                 {
                     if (auto propIt = ttv->props.find(indexName->index.value); propIt != ttv->props.end())
-                    {
+                        return checkOverloadedDocumentationSymbol(module, propIt->second.type, parentExpr, propIt->second.documentationSymbol);
-                        if (FFlag::LuauCheckOverloadedDocSymbol)
-                            return checkOverloadedDocumentationSymbol(module, propIt->second.type, parentExpr, propIt->second.documentationSymbol);
-                        else
-                            return propIt->second.documentationSymbol;
-                    }
                 }
                 else if (const ClassTypeVar* ctv = get<ClassTypeVar>(parentTy))
                 {
                     if (auto propIt = ctv->props.find(indexName->index.value); propIt != ctv->props.end())
-                    {
+                        return checkOverloadedDocumentationSymbol(module, propIt->second.type, parentExpr, propIt->second.documentationSymbol);
-                        if (FFlag::LuauCheckOverloadedDocSymbol)
-                            return checkOverloadedDocumentationSymbol(module, propIt->second.type, parentExpr, propIt->second.documentationSymbol);
-                        else
-                            return propIt->second.documentationSymbol;
-                    }
                 }
             }
         }

Analysis/src/Autocomplete.cpp

@@ -1457,7 +1457,8 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
         return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
     else if (AstStatRepeat* statRepeat = extractStat<AstStatRepeat>(ancestry); statRepeat)
         return {autocompleteStatement(sourceModule, *module, ancestry, position), ancestry, AutocompleteContext::Statement};
-    else if (AstExprTable* exprTable = parent->as<AstExprTable>(); exprTable && (node->is<AstExprGlobal>() || node->is<AstExprConstantString>() || node->is<AstExprInterpString>()))
+    else if (AstExprTable* exprTable = parent->as<AstExprTable>();
+             exprTable && (node->is<AstExprGlobal>() || node->is<AstExprConstantString>() || node->is<AstExprInterpString>()))
     {
         for (const auto& [kind, key, value] : exprTable->items)
         {

Analysis/src/BuiltinDefinitions.cpp

@@ -132,6 +132,14 @@ void attachDcrMagicFunction(TypeId ty, DcrMagicFunction fn)
         LUAU_ASSERT(!"Got a non functional type");
 }
 
+void attachDcrMagicRefinement(TypeId ty, DcrMagicRefinement fn)
+{
+    if (auto ftv = getMutable<FunctionTypeVar>(ty))
+        ftv->dcrMagicRefinement = fn;
+    else
+        LUAU_ASSERT(!"Got a non functional type");
+}
+
 Property makeProperty(TypeId ty, std::optional<std::string> documentationSymbol)
 {
     return {

Analysis/src/ConstraintGraphBuilder.cpp

@@ -9,7 +9,9 @@
 #include "Luau/ModuleResolver.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Scope.h"
+#include "Luau/Substitution.h"
 #include "Luau/ToString.h"
+#include "Luau/TxnLog.h"
 #include "Luau/TypeUtils.h"
 #include "Luau/TypeVar.h"
 
@@ -191,7 +193,7 @@ static void unionRefinements(const std::unordered_map<DefId, TypeId>& lhs, const
 }
 
 static void computeRefinement(const ScopePtr& scope, ConnectiveId connective, std::unordered_map<DefId, TypeId>* refis, bool sense,
-    NotNull<TypeArena> arena, bool eq, std::vector<SingletonOrTopTypeConstraint>* constraints)
+    NotNull<TypeArena> arena, bool eq, std::vector<ConstraintV>* constraints)
 {
     using RefinementMap = std::unordered_map<DefId, TypeId>;
 
@@ -231,10 +233,10 @@ static void computeRefinement(const ScopePtr& scope, ConnectiveId connective, st
         TypeId discriminantTy = proposition->discriminantTy;
         if (!sense && !eq)
             discriminantTy = arena->addType(NegationTypeVar{proposition->discriminantTy});
-        else if (!sense && eq)
+        else if (eq)
         {
             discriminantTy = arena->addType(BlockedTypeVar{});
-            constraints->push_back(SingletonOrTopTypeConstraint{discriminantTy, proposition->discriminantTy});
+            constraints->push_back(SingletonOrTopTypeConstraint{discriminantTy, proposition->discriminantTy, !sense});
         }
 
         if (auto it = refis->find(proposition->def); it != refis->end())
@@ -244,23 +246,43 @@ static void computeRefinement(const ScopePtr& scope, ConnectiveId connective, st
     }
 }
 
+static std::pair<DefId, TypeId> computeDiscriminantType(NotNull<TypeArena> arena, const ScopePtr& scope, DefId def, TypeId discriminantTy)
+{
+    LUAU_ASSERT(get<Cell>(def));
+
+    while (const Cell* current = get<Cell>(def))
+    {
+        if (!current->field)
+            break;
+
+        TableTypeVar::Props props{{current->field->propName, Property{discriminantTy}}};
+        discriminantTy = arena->addType(TableTypeVar{std::move(props), std::nullopt, TypeLevel{}, scope.get(), TableState::Sealed});
+
+        def = current->field->parent;
+        current = get<Cell>(def);
+    }
+
+    return {def, discriminantTy};
+}
+
 void ConstraintGraphBuilder::applyRefinements(const ScopePtr& scope, Location location, ConnectiveId connective)
 {
     if (!connective)
         return;
 
     std::unordered_map<DefId, TypeId> refinements;
-    std::vector<SingletonOrTopTypeConstraint> constraints;
+    std::vector<ConstraintV> constraints;
     computeRefinement(scope, connective, &refinements, /*sense*/ true, arena, /*eq*/ false, &constraints);
 
     for (auto [def, discriminantTy] : refinements)
     {
-        std::optional<TypeId> defTy = scope->lookup(def);
+        auto [def2, discriminantTy2] = computeDiscriminantType(arena, scope, def, discriminantTy);
+        std::optional<TypeId> defTy = scope->lookup(def2);
         if (!defTy)
             ice->ice("Every DefId must map to a type!");
 
-        TypeId resultTy = arena->addType(IntersectionTypeVar{{*defTy, discriminantTy}});
+        TypeId resultTy = arena->addType(IntersectionTypeVar{{*defTy, discriminantTy2}});
-        scope->dcrRefinements[def] = resultTy;
+        scope->dcrRefinements[def2] = resultTy;
     }
 
     for (auto& c : constraints)
@@ -446,15 +468,15 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatLocal* local)
 
             if (i < local->vars.size)
             {
-                std::vector<TypeId> packTypes = flatten(*arena, singletonTypes, exprPack, varTypes.size() - i);
+                TypePack packTypes = extendTypePack(*arena, singletonTypes, exprPack, varTypes.size() - i);
 
                 // fill out missing values in varTypes with values from exprPack
                 for (size_t j = i; j < varTypes.size(); ++j)
                 {
                     if (!varTypes[j])
                     {
-                        if (j - i < packTypes.size())
+                        if (j - i < packTypes.head.size())
-                            varTypes[j] = packTypes[j - i];
+                            varTypes[j] = packTypes.head[j - i];
                         else
                             varTypes[j] = freshType(scope);
                     }
@@ -591,9 +613,9 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatLocalFunction*
     FunctionSignature sig = checkFunctionSignature(scope, function->func);
     sig.bodyScope->bindings[function->name] = Binding{sig.signature, function->func->location};
 
-    auto start = checkpoint(this);
+    Checkpoint start = checkpoint(this);
     checkFunctionBody(sig.bodyScope, function->func);
-    auto end = checkpoint(this);
+    Checkpoint end = checkpoint(this);
 
     NotNull<Scope> constraintScope{sig.signatureScope ? sig.signatureScope.get() : sig.bodyScope.get()};
     std::unique_ptr<Constraint> c =
@@ -611,7 +633,7 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatFunction* funct
     // Name could be AstStatLocal, AstStatGlobal, AstStatIndexName.
     // With or without self
 
-    TypeId functionType = nullptr;
+    TypeId generalizedType = arena->addType(BlockedTypeVar{});
 
     FunctionSignature sig = checkFunctionSignature(scope, function->func);
 
@@ -620,62 +642,59 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatFunction* funct
         std::optional<TypeId> existingFunctionTy = scope->lookup(localName->local);
         if (existingFunctionTy)
         {
-            // Duplicate definition
+            addConstraint(scope, function->name->location, SubtypeConstraint{generalizedType, *existingFunctionTy});
-            functionType = *existingFunctionTy;
+
+            Symbol sym{localName->local};
+            std::optional<DefId> def = dfg->getDef(sym);
+            LUAU_ASSERT(def);
+            scope->bindings[sym].typeId = generalizedType;
+            scope->dcrRefinements[*def] = generalizedType;
         }
         else
-        {
+            scope->bindings[localName->local] = Binding{generalizedType, localName->location};
-            functionType = arena->addType(BlockedTypeVar{});
+
-            scope->bindings[localName->local] = Binding{functionType, localName->location};
-        }
         sig.bodyScope->bindings[localName->local] = Binding{sig.signature, localName->location};
     }
     else if (AstExprGlobal* globalName = function->name->as<AstExprGlobal>())
     {
         std::optional<TypeId> existingFunctionTy = scope->lookup(globalName->name);
-        if (existingFunctionTy)
+        if (!existingFunctionTy)
-        {
+            ice->ice("prepopulateGlobalScope did not populate a global name", globalName->location);
-            // Duplicate definition
+
-            functionType = *existingFunctionTy;
+        generalizedType = *existingFunctionTy;
-        }
+
-        else
-        {
-            functionType = arena->addType(BlockedTypeVar{});
-            rootScope->bindings[globalName->name] = Binding{functionType, globalName->location};
-        }
         sig.bodyScope->bindings[globalName->name] = Binding{sig.signature, globalName->location};
     }
     else if (AstExprIndexName* indexName = function->name->as<AstExprIndexName>())
     {
         TypeId containingTableType = check(scope, indexName->expr).ty;
 
-        functionType = arena->addType(BlockedTypeVar{});
-
         // TODO look into stack utilization.  This is probably ok because it scales with AST depth.
         TypeId prospectiveTableType = arena->addType(TableTypeVar{TableState::Unsealed, TypeLevel{}, scope.get()});
 
         NotNull<TableTypeVar> prospectiveTable{getMutable<TableTypeVar>(prospectiveTableType)};
 
         Property& prop = prospectiveTable->props[indexName->index.value];
-        prop.type = functionType;
+        prop.type = generalizedType;
         prop.location = function->name->location;
 
         addConstraint(scope, indexName->location, SubtypeConstraint{containingTableType, prospectiveTableType});
     }
     else if (AstExprError* err = function->name->as<AstExprError>())
     {
-        functionType = singletonTypes->errorRecoveryType();
+        generalizedType = singletonTypes->errorRecoveryType();
     }
 
-    LUAU_ASSERT(functionType != nullptr);
+    if (generalizedType == nullptr)
+        ice->ice("generalizedType == nullptr", function->location);
 
-    auto start = checkpoint(this);
+    Checkpoint start = checkpoint(this);
     checkFunctionBody(sig.bodyScope, function->func);
-    auto end = checkpoint(this);
+    Checkpoint end = checkpoint(this);
 
     NotNull<Scope> constraintScope{sig.signatureScope ? sig.signatureScope.get() : sig.bodyScope.get()};
     std::unique_ptr<Constraint> c =
-        std::make_unique<Constraint>(constraintScope, function->name->location, GeneralizationConstraint{functionType, sig.signature});
+        std::make_unique<Constraint>(constraintScope, function->name->location, GeneralizationConstraint{generalizedType, sig.signature});
 
     forEachConstraint(start, end, this, [&c](const ConstraintPtr& constraint) {
         c->dependencies.push_back(NotNull{constraint.get()});
@@ -708,7 +727,9 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatBlock* block)
 void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatAssign* assign)
 {
     TypePackId varPackId = checkLValues(scope, assign->vars);
-    TypePackId valuePack = checkPack(scope, assign->values).tp;
+
+    TypePack expectedTypes = extendTypePack(*arena, singletonTypes, varPackId, assign->values.size);
+    TypePackId valuePack = checkPack(scope, assign->values, expectedTypes.head).tp;
 
     addConstraint(scope, assign->location, PackSubtypeConstraint{valuePack, varPackId});
 }
@@ -729,8 +750,6 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatCompoundAssign*
 
 void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatIf* ifStatement)
 {
-    // TODO: Optimization opportunity, the interior scope of the condition could be
-    // reused for the then body, so we don't need to refine twice.
     ScopePtr condScope = childScope(ifStatement->condition, scope);
     auto [_, connective] = check(condScope, ifStatement->condition, std::nullopt);
 
@@ -986,7 +1005,7 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExpr*
     InferencePack result;
 
     if (AstExprCall* call = expr->as<AstExprCall>())
-        result = {checkPack(scope, call, expectedTypes)};
+        result = checkPack(scope, call, expectedTypes);
     else if (AstExprVarargs* varargs = expr->as<AstExprVarargs>())
     {
         if (scope->varargPack)
@@ -1010,38 +1029,101 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExpr*
 
 InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExprCall* call, const std::vector<TypeId>& expectedTypes)
 {
-    TypeId fnType = check(scope, call->func).ty;
+    std::vector<AstExpr*> exprArgs;
-    auto startCheckpoint = checkpoint(this);
-
-    std::vector<TypeId> args;
-
-    for (AstExpr* arg : call->args)
-    {
-        args.push_back(check(scope, arg).ty);
-    }
-
     if (call->self)
     {
         AstExprIndexName* indexExpr = call->func->as<AstExprIndexName>();
         if (!indexExpr)
             ice->ice("method call expression has no 'self'");
 
-        // The call to `check` we already did on `call->func` should have already produced a type for
+        exprArgs.push_back(indexExpr->expr);
-        // `indexExpr->expr`, so we can get it from `astTypes` to avoid exponential blow-up.
-        TypeId selfType = astTypes[indexExpr->expr];
-
-        // If we don't have a type for self, it means we had a code too complex error already.
-        if (selfType == nullptr)
-            selfType = singletonTypes->errorRecoveryType();
-
-        args.insert(args.begin(), selfType);
     }
+    exprArgs.insert(exprArgs.end(), call->args.begin(), call->args.end());
+
+    Checkpoint startCheckpoint = checkpoint(this);
+    TypeId fnType = check(scope, call->func).ty;
+    Checkpoint fnEndCheckpoint = checkpoint(this);
+
+    TypePackId expectedArgPack = arena->freshTypePack(scope.get());
+    TypePackId expectedRetPack = arena->freshTypePack(scope.get());
+    TypeId expectedFunctionType = arena->addType(FunctionTypeVar{expectedArgPack, expectedRetPack});
+
+    TypeId instantiatedFnType = arena->addType(BlockedTypeVar{});
+    addConstraint(scope, call->location, InstantiationConstraint{instantiatedFnType, fnType});
+
+    NotNull<Constraint> extractArgsConstraint = addConstraint(scope, call->location, SubtypeConstraint{instantiatedFnType, expectedFunctionType});
+
+    // Fully solve fnType, then extract its argument list as expectedArgPack.
+    forEachConstraint(startCheckpoint, fnEndCheckpoint, this, [extractArgsConstraint](const ConstraintPtr& constraint) {
+        extractArgsConstraint->dependencies.emplace_back(constraint.get());
+    });
+
+    const AstExpr* lastArg = exprArgs.size() ? exprArgs[exprArgs.size() - 1] : nullptr;
+    const bool needTail = lastArg && (lastArg->is<AstExprCall>() || lastArg->is<AstExprVarargs>());
+
+    TypePack expectedArgs;
+
+    if (!needTail)
+        expectedArgs = extendTypePack(*arena, singletonTypes, expectedArgPack, exprArgs.size());
+    else
+        expectedArgs = extendTypePack(*arena, singletonTypes, expectedArgPack, exprArgs.size() - 1);
+
+    std::vector<ConnectiveId> connectives;
+    if (auto ftv = get<FunctionTypeVar>(follow(fnType)); ftv && ftv->dcrMagicRefinement)
+    {
+        MagicRefinementContext ctx{globalScope, dfg, NotNull{&connectiveArena}, call};
+        connectives = ftv->dcrMagicRefinement(ctx);
+    }
+
+
+    std::vector<TypeId> args;
+    std::optional<TypePackId> argTail;
+
+    Checkpoint argCheckpoint = checkpoint(this);
+
+    for (size_t i = 0; i < exprArgs.size(); ++i)
+    {
+        AstExpr* arg = exprArgs[i];
+        std::optional<TypeId> expectedType;
+        if (i < expectedArgs.head.size())
+            expectedType = expectedArgs.head[i];
+
+        if (i == 0 && call->self)
+        {
+            // The self type has already been computed as a side effect of
+            // computing fnType.  If computing that did not cause us to exceed a
+            // recursion limit, we can fetch it from astTypes rather than
+            // recomputing it.
+            TypeId* selfTy = astTypes.find(exprArgs[0]);
+            if (selfTy)
+                args.push_back(*selfTy);
+            else
+                args.push_back(arena->freshType(scope.get()));
+        }
+        else if (i < exprArgs.size() - 1 || !(arg->is<AstExprCall>() || arg->is<AstExprVarargs>()))
+            args.push_back(check(scope, arg, expectedType).ty);
+        else
+            argTail = checkPack(scope, arg, {}).tp; // FIXME? not sure about expectedTypes here
+    }
+
+    Checkpoint argEndCheckpoint = checkpoint(this);
+
+    // Do not solve argument constraints until after we have extracted the
+    // expected types from the callable.
+    forEachConstraint(argCheckpoint, argEndCheckpoint, this, [extractArgsConstraint](const ConstraintPtr& constraint) {
+        constraint->dependencies.push_back(extractArgsConstraint);
+    });
 
     if (matchSetmetatable(*call))
     {
-        LUAU_ASSERT(args.size() == 2);
+        TypePack argTailPack;
-        TypeId target = args[0];
+        if (argTail && args.size() < 2)
-        TypeId mt = args[1];
+            argTailPack = extendTypePack(*arena, singletonTypes, *argTail, 2 - args.size());
+
+        LUAU_ASSERT(args.size() + argTailPack.head.size() == 2);
+
+        TypeId target = args.size() > 0 ? args[0] : argTailPack.head[0];
+        TypeId mt = args.size() > 1 ? args[1] : argTailPack.head[args.size() == 0 ? 1 : 0];
 
         AstExpr* targetExpr = call->args.data[0];
 
@@ -1051,18 +1133,16 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExprCa
         if (AstExprLocal* targetLocal = targetExpr->as<AstExprLocal>())
             scope->bindings[targetLocal->local].typeId = resultTy;
 
-        return InferencePack{arena->addTypePack({resultTy})};
+        return InferencePack{arena->addTypePack({resultTy}), std::move(connectives)};
     }
     else
     {
-        auto endCheckpoint = checkpoint(this);
-
         astOriginalCallTypes[call->func] = fnType;
 
         TypeId instantiatedType = arena->addType(BlockedTypeVar{});
         // TODO: How do expectedTypes play into this?  Do they?
         TypePackId rets = arena->addTypePack(BlockedTypePack{});
-        TypePackId argPack = arena->addTypePack(TypePack{args, {}});
+        TypePackId argPack = arena->addTypePack(TypePack{args, argTail});
         FunctionTypeVar ftv(TypeLevel{}, scope.get(), argPack, rets);
         TypeId inferredFnType = arena->addType(ftv);
 
@@ -1071,19 +1151,10 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExprCa
         NotNull<const Constraint> ic(unqueuedConstraints.back().get());
 
         unqueuedConstraints.push_back(
-            std::make_unique<Constraint>(NotNull{scope.get()}, call->func->location, SubtypeConstraint{inferredFnType, instantiatedType}));
+            std::make_unique<Constraint>(NotNull{scope.get()}, call->func->location, SubtypeConstraint{instantiatedType, inferredFnType}));
         NotNull<Constraint> sc(unqueuedConstraints.back().get());
 
-        // We force constraints produced by checking function arguments to wait
+        NotNull<Constraint> fcc = addConstraint(scope, call->func->location,
-        // until after we have resolved the constraint on the function itself.
-        // This ensures, for instance, that we start inferring the contents of
-        // lambdas under the assumption that their arguments and return types
-        // will be compatible with the enclosing function call.
-        forEachConstraint(startCheckpoint, endCheckpoint, this, [sc](const ConstraintPtr& constraint) {
-            constraint->dependencies.push_back(sc);
-        });
-
-        addConstraint(scope, call->func->location,
             FunctionCallConstraint{
                 {ic, sc},
                 fnType,
@@ -1092,7 +1163,16 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExprCa
                 call,
             });
 
-        return InferencePack{rets};
+        // We force constraints produced by checking function arguments to wait
+        // until after we have resolved the constraint on the function itself.
+        // This ensures, for instance, that we start inferring the contents of
+        // lambdas under the assumption that their arguments and return types
+        // will be compatible with the enclosing function call.
+        forEachConstraint(fnEndCheckpoint, argEndCheckpoint, this, [fcc](const ConstraintPtr& constraint) {
+            fcc->dependencies.emplace_back(constraint.get());
+        });
+
+        return InferencePack{rets, std::move(connectives)};
     }
 }
 
@@ -1133,9 +1213,19 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExpr* expr, st
     }
     else if (auto a = expr->as<AstExprFunction>())
     {
-        FunctionSignature sig = checkFunctionSignature(scope, a);
+        Checkpoint startCheckpoint = checkpoint(this);
+        FunctionSignature sig = checkFunctionSignature(scope, a, expectedType);
         checkFunctionBody(sig.bodyScope, a);
-        return Inference{sig.signature};
+        Checkpoint endCheckpoint = checkpoint(this);
+
+        TypeId generalizedTy = arena->addType(BlockedTypeVar{});
+        NotNull<Constraint> gc = addConstraint(scope, expr->location, GeneralizationConstraint{generalizedTy, sig.signature});
+
+        forEachConstraint(startCheckpoint, endCheckpoint, this, [gc](const ConstraintPtr& constraint) {
+            gc->dependencies.emplace_back(constraint.get());
+        });
+
+        return Inference{generalizedTy};
     }
     else if (auto indexName = expr->as<AstExprIndexName>())
         result = check(scope, indexName);
@@ -1253,10 +1343,83 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprGlobal* gl
     return Inference{singletonTypes->errorRecoveryType()};
 }
 
+static std::optional<TypeId> lookupProp(TypeId ty, const std::string& propName, NotNull<TypeArena> arena)
+{
+    ty = follow(ty);
+
+    if (auto ctv = get<ClassTypeVar>(ty))
+    {
+        if (auto prop = lookupClassProp(ctv, propName))
+            return prop->type;
+    }
+    else if (auto ttv = get<TableTypeVar>(ty))
+    {
+        if (auto it = ttv->props.find(propName); it != ttv->props.end())
+            return it->second.type;
+    }
+    else if (auto utv = get<IntersectionTypeVar>(ty))
+    {
+        std::vector<TypeId> types;
+
+        for (TypeId ty : utv)
+        {
+            if (auto prop = lookupProp(ty, propName, arena))
+            {
+                if (std::find(begin(types), end(types), *prop) == end(types))
+                    types.push_back(*prop);
+            }
+            else
+                return std::nullopt;
+        }
+
+        if (types.size() == 1)
+            return types[0];
+        else
+            return arena->addType(IntersectionTypeVar{std::move(types)});
+    }
+    else if (auto utv = get<UnionTypeVar>(ty))
+    {
+        std::vector<TypeId> types;
+
+        for (TypeId ty : utv)
+        {
+            if (auto prop = lookupProp(ty, propName, arena))
+            {
+                if (std::find(begin(types), end(types), *prop) == end(types))
+                    types.push_back(*prop);
+            }
+            else
+                return std::nullopt;
+        }
+
+        if (types.size() == 1)
+            return types[0];
+        else
+            return arena->addType(UnionTypeVar{std::move(types)});
+    }
+
+    return std::nullopt;
+}
+
 Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprIndexName* indexName)
 {
     TypeId obj = check(scope, indexName->expr).ty;
-    TypeId result = freshType(scope);
+
+    // HACK: We need to return the actual type for type refinements so that it can invoke the dcrMagicRefinement function.
+    TypeId result;
+    if (auto prop = lookupProp(obj, indexName->index.value, arena))
+        result = *prop;
+    else
+        result = freshType(scope);
+
+    std::optional<DefId> def = dfg->getDef(indexName);
+    if (def)
+    {
+        if (auto ty = scope->lookup(*def))
+            return Inference{*ty, connectiveArena.proposition(*def, singletonTypes->truthyType)};
+        else
+            scope->dcrRefinements[*def] = result;
+    }
 
     TableTypeVar::Props props{{indexName->index.value, Property{result}}};
     const std::optional<TableIndexer> indexer;
@@ -1266,7 +1429,10 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprIndexName*
 
     addConstraint(scope, indexName->expr->location, SubtypeConstraint{obj, expectedTableType});
 
-    return Inference{result};
+    if (def)
+        return Inference{result, connectiveArena.proposition(*def, singletonTypes->truthyType)};
+    else
+        return Inference{result};
 }
 
 Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprIndexExpr* indexExpr)
@@ -1555,8 +1721,16 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprTable* exp
         {
             if (auto stringKey = item.key->as<AstExprConstantString>())
             {
-                expectedValueType = arena->addType(BlockedTypeVar{});
+                ErrorVec errorVec;
-                addConstraint(scope, item.value->location, HasPropConstraint{*expectedValueType, *expectedType, stringKey->value.data});
+                std::optional<TypeId> propTy =
+                    findTablePropertyRespectingMeta(singletonTypes, errorVec, follow(*expectedType), stringKey->value.data, item.value->location);
+                if (propTy)
+                    expectedValueType = propTy;
+                else
+                {
+                    expectedValueType = arena->addType(BlockedTypeVar{});
+                    addConstraint(scope, item.value->location, HasPropConstraint{*expectedValueType, *expectedType, stringKey->value.data});
+                }
             }
         }
 
@@ -1590,7 +1764,8 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprTable* exp
     return Inference{ty};
 }
 
-ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionSignature(const ScopePtr& parent, AstExprFunction* fn)
+ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionSignature(
+    const ScopePtr& parent, AstExprFunction* fn, std::optional<TypeId> expectedType)
 {
     ScopePtr signatureScope = nullptr;
     ScopePtr bodyScope = nullptr;
@@ -1599,22 +1774,22 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
     std::vector<TypeId> genericTypes;
     std::vector<TypePackId> genericTypePacks;
 
+    if (expectedType)
+        expectedType = follow(*expectedType);
+
     bool hasGenerics = fn->generics.size > 0 || fn->genericPacks.size > 0;
 
-    // If we don't have any generics, we can save some memory and compute by not
+    signatureScope = childScope(fn, parent);
-    // creating the signatureScope, which is only used to scope the declared
+
-    // generics properly.
+    // We need to assign returnType before creating bodyScope so that the
+    // return type gets propogated to bodyScope.
+    returnType = freshTypePack(signatureScope);
+    signatureScope->returnType = returnType;
+
+    bodyScope = childScope(fn->body, signatureScope);
+
     if (hasGenerics)
     {
-        signatureScope = childScope(fn, parent);
-
-        // We need to assign returnType before creating bodyScope so that the
-        // return type gets propogated to bodyScope.
-        returnType = freshTypePack(signatureScope);
-        signatureScope->returnType = returnType;
-
-        bodyScope = childScope(fn->body, signatureScope);
-
         std::vector<std::pair<Name, GenericTypeDefinition>> genericDefinitions = createGenerics(signatureScope, fn->generics);
         std::vector<std::pair<Name, GenericTypePackDefinition>> genericPackDefinitions = createGenericPacks(signatureScope, fn->genericPacks);
 
@@ -1631,18 +1806,50 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
             genericTypePacks.push_back(g.tp);
             signatureScope->privateTypePackBindings[name] = g.tp;
         }
+
+        // Local variable works around an odd gcc 11.3 warning: <anonymous> may be used uninitialized
+        std::optional<TypeId> none = std::nullopt;
+        expectedType = none;
     }
-    else
+
+    std::vector<TypeId> argTypes;
+    TypePack expectedArgPack;
+
+    const FunctionTypeVar* expectedFunction = expectedType ? get<FunctionTypeVar>(*expectedType) : nullptr;
+
+    if (expectedFunction)
     {
-        bodyScope = childScope(fn, parent);
+        expectedArgPack = extendTypePack(*arena, singletonTypes, expectedFunction->argTypes, fn->args.size);
 
-        returnType = freshTypePack(bodyScope);
+        genericTypes = expectedFunction->generics;
-        bodyScope->returnType = returnType;
+        genericTypePacks = expectedFunction->genericPacks;
+    }
 
-        // To eliminate the need to branch on hasGenerics below, we say that the
+    for (size_t i = 0; i < fn->args.size; ++i)
-        // signature scope is the body scope when there is no real signature
+    {
-        // scope.
+        AstLocal* local = fn->args.data[i];
-        signatureScope = bodyScope;
+
+        TypeId t = freshType(signatureScope);
+        argTypes.push_back(t);
+        signatureScope->bindings[local] = Binding{t, local->location};
+
+        TypeId annotationTy = t;
+
+        if (local->annotation)
+        {
+            annotationTy = resolveType(signatureScope, local->annotation, /* topLevel */ true);
+            addConstraint(signatureScope, local->annotation->location, SubtypeConstraint{t, annotationTy});
+        }
+        else if (i < expectedArgPack.head.size())
+        {
+            addConstraint(signatureScope, local->location, SubtypeConstraint{t, expectedArgPack.head[i]});
+        }
+
+        // HACK: This is the one case where the type of the definition will diverge from the type of the binding.
+        // We need to do this because there are cases where type refinements needs to have the information available
+        // at constraint generation time.
+        if (auto def = dfg->getDef(local))
+            signatureScope->dcrRefinements[*def] = annotationTy;
     }
 
     TypePackId varargPack = nullptr;
@@ -1654,22 +1861,28 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
             TypePackId annotationType = resolveTypePack(signatureScope, fn->varargAnnotation);
             varargPack = annotationType;
         }
+        else if (expectedArgPack.tail && get<VariadicTypePack>(*expectedArgPack.tail))
+            varargPack = *expectedArgPack.tail;
         else
-        {
+            varargPack = singletonTypes->anyTypePack;
-            varargPack = arena->freshTypePack(signatureScope.get());
-        }
 
         signatureScope->varargPack = varargPack;
+        bodyScope->varargPack = varargPack;
     }
     else
     {
         varargPack = arena->addTypePack(VariadicTypePack{singletonTypes->anyType, /*hidden*/ true});
         // We do not add to signatureScope->varargPack because ... is not valid
         // in functions without an explicit ellipsis.
+
+        signatureScope->varargPack = std::nullopt;
+        bodyScope->varargPack = std::nullopt;
     }
 
     LUAU_ASSERT(nullptr != varargPack);
 
+    // If there is both an annotation and an expected type, the annotation wins.
+    // Type checking will sort out any discrepancies later.
     if (fn->returnAnnotation)
     {
         TypePackId annotatedRetType = resolveTypePack(signatureScope, *fn->returnAnnotation);
@@ -1680,26 +1893,11 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
         LUAU_ASSERT(get<FreeTypePack>(returnType));
         asMutable(returnType)->ty.emplace<BoundTypePack>(annotatedRetType);
     }
-
+    else if (expectedFunction)
-    std::vector<TypeId> argTypes;
-
-    for (AstLocal* local : fn->args)
     {
-        TypeId t = freshType(signatureScope);
+        asMutable(returnType)->ty.emplace<BoundTypePack>(expectedFunction->retTypes);
-        argTypes.push_back(t);
-        signatureScope->bindings[local] = Binding{t, local->location};
-
-        if (auto def = dfg->getDef(local))
-            signatureScope->dcrRefinements[*def] = t;
-
-        if (local->annotation)
-        {
-            TypeId argAnnotation = resolveType(signatureScope, local->annotation, /* topLevel */ true);
-            addConstraint(signatureScope, local->annotation->location, SubtypeConstraint{t, argAnnotation});
-        }
     }
 
-    // TODO: Vararg annotation.
     // TODO: Preserve argument names in the function's type.
 
     FunctionTypeVar actualFunction{TypeLevel{}, parent.get(), arena->addTypePack(argTypes, varargPack), returnType};
@@ -1711,11 +1909,14 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
     LUAU_ASSERT(actualFunctionType);
     astTypes[fn] = actualFunctionType;
 
+    if (expectedType && get<FreeTypeVar>(*expectedType))
+    {
+        asMutable(*expectedType)->ty.emplace<BoundTypeVar>(actualFunctionType);
+    }
+
     return {
         /* signature */ actualFunctionType,
-        // Undo the workaround we made above: if there's no signature scope,
+        /* signatureScope */ signatureScope,
-        // don't report it.
-        /* signatureScope */ hasGenerics ? signatureScope : nullptr,
         /* bodyScope */ bodyScope,
     };
 }

Analysis/src/ConstraintSolver.cpp

@@ -1233,9 +1233,22 @@ bool ConstraintSolver::tryDispatch(const HasPropConstraint& c, NotNull<const Con
     if (isBlocked(subjectType) || get<PendingExpansionTypeVar>(subjectType))
         return block(subjectType, constraint);
 
+    if (get<FreeTypeVar>(subjectType))
+    {
+        TableTypeVar& ttv = asMutable(subjectType)->ty.emplace<TableTypeVar>(TableState::Free, TypeLevel{}, constraint->scope);
+        ttv.props[c.prop] = Property{c.resultType};
+        asMutable(c.resultType)->ty.emplace<FreeTypeVar>(constraint->scope);
+        unblock(c.resultType);
+        return true;
+    }
+
     std::optional<TypeId> resultType = lookupTableProp(subjectType, c.prop);
     if (!resultType)
-        return false;
+    {
+        asMutable(c.resultType)->ty.emplace<BoundTypeVar>(singletonTypes->errorRecoveryType());
+        unblock(c.resultType);
+        return true;
+    }
 
     if (isBlocked(*resultType))
     {
@@ -1418,8 +1431,10 @@ bool ConstraintSolver::tryDispatch(const SingletonOrTopTypeConstraint& c, NotNul
     TypeId followed = follow(c.discriminantType);
 
     // `nil` is a singleton type too! There's only one value of type `nil`.
-    if (get<SingletonTypeVar>(followed) || isNil(followed))
+    if (c.negated && (get<SingletonTypeVar>(followed) || isNil(followed)))
         *asMutable(c.resultType) = NegationTypeVar{c.discriminantType};
+    else if (!c.negated && get<SingletonTypeVar>(followed))
+        *asMutable(c.resultType) = BoundTypeVar{c.discriminantType};
     else
         *asMutable(c.resultType) = BoundTypeVar{singletonTypes->unknownType};
 
@@ -1509,17 +1524,17 @@ bool ConstraintSolver::tryDispatchIterableTable(TypeId iteratorTy, const Iterabl
                 TypePackId expectedIterArgs = arena->addTypePack({iteratorTy});
                 unify(iterFtv->argTypes, expectedIterArgs, constraint->scope);
 
-                std::vector<TypeId> iterRets = flatten(*arena, singletonTypes, iterFtv->retTypes, 2);
+                TypePack iterRets = extendTypePack(*arena, singletonTypes, iterFtv->retTypes, 2);
 
-                if (iterRets.size() < 1)
+                if (iterRets.head.size() < 1)
                 {
                     // We've done what we can; this will get reported as an
                     // error by the type checker.
                     return true;
                 }
 
-                TypeId nextFn = iterRets[0];
+                TypeId nextFn = iterRets.head[0];
-                TypeId table = iterRets.size() == 2 ? iterRets[1] : arena->freshType(constraint->scope);
+                TypeId table = iterRets.head.size() == 2 ? iterRets.head[1] : arena->freshType(constraint->scope);
 
                 if (std::optional<TypeId> instantiatedNextFn = instantiation.substitute(nextFn))
                 {

Analysis/src/DataFlowGraph.cpp

@@ -1,5 +1,5 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
-#include "Luau/DataFlowGraphBuilder.h"
+#include "Luau/DataFlowGraph.h"
 
 #include "Luau/Error.h"
 
@@ -11,6 +11,9 @@ namespace Luau
 
 std::optional<DefId> DataFlowGraph::getDef(const AstExpr* expr) const
 {
+    // We need to skip through AstExprGroup because DFG doesn't try its best to transitively
+    while (auto group = expr->as<AstExprGroup>())
+        expr = group->expr;
     if (auto def = astDefs.find(expr))
         return NotNull{*def};
     return std::nullopt;
@@ -52,16 +55,25 @@ std::optional<DefId> DataFlowGraphBuilder::use(DfgScope* scope, Symbol symbol, A
 {
     for (DfgScope* current = scope; current; current = current->parent)
     {
-        if (auto loc = current->bindings.find(symbol))
+        if (auto def = current->bindings.find(symbol))
         {
-            graph.astDefs[e] = *loc;
+            graph.astDefs[e] = *def;
-            return NotNull{*loc};
+            return NotNull{*def};
         }
     }
 
     return std::nullopt;
 }
 
+DefId DataFlowGraphBuilder::use(DefId def, AstExprIndexName* e)
+{
+    auto& propertyDef = props[def][e->index.value];
+    if (!propertyDef)
+        propertyDef = arena->freshCell(def, e->index.value);
+    graph.astDefs[e] = propertyDef;
+    return NotNull{propertyDef};
+}
+
 void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatBlock* b)
 {
     DfgScope* child = childScope(scope);
@@ -180,7 +192,7 @@ void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatLocal* l)
 
     for (AstLocal* local : l->vars)
     {
-        DefId def = arena->freshDef();
+        DefId def = arena->freshCell();
         graph.localDefs[local] = def;
         scope->bindings[local] = def;
     }
@@ -189,7 +201,7 @@ void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatLocal* l)
 void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatFor* f)
 {
     DfgScope* forScope = childScope(scope); // TODO: loop scope.
-    DefId def = arena->freshDef();
+    DefId def = arena->freshCell();
     graph.localDefs[f->var] = def;
     scope->bindings[f->var] = def;
 
@@ -203,7 +215,7 @@ void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatForIn* f)
 
     for (AstLocal* local : f->vars)
     {
-        DefId def = arena->freshDef();
+        DefId def = arena->freshCell();
         graph.localDefs[local] = def;
         forScope->bindings[local] = def;
     }
@@ -245,7 +257,7 @@ void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatAssign* a)
             // TODO global?
             if (auto exprLocal = root->as<AstExprLocal>())
             {
-                DefId def = arena->freshDef();
+                DefId def = arena->freshCell();
                 graph.astDefs[exprLocal] = def;
 
                 // Update the def in the scope that introduced the local.  Not
@@ -277,7 +289,7 @@ void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatFunction* f)
 
 void DataFlowGraphBuilder::visit(DfgScope* scope, AstStatLocalFunction* l)
 {
-    DefId def = arena->freshDef();
+    DefId def = arena->freshCell();
     graph.localDefs[l->name] = def;
     scope->bindings[l->name] = def;
 
@@ -354,8 +366,7 @@ ExpressionFlowGraph DataFlowGraphBuilder::visitExpr(DfgScope* scope, AstExprInde
     if (!def)
         return {};
 
-    // TODO: properties for the above def.
+    return {use(*def, i)};
-    return {};
 }
 
 ExpressionFlowGraph DataFlowGraphBuilder::visitExpr(DfgScope* scope, AstExprIndexExpr* i)
@@ -375,14 +386,14 @@ ExpressionFlowGraph DataFlowGraphBuilder::visitExpr(DfgScope* scope, AstExprFunc
 {
     if (AstLocal* self = f->self)
     {
-        DefId def = arena->freshDef();
+        DefId def = arena->freshCell();
         graph.localDefs[self] = def;
         scope->bindings[self] = def;
     }
 
     for (AstLocal* param : f->args)
     {
-        DefId def = arena->freshDef();
+        DefId def = arena->freshCell();
         graph.localDefs[param] = def;
         scope->bindings[param] = def;
     }

Analysis/src/Def.cpp

@@ -4,9 +4,14 @@
 namespace Luau
 {
 
-DefId DefArena::freshDef()
+DefId DefArena::freshCell()
 {
-    return NotNull{allocator.allocate<Def>(Undefined{})};
+    return NotNull{allocator.allocate<Def>(Def{Cell{std::nullopt}})};
+}
+
+DefId DefArena::freshCell(DefId parent, const std::string& prop)
+{
+    return NotNull{allocator.allocate<Def>(Def{Cell{FieldMetadata{parent, prop}}})};
 }
 
 } // namespace Luau

Analysis/src/Error.cpp

@@ -2,12 +2,14 @@
 #include "Luau/Error.h"
 
 #include "Luau/Clone.h"
+#include "Luau/Common.h"
 #include "Luau/StringUtils.h"
 #include "Luau/ToString.h"
 
 #include <stdexcept>
+#include <type_traits>
 
-LUAU_FASTFLAGVARIABLE(LuauIceExceptionInheritanceChange, false)
+LUAU_FASTFLAGVARIABLE(LuauTypeMismatchInvarianceInError, false)
 
 static std::string wrongNumberOfArgsString(
     size_t expectedCount, std::optional<size_t> maximumCount, size_t actualCount, const char* argPrefix = nullptr, bool isVariadic = false)
@@ -89,6 +91,7 @@ struct ErrorConverter
         if (result.empty())
             result = "Type '" + givenTypeName + "' could not be converted into '" + wantedTypeName + "'";
 
+
         if (tm.error)
         {
             result += "\ncaused by:\n  ";
@@ -102,6 +105,10 @@ struct ErrorConverter
         {
             result += "; " + tm.reason;
         }
+        else if (FFlag::LuauTypeMismatchInvarianceInError && tm.context == TypeMismatch::InvariantContext)
+        {
+            result += " in an invariant context";
+        }
 
         return result;
     }
@@ -467,6 +474,11 @@ struct ErrorConverter
     {
         return "Type pack '" + toString(e.givenTp) + "' could not be converted into '" + toString(e.wantedTp) + "'";
     }
+
+    std::string operator()(const DynamicPropertyLookupOnClassesUnsafe& e) const
+    {
+        return "Attempting a dynamic property access on type '" + Luau::toString(e.ty) + "' is unsafe and may cause exceptions at runtime";
+    }
 };
 
 struct InvalidNameChecker
@@ -514,6 +526,30 @@ TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, std::string reas
 {
 }
 
+TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, TypeMismatch::Context context)
+    : wantedType(wantedType)
+    , givenType(givenType)
+    , context(context)
+{
+}
+
+TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, TypeMismatch::Context context)
+    : wantedType(wantedType)
+    , givenType(givenType)
+    , context(context)
+    , reason(reason)
+{
+}
+
+TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, std::optional<TypeError> error, TypeMismatch::Context context)
+    : wantedType(wantedType)
+    , givenType(givenType)
+    , context(context)
+    , reason(reason)
+    , error(error ? std::make_shared<TypeError>(std::move(*error)) : nullptr)
+{
+}
+
 bool TypeMismatch::operator==(const TypeMismatch& rhs) const
 {
     if (!!error != !!rhs.error)
@@ -522,7 +558,7 @@ bool TypeMismatch::operator==(const TypeMismatch& rhs) const
     if (error && !(*error == *rhs.error))
         return false;
 
-    return *wantedType == *rhs.wantedType && *givenType == *rhs.givenType && reason == rhs.reason;
+    return *wantedType == *rhs.wantedType && *givenType == *rhs.givenType && reason == rhs.reason && context == rhs.context;
 }
 
 bool UnknownSymbol::operator==(const UnknownSymbol& rhs) const
@@ -662,7 +698,17 @@ bool FunctionExitsWithoutReturning::operator==(const FunctionExitsWithoutReturni
 
 int TypeError::code() const
 {
-    return 1000 + int(data.index());
+    return minCode() + int(data.index());
+}
+
+int TypeError::minCode()
+{
+    return 1000;
+}
+
+TypeErrorSummary TypeError::summary() const
+{
+    return TypeErrorSummary{location, moduleName, code()};
 }
 
 bool TypeError::operator==(const TypeError& rhs) const
@@ -730,6 +776,11 @@ bool TypePackMismatch::operator==(const TypePackMismatch& rhs) const
     return *wantedTp == *rhs.wantedTp && *givenTp == *rhs.givenTp;
 }
 
+bool DynamicPropertyLookupOnClassesUnsafe::operator==(const DynamicPropertyLookupOnClassesUnsafe& rhs) const
+{
+    return ty == rhs.ty;
+}
+
 std::string toString(const TypeError& error)
 {
     return toString(error, TypeErrorToStringOptions{});
@@ -886,6 +937,8 @@ void copyError(T& e, TypeArena& destArena, CloneState cloneState)
         e.wantedTp = clone(e.wantedTp);
         e.givenTp = clone(e.givenTp);
     }
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnClassesUnsafe>)
+        e.ty = clone(e.ty);
     else
         static_assert(always_false_v<T>, "Non-exhaustive type switch");
 }
@@ -930,30 +983,4 @@ const char* InternalCompilerError::what() const throw()
     return this->message.data();
 }
 
-// TODO: Inline me when LuauIceExceptionInheritanceChange is deleted.
-void throwRuntimeError(const std::string& message)
-{
-    if (FFlag::LuauIceExceptionInheritanceChange)
-    {
-        throw InternalCompilerError(message);
-    }
-    else
-    {
-        throw std::runtime_error(message);
-    }
-}
-
-// TODO: Inline me when LuauIceExceptionInheritanceChange is deleted.
-void throwRuntimeError(const std::string& message, const std::string& moduleName)
-{
-    if (FFlag::LuauIceExceptionInheritanceChange)
-    {
-        throw InternalCompilerError(message, moduleName);
-    }
-    else
-    {
-        throw std::runtime_error(message);
-    }
-}
-
 } // namespace Luau

Analysis/src/Frontend.cpp

@@ -7,7 +7,7 @@
 #include "Luau/Config.h"
 #include "Luau/ConstraintGraphBuilder.h"
 #include "Luau/ConstraintSolver.h"
-#include "Luau/DataFlowGraphBuilder.h"
+#include "Luau/DataFlowGraph.h"
 #include "Luau/DcrLogger.h"
 #include "Luau/FileResolver.h"
 #include "Luau/Parser.h"
@@ -31,7 +31,6 @@ LUAU_FASTINTVARIABLE(LuauAutocompleteCheckTimeoutMs, 100)
 LUAU_FASTFLAGVARIABLE(DebugLuauDeferredConstraintResolution, false)
 LUAU_FASTFLAG(DebugLuauLogSolverToJson);
 LUAU_FASTFLAGVARIABLE(LuauFixMarkDirtyReverseDeps, false)
-LUAU_FASTFLAGVARIABLE(LuauPersistTypesAfterGeneratingDocSyms, false)
 
 namespace Luau
 {
@@ -112,57 +111,32 @@ LoadDefinitionFileResult Frontend::loadDefinitionFile(std::string_view source, c
 
     CloneState cloneState;
 
-    if (FFlag::LuauPersistTypesAfterGeneratingDocSyms)
+    std::vector<TypeId> typesToPersist;
+    typesToPersist.reserve(checkedModule->declaredGlobals.size() + checkedModule->getModuleScope()->exportedTypeBindings.size());
+
+    for (const auto& [name, ty] : checkedModule->declaredGlobals)
     {
-        std::vector<TypeId> typesToPersist;
+        TypeId globalTy = clone(ty, globalTypes, cloneState);
-        typesToPersist.reserve(checkedModule->declaredGlobals.size() + checkedModule->getModuleScope()->exportedTypeBindings.size());
+        std::string documentationSymbol = packageName + "/global/" + name;
+        generateDocumentationSymbols(globalTy, documentationSymbol);
+        globalScope->bindings[typeChecker.globalNames.names->getOrAdd(name.c_str())] = {globalTy, Location(), false, {}, documentationSymbol};
 
-        for (const auto& [name, ty] : checkedModule->declaredGlobals)
+        typesToPersist.push_back(globalTy);
-        {
-            TypeId globalTy = clone(ty, globalTypes, cloneState);
-            std::string documentationSymbol = packageName + "/global/" + name;
-            generateDocumentationSymbols(globalTy, documentationSymbol);
-            globalScope->bindings[typeChecker.globalNames.names->getOrAdd(name.c_str())] = {globalTy, Location(), false, {}, documentationSymbol};
-
-            typesToPersist.push_back(globalTy);
-        }
-
-        for (const auto& [name, ty] : checkedModule->getModuleScope()->exportedTypeBindings)
-        {
-            TypeFun globalTy = clone(ty, globalTypes, cloneState);
-            std::string documentationSymbol = packageName + "/globaltype/" + name;
-            generateDocumentationSymbols(globalTy.type, documentationSymbol);
-            globalScope->exportedTypeBindings[name] = globalTy;
-
-            typesToPersist.push_back(globalTy.type);
-        }
-
-        for (TypeId ty : typesToPersist)
-        {
-            persist(ty);
-        }
     }
-    else
+
+    for (const auto& [name, ty] : checkedModule->getModuleScope()->exportedTypeBindings)
     {
-        for (const auto& [name, ty] : checkedModule->declaredGlobals)
+        TypeFun globalTy = clone(ty, globalTypes, cloneState);
-        {
+        std::string documentationSymbol = packageName + "/globaltype/" + name;
-            TypeId globalTy = clone(ty, globalTypes, cloneState);
+        generateDocumentationSymbols(globalTy.type, documentationSymbol);
-            std::string documentationSymbol = packageName + "/global/" + name;
+        globalScope->exportedTypeBindings[name] = globalTy;
-            generateDocumentationSymbols(globalTy, documentationSymbol);
-            globalScope->bindings[typeChecker.globalNames.names->getOrAdd(name.c_str())] = {globalTy, Location(), false, {}, documentationSymbol};
 
-            persist(globalTy);
+        typesToPersist.push_back(globalTy.type);
-        }
+    }
 
-        for (const auto& [name, ty] : checkedModule->getModuleScope()->exportedTypeBindings)
+    for (TypeId ty : typesToPersist)
-        {
+    {
-            TypeFun globalTy = clone(ty, globalTypes, cloneState);
+        persist(ty);
-            std::string documentationSymbol = packageName + "/globaltype/" + name;
-            generateDocumentationSymbols(globalTy.type, documentationSymbol);
-            globalScope->exportedTypeBindings[name] = globalTy;
-
-            persist(globalTy.type);
-        }
     }
 
     return LoadDefinitionFileResult{true, parseResult, checkedModule};
@@ -194,57 +168,32 @@ LoadDefinitionFileResult loadDefinitionFile(TypeChecker& typeChecker, ScopePtr t
 
     CloneState cloneState;
 
-    if (FFlag::LuauPersistTypesAfterGeneratingDocSyms)
+    std::vector<TypeId> typesToPersist;
+    typesToPersist.reserve(checkedModule->declaredGlobals.size() + checkedModule->getModuleScope()->exportedTypeBindings.size());
+
+    for (const auto& [name, ty] : checkedModule->declaredGlobals)
     {
-        std::vector<TypeId> typesToPersist;
+        TypeId globalTy = clone(ty, typeChecker.globalTypes, cloneState);
-        typesToPersist.reserve(checkedModule->declaredGlobals.size() + checkedModule->getModuleScope()->exportedTypeBindings.size());
+        std::string documentationSymbol = packageName + "/global/" + name;
+        generateDocumentationSymbols(globalTy, documentationSymbol);
+        targetScope->bindings[typeChecker.globalNames.names->getOrAdd(name.c_str())] = {globalTy, Location(), false, {}, documentationSymbol};
 
-        for (const auto& [name, ty] : checkedModule->declaredGlobals)
+        typesToPersist.push_back(globalTy);
-        {
-            TypeId globalTy = clone(ty, typeChecker.globalTypes, cloneState);
-            std::string documentationSymbol = packageName + "/global/" + name;
-            generateDocumentationSymbols(globalTy, documentationSymbol);
-            targetScope->bindings[typeChecker.globalNames.names->getOrAdd(name.c_str())] = {globalTy, Location(), false, {}, documentationSymbol};
-
-            typesToPersist.push_back(globalTy);
-        }
-
-        for (const auto& [name, ty] : checkedModule->getModuleScope()->exportedTypeBindings)
-        {
-            TypeFun globalTy = clone(ty, typeChecker.globalTypes, cloneState);
-            std::string documentationSymbol = packageName + "/globaltype/" + name;
-            generateDocumentationSymbols(globalTy.type, documentationSymbol);
-            targetScope->exportedTypeBindings[name] = globalTy;
-
-            typesToPersist.push_back(globalTy.type);
-        }
-
-        for (TypeId ty : typesToPersist)
-        {
-            persist(ty);
-        }
     }
-    else
+
+    for (const auto& [name, ty] : checkedModule->getModuleScope()->exportedTypeBindings)
     {
-        for (const auto& [name, ty] : checkedModule->declaredGlobals)
+        TypeFun globalTy = clone(ty, typeChecker.globalTypes, cloneState);
-        {
+        std::string documentationSymbol = packageName + "/globaltype/" + name;
-            TypeId globalTy = clone(ty, typeChecker.globalTypes, cloneState);
+        generateDocumentationSymbols(globalTy.type, documentationSymbol);
-            std::string documentationSymbol = packageName + "/global/" + name;
+        targetScope->exportedTypeBindings[name] = globalTy;
-            generateDocumentationSymbols(globalTy, documentationSymbol);
-            targetScope->bindings[typeChecker.globalNames.names->getOrAdd(name.c_str())] = {globalTy, Location(), false, {}, documentationSymbol};
 
-            persist(globalTy);
+        typesToPersist.push_back(globalTy.type);
-        }
+    }
 
-        for (const auto& [name, ty] : checkedModule->getModuleScope()->exportedTypeBindings)
+    for (TypeId ty : typesToPersist)
-        {
+    {
-            TypeFun globalTy = clone(ty, typeChecker.globalTypes, cloneState);
+        persist(ty);
-            std::string documentationSymbol = packageName + "/globaltype/" + name;
-            generateDocumentationSymbols(globalTy.type, documentationSymbol);
-            targetScope->exportedTypeBindings[name] = globalTy;
-
-            persist(globalTy.type);
-        }
     }
 
     return LoadDefinitionFileResult{true, parseResult, checkedModule};
@@ -493,13 +442,13 @@ CheckResult Frontend::check(const ModuleName& name, std::optional<FrontendOption
         {
             auto it2 = moduleResolverForAutocomplete.modules.find(name);
             if (it2 == moduleResolverForAutocomplete.modules.end() || it2->second == nullptr)
-                throwRuntimeError("Frontend::modules does not have data for " + name, name);
+                throw InternalCompilerError("Frontend::modules does not have data for " + name, name);
         }
         else
         {
             auto it2 = moduleResolver.modules.find(name);
             if (it2 == moduleResolver.modules.end() || it2->second == nullptr)
-                throwRuntimeError("Frontend::modules does not have data for " + name, name);
+                throw InternalCompilerError("Frontend::modules does not have data for " + name, name);
         }
 
         return CheckResult{
@@ -606,7 +555,7 @@ CheckResult Frontend::check(const ModuleName& name, std::optional<FrontendOption
         stats.filesNonstrict += mode == Mode::Nonstrict;
 
         if (module == nullptr)
-            throwRuntimeError("Frontend::check produced a nullptr module for " + moduleName, moduleName);
+            throw InternalCompilerError("Frontend::check produced a nullptr module for " + moduleName, moduleName);
 
         if (!frontendOptions.retainFullTypeGraphs)
         {

Analysis/src/IostreamHelpers.cpp

@@ -190,6 +190,8 @@ static void errorToString(std::ostream& stream, const T& err)
         stream << "NormalizationTooComplex { }";
     else if constexpr (std::is_same_v<T, TypePackMismatch>)
         stream << "TypePackMismatch { wanted = '" + toString(err.wantedTp) + "', given = '" + toString(err.givenTp) + "' }";
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnClassesUnsafe>)
+        stream << "DynamicPropertyLookupOnClassesUnsafe { " << toString(err.ty) << " }";
     else
         static_assert(always_false_v<T>, "Non-exhaustive type switch");
 }

Analysis/src/Normalize.cpp

@@ -24,6 +24,7 @@ LUAU_FASTFLAGVARIABLE(LuauNegatedFunctionTypes, false);
 LUAU_FASTFLAG(LuauUnknownAndNeverType)
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 LUAU_FASTFLAG(LuauOverloadedFunctionSubtypingPerf);
+LUAU_FASTFLAG(LuauUninhabitedSubAnything)
 
 namespace Luau
 {
@@ -240,13 +241,75 @@ NormalizedType::NormalizedType(NotNull<SingletonTypes> singletonTypes)
 {
 }
 
-static bool isInhabited(const NormalizedType& norm)
+static bool isShallowInhabited(const NormalizedType& norm)
 {
+    // This test is just a shallow check, for example it returns `true` for `{ p : never }`
     return !get<NeverTypeVar>(norm.tops) || !get<NeverTypeVar>(norm.booleans) || !norm.classes.empty() || !get<NeverTypeVar>(norm.errors) ||
            !get<NeverTypeVar>(norm.nils) || !get<NeverTypeVar>(norm.numbers) || !norm.strings.isNever() || !get<NeverTypeVar>(norm.threads) ||
            !norm.functions.isNever() || !norm.tables.empty() || !norm.tyvars.empty();
 }
 
+bool isInhabited_DEPRECATED(const NormalizedType& norm)
+{
+    LUAU_ASSERT(!FFlag::LuauUninhabitedSubAnything);
+    return isShallowInhabited(norm);
+}
+
+bool Normalizer::isInhabited(const NormalizedType* norm, std::unordered_set<TypeId> seen)
+{
+    if (!get<NeverTypeVar>(norm->tops) || !get<NeverTypeVar>(norm->booleans) || !get<NeverTypeVar>(norm->errors) ||
+        !get<NeverTypeVar>(norm->nils) || !get<NeverTypeVar>(norm->numbers) || !get<NeverTypeVar>(norm->threads) ||
+        !norm->classes.empty() || !norm->strings.isNever() || !norm->functions.isNever())
+        return true;
+    
+    for (const auto& [_, intersect] : norm->tyvars)
+    {
+        if (isInhabited(intersect.get(), seen))
+            return true;
+    }
+
+    for (TypeId table : norm->tables)
+    {
+        if (isInhabited(table, seen))
+            return true;
+    }
+
+    return false;
+}
+
+bool Normalizer::isInhabited(TypeId ty, std::unordered_set<TypeId> seen)
+{
+    // TODO: use log.follow(ty), CLI-64291
+    ty = follow(ty);
+
+    if (get<NeverTypeVar>(ty))
+        return false;
+
+    if (!get<IntersectionTypeVar>(ty) && !get<UnionTypeVar>(ty) && !get<TableTypeVar>(ty) && !get<MetatableTypeVar>(ty))
+        return true;
+
+    if (seen.count(ty))
+        return true;
+
+    seen.insert(ty);
+
+    if (const TableTypeVar* ttv = get<TableTypeVar>(ty))
+    {
+        for (const auto& [_, prop] : ttv->props)
+        {
+            if (!isInhabited(prop.type, seen))
+                return false;
+        }
+        return true;
+    }
+
+    if (const MetatableTypeVar* mtv = get<MetatableTypeVar>(ty))
+        return isInhabited(mtv->table, seen) && isInhabited(mtv->metatable, seen);
+
+    const NormalizedType* norm = normalize(ty);
+    return isInhabited(norm, seen);
+}
+
 static int tyvarIndex(TypeId ty)
 {
     if (const GenericTypeVar* gtv = get<GenericTypeVar>(ty))
@@ -378,7 +441,7 @@ static bool isNormalizedTyvar(const NormalizedTyvars& tyvars)
     {
         if (!isPlainTyvar(tyvar))
             return false;
-        if (!isInhabited(*intersect))
+        if (!isShallowInhabited(*intersect))
             return false;
         for (auto& [other, _] : intersect->tyvars)
             if (tyvarIndex(other) <= tyvarIndex(tyvar))
@@ -1852,7 +1915,7 @@ bool Normalizer::intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there)
         NormalizedType& inter = *it->second;
         if (!intersectNormalWithTy(inter, there))
             return false;
-        if (isInhabited(inter))
+        if (isShallowInhabited(inter))
             ++it;
         else
             it = here.erase(it);
@@ -1914,7 +1977,7 @@ bool Normalizer::intersectNormals(NormalizedType& here, const NormalizedType& th
             if (!intersectNormals(inter, *found->second, index))
                 return false;
         }
-        if (isInhabited(inter))
+        if (isShallowInhabited(inter))
             it++;
         else
             it = here.tyvars.erase(it);

Analysis/src/ToString.cpp

@@ -11,8 +11,8 @@
 #include <stdexcept>
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
-LUAU_FASTFLAG(LuauLvaluelessPath)
 LUAU_FASTFLAG(LuauUnknownAndNeverType)
+LUAU_FASTFLAGVARIABLE(LuauLineBreaksDetermineIndents, false)
 LUAU_FASTFLAGVARIABLE(LuauFunctionReturnStringificationFixup, false)
 LUAU_FASTFLAGVARIABLE(LuauUnseeArrayTtv, false)
 
@@ -272,10 +272,20 @@ struct StringifierState
 private:
     void emitIndentation()
     {
-        if (!opts.indent)
+        if (!FFlag::LuauLineBreaksDetermineIndents)
-            return;
+        {
+            if (!opts.DEPRECATED_indent)
+                return;
 
-        emit(std::string(indentation, ' '));
+            emit(std::string(indentation, ' '));
+        }
+        else
+        {
+            if (!opts.useLineBreaks)
+                return;
+
+            emit(std::string(indentation, ' '));
+        }
     }
 };
 
@@ -445,7 +455,7 @@ struct TypeVarStringifier
             return;
         default:
             LUAU_ASSERT(!"Unknown primitive type");
-            throwRuntimeError("Unknown primitive type " + std::to_string(ptv.type));
+            throw InternalCompilerError("Unknown primitive type " + std::to_string(ptv.type));
         }
     }
 
@@ -462,7 +472,7 @@ struct TypeVarStringifier
         else
         {
             LUAU_ASSERT(!"Unknown singleton type");
-            throwRuntimeError("Unknown singleton type");
+            throw InternalCompilerError("Unknown singleton type");
         }
     }
 
@@ -508,24 +518,13 @@ struct TypeVarStringifier
 
         bool plural = true;
 
-        if (FFlag::LuauFunctionReturnStringificationFixup)
+        auto retBegin = begin(ftv.retTypes);
+        auto retEnd = end(ftv.retTypes);
+        if (retBegin != retEnd)
         {
-            auto retBegin = begin(ftv.retTypes);
+            ++retBegin;
-            auto retEnd = end(ftv.retTypes);
+            if (retBegin == retEnd && !retBegin.tail())
-            if (retBegin != retEnd)
+                plural = false;
-            {
-                ++retBegin;
-                if (retBegin == retEnd && !retBegin.tail())
-                    plural = false;
-            }
-        }
-        else
-        {
-            if (auto retPack = get<TypePack>(follow(ftv.retTypes)))
-            {
-                if (retPack->head.size() == 1 && !retPack->tail)
-                    plural = false;
-            }
         }
 
         if (plural)
@@ -980,8 +979,6 @@ struct TypePackStringifier
 
     void operator()(TypePackId tp, const GenericTypePack& pack)
     {
-        if (FFlag::DebugLuauVerboseTypeNames)
-            state.emit("gen-");
         if (pack.explicitName)
         {
             state.usedNames.insert(pack.name);
@@ -992,6 +989,15 @@ struct TypePackStringifier
         {
             state.emit(state.getName(tp));
         }
+
+        if (FFlag::DebugLuauVerboseTypeNames)
+        {
+            state.emit("-");
+            if (FFlag::DebugLuauDeferredConstraintResolution)
+                state.emitLevel(pack.scope);
+            else
+                state.emit(pack.level);
+        }
         state.emit("...");
     }
 
@@ -1143,7 +1149,7 @@ ToStringResult toStringDetailed(TypeId ty, ToStringOptions& opts)
     else
         tvs.stringify(ty);
 
-    if (!state.cycleNames.empty())
+    if (!state.cycleNames.empty() || !state.cycleTpNames.empty())
     {
         result.cycle = true;
         state.emit(" where ");
@@ -1176,6 +1182,29 @@ ToStringResult toStringDetailed(TypeId ty, ToStringOptions& opts)
         semi = true;
     }
 
+    std::vector<std::pair<TypePackId, std::string>> sortedCycleTpNames(state.cycleTpNames.begin(), state.cycleTpNames.end());
+    std::sort(sortedCycleTpNames.begin(), sortedCycleTpNames.end(), [](const auto& a, const auto& b) {
+        return a.second < b.second;
+    });
+
+    TypePackStringifier tps{state};
+
+    for (const auto& [cycleTp, name] : sortedCycleTpNames)
+    {
+        if (semi)
+            state.emit(" ; ");
+
+        state.emit(name);
+        state.emit(" = ");
+        Luau::visit(
+            [&tps, cycleTy = cycleTp](auto&& t) {
+                return tps(cycleTy, t);
+            },
+            cycleTp->ty);
+
+        semi = true;
+    }
+
     if (opts.maxTypeLength > 0 && result.name.length() > opts.maxTypeLength)
     {
         result.truncated = true;
@@ -1361,22 +1390,30 @@ std::string toStringNamedFunction(const std::string& funcName, const FunctionTyp
     return result.name;
 }
 
+static ToStringOptions& dumpOptions()
+{
+    static ToStringOptions opts = ([]() {
+        ToStringOptions o;
+        o.exhaustive = true;
+        o.functionTypeArguments = true;
+        o.maxTableLength = 0;
+        o.maxTypeLength = 0;
+        return o;
+    })();
+
+    return opts;
+}
+
 std::string dump(TypeId ty)
 {
-    ToStringOptions opts;
+    std::string s = toString(ty, dumpOptions());
-    opts.exhaustive = true;
-    opts.functionTypeArguments = true;
-    std::string s = toString(ty, opts);
     printf("%s\n", s.c_str());
     return s;
 }
 
 std::string dump(TypePackId ty)
 {
-    ToStringOptions opts;
+    std::string s = toString(ty, dumpOptions());
-    opts.exhaustive = true;
-    opts.functionTypeArguments = true;
-    std::string s = toString(ty, opts);
     printf("%s\n", s.c_str());
     return s;
 }
@@ -1391,10 +1428,7 @@ std::string dump(const ScopePtr& scope, const char* name)
     }
 
     TypeId ty = binding->typeId;
-    ToStringOptions opts;
+    std::string s = toString(ty, dumpOptions());
-    opts.exhaustive = true;
-    opts.functionTypeArguments = true;
-    std::string s = toString(ty, opts);
     printf("%s\n", s.c_str());
     return s;
 }
@@ -1413,8 +1447,7 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
     auto go = [&opts](auto&& c) -> std::string {
         using T = std::decay_t<decltype(c)>;
 
-        auto tos = [&opts](auto&& a)
+        auto tos = [&opts](auto&& a) {
-        {
             return toString(a, opts);
         };
 
@@ -1480,8 +1513,7 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
         }
         else if constexpr (std::is_same_v<T, PrimitiveTypeConstraint>)
         {
-            return tos(c.resultType) + " ~ prim " + tos(c.expectedType) + ", " + tos(c.singletonType) + ", " +
+            return tos(c.resultType) + " ~ prim " + tos(c.expectedType) + ", " + tos(c.singletonType) + ", " + tos(c.multitonType);
-                   tos(c.multitonType);
         }
         else if constexpr (std::is_same_v<T, HasPropConstraint>)
         {
@@ -1497,7 +1529,10 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
             std::string result = tos(c.resultType);
             std::string discriminant = tos(c.discriminantType);
 
-            return result + " ~ if isSingleton D then ~D else unknown where D = " + discriminant;
+            if (c.negated)
+                return result + " ~ if isSingleton D then ~D else unknown where D = " + discriminant;
+            else
+                return result + " ~ if isSingleton D then D else unknown where D = " + discriminant;
         }
         else
             static_assert(always_false_v<T>, "Non-exhaustive constraint switch");
@@ -1516,28 +1551,8 @@ std::string dump(const Constraint& c)
     return s;
 }
 
-std::string toString(const LValue& lvalue)
-{
-    LUAU_ASSERT(!FFlag::LuauLvaluelessPath);
-
-    std::string s;
-    for (const LValue* current = &lvalue; current; current = baseof(*current))
-    {
-        if (auto field = get<Field>(*current))
-            s = "." + field->key + s;
-        else if (auto symbol = get<Symbol>(*current))
-            s = toString(*symbol) + s;
-        else
-            LUAU_ASSERT(!"Unknown LValue");
-    }
-
-    return s;
-}
-
 std::optional<std::string> getFunctionNameAsString(const AstExpr& expr)
 {
-    LUAU_ASSERT(FFlag::LuauLvaluelessPath);
-
     const AstExpr* curr = &expr;
     std::string s;
 

Analysis/src/TopoSortStatements.cpp

@@ -150,7 +150,7 @@ Identifier mkName(const AstStatFunction& function)
     auto name = mkName(*function.name);
     LUAU_ASSERT(bool(name));
     if (!name)
-        throwRuntimeError("Internal error: Function declaration has a bad name");
+        throw InternalCompilerError("Internal error: Function declaration has a bad name");
 
     return *name;
 }
@@ -256,7 +256,7 @@ struct ArcCollector : public AstVisitor
     {
         auto name = mkName(*node->name);
         if (!name)
-            throwRuntimeError("Internal error: AstStatFunction has a bad name");
+            throw InternalCompilerError("Internal error: AstStatFunction has a bad name");
 
         add(*name);
         return true;

Analysis/src/TxnLog.cpp

@@ -78,6 +78,42 @@ void TxnLog::concat(TxnLog rhs)
         typePackChanges[tp] = std::move(rep);
 }
 
+void TxnLog::concatAsIntersections(TxnLog rhs, NotNull<TypeArena> arena)
+{
+    for (auto& [ty, rightRep] : rhs.typeVarChanges)
+    {
+        if (auto leftRep = typeVarChanges.find(ty))
+        {
+            TypeId leftTy = arena->addType((*leftRep)->pending);
+            TypeId rightTy = arena->addType(rightRep->pending);
+            typeVarChanges[ty]->pending.ty = IntersectionTypeVar{{leftTy, rightTy}};
+        }
+        else
+            typeVarChanges[ty] = std::move(rightRep);
+    }
+
+    for (auto& [tp, rep] : rhs.typePackChanges)
+        typePackChanges[tp] = std::move(rep);
+}
+
+void TxnLog::concatAsUnion(TxnLog rhs, NotNull<TypeArena> arena)
+{
+    for (auto& [ty, rightRep] : rhs.typeVarChanges)
+    {
+        if (auto leftRep = typeVarChanges.find(ty))
+        {
+            TypeId leftTy = arena->addType((*leftRep)->pending);
+            TypeId rightTy = arena->addType(rightRep->pending);
+            typeVarChanges[ty]->pending.ty = UnionTypeVar{{leftTy, rightTy}};
+        }
+        else
+            typeVarChanges[ty] = std::move(rightRep);
+    }
+
+    for (auto& [tp, rep] : rhs.typePackChanges)
+        typePackChanges[tp] = std::move(rep);
+}
+
 void TxnLog::commit()
 {
     for (auto& [ty, rep] : typeVarChanges)

Analysis/src/TypeAttach.cpp

@@ -341,7 +341,7 @@ public:
     AstType* operator()(const NegationTypeVar& ntv)
     {
         // FIXME: do the same thing we do with ErrorTypeVar
-        throwRuntimeError("Cannot convert NegationTypeVar into AstNode");
+        throw InternalCompilerError("Cannot convert NegationTypeVar into AstNode");
     }
 
 private:

Analysis/src/TypeChecker2.cpp

@@ -295,11 +295,11 @@ struct TypeChecker2
         Scope* scope = findInnermostScope(ret->location);
         TypePackId expectedRetType = scope->returnType;
 
-        TypeArena arena;
+        TypeArena* arena = &module->internalTypes;
-        TypePackId actualRetType = reconstructPack(ret->list, arena);
+        TypePackId actualRetType = reconstructPack(ret->list, *arena);
 
         UnifierSharedState sharedState{&ice};
-        Normalizer normalizer{&arena, singletonTypes, NotNull{&sharedState}};
+        Normalizer normalizer{arena, singletonTypes, NotNull{&sharedState}};
         Unifier u{NotNull{&normalizer}, Mode::Strict, stack.back(), ret->location, Covariant};
 
         u.tryUnify(actualRetType, expectedRetType);
@@ -424,13 +424,13 @@ struct TypeChecker2
         TypePackId iteratorPack = arena.addTypePack(valueTypes, iteratorTail);
 
         // ... and then expand it out to 3 values (if possible)
-        const std::vector<TypeId> iteratorTypes = flatten(arena, singletonTypes, iteratorPack, 3);
+        TypePack iteratorTypes = extendTypePack(arena, singletonTypes, iteratorPack, 3);
-        if (iteratorTypes.empty())
+        if (iteratorTypes.head.empty())
         {
             reportError(GenericError{"for..in loops require at least one value to iterate over.  Got zero"}, getLocation(forInStatement->values));
             return;
         }
-        TypeId iteratorTy = follow(iteratorTypes[0]);
+        TypeId iteratorTy = follow(iteratorTypes.head[0]);
 
         auto checkFunction = [this, &arena, &scope, &forInStatement, &variableTypes](
                                  const FunctionTypeVar* iterFtv, std::vector<TypeId> iterTys, bool isMm) {
@@ -445,8 +445,8 @@ struct TypeChecker2
             }
 
             // It is okay if there aren't enough iterators, but the iteratee must provide enough.
-            std::vector<TypeId> expectedVariableTypes = flatten(arena, singletonTypes, iterFtv->retTypes, variableTypes.size());
+            TypePack expectedVariableTypes = extendTypePack(arena, singletonTypes, iterFtv->retTypes, variableTypes.size());
-            if (expectedVariableTypes.size() < variableTypes.size())
+            if (expectedVariableTypes.head.size() < variableTypes.size())
             {
                 if (isMm)
                     reportError(
@@ -455,8 +455,8 @@ struct TypeChecker2
                     reportError(GenericError{"next() does not return enough values"}, forInStatement->values.data[0]->location);
             }
 
-            for (size_t i = 0; i < std::min(expectedVariableTypes.size(), variableTypes.size()); ++i)
+            for (size_t i = 0; i < std::min(expectedVariableTypes.head.size(), variableTypes.size()); ++i)
-                reportErrors(tryUnify(scope, forInStatement->vars.data[i]->location, variableTypes[i], expectedVariableTypes[i]));
+                reportErrors(tryUnify(scope, forInStatement->vars.data[i]->location, variableTypes[i], expectedVariableTypes.head[i]));
 
             // nextFn is going to be invoked with (arrayTy, startIndexTy)
 
@@ -477,25 +477,25 @@ struct TypeChecker2
             if (maxCount && *maxCount < 2)
                 reportError(CountMismatch{2, std::nullopt, *maxCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
 
-            const std::vector<TypeId> flattenedArgTypes = flatten(arena, singletonTypes, iterFtv->argTypes, 2);
+            TypePack flattenedArgTypes = extendTypePack(arena, singletonTypes, iterFtv->argTypes, 2);
             size_t firstIterationArgCount = iterTys.empty() ? 0 : iterTys.size() - 1;
-            size_t actualArgCount = expectedVariableTypes.size();
+            size_t actualArgCount = expectedVariableTypes.head.size();
 
             if (firstIterationArgCount < minCount)
                 reportError(CountMismatch{2, std::nullopt, firstIterationArgCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
             else if (actualArgCount < minCount)
                 reportError(CountMismatch{2, std::nullopt, actualArgCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
 
-            if (iterTys.size() >= 2 && flattenedArgTypes.size() > 0)
+            if (iterTys.size() >= 2 && flattenedArgTypes.head.size() > 0)
             {
                 size_t valueIndex = forInStatement->values.size > 1 ? 1 : 0;
-                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iterTys[1], flattenedArgTypes[0]));
+                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iterTys[1], flattenedArgTypes.head[0]));
             }
 
-            if (iterTys.size() == 3 && flattenedArgTypes.size() > 1)
+            if (iterTys.size() == 3 && flattenedArgTypes.head.size() > 1)
             {
                 size_t valueIndex = forInStatement->values.size > 2 ? 2 : 0;
-                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iterTys[2], flattenedArgTypes[1]));
+                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iterTys[2], flattenedArgTypes.head[1]));
             }
         };
 
@@ -516,7 +516,7 @@ struct TypeChecker2
          */
         if (const FunctionTypeVar* nextFn = get<FunctionTypeVar>(iteratorTy))
         {
-            checkFunction(nextFn, iteratorTypes, false);
+            checkFunction(nextFn, iteratorTypes.head, false);
         }
         else if (const TableTypeVar* ttv = get<TableTypeVar>(iteratorTy))
         {
@@ -545,19 +545,19 @@ struct TypeChecker2
                     TypePackId argPack = arena.addTypePack({iteratorTy});
                     reportErrors(tryUnify(scope, forInStatement->values.data[0]->location, argPack, iterMmFtv->argTypes));
 
-                    std::vector<TypeId> mmIteratorTypes = flatten(arena, singletonTypes, iterMmFtv->retTypes, 3);
+                    TypePack mmIteratorTypes = extendTypePack(arena, singletonTypes, iterMmFtv->retTypes, 3);
 
-                    if (mmIteratorTypes.size() == 0)
+                    if (mmIteratorTypes.head.size() == 0)
                     {
                         reportError(GenericError{"__iter must return at least one value"}, forInStatement->values.data[0]->location);
                         return;
                     }
 
-                    TypeId nextFn = follow(mmIteratorTypes[0]);
+                    TypeId nextFn = follow(mmIteratorTypes.head[0]);
 
                     if (std::optional<TypeId> instantiatedNextFn = instantiation.substitute(nextFn))
                     {
-                        std::vector<TypeId> instantiatedIteratorTypes = mmIteratorTypes;
+                        std::vector<TypeId> instantiatedIteratorTypes = mmIteratorTypes.head;
                         instantiatedIteratorTypes[0] = *instantiatedNextFn;
 
                         if (const FunctionTypeVar* nextFtv = get<FunctionTypeVar>(*instantiatedNextFn))
@@ -800,8 +800,8 @@ struct TypeChecker2
         for (AstExpr* arg : call->args)
             visit(arg);
 
-        TypeArena arena;
+        TypeArena* arena = &module->internalTypes;
-        Instantiation instantiation{TxnLog::empty(), &arena, TypeLevel{}, stack.back()};
+        Instantiation instantiation{TxnLog::empty(), arena, TypeLevel{}, stack.back()};
 
         TypePackId expectedRetType = lookupPack(call);
         TypeId functionType = lookupType(call->func);
@@ -845,30 +845,70 @@ struct TypeChecker2
                 return;
             }
         }
+        else if (auto utv = get<UnionTypeVar>(functionType))
+        {
+            // Sometimes it's okay to call a union of functions, but only if all of the functions are the same.
+            std::optional<TypeId> fst;
+            for (TypeId ty : utv)
+            {
+                if (!fst)
+                    fst = follow(ty);
+                else if (fst != follow(ty))
+                {
+                    reportError(CannotCallNonFunction{functionType}, call->func->location);
+                    return;
+                }
+            }
+
+            if (!fst)
+                ice.ice("UnionTypeVar had no elements, so fst is nullopt?");
+
+            if (std::optional<TypeId> instantiatedFunctionType = instantiation.substitute(*fst))
+            {
+                testFunctionType = *instantiatedFunctionType;
+            }
+            else
+            {
+                reportError(UnificationTooComplex{}, call->func->location);
+                return;
+            }
+        }
         else
         {
             reportError(CannotCallNonFunction{functionType}, call->func->location);
             return;
         }
 
-        for (AstExpr* arg : call->args)
-        {
-            TypeId argTy = lookupType(arg);
-            args.head.push_back(argTy);
-        }
-
         if (call->self)
         {
             AstExprIndexName* indexExpr = call->func->as<AstExprIndexName>();
             if (!indexExpr)
                 ice.ice("method call expression has no 'self'");
 
-            args.head.insert(args.head.begin(), lookupType(indexExpr->expr));
+            args.head.push_back(lookupType(indexExpr->expr));
         }
 
-        TypePackId argsTp = arena.addTypePack(args);
+        for (size_t i = 0; i < call->args.size; ++i)
+        {
+            AstExpr* arg = call->args.data[i];
+            TypeId* argTy = module->astTypes.find(arg);
+            if (argTy)
+                args.head.push_back(*argTy);
+            else if (i == call->args.size - 1)
+            {
+                TypePackId* argTail = module->astTypePacks.find(arg);
+                if (argTail)
+                    args.tail = *argTail;
+                else
+                    args.tail = singletonTypes->anyTypePack;
+            }
+            else
+                args.head.push_back(singletonTypes->anyType);
+        }
+
+        TypePackId argsTp = arena->addTypePack(args);
         FunctionTypeVar ftv{argsTp, expectedRetType};
-        TypeId expectedType = arena.addType(ftv);
+        TypeId expectedType = arena->addType(ftv);
 
         if (!isSubtype(testFunctionType, expectedType, stack.back()))
         {
@@ -881,19 +921,7 @@ struct TypeChecker2
     void visit(AstExprIndexName* indexName)
     {
         TypeId leftType = lookupType(indexName->expr);
-        TypeId resultType = lookupType(indexName);
+        getIndexTypeFromType(module->getModuleScope(), leftType, indexName->index.value, indexName->location, /* addErrors */ true);
-
-        // leftType must have a property called indexName->index
-
-        std::optional<TypeId> ty =
-            getIndexTypeFromType(module->getModuleScope(), leftType, indexName->index.value, indexName->location, /* addErrors */ true);
-        if (ty)
-        {
-            if (!isSubtype(resultType, *ty, stack.back()))
-            {
-                reportError(TypeMismatch{resultType, *ty}, indexName->location);
-            }
-        }
     }
 
     void visit(AstExprIndexExpr* indexExpr)
@@ -1085,7 +1113,7 @@ struct TypeChecker2
 
             if (mm)
             {
-                if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(*mm))
+                if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(follow(*mm)))
                 {
                     TypePackId expectedArgs;
                     // For >= and > we invoke __lt and __le respectively with

Analysis/src/TypeInfer.cpp

@@ -35,11 +35,12 @@ LUAU_FASTFLAG(LuauTypeNormalization2)
 LUAU_FASTFLAGVARIABLE(DebugLuauFreezeDuringUnification, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnAnyInsteadOfICE, false) // Eventually removed as false.
 LUAU_FASTFLAGVARIABLE(DebugLuauSharedSelf, false)
-LUAU_FASTFLAGVARIABLE(LuauLvaluelessPath, false)
 LUAU_FASTFLAGVARIABLE(LuauNilIterator, false)
 LUAU_FASTFLAGVARIABLE(LuauUnknownAndNeverType, false)
+LUAU_FASTFLAGVARIABLE(LuauTypeInferMissingFollows, false)
 LUAU_FASTFLAGVARIABLE(LuauBinaryNeedsExpectedTypesToo, false)
 LUAU_FASTFLAGVARIABLE(LuauNeverTypesAndOperatorsInference, false)
+LUAU_FASTFLAGVARIABLE(LuauFollowInLvalueIndexCheck, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnsFromCallsitesAreNotWidened, false)
 LUAU_FASTFLAGVARIABLE(LuauTryhardAnd, false)
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
@@ -47,18 +48,15 @@ LUAU_FASTFLAGVARIABLE(LuauCompleteVisitor, false)
 LUAU_FASTFLAGVARIABLE(LuauOptionalNextKey, false)
 LUAU_FASTFLAGVARIABLE(LuauReportShadowedTypeAlias, false)
 LUAU_FASTFLAGVARIABLE(LuauBetterMessagingOnCountMismatch, false)
-LUAU_FASTFLAGVARIABLE(LuauArgMismatchReportFunctionLocation, false)
+LUAU_FASTFLAGVARIABLE(LuauIntersectionTestForEquality, false)
 LUAU_FASTFLAGVARIABLE(LuauImplicitElseRefinement, false)
+LUAU_FASTFLAGVARIABLE(LuauAllowIndexClassParameters, false)
 LUAU_FASTFLAGVARIABLE(LuauDeclareClassPrototype, false)
+LUAU_FASTFLAG(LuauUninhabitedSubAnything)
 LUAU_FASTFLAGVARIABLE(LuauCallableClasses, false)
 
 namespace Luau
 {
-const char* TimeLimitError_DEPRECATED::what() const throw()
-{
-    LUAU_ASSERT(!FFlag::LuauIceExceptionInheritanceChange);
-    return "Typeinfer failed to complete in allotted time";
-}
 
 static bool typeCouldHaveMetatable(TypeId ty)
 {
@@ -269,11 +267,6 @@ ModulePtr TypeChecker::check(const SourceModule& module, Mode mode, std::optiona
         reportErrorCodeTooComplex(module.root->location);
         return std::move(currentModule);
     }
-    catch (const RecursionLimitException_DEPRECATED&)
-    {
-        reportErrorCodeTooComplex(module.root->location);
-        return std::move(currentModule);
-    }
 }
 
 ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mode mode, std::optional<ScopePtr> environmentScope)
@@ -318,10 +311,6 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
     {
         currentModule->timeout = true;
     }
-    catch (const TimeLimitError_DEPRECATED&)
-    {
-        currentModule->timeout = true;
-    }
 
     if (FFlag::DebugLuauSharedSelf)
     {
@@ -429,7 +418,7 @@ void TypeChecker::check(const ScopePtr& scope, const AstStat& program)
         ice("Unknown AstStat");
 
     if (finishTime && TimeTrace::getClock() > *finishTime)
-        throwTimeLimitError();
+        throw TimeLimitError(iceHandler->moduleName);
 }
 
 // This particular overload is for do...end. If you need to not increase the scope level, use checkBlock directly.
@@ -456,11 +445,6 @@ void TypeChecker::checkBlock(const ScopePtr& scope, const AstStatBlock& block)
         reportErrorCodeTooComplex(block.location);
         return;
     }
-    catch (const RecursionLimitException_DEPRECATED&)
-    {
-        reportErrorCodeTooComplex(block.location);
-        return;
-    }
 }
 
 struct InplaceDemoter : TypeVarOnceVisitor
@@ -966,9 +950,9 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatAssign& assign)
 
         TypeId right = nullptr;
 
-        Location loc = 0 == assign.values.size  ? assign.location
+        Location loc = 0 == assign.values.size
-                       : i < assign.values.size ? assign.values.data[i]->location
+                           ? assign.location
-                                                : assign.values.data[assign.values.size - 1]->location;
+                           : i < assign.values.size ? assign.values.data[i]->location : assign.values.data[assign.values.size - 1]->location;
 
         if (valueIter != valueEnd)
         {
@@ -2671,6 +2655,48 @@ static std::optional<std::string> getIdentifierOfBaseVar(AstExpr* node)
     return std::nullopt;
 }
 
+/** Return true if comparison between the types a and b should be permitted with
+ * the == or ~= operators.
+ *
+ * Two types are considered eligible for equality testing if it is possible for
+ * the test to ever succeed.  In other words, we test to see whether the two
+ * types have any overlap at all.
+ *
+ * In order to make things work smoothly with the greedy solver, this function
+ * exempts any and FreeTypeVars from this requirement.
+ *
+ * This function does not (yet?) take into account extra Lua restrictions like
+ * that two tables can only be compared if they have the same metatable.  That
+ * is presently handled by the caller.
+ *
+ * @return True if the types are comparable.  False if they are not.
+ *
+ * If an internal recursion limit is reached while performing this test, the
+ * function returns std::nullopt.
+ */
+static std::optional<bool> areEqComparable(NotNull<TypeArena> arena, NotNull<Normalizer> normalizer, TypeId a, TypeId b)
+{
+    a = follow(a);
+    b = follow(b);
+
+    auto isExempt = [](TypeId t) {
+        return isNil(t) || get<FreeTypeVar>(t);
+    };
+
+    if (isExempt(a) || isExempt(b))
+        return true;
+
+    TypeId c = arena->addType(IntersectionTypeVar{{a, b}});
+    const NormalizedType* n = normalizer->normalize(c);
+    if (!n)
+        return std::nullopt;
+
+    if (FFlag::LuauUninhabitedSubAnything)
+        return normalizer->isInhabited(n);
+    else
+        return isInhabited_DEPRECATED(*n);
+}
+
 TypeId TypeChecker::checkRelationalOperation(
     const ScopePtr& scope, const AstExprBinary& expr, TypeId lhsType, TypeId rhsType, const PredicateVec& predicates)
 {
@@ -2741,6 +2767,28 @@ TypeId TypeChecker::checkRelationalOperation(
                 return booleanType;
         }
 
+        if (FFlag::LuauIntersectionTestForEquality && isEquality)
+        {
+            // Unless either type is free or any, an equality comparison is only
+            // valid when the intersection of the two operands is non-empty.
+            //
+            // eg it is okay to compare string? == number? because the two types
+            // have nil in common, but string == number is not allowed.
+            std::optional<bool> eqTestResult = areEqComparable(NotNull{&currentModule->internalTypes}, NotNull{&normalizer}, lhsType, rhsType);
+            if (!eqTestResult)
+            {
+                reportErrorCodeTooComplex(expr.location);
+                return errorRecoveryType(booleanType);
+            }
+
+            if (!*eqTestResult)
+            {
+                reportError(
+                    expr.location, GenericError{format("Type %s cannot be compared with %s", toString(lhsType).c_str(), toString(rhsType).c_str())});
+                return errorRecoveryType(booleanType);
+            }
+        }
+
         /* Subtlety here:
          * We need to do this unification first, but there are situations where we don't actually want to
          * report any problems that might have been surfaced as a result of this step because we might already
@@ -2753,7 +2801,7 @@ TypeId TypeChecker::checkRelationalOperation(
             state.log.commit();
         }
 
-        bool needsMetamethod = !isEquality;
+        const bool needsMetamethod = !isEquality;
 
         TypeId leftType = follow(lhsType);
         if (get<PrimitiveTypeVar>(leftType) || get<AnyTypeVar>(leftType) || get<ErrorTypeVar>(leftType) || get<UnionTypeVar>(leftType))
@@ -3335,6 +3383,9 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
 
     TypeId indexType = checkExpr(scope, *expr.index).type;
 
+    if (FFlag::LuauFollowInLvalueIndexCheck)
+        exprType = follow(exprType);
+
     if (get<AnyTypeVar>(exprType) || get<ErrorTypeVar>(exprType))
         return exprType;
 
@@ -3356,6 +3407,16 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
             return prop->type;
         }
     }
+    else if (FFlag::LuauAllowIndexClassParameters)
+    {
+        if (const ClassTypeVar* exprClass = get<ClassTypeVar>(exprType))
+        {
+            if (isNonstrictMode())
+                return unknownType;
+            reportError(TypeError{expr.location, DynamicPropertyLookupOnClassesUnsafe{exprType}});
+            return errorRecoveryType(scope);
+        }
+    }
 
     TableTypeVar* exprTable = getMutableTableType(exprType);
 
@@ -3810,16 +3871,8 @@ void TypeChecker::checkArgumentList(const ScopePtr& scope, const AstExpr& funNam
 
         std::string namePath;
 
-        if (FFlag::LuauLvaluelessPath)
+        if (std::optional<std::string> path = getFunctionNameAsString(funName))
-        {
+            namePath = *path;
-            if (std::optional<std::string> path = getFunctionNameAsString(funName))
-                namePath = *path;
-        }
-        else
-        {
-            if (std::optional<LValue> lValue = tryGetLValue(funName))
-                namePath = toString(*lValue);
-        }
 
         auto [minParams, optMaxParams] = getParameterExtents(&state.log, paramPack);
         state.reportError(TypeError{location,
@@ -3929,27 +3982,11 @@ void TypeChecker::checkArgumentList(const ScopePtr& scope, const AstExpr& funNam
 
                     std::string namePath;
 
-                    if (FFlag::LuauLvaluelessPath)
+                    if (std::optional<std::string> path = getFunctionNameAsString(funName))
-                    {
+                        namePath = *path;
-                        if (std::optional<std::string> path = getFunctionNameAsString(funName))
-                            namePath = *path;
-                    }
-                    else
-                    {
-                        if (std::optional<LValue> lValue = tryGetLValue(funName))
-                            namePath = toString(*lValue);
-                    }
 
-                    if (FFlag::LuauArgMismatchReportFunctionLocation)
+                    state.reportError(TypeError{
-                    {
+                        funName.location, CountMismatch{minParams, optMaxParams, paramIndex, CountMismatch::Context::Arg, isVariadic, namePath}});
-                        state.reportError(TypeError{
-                            funName.location, CountMismatch{minParams, optMaxParams, paramIndex, CountMismatch::Context::Arg, isVariadic, namePath}});
-                    }
-                    else
-                    {
-                        state.reportError(TypeError{
-                            state.location, CountMismatch{minParams, optMaxParams, paramIndex, CountMismatch::Context::Arg, isVariadic, namePath}});
-                    }
                     return;
                 }
                 ++paramIter;
@@ -4461,7 +4498,7 @@ void TypeChecker::reportOverloadResolutionError(const ScopePtr& scope, const Ast
     std::string s;
     for (size_t i = 0; i < overloadTypes.size(); ++i)
     {
-        TypeId overload = overloadTypes[i];
+        TypeId overload = FFlag::LuauTypeInferMissingFollows ? follow(overloadTypes[i]) : overloadTypes[i];
         Unifier state = mkUnifier(scope, expr.location);
 
         // Unify return types
@@ -4842,7 +4879,10 @@ TypePackId TypeChecker::anyifyModuleReturnTypePackGenerics(TypePackId tp)
     tp = follow(tp);
 
     if (const VariadicTypePack* vtp = get<VariadicTypePack>(tp))
-        return get<GenericTypeVar>(vtp->ty) ? anyTypePack : tp;
+    {
+        TypeId ty = FFlag::LuauTypeInferMissingFollows ? follow(vtp->ty) : vtp->ty;
+        return get<GenericTypeVar>(ty) ? anyTypePack : tp;
+    }
 
     if (!get<TypePack>(follow(tp)))
         return tp;
@@ -4893,19 +4933,6 @@ void TypeChecker::ice(const std::string& message)
     iceHandler->ice(message);
 }
 
-// TODO: Inline me when LuauIceExceptionInheritanceChange is deleted.
-void TypeChecker::throwTimeLimitError()
-{
-    if (FFlag::LuauIceExceptionInheritanceChange)
-    {
-        throw TimeLimitError(iceHandler->moduleName);
-    }
-    else
-    {
-        throw TimeLimitError_DEPRECATED();
-    }
-}
-
 void TypeChecker::prepareErrorsForDisplay(ErrorVec& errVec)
 {
     // Remove errors with names that were generated by recovery from a parse error
@@ -6085,11 +6112,11 @@ void TypeChecker::resolve(const EqPredicate& eqP, RefinementMap& refis, const Sc
                     if (optionIsSubtype && !targetIsSubtype)
                         return option;
                     else if (!optionIsSubtype && targetIsSubtype)
-                        return eqP.type;
+                        return FFlag::LuauTypeInferMissingFollows ? follow(eqP.type) : eqP.type;
                     else if (!optionIsSubtype && !targetIsSubtype)
                         return nope;
                     else if (optionIsSubtype && targetIsSubtype)
-                        return eqP.type;
+                        return FFlag::LuauTypeInferMissingFollows ? follow(eqP.type) : eqP.type;
                 }
                 else
                 {

Analysis/src/TypePack.cpp

@@ -6,6 +6,8 @@
 
 #include <stdexcept>
 
+LUAU_FASTFLAGVARIABLE(LuauTxnLogTypePackIterator, false)
+
 namespace Luau
 {
 
@@ -60,8 +62,8 @@ TypePackIterator::TypePackIterator(TypePackId typePack)
 }
 
 TypePackIterator::TypePackIterator(TypePackId typePack, const TxnLog* log)
-    : currentTypePack(follow(typePack))
+    : currentTypePack(FFlag::LuauTxnLogTypePackIterator ? log->follow(typePack) : follow(typePack))
-    , tp(get<TypePack>(currentTypePack))
+    , tp(FFlag::LuauTxnLogTypePackIterator ? log->get<TypePack>(currentTypePack) : get<TypePack>(currentTypePack))
     , currentIndex(0)
     , log(log)
 {
@@ -235,7 +237,7 @@ TypePackId follow(TypePackId tp, std::function<TypePackId(TypePackId)> mapper)
                 cycleTester = nullptr;
 
             if (tp == cycleTester)
-                throwRuntimeError("Luau::follow detected a TypeVar cycle!!");
+                throw InternalCompilerError("Luau::follow detected a TypeVar cycle!!");
         }
     }
 }

Analysis/src/TypeUtils.cpp

@@ -122,10 +122,6 @@ std::optional<TypeId> getIndexTypeFromType(const ScopePtr& scope, ErrorVec& erro
 
         for (TypeId t : utv)
         {
-            // TODO: we should probably limit recursion here?
-            // RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit);
-
-            // Not needed when we normalize types.
             if (get<AnyTypeVar>(follow(t)))
                 return t;
 
@@ -164,9 +160,6 @@ std::optional<TypeId> getIndexTypeFromType(const ScopePtr& scope, ErrorVec& erro
 
         for (TypeId t : itv->parts)
         {
-            // TODO: we should probably limit recursion here?
-            // RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit);
-
             if (std::optional<TypeId> ty =
                     getIndexTypeFromType(scope, errors, arena, singletonTypes, t, prop, location, /* addErrors= */ false, handle))
                 parts.push_back(*ty);
@@ -183,7 +176,7 @@ std::optional<TypeId> getIndexTypeFromType(const ScopePtr& scope, ErrorVec& erro
         if (parts.size() == 1)
             return parts[0];
 
-        return arena->addType(IntersectionTypeVar{std::move(parts)}); // Not at all correct.
+        return arena->addType(IntersectionTypeVar{std::move(parts)});
     }
 
     if (addErrors)
@@ -221,46 +214,95 @@ std::pair<size_t, std::optional<size_t>> getParameterExtents(const TxnLog* log,
         return {minCount, minCount + optionalCount};
 }
 
-std::vector<TypeId> flatten(TypeArena& arena, NotNull<SingletonTypes> singletonTypes, TypePackId pack, size_t length)
+TypePack extendTypePack(TypeArena& arena, NotNull<SingletonTypes> singletonTypes, TypePackId pack, size_t length)
 {
-    std::vector<TypeId> result;
+    TypePack result;
 
-    auto it = begin(pack);
+    while (true)
-    auto endIt = end(pack);
-
-    while (it != endIt)
     {
-        result.push_back(*it);
+        pack = follow(pack);
 
-        if (result.size() >= length)
+        if (const TypePack* p = get<TypePack>(pack))
+        {
+            size_t i = 0;
+            while (i < p->head.size() && result.head.size() < length)
+            {
+                result.head.push_back(p->head[i]);
+                ++i;
+            }
+
+            if (result.head.size() == length)
+            {
+                if (i == p->head.size())
+                    result.tail = p->tail;
+                else
+                {
+                    TypePackId newTail = arena.addTypePack(TypePack{});
+                    TypePack* newTailPack = getMutable<TypePack>(newTail);
+
+                    newTailPack->head.insert(newTailPack->head.begin(), p->head.begin() + i, p->head.end());
+                    newTailPack->tail = p->tail;
+
+                    result.tail = newTail;
+                }
+
+                return result;
+            }
+            else if (p->tail)
+            {
+                pack = *p->tail;
+                continue;
+            }
+            else
+            {
+                // There just aren't enough types in this pack to satisfy the request.
+                return result;
+            }
+        }
+        else if (const VariadicTypePack* vtp = get<VariadicTypePack>(pack))
+        {
+            while (result.head.size() < length)
+                result.head.push_back(vtp->ty);
+            result.tail = pack;
             return result;
+        }
+        else if (FreeTypePack* ftp = getMutable<FreeTypePack>(pack))
+        {
+            // If we need to get concrete types out of a free pack, we choose to
+            // interpret this as proof that the pack must have at least 'length'
+            // elements.  We mint fresh types for each element we're extracting
+            // and rebind the free pack to be a TypePack containing them. We
+            // also have to create a new tail.
 
-        ++it;
+            TypePack newPack;
-    }
+            newPack.tail = arena.freshTypePack(ftp->scope);
 
-    if (!it.tail())
+            while (result.head.size() < length)
-        return result;
+            {
+                newPack.head.push_back(arena.freshType(ftp->scope));
+                result.head.push_back(newPack.head.back());
+            }
 
-    TypePackId tail = *it.tail();
+            asMutable(pack)->ty.emplace<TypePack>(std::move(newPack));
-    if (get<TypePack>(tail))
-        LUAU_ASSERT(0);
-    else if (auto vtp = get<VariadicTypePack>(tail))
-    {
-        while (result.size() < length)
-            result.push_back(vtp->ty);
-    }
-    else if (get<FreeTypePack>(tail) || get<GenericTypePack>(tail))
-    {
-        while (result.size() < length)
-            result.push_back(arena.addType(FreeTypeVar{nullptr}));
-    }
-    else if (auto etp = get<Unifiable::Error>(tail))
-    {
-        while (result.size() < length)
-            result.push_back(singletonTypes->errorRecoveryType());
-    }
 
-    return result;
+            return result;
+        }
+        else if (const Unifiable::Error* etp = getMutable<Unifiable::Error>(pack))
+        {
+            while (result.head.size() < length)
+                result.head.push_back(singletonTypes->errorRecoveryType());
+
+            result.tail = pack;
+            return result;
+        }
+        else
+        {
+            // If the pack is blocked or generic, we can't extract.
+            // Return whatever we've got with this pack as the tail.
+            result.tail = pack;
+            return result;
+        }
+    }
 }
 
 std::vector<TypeId> reduceUnion(const std::vector<TypeId>& types)

Analysis/src/TypeVar.cpp

@@ -72,7 +72,7 @@ TypeId follow(TypeId t, std::function<TypeId(TypeId)> mapper)
         {
             TypeId res = ltv->thunk();
             if (get<LazyTypeVar>(res))
-                throwRuntimeError("Lazy TypeVar cannot resolve to another Lazy TypeVar");
+                throw InternalCompilerError("Lazy TypeVar cannot resolve to another Lazy TypeVar");
 
             *asMutable(ty) = BoundTypeVar(res);
         }
@@ -110,7 +110,7 @@ TypeId follow(TypeId t, std::function<TypeId(TypeId)> mapper)
                 cycleTester = nullptr;
 
             if (t == cycleTester)
-                throwRuntimeError("Luau::follow detected a TypeVar cycle!!");
+                throw InternalCompilerError("Luau::follow detected a TypeVar cycle!!");
         }
     }
 }
@@ -468,65 +468,65 @@ PendingExpansionTypeVar::PendingExpansionTypeVar(
 size_t PendingExpansionTypeVar::nextIndex = 0;
 
 FunctionTypeVar::FunctionTypeVar(TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
-    : argTypes(argTypes)
+    : definition(std::move(defn))
+    , argTypes(argTypes)
     , retTypes(retTypes)
-    , definition(std::move(defn))
     , hasSelf(hasSelf)
 {
 }
 
 FunctionTypeVar::FunctionTypeVar(TypeLevel level, TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
-    : level(level)
+    : definition(std::move(defn))
+    , level(level)
     , argTypes(argTypes)
     , retTypes(retTypes)
-    , definition(std::move(defn))
     , hasSelf(hasSelf)
 {
 }
 
 FunctionTypeVar::FunctionTypeVar(
     TypeLevel level, Scope* scope, TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
-    : level(level)
+    : definition(std::move(defn))
+    , level(level)
     , scope(scope)
     , argTypes(argTypes)
     , retTypes(retTypes)
-    , definition(std::move(defn))
     , hasSelf(hasSelf)
 {
 }
 
 FunctionTypeVar::FunctionTypeVar(std::vector<TypeId> generics, std::vector<TypePackId> genericPacks, TypePackId argTypes, TypePackId retTypes,
     std::optional<FunctionDefinition> defn, bool hasSelf)
-    : generics(generics)
+    : definition(std::move(defn))
+    , generics(generics)
     , genericPacks(genericPacks)
     , argTypes(argTypes)
     , retTypes(retTypes)
-    , definition(std::move(defn))
     , hasSelf(hasSelf)
 {
 }
 
 FunctionTypeVar::FunctionTypeVar(TypeLevel level, std::vector<TypeId> generics, std::vector<TypePackId> genericPacks, TypePackId argTypes,
     TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
-    : level(level)
+    : definition(std::move(defn))
     , generics(generics)
     , genericPacks(genericPacks)
+    , level(level)
     , argTypes(argTypes)
     , retTypes(retTypes)
-    , definition(std::move(defn))
     , hasSelf(hasSelf)
 {
 }
 
 FunctionTypeVar::FunctionTypeVar(TypeLevel level, Scope* scope, std::vector<TypeId> generics, std::vector<TypePackId> genericPacks,
     TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
-    : level(level)
+    : definition(std::move(defn))
-    , scope(scope)
     , generics(generics)
     , genericPacks(genericPacks)
+    , level(level)
+    , scope(scope)
     , argTypes(argTypes)
     , retTypes(retTypes)
-    , definition(std::move(defn))
     , hasSelf(hasSelf)
 {
 }

Analysis/src/TypedAllocator.cpp

@@ -48,6 +48,8 @@ void* pagedAllocate(size_t size)
     // On Linux, we must use mmap because using regular heap results in mprotect() fragmenting the page table and us bumping into 64K mmap limit.
 #ifdef _WIN32
     return _aligned_malloc(size, kPageSize);
+#elif defined(__FreeBSD__)
+    return aligned_alloc(kPageSize, size);
 #else
     return mmap(nullptr, pageAlign(size), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
 #endif
@@ -61,6 +63,8 @@ void pagedDeallocate(void* ptr, size_t size)
 
 #ifdef _WIN32
     _aligned_free(ptr);
+#elif defined(__FreeBSD__)
+    free(ptr);
 #else
     int rc = munmap(ptr, size);
     LUAU_ASSERT(rc == 0);

Analysis/src/Unifier.cpp

@@ -22,8 +22,10 @@ LUAU_FASTFLAGVARIABLE(LuauSubtypeNormalizer, false);
 LUAU_FASTFLAGVARIABLE(LuauScalarShapeSubtyping, false)
 LUAU_FASTFLAGVARIABLE(LuauInstantiateInSubtyping, false)
 LUAU_FASTFLAGVARIABLE(LuauOverloadedFunctionSubtypingPerf, false);
-LUAU_FASTFLAGVARIABLE(LuauScalarShapeUnifyToMtOwner, false)
+LUAU_FASTFLAGVARIABLE(LuauScalarShapeUnifyToMtOwner2, false)
+LUAU_FASTFLAGVARIABLE(LuauUninhabitedSubAnything, false)
 LUAU_FASTFLAG(LuauClassTypeVarsInSubstitution)
+LUAU_FASTFLAG(LuauTxnLogTypePackIterator)
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 LUAU_FASTFLAG(LuauNegatedFunctionTypes)
 
@@ -51,6 +53,9 @@ struct PromoteTypeLevels final : TypeVarOnceVisitor
     template<typename TID, typename T>
     void promote(TID ty, T* t)
     {
+        if (FFlag::DebugLuauDeferredConstraintResolution && !t)
+            return;
+
         LUAU_ASSERT(t);
 
         if (useScopes)
@@ -102,6 +107,11 @@ struct PromoteTypeLevels final : TypeVarOnceVisitor
         if (ty->owningArena != typeArena)
             return false;
 
+        // Surprise, it's actually a BoundTypePack that hasn't been committed yet.
+        // Calling getMutable on this will trigger an assertion.
+        if (FFlag::LuauScalarShapeUnifyToMtOwner2 && !log.is<FunctionTypeVar>(ty))
+            return true;
+
         promote(ty, log.getMutable<FunctionTypeVar>(ty));
         return true;
     }
@@ -115,6 +125,11 @@ struct PromoteTypeLevels final : TypeVarOnceVisitor
         if (ttv.state != TableState::Free && ttv.state != TableState::Generic)
             return true;
 
+        // Surprise, it's actually a BoundTypePack that hasn't been committed yet.
+        // Calling getMutable on this will trigger an assertion.
+        if (FFlag::LuauScalarShapeUnifyToMtOwner2 && !log.is<TableTypeVar>(ty))
+            return true;
+
         promote(ty, log.getMutable<TableTypeVar>(ty));
         return true;
     }
@@ -277,7 +292,7 @@ TypeId Widen::clean(TypeId ty)
 
 TypePackId Widen::clean(TypePackId)
 {
-    throwRuntimeError("Widen attempted to clean a dirty type pack?");
+    throw InternalCompilerError("Widen attempted to clean a dirty type pack?");
 }
 
 bool Widen::ignoreChildren(TypeId ty)
@@ -336,6 +351,20 @@ static bool subsumes(bool useScopes, TY_A* left, TY_B* right)
         return left->level.subsumes(right->level);
 }
 
+TypeMismatch::Context Unifier::mismatchContext()
+{
+    switch (variance)
+    {
+    case Covariant:
+        return TypeMismatch::CovariantContext;
+    case Invariant:
+        return TypeMismatch::InvariantContext;
+    default:
+        LUAU_ASSERT(false); // This codepath should be unreachable.
+        return TypeMismatch::CovariantContext;
+    }
+}
+
 Unifier::Unifier(NotNull<Normalizer> normalizer, Mode mode, NotNull<Scope> scope, const Location& location, Variance variance, TxnLog* parentLog)
     : types(normalizer->arena)
     , singletonTypes(normalizer->singletonTypes)
@@ -559,8 +588,11 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     else if (log.get<NegationTypeVar>(subTy))
         tryUnifyNegationWithType(subTy, superTy);
 
+    else if (FFlag::LuauUninhabitedSubAnything && !normalizer->isInhabited(subTy))
+        {}
+
     else
-        reportError(location, TypeMismatch{superTy, subTy});
+        reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
 
     if (cacheEnabled)
         cacheResult(subTy, superTy, errorCount);
@@ -575,11 +607,16 @@ void Unifier::tryUnifyUnionWithType(TypeId subTy, const UnionTypeVar* subUnion,
     std::optional<TypeError> unificationTooComplex;
     std::optional<TypeError> firstFailedOption;
 
+    std::vector<TxnLog> logs;
+
     for (TypeId type : subUnion->options)
     {
         Unifier innerState = makeChildUnifier();
         innerState.tryUnify_(type, superTy);
 
+        if (FFlag::DebugLuauDeferredConstraintResolution)
+            logs.push_back(std::move(innerState.log));
+
         if (auto e = hasUnificationTooComplex(innerState.errors))
             unificationTooComplex = e;
         else if (!innerState.errors.empty())
@@ -592,51 +629,56 @@ void Unifier::tryUnifyUnionWithType(TypeId subTy, const UnionTypeVar* subUnion,
         }
     }
 
-    // even if A | B <: T fails, we want to bind some options of T with A | B iff A | B was a subtype of that option.
+    if (FFlag::DebugLuauDeferredConstraintResolution)
-    auto tryBind = [this, subTy](TypeId superOption) {
+        log.concatAsUnion(combineLogsIntoUnion(std::move(logs)), NotNull{types});
-        superOption = log.follow(superOption);
-
-        // just skip if the superOption is not free-ish.
-        auto ttv = log.getMutable<TableTypeVar>(superOption);
-        if (!log.is<FreeTypeVar>(superOption) && (!ttv || ttv->state != TableState::Free))
-            return;
-
-        // If superOption is already present in subTy, do nothing.  Nothing new has been learned, but the subtype
-        // test is successful.
-        if (auto subUnion = get<UnionTypeVar>(subTy))
-        {
-            if (end(subUnion) != std::find(begin(subUnion), end(subUnion), superOption))
-                return;
-        }
-
-        // Since we have already checked if S <: T, checking it again will not queue up the type for replacement.
-        // So we'll have to do it ourselves. We assume they unified cleanly if they are still in the seen set.
-        if (log.haveSeen(subTy, superOption))
-        {
-            // TODO: would it be nice for TxnLog::replace to do this?
-            if (log.is<TableTypeVar>(superOption))
-                log.bindTable(superOption, subTy);
-            else
-                log.replace(superOption, *subTy);
-        }
-    };
-
-    if (auto superUnion = log.getMutable<UnionTypeVar>(superTy))
-    {
-        for (TypeId ty : superUnion)
-            tryBind(ty);
-    }
     else
-        tryBind(superTy);
+    {
+        // even if A | B <: T fails, we want to bind some options of T with A | B iff A | B was a subtype of that option.
+        auto tryBind = [this, subTy](TypeId superOption) {
+            superOption = log.follow(superOption);
+
+            // just skip if the superOption is not free-ish.
+            auto ttv = log.getMutable<TableTypeVar>(superOption);
+            if (!log.is<FreeTypeVar>(superOption) && (!ttv || ttv->state != TableState::Free))
+                return;
+
+            // If superOption is already present in subTy, do nothing.  Nothing new has been learned, but the subtype
+            // test is successful.
+            if (auto subUnion = get<UnionTypeVar>(subTy))
+            {
+                if (end(subUnion) != std::find(begin(subUnion), end(subUnion), superOption))
+                    return;
+            }
+
+            // Since we have already checked if S <: T, checking it again will not queue up the type for replacement.
+            // So we'll have to do it ourselves. We assume they unified cleanly if they are still in the seen set.
+            if (log.haveSeen(subTy, superOption))
+            {
+                // TODO: would it be nice for TxnLog::replace to do this?
+                if (log.is<TableTypeVar>(superOption))
+                    log.bindTable(superOption, subTy);
+                else
+                    log.replace(superOption, *subTy);
+            }
+        };
+
+        if (auto superUnion = log.getMutable<UnionTypeVar>(superTy))
+        {
+            for (TypeId ty : superUnion)
+                tryBind(ty);
+        }
+        else
+            tryBind(superTy);
+    }
 
     if (unificationTooComplex)
         reportError(*unificationTooComplex);
     else if (failed)
     {
         if (firstFailedOption)
-            reportError(location, TypeMismatch{superTy, subTy, "Not all union options are compatible.", *firstFailedOption});
+            reportError(location, TypeMismatch{superTy, subTy, "Not all union options are compatible.", *firstFailedOption, mismatchContext()});
         else
-            reportError(location, TypeMismatch{superTy, subTy});
+            reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
     }
 }
 
@@ -696,6 +738,8 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
         }
     }
 
+    std::vector<TxnLog> logs;
+
     for (size_t i = 0; i < uv->options.size(); ++i)
     {
         TypeId type = uv->options[(i + startIndex) % uv->options.size()];
@@ -706,9 +750,13 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
         if (innerState.errors.empty())
         {
             found = true;
-            log.concat(std::move(innerState.log));
+            if (FFlag::DebugLuauDeferredConstraintResolution)
-
+                logs.push_back(std::move(innerState.log));
-            break;
+            else
+            {
+                log.concat(std::move(innerState.log));
+                break;
+            }
         }
         else if (auto e = hasUnificationTooComplex(innerState.errors))
         {
@@ -723,6 +771,9 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
         }
     }
 
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+        log.concatAsUnion(combineLogsIntoUnion(std::move(logs)), NotNull{types});
+
     if (unificationTooComplex)
     {
         reportError(*unificationTooComplex);
@@ -744,9 +795,10 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
     else if (!found)
     {
         if ((failedOptionCount == 1 || foundHeuristic) && failedOption)
-            reportError(location, TypeMismatch{superTy, subTy, "None of the union options are compatible. For example:", *failedOption});
+            reportError(
+                location, TypeMismatch{superTy, subTy, "None of the union options are compatible. For example:", *failedOption, mismatchContext()});
         else
-            reportError(location, TypeMismatch{superTy, subTy, "none of the union options are compatible"});
+            reportError(location, TypeMismatch{superTy, subTy, "none of the union options are compatible", mismatchContext()});
     }
 }
 
@@ -755,6 +807,8 @@ void Unifier::tryUnifyTypeWithIntersection(TypeId subTy, TypeId superTy, const I
     std::optional<TypeError> unificationTooComplex;
     std::optional<TypeError> firstFailedOption;
 
+    std::vector<TxnLog> logs;
+
     // T <: A & B if and only if  T <: A and T <: B
     for (TypeId type : uv->parts)
     {
@@ -769,13 +823,19 @@ void Unifier::tryUnifyTypeWithIntersection(TypeId subTy, TypeId superTy, const I
                 firstFailedOption = {innerState.errors.front()};
         }
 
-        log.concat(std::move(innerState.log));
+        if (FFlag::DebugLuauDeferredConstraintResolution)
+            logs.push_back(std::move(innerState.log));
+        else
+            log.concat(std::move(innerState.log));
     }
 
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+        log.concat(combineLogsIntoIntersection(std::move(logs)));
+
     if (unificationTooComplex)
         reportError(*unificationTooComplex);
     else if (firstFailedOption)
-        reportError(location, TypeMismatch{superTy, subTy, "Not all intersection parts are compatible.", *firstFailedOption});
+        reportError(location, TypeMismatch{superTy, subTy, "Not all intersection parts are compatible.", *firstFailedOption, mismatchContext()});
 }
 
 void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeVar* uv, TypeId superTy, bool cacheEnabled, bool isFunctionCall)
@@ -802,6 +862,8 @@ void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeV
         }
     }
 
+    std::vector<TxnLog> logs;
+
     for (size_t i = 0; i < uv->parts.size(); ++i)
     {
         TypeId type = uv->parts[(i + startIndex) % uv->parts.size()];
@@ -812,8 +874,13 @@ void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeV
         if (innerState.errors.empty())
         {
             found = true;
-            log.concat(std::move(innerState.log));
+            if (FFlag::DebugLuauDeferredConstraintResolution)
-            break;
+                logs.push_back(std::move(innerState.log));
+            else
+            {
+                log.concat(std::move(innerState.log));
+                break;
+            }
         }
         else if (auto e = hasUnificationTooComplex(innerState.errors))
         {
@@ -821,6 +888,9 @@ void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeV
         }
     }
 
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+        log.concat(combineLogsIntoIntersection(std::move(logs)));
+
     if (unificationTooComplex)
         reportError(*unificationTooComplex);
     else if (!found && normalize)
@@ -837,7 +907,7 @@ void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeV
     }
     else if (!found)
     {
-        reportError(location, TypeMismatch{superTy, subTy, "none of the intersection parts are compatible"});
+        reportError(location, TypeMismatch{superTy, subTy, "none of the intersection parts are compatible", mismatchContext()});
     }
 }
 
@@ -849,37 +919,37 @@ void Unifier::tryUnifyNormalizedTypes(
     if (get<UnknownTypeVar>(superNorm.tops) || get<AnyTypeVar>(superNorm.tops) || get<AnyTypeVar>(subNorm.tops))
         return;
     else if (get<UnknownTypeVar>(subNorm.tops))
-        return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+        return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
     if (get<ErrorTypeVar>(subNorm.errors))
         if (!get<ErrorTypeVar>(superNorm.errors))
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
     if (get<PrimitiveTypeVar>(subNorm.booleans))
     {
         if (!get<PrimitiveTypeVar>(superNorm.booleans))
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
     }
     else if (const SingletonTypeVar* stv = get<SingletonTypeVar>(subNorm.booleans))
     {
         if (!get<PrimitiveTypeVar>(superNorm.booleans) && stv != get<SingletonTypeVar>(superNorm.booleans))
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
     }
 
     if (get<PrimitiveTypeVar>(subNorm.nils))
         if (!get<PrimitiveTypeVar>(superNorm.nils))
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
     if (get<PrimitiveTypeVar>(subNorm.numbers))
         if (!get<PrimitiveTypeVar>(superNorm.numbers))
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
     if (!isSubtype(subNorm.strings, superNorm.strings))
-        return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+        return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
     if (get<PrimitiveTypeVar>(subNorm.threads))
         if (!get<PrimitiveTypeVar>(superNorm.errors))
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
     for (TypeId subClass : subNorm.classes)
     {
@@ -895,7 +965,7 @@ void Unifier::tryUnifyNormalizedTypes(
             }
         }
         if (!found)
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
     }
 
     for (TypeId subTable : subNorm.tables)
@@ -920,19 +990,19 @@ void Unifier::tryUnifyNormalizedTypes(
                 return reportError(*e);
         }
         if (!found)
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
     }
 
     if (!subNorm.functions.isNever())
     {
         if (superNorm.functions.isNever())
-            return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+            return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
         for (TypeId superFun : *superNorm.functions.parts)
         {
             Unifier innerState = makeChildUnifier();
             const FunctionTypeVar* superFtv = get<FunctionTypeVar>(superFun);
             if (!superFtv)
-                return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+                return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
             TypePackId tgt = innerState.tryApplyOverloadedFunction(subTy, subNorm.functions, superFtv->argTypes);
             innerState.tryUnify_(tgt, superFtv->retTypes);
             if (innerState.errors.empty())
@@ -940,7 +1010,7 @@ void Unifier::tryUnifyNormalizedTypes(
             else if (auto e = hasUnificationTooComplex(innerState.errors))
                 return reportError(*e);
             else
-                return reportError(location, TypeMismatch{superTy, subTy, reason, error});
+                return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
         }
     }
 
@@ -1306,7 +1376,7 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
             // If both are at the end, we're done
             if (!superIter.good() && !subIter.good())
             {
-                if (subTpv->tail && superTpv->tail)
+                if (!FFlag::LuauTxnLogTypePackIterator && subTpv->tail && superTpv->tail)
                 {
                     tryUnify_(*subTpv->tail, *superTpv->tail);
                     break;
@@ -1314,10 +1384,27 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
 
                 const bool lFreeTail = superTpv->tail && log.getMutable<FreeTypePack>(log.follow(*superTpv->tail)) != nullptr;
                 const bool rFreeTail = subTpv->tail && log.getMutable<FreeTypePack>(log.follow(*subTpv->tail)) != nullptr;
-                if (lFreeTail)
+                if (FFlag::LuauTxnLogTypePackIterator && lFreeTail && rFreeTail)
+                {
+                    tryUnify_(*subTpv->tail, *superTpv->tail);
+                }
+                else if (lFreeTail)
+                {
                     tryUnify_(emptyTp, *superTpv->tail);
+                }
                 else if (rFreeTail)
+                {
                     tryUnify_(emptyTp, *subTpv->tail);
+                }
+                else if (FFlag::LuauTxnLogTypePackIterator && subTpv->tail && superTpv->tail)
+                {
+                    if (log.getMutable<VariadicTypePack>(superIter.packId))
+                        tryUnifyVariadics(subIter.packId, superIter.packId, false, int(subIter.index));
+                    else if (log.getMutable<VariadicTypePack>(subIter.packId))
+                        tryUnifyVariadics(superIter.packId, subIter.packId, true, int(superIter.index));
+                    else
+                        tryUnify_(*subTpv->tail, *superTpv->tail);
+                }
 
                 break;
             }
@@ -1407,7 +1494,7 @@ void Unifier::tryUnifyPrimitives(TypeId subTy, TypeId superTy)
         ice("passed non primitive types to unifyPrimitives");
 
     if (superPrim->type != subPrim->type)
-        reportError(location, TypeMismatch{superTy, subTy});
+        reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
 }
 
 void Unifier::tryUnifySingletons(TypeId subTy, TypeId superTy)
@@ -1428,7 +1515,7 @@ void Unifier::tryUnifySingletons(TypeId subTy, TypeId superTy)
     if (superPrim && superPrim->type == PrimitiveTypeVar::String && get<StringSingleton>(subSingleton) && variance == Covariant)
         return;
 
-    reportError(location, TypeMismatch{superTy, subTy});
+    reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
 }
 
 void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCall)
@@ -1471,14 +1558,14 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
     {
         numGenerics = std::min(superFunction->generics.size(), subFunction->generics.size());
 
-        reportError(location, TypeMismatch{superTy, subTy, "different number of generic type parameters"});
+        reportError(location, TypeMismatch{superTy, subTy, "different number of generic type parameters", mismatchContext()});
     }
 
     if (numGenericPacks != subFunction->genericPacks.size())
     {
         numGenericPacks = std::min(superFunction->genericPacks.size(), subFunction->genericPacks.size());
 
-        reportError(location, TypeMismatch{superTy, subTy, "different number of generic type pack parameters"});
+        reportError(location, TypeMismatch{superTy, subTy, "different number of generic type pack parameters", mismatchContext()});
     }
 
     for (size_t i = 0; i < numGenerics; i++)
@@ -1506,9 +1593,9 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
             reportError(*e);
         else if (!innerState.errors.empty() && innerState.firstPackErrorPos)
             reportError(location, TypeMismatch{superTy, subTy, format("Argument #%d type is not compatible.", *innerState.firstPackErrorPos),
-                                      innerState.errors.front()});
+                                      innerState.errors.front(), mismatchContext()});
         else if (!innerState.errors.empty())
-            reportError(location, TypeMismatch{superTy, subTy, "", innerState.errors.front()});
+            reportError(location, TypeMismatch{superTy, subTy, "", innerState.errors.front(), mismatchContext()});
 
         innerState.ctx = CountMismatch::FunctionResult;
         innerState.tryUnify_(subFunction->retTypes, superFunction->retTypes);
@@ -1518,12 +1605,12 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
             if (auto e = hasUnificationTooComplex(innerState.errors))
                 reportError(*e);
             else if (!innerState.errors.empty() && size(superFunction->retTypes) == 1 && finite(superFunction->retTypes))
-                reportError(location, TypeMismatch{superTy, subTy, "Return type is not compatible.", innerState.errors.front()});
+                reportError(location, TypeMismatch{superTy, subTy, "Return type is not compatible.", innerState.errors.front(), mismatchContext()});
             else if (!innerState.errors.empty() && innerState.firstPackErrorPos)
                 reportError(location, TypeMismatch{superTy, subTy, format("Return #%d type is not compatible.", *innerState.firstPackErrorPos),
-                                          innerState.errors.front()});
+                                          innerState.errors.front(), mismatchContext()});
             else if (!innerState.errors.empty())
-                reportError(location, TypeMismatch{superTy, subTy, "", innerState.errors.front()});
+                reportError(location, TypeMismatch{superTy, subTy, "", innerState.errors.front(), mismatchContext()});
         }
 
         log.concat(std::move(innerState.log));
@@ -1700,10 +1787,10 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         // Recursive unification can change the txn log, and invalidate the old
         // table. If we detect that this has happened, we start over, with the updated
         // txn log.
-        TypeId superTyNew = FFlag::LuauScalarShapeUnifyToMtOwner ? log.follow(superTy) : superTy;
+        TypeId superTyNew = FFlag::LuauScalarShapeUnifyToMtOwner2 ? log.follow(superTy) : superTy;
-        TypeId subTyNew = FFlag::LuauScalarShapeUnifyToMtOwner ? log.follow(subTy) : subTy;
+        TypeId subTyNew = FFlag::LuauScalarShapeUnifyToMtOwner2 ? log.follow(subTy) : subTy;
 
-        if (FFlag::LuauScalarShapeUnifyToMtOwner)
+        if (FFlag::LuauScalarShapeUnifyToMtOwner2)
         {
             // If one of the types stopped being a table altogether, we need to restart from the top
             if ((superTy != superTyNew || subTy != subTyNew) && errors.empty())
@@ -1771,11 +1858,21 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         else
             extraProperties.push_back(name);
 
+        TypeId superTyNew = FFlag::LuauScalarShapeUnifyToMtOwner2 ? log.follow(superTy) : superTy;
+        TypeId subTyNew = FFlag::LuauScalarShapeUnifyToMtOwner2 ? log.follow(subTy) : subTy;
+
+        if (FFlag::LuauScalarShapeUnifyToMtOwner2)
+        {
+            // If one of the types stopped being a table altogether, we need to restart from the top
+            if ((superTy != superTyNew || subTy != subTyNew) && errors.empty())
+                return tryUnify(subTy, superTy, false, isIntersection);
+        }
+
         // Recursive unification can change the txn log, and invalidate the old
         // table. If we detect that this has happened, we start over, with the updated
         // txn log.
-        TableTypeVar* newSuperTable = log.getMutable<TableTypeVar>(superTy);
+        TableTypeVar* newSuperTable = log.getMutable<TableTypeVar>(superTyNew);
-        TableTypeVar* newSubTable = log.getMutable<TableTypeVar>(subTy);
+        TableTypeVar* newSubTable = log.getMutable<TableTypeVar>(subTyNew);
         if (superTable != newSuperTable || (subTable != newSubTable && subTable != instantiatedSubTable))
         {
             if (errors.empty())
@@ -1829,8 +1926,19 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
     }
 
     // Changing the indexer can invalidate the table pointers.
-    superTable = log.getMutable<TableTypeVar>(superTy);
+    if (FFlag::LuauScalarShapeUnifyToMtOwner2)
-    subTable = log.getMutable<TableTypeVar>(subTy);
+    {
+        superTable = log.getMutable<TableTypeVar>(log.follow(superTy));
+        subTable = log.getMutable<TableTypeVar>(log.follow(subTy));
+
+        if (!superTable || !subTable)
+            return;
+    }
+    else
+    {
+        superTable = log.getMutable<TableTypeVar>(superTy);
+        subTable = log.getMutable<TableTypeVar>(subTy);
+    }
 
     if (!missingProperties.empty())
     {
@@ -1872,20 +1980,23 @@ void Unifier::tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed)
     TypeId osubTy = subTy;
     TypeId osuperTy = superTy;
 
+    if (FFlag::LuauUninhabitedSubAnything && !normalizer->isInhabited(subTy))
+        return;
+
     if (reversed)
         std::swap(subTy, superTy);
 
     TableTypeVar* superTable = log.getMutable<TableTypeVar>(superTy);
 
     if (!superTable || superTable->state != TableState::Free)
-        return reportError(location, TypeMismatch{osuperTy, osubTy});
+        return reportError(location, TypeMismatch{osuperTy, osubTy, mismatchContext()});
 
     auto fail = [&](std::optional<TypeError> e) {
         std::string reason = "The former's metatable does not satisfy the requirements.";
         if (e)
-            reportError(location, TypeMismatch{osuperTy, osubTy, reason, *e});
+            reportError(location, TypeMismatch{osuperTy, osubTy, reason, *e, mismatchContext()});
         else
-            reportError(location, TypeMismatch{osuperTy, osubTy, reason});
+            reportError(location, TypeMismatch{osuperTy, osubTy, reason, mismatchContext()});
     };
 
     // Given t1 where t1 = { lower: (t1) -> (a, b...) }
@@ -1902,7 +2013,7 @@ void Unifier::tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed)
             Unifier child = makeChildUnifier();
             child.tryUnify_(ty, superTy);
 
-            if (FFlag::LuauScalarShapeUnifyToMtOwner)
+            if (FFlag::LuauScalarShapeUnifyToMtOwner2)
             {
                 // To perform subtype <: free table unification, we have tried to unify (subtype's metatable) <: free table
                 // There is a chance that it was unified with the origial subtype, but then, (subtype's metatable) <: subtype could've failed
@@ -1923,7 +2034,7 @@ void Unifier::tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed)
 
             log.concat(std::move(child.log));
 
-            if (FFlag::LuauScalarShapeUnifyToMtOwner)
+            if (FFlag::LuauScalarShapeUnifyToMtOwner2)
             {
                 // To perform subtype <: free table unification, we have tried to unify (subtype's metatable) <: free table
                 // We return success because subtype <: free table which means that correct unification is to replace free table with the subtype
@@ -1939,7 +2050,7 @@ void Unifier::tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed)
         }
     }
 
-    reportError(location, TypeMismatch{osuperTy, osubTy});
+    reportError(location, TypeMismatch{osuperTy, osubTy, mismatchContext()});
     return;
 }
 
@@ -1969,7 +2080,7 @@ void Unifier::tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed)
     if (!superMetatable)
         ice("tryUnifyMetatable invoked with non-metatable TypeVar");
 
-    TypeError mismatchError = TypeError{location, TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy}};
+    TypeError mismatchError = TypeError{location, TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy, mismatchContext()}};
 
     if (const MetatableTypeVar* subMetatable = log.getMutable<MetatableTypeVar>(subTy))
     {
@@ -1980,7 +2091,8 @@ void Unifier::tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed)
         if (auto e = hasUnificationTooComplex(innerState.errors))
             reportError(*e);
         else if (!innerState.errors.empty())
-            reportError(location, TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy, "", innerState.errors.front()});
+            reportError(
+                location, TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy, "", innerState.errors.front(), mismatchContext()});
 
         log.concat(std::move(innerState.log));
     }
@@ -2017,8 +2129,8 @@ void Unifier::tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed)
                 if (auto e = hasUnificationTooComplex(innerState.errors))
                     reportError(*e);
                 else if (!innerState.errors.empty())
-                    reportError(
+                    reportError(TypeError{location,
-                        TypeError{location, TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy, "", innerState.errors.front()}});
+                        TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy, "", innerState.errors.front(), mismatchContext()}});
                 else if (!missingProperty)
                 {
                     log.concat(std::move(innerState.log));
@@ -2057,9 +2169,9 @@ void Unifier::tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed)
 
     auto fail = [&]() {
         if (!reversed)
-            reportError(location, TypeMismatch{superTy, subTy});
+            reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
         else
-            reportError(location, TypeMismatch{subTy, superTy});
+            reportError(location, TypeMismatch{subTy, superTy, mismatchContext()});
     };
 
     const ClassTypeVar* superClass = get<ClassTypeVar>(superTy);
@@ -2155,7 +2267,7 @@ void Unifier::tryUnifyTypeWithNegation(TypeId subTy, TypeId superTy)
     Unifier state = makeChildUnifier();
     state.tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "");
     if (state.errors.empty())
-        reportError(location, TypeMismatch{superTy, subTy});
+        reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
 }
 
 void Unifier::tryUnifyNegationWithType(TypeId subTy, TypeId superTy)
@@ -2165,7 +2277,7 @@ void Unifier::tryUnifyNegationWithType(TypeId subTy, TypeId superTy)
         ice("tryUnifyNegationWithType subTy must be a negation type");
 
     // TODO: ~T </: U iff T <: U
-    reportError(location, TypeMismatch{superTy, subTy});
+    reportError(location, TypeMismatch{superTy, subTy, mismatchContext()});
 }
 
 static void queueTypePack(std::vector<TypeId>& queue, DenseHashSet<TypePackId>& seenTypePacks, Unifier& state, TypePackId a, TypePackId anyTypePack)
@@ -2200,9 +2312,11 @@ void Unifier::tryUnifyVariadics(TypePackId subTp, TypePackId superTp, bool rever
     if (!superVariadic)
         ice("passed non-variadic pack to tryUnifyVariadics");
 
-    if (const VariadicTypePack* subVariadic = get<VariadicTypePack>(subTp))
+    if (const VariadicTypePack* subVariadic = FFlag::LuauTxnLogTypePackIterator ? log.get<VariadicTypePack>(subTp) : get<VariadicTypePack>(subTp))
+    {
         tryUnify_(reversed ? superVariadic->ty : subVariadic->ty, reversed ? subVariadic->ty : superVariadic->ty);
-    else if (get<TypePack>(subTp))
+    }
+    else if (FFlag::LuauTxnLogTypePackIterator ? log.get<TypePack>(subTp) : get<TypePack>(subTp))
     {
         TypePackIterator subIter = begin(subTp, &log);
         TypePackIterator subEnd = end(subTp);
@@ -2350,6 +2464,24 @@ std::optional<TypeId> Unifier::findTablePropertyRespectingMeta(TypeId lhsType, N
     return Luau::findTablePropertyRespectingMeta(singletonTypes, errors, lhsType, name, location);
 }
 
+TxnLog Unifier::combineLogsIntoIntersection(std::vector<TxnLog> logs)
+{
+    LUAU_ASSERT(FFlag::DebugLuauDeferredConstraintResolution);
+    TxnLog result;
+    for (TxnLog& log : logs)
+        result.concatAsIntersections(std::move(log), NotNull{types});
+    return result;
+}
+
+TxnLog Unifier::combineLogsIntoUnion(std::vector<TxnLog> logs)
+{
+    LUAU_ASSERT(FFlag::DebugLuauDeferredConstraintResolution);
+    TxnLog result;
+    for (TxnLog& log : logs)
+        result.concatAsUnion(std::move(log), NotNull{types});
+    return result;
+}
+
 bool Unifier::occursCheck(TypeId needle, TypeId haystack)
 {
     sharedState.tempSeenTy.clear();
@@ -2491,7 +2623,7 @@ void Unifier::checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, TypeId
     if (auto e = hasUnificationTooComplex(innerErrors))
         reportError(*e);
     else if (!innerErrors.empty())
-        reportError(location, TypeMismatch{wantedType, givenType});
+        reportError(location, TypeMismatch{wantedType, givenType, mismatchContext()});
 }
 
 void Unifier::checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, const std::string& prop, TypeId wantedType, TypeId givenType)
@@ -2499,8 +2631,8 @@ void Unifier::checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, const s
     if (auto e = hasUnificationTooComplex(innerErrors))
         reportError(*e);
     else if (!innerErrors.empty())
-        reportError(
+        reportError(TypeError{location,
-            TypeError{location, TypeMismatch{wantedType, givenType, format("Property '%s' is not compatible.", prop.c_str()), innerErrors.front()}});
+            TypeMismatch{wantedType, givenType, format("Property '%s' is not compatible.", prop.c_str()), innerErrors.front(), mismatchContext()}});
 }
 
 void Unifier::ice(const std::string& message, const Location& location)

Ast/include/Luau/Location.h

@@ -50,6 +50,20 @@ struct Position
     {
         return *this == rhs || *this > rhs;
     }
+
+    void shift(const Position& start, const Position& oldEnd, const Position& newEnd)
+    {
+        if (*this >= start)
+        {
+            if (this->line > oldEnd.line)
+                this->line += (newEnd.line - oldEnd.line);
+            else
+            {
+                this->line = newEnd.line;
+                this->column += (newEnd.column - oldEnd.column);
+            }
+        }
+    }
 };
 
 struct Location
@@ -93,6 +107,10 @@ struct Location
     {
         return begin <= l.begin && end >= l.end;
     }
+    bool overlaps(const Location& l) const
+    {
+        return (begin <= l.begin && end >= l.begin) || (begin <= l.end && end >= l.end) || (begin >= l.begin && end <= l.end);
+    }
     bool contains(const Position& p) const
     {
         return begin <= p && p < end;
@@ -101,6 +119,18 @@ struct Location
     {
         return begin <= p && p <= end;
     }
+    void extend(const Location& other)
+    {
+        if (other.begin < begin)
+            begin = other.begin;
+        if (other.end > end)
+            end = other.end;
+    }
+    void shift(const Position& start, const Position& oldEnd, const Position& newEnd)
+    {
+        begin.shift(start, oldEnd, newEnd);
+        end.shift(start, oldEnd, newEnd);
+    }
 };
 
 std::string toString(const Position& position);

Ast/src/Parser.cpp

@@ -24,9 +24,6 @@ LUAU_DYNAMIC_FASTFLAGVARIABLE(LuaReportParseIntegerIssues, false)
 
 LUAU_FASTFLAGVARIABLE(LuauInterpolatedStringBaseSupport, false)
 
-LUAU_FASTFLAGVARIABLE(LuauCommaParenWarnings, false)
-LUAU_FASTFLAGVARIABLE(LuauTableConstructorRecovery, false)
-
 LUAU_FASTFLAGVARIABLE(LuauParserErrorsOnMissingDefaultTypePackArgument, false)
 
 bool lua_telemetry_parsed_out_of_range_bin_integer = false;
@@ -1084,7 +1081,7 @@ void Parser::parseExprList(TempVector<AstExpr*>& result)
     {
         nextLexeme();
 
-        if (FFlag::LuauCommaParenWarnings && lexer.current().type == ')')
+        if (lexer.current().type == ')')
         {
             report(lexer.current().location, "Expected expression after ',' but got ')' instead");
             break;
@@ -1179,7 +1176,7 @@ AstTypePack* Parser::parseTypeList(TempVector<AstType*>& result, TempVector<std:
 
         nextLexeme();
 
-        if (FFlag::LuauCommaParenWarnings && lexer.current().type == ')')
+        if (lexer.current().type == ')')
         {
             report(lexer.current().location, "Expected type after ',' but got ')' instead");
             break;
@@ -2317,8 +2314,7 @@ AstExpr* Parser::parseTableConstructor()
 
     while (lexer.current().type != '}')
     {
-        if (FFlag::LuauTableConstructorRecovery)
+        lastElementIndent = lexer.current().location.begin.column;
-            lastElementIndent = lexer.current().location.begin.column;
 
         if (lexer.current().type == '[')
         {
@@ -2364,8 +2360,7 @@ AstExpr* Parser::parseTableConstructor()
         {
             nextLexeme();
         }
-        else if (FFlag::LuauTableConstructorRecovery && (lexer.current().type == '[' || lexer.current().type == Lexeme::Name) &&
+        else if ((lexer.current().type == '[' || lexer.current().type == Lexeme::Name) && lexer.current().location.begin.column == lastElementIndent)
-                 lexer.current().location.begin.column == lastElementIndent)
         {
             report(lexer.current().location, "Expected ',' after table constructor element");
         }
@@ -2556,7 +2551,7 @@ std::pair<AstArray<AstGenericType>, AstArray<AstGenericTypePack>> Parser::parseG
             {
                 nextLexeme();
 
-                if (FFlag::LuauCommaParenWarnings && lexer.current().type == '>')
+                if (lexer.current().type == '>')
                 {
                     report(lexer.current().location, "Expected type after ',' but got '>' instead");
                     break;

Compiler/src/BytecodeBuilder.cpp

@@ -1895,10 +1895,7 @@ void BytecodeBuilder::dumpInstruction(const uint32_t* code, std::string& result,
 
     case LOP_CAPTURE:
         formatAppend(result, "CAPTURE %s %c%d\n",
-            LUAU_INSN_A(insn) == LCT_UPVAL ? "UPVAL"
+            LUAU_INSN_A(insn) == LCT_UPVAL ? "UPVAL" : LUAU_INSN_A(insn) == LCT_REF ? "REF" : LUAU_INSN_A(insn) == LCT_VAL ? "VAL" : "",
-            : LUAU_INSN_A(insn) == LCT_REF ? "REF"
-            : LUAU_INSN_A(insn) == LCT_VAL ? "VAL"
-                                           : "",
             LUAU_INSN_A(insn) == LCT_UPVAL ? 'U' : 'R', LUAU_INSN_B(insn));
         break;
 

Compiler/src/Compiler.cpp

@@ -26,6 +26,7 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineThresholdMaxBoost, 300)
 LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
 LUAU_FASTFLAG(LuauInterpolatedStringBaseSupport)
+LUAU_FASTFLAGVARIABLE(LuauMultiAssignmentConflictFix, false)
 
 namespace Luau
 {
@@ -2977,16 +2978,46 @@ struct Compiler
 
         Visitor visitor(this);
 
-        // mark any registers that are used *after* assignment as conflicting
+        if (FFlag::LuauMultiAssignmentConflictFix)
-        for (size_t i = 0; i < vars.size(); ++i)
         {
-            const LValue& li = vars[i].lvalue;
+            // mark any registers that are used *after* assignment as conflicting
 
-            if (i < values.size)
+            // first we go through assignments to locals, since they are performed before assignments to other l-values
-                values.data[i]->visit(&visitor);
+            for (size_t i = 0; i < vars.size(); ++i)
+            {
+                const LValue& li = vars[i].lvalue;
 
-            if (li.kind == LValue::Kind_Local)
+                if (li.kind == LValue::Kind_Local)
-                visitor.assigned[li.reg] = true;
+                {
+                    if (i < values.size)
+                        values.data[i]->visit(&visitor);
+
+                    visitor.assigned[li.reg] = true;
+                }
+            }
+
+            // and now we handle all other l-values
+            for (size_t i = 0; i < vars.size(); ++i)
+            {
+                const LValue& li = vars[i].lvalue;
+
+                if (li.kind != LValue::Kind_Local && i < values.size)
+                    values.data[i]->visit(&visitor);
+            }
+        }
+        else
+        {
+            // mark any registers that are used *after* assignment as conflicting
+            for (size_t i = 0; i < vars.size(); ++i)
+            {
+                const LValue& li = vars[i].lvalue;
+
+                if (i < values.size)
+                    values.data[i]->visit(&visitor);
+
+                if (li.kind == LValue::Kind_Local)
+                    visitor.assigned[li.reg] = true;
+            }
         }
 
         // mark any registers used in trailing expressions as conflicting as well

Sources.cmake

@@ -112,7 +112,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/Constraint.h
     Analysis/include/Luau/ConstraintGraphBuilder.h
     Analysis/include/Luau/ConstraintSolver.h
-    Analysis/include/Luau/DataFlowGraphBuilder.h
+    Analysis/include/Luau/DataFlowGraph.h
     Analysis/include/Luau/DcrLogger.h
     Analysis/include/Luau/Def.h
     Analysis/include/Luau/Documentation.h
@@ -166,7 +166,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/src/Constraint.cpp
     Analysis/src/ConstraintGraphBuilder.cpp
     Analysis/src/ConstraintSolver.cpp
-    Analysis/src/DataFlowGraphBuilder.cpp
+    Analysis/src/DataFlowGraph.cpp
     Analysis/src/DcrLogger.cpp
     Analysis/src/Def.cpp
     Analysis/src/EmbeddedBuiltinDefinitions.cpp
@@ -298,15 +298,16 @@ endif()
 if(TARGET Luau.UnitTest)
     # Luau.UnitTest Sources
     target_sources(Luau.UnitTest PRIVATE
+        tests/AstQueryDsl.cpp
         tests/AstQueryDsl.h
+        tests/ClassFixture.cpp
+        tests/ClassFixture.h
+        tests/ConstraintGraphBuilderFixture.cpp
         tests/ConstraintGraphBuilderFixture.h
+        tests/Fixture.cpp
         tests/Fixture.h
         tests/IostreamOptional.h
         tests/ScopedFlags.h
-        tests/AstQueryDsl.cpp
-        tests/ConstraintGraphBuilderFixture.cpp
-        tests/Fixture.cpp
-        tests/AssemblyBuilderA64.test.cpp
         tests/AssemblyBuilderX64.test.cpp
         tests/AstJsonEncoder.test.cpp
         tests/AstQuery.test.cpp
@@ -318,7 +319,7 @@ if(TARGET Luau.UnitTest)
         tests/Config.test.cpp
         tests/ConstraintSolver.test.cpp
         tests/CostModel.test.cpp
-        tests/DataFlowGraphBuilder.test.cpp
+        tests/DataFlowGraph.test.cpp
         tests/Error.test.cpp
         tests/Frontend.test.cpp
         tests/JsonEmitter.test.cpp

VM/src/loslib.cpp

@@ -22,6 +22,21 @@ static time_t timegm(struct tm* timep)
 {
     return _mkgmtime(timep);
 }
+#elif defined(__FreeBSD__)
+static tm* gmtime_r(const time_t* timep, tm* result)
+{
+    return gmtime_s(timep, result) == 0 ? result : NULL;
+}
+
+static tm* localtime_r(const time_t* timep, tm* result)
+{
+    return localtime_s(timep, result) == 0 ? result : NULL;
+}
+
+static time_t timegm(struct tm* timep)
+{
+    return mktime(timep);
+}
 #endif
 
 static int os_clock(lua_State* L)

tests/AstQuery.test.cpp

@@ -91,8 +91,6 @@ TEST_CASE_FIXTURE(DocumentationSymbolFixture, "class_method")
 
 TEST_CASE_FIXTURE(DocumentationSymbolFixture, "overloaded_class_method")
 {
-    ScopedFastFlag luauCheckOverloadedDocSymbol{"LuauCheckOverloadedDocSymbol", true};
-
     loadDefinition(R"(
         declare class Foo
             function bar(self, x: string): number
@@ -127,8 +125,6 @@ TEST_CASE_FIXTURE(DocumentationSymbolFixture, "table_function_prop")
 
 TEST_CASE_FIXTURE(DocumentationSymbolFixture, "table_overloaded_function_prop")
 {
-    ScopedFastFlag luauCheckOverloadedDocSymbol{"LuauCheckOverloadedDocSymbol", true};
-
     loadDefinition(R"(
         declare Foo: {
             new: ((number) -> string) & ((string) -> number)

tests/ClassFixture.cpp

@@ -0,0 +1,113 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#include "ClassFixture.h"
+
+#include "Luau/BuiltinDefinitions.h"
+
+using std::nullopt;
+
+namespace Luau
+{
+
+ClassFixture::ClassFixture()
+{
+    TypeArena& arena = typeChecker.globalTypes;
+    TypeId numberType = typeChecker.numberType;
+
+    unfreeze(arena);
+
+    TypeId baseClassInstanceType = arena.addType(ClassTypeVar{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(baseClassInstanceType)->props = {
+        {"BaseMethod", {makeFunction(arena, baseClassInstanceType, {numberType}, {})}},
+        {"BaseField", {numberType}},
+    };
+
+    TypeId baseClassType = arena.addType(ClassTypeVar{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(baseClassType)->props = {
+        {"StaticMethod", {makeFunction(arena, nullopt, {}, {numberType})}},
+        {"Clone", {makeFunction(arena, nullopt, {baseClassInstanceType}, {baseClassInstanceType})}},
+        {"New", {makeFunction(arena, nullopt, {}, {baseClassInstanceType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["BaseClass"] = TypeFun{{}, baseClassInstanceType};
+    addGlobalBinding(frontend, "BaseClass", baseClassType, "@test");
+
+    TypeId childClassInstanceType = arena.addType(ClassTypeVar{"ChildClass", {}, baseClassInstanceType, nullopt, {}, {}, "Test"});
+
+    getMutable<ClassTypeVar>(childClassInstanceType)->props = {
+        {"Method", {makeFunction(arena, childClassInstanceType, {}, {typeChecker.stringType})}},
+    };
+
+    TypeId childClassType = arena.addType(ClassTypeVar{"ChildClass", {}, baseClassType, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(childClassType)->props = {
+        {"New", {makeFunction(arena, nullopt, {}, {childClassInstanceType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["ChildClass"] = TypeFun{{}, childClassInstanceType};
+    addGlobalBinding(frontend, "ChildClass", childClassType, "@test");
+
+    TypeId grandChildInstanceType = arena.addType(ClassTypeVar{"GrandChild", {}, childClassInstanceType, nullopt, {}, {}, "Test"});
+
+    getMutable<ClassTypeVar>(grandChildInstanceType)->props = {
+        {"Method", {makeFunction(arena, grandChildInstanceType, {}, {typeChecker.stringType})}},
+    };
+
+    TypeId grandChildType = arena.addType(ClassTypeVar{"GrandChild", {}, baseClassType, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(grandChildType)->props = {
+        {"New", {makeFunction(arena, nullopt, {}, {grandChildInstanceType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["GrandChild"] = TypeFun{{}, grandChildInstanceType};
+    addGlobalBinding(frontend, "GrandChild", childClassType, "@test");
+
+    TypeId anotherChildInstanceType = arena.addType(ClassTypeVar{"AnotherChild", {}, baseClassInstanceType, nullopt, {}, {}, "Test"});
+
+    getMutable<ClassTypeVar>(anotherChildInstanceType)->props = {
+        {"Method", {makeFunction(arena, anotherChildInstanceType, {}, {typeChecker.stringType})}},
+    };
+
+    TypeId anotherChildType = arena.addType(ClassTypeVar{"AnotherChild", {}, baseClassType, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(anotherChildType)->props = {
+        {"New", {makeFunction(arena, nullopt, {}, {anotherChildInstanceType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["AnotherChild"] = TypeFun{{}, anotherChildInstanceType};
+    addGlobalBinding(frontend, "AnotherChild", childClassType, "@test");
+
+    TypeId unrelatedClassInstanceType = arena.addType(ClassTypeVar{"UnrelatedClass", {}, nullopt, nullopt, {}, {}, "Test"});
+
+    TypeId unrelatedClassType = arena.addType(ClassTypeVar{"UnrelatedClass", {}, nullopt, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(unrelatedClassType)->props = {
+        {"New", {makeFunction(arena, nullopt, {}, {unrelatedClassInstanceType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["UnrelatedClass"] = TypeFun{{}, unrelatedClassInstanceType};
+    addGlobalBinding(frontend, "UnrelatedClass", unrelatedClassType, "@test");
+
+    TypeId vector2MetaType = arena.addType(TableTypeVar{});
+
+    TypeId vector2InstanceType = arena.addType(ClassTypeVar{"Vector2", {}, nullopt, vector2MetaType, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(vector2InstanceType)->props = {
+        {"X", {numberType}},
+        {"Y", {numberType}},
+    };
+
+    TypeId vector2Type = arena.addType(ClassTypeVar{"Vector2", {}, nullopt, nullopt, {}, {}, "Test"});
+    getMutable<ClassTypeVar>(vector2Type)->props = {
+        {"New", {makeFunction(arena, nullopt, {numberType, numberType}, {vector2InstanceType})}},
+    };
+    getMutable<TableTypeVar>(vector2MetaType)->props = {
+        {"__add", {makeFunction(arena, nullopt, {vector2InstanceType, vector2InstanceType}, {vector2InstanceType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["Vector2"] = TypeFun{{}, vector2InstanceType};
+    addGlobalBinding(frontend, "Vector2", vector2Type, "@test");
+
+    TypeId callableClassMetaType = arena.addType(TableTypeVar{});
+    TypeId callableClassType = arena.addType(ClassTypeVar{"CallableClass", {}, nullopt, callableClassMetaType, {}, {}, "Test"});
+    getMutable<TableTypeVar>(callableClassMetaType)->props = {
+        {"__call", {makeFunction(arena, nullopt, {callableClassType, typeChecker.stringType}, {typeChecker.numberType})}},
+    };
+    typeChecker.globalScope->exportedTypeBindings["CallableClass"] = TypeFun{{}, callableClassType};
+
+    for (const auto& [name, tf] : typeChecker.globalScope->exportedTypeBindings)
+        persist(tf.type);
+
+    freeze(arena);
+}
+
+} // namespace Luau

tests/ClassFixture.h

@@ -0,0 +1,13 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#include "Fixture.h"
+
+namespace Luau
+{
+
+struct ClassFixture : BuiltinsFixture
+{
+    ClassFixture();
+};
+
+} // namespace Luau

tests/Compiler.test.cpp

@@ -6751,6 +6751,21 @@ ADD R4 R0 R1
 MOVE R0 R2
 MOVE R1 R3
 RETURN R0 0
+)");
+
+    ScopedFastFlag luauMultiAssignmentConflictFix{"LuauMultiAssignmentConflictFix", true};
+
+    // because we perform assignments to complex l-values after assignments to locals, we make sure register conflicts are tracked accordingly
+    CHECK_EQ("\n" + compileFunction0(R"(
+        local a, b = ...
+        a[1], b = b, b + 1
+    )"),
+        R"(
+GETVARARGS R0 2
+ADDK R2 R1 K0
+SETTABLEN R1 R0 1
+MOVE R1 R2
+RETURN R0 0
 )");
 }
 

tests/DataFlowGraph.test.cpp

@@ -1,5 +1,5 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
-#include "Luau/DataFlowGraphBuilder.h"
+#include "Luau/DataFlowGraph.h"
 #include "Luau/Error.h"
 #include "Luau/Parser.h"
 

tests/Module.test.cpp

@@ -11,7 +11,6 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
-LUAU_FASTFLAG(LuauIceExceptionInheritanceChange);
 
 TEST_SUITE_BEGIN("ModuleTests");
 
@@ -279,14 +278,7 @@ TEST_CASE_FIXTURE(Fixture, "clone_recursion_limit")
     TypeArena dest;
     CloneState cloneState;
 
-    if (FFlag::LuauIceExceptionInheritanceChange)
+    CHECK_THROWS_AS(clone(table, dest, cloneState), RecursionLimitException);
-    {
-        CHECK_THROWS_AS(clone(table, dest, cloneState), RecursionLimitException);
-    }
-    else
-    {
-        CHECK_THROWS_AS(clone(table, dest, cloneState), RecursionLimitException_DEPRECATED);
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "any_persistance_does_not_leak")

tests/NotNull.test.cpp

@@ -9,6 +9,8 @@
 
 using Luau::NotNull;
 
+static_assert(!std::is_convertible<NotNull<int>, bool>::value, "NotNull<T> ought not to be convertible into bool");
+
 namespace
 {
 

tests/Parser.test.cpp

@@ -2723,8 +2723,6 @@ TEST_CASE_FIXTURE(Fixture, "error_message_for_using_function_as_type_annotation"
 
 TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the_end_of_a_function_argument_list")
 {
-    ScopedFastFlag sff{"LuauCommaParenWarnings", true};
-
     ParseResult result = tryParse(R"(
         foo(a, b, c,)
     )");
@@ -2737,8 +2735,6 @@ TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the
 
 TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the_end_of_a_function_parameter_list")
 {
-    ScopedFastFlag sff{"LuauCommaParenWarnings", true};
-
     ParseResult result = tryParse(R"(
         export type VisitFn = (
             any,
@@ -2754,8 +2750,6 @@ TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the
 
 TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the_end_of_a_generic_parameter_list")
 {
-    ScopedFastFlag sff{"LuauCommaParenWarnings", true};
-
     ParseResult result = tryParse(R"(
         export type VisitFn = <A, B,>(a: A, b: B) -> ()
     )");
@@ -2778,8 +2772,6 @@ TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the
 
 TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_no_comma_between_table_members")
 {
-    ScopedFastFlag luauTableConstructorRecovery{"LuauTableConstructorRecovery", true};
-
     ParseResult result = tryParse(R"(
         local t = {
             first = 1

tests/ToString.test.cpp

@@ -10,7 +10,6 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauRecursiveTypeParameterRestriction);
-LUAU_FASTFLAG(LuauFunctionReturnStringificationFixup);
 
 TEST_SUITE_BEGIN("ToString");
 
@@ -83,7 +82,7 @@ TEST_CASE_FIXTURE(Fixture, "table_respects_use_line_break")
 
     ToStringOptions opts;
     opts.useLineBreaks = true;
-    opts.indent = true;
+    opts.DEPRECATED_indent = true;
 
     //clang-format off
     CHECK_EQ("{|\n"
@@ -568,10 +567,7 @@ TEST_CASE_FIXTURE(Fixture, "no_parentheses_around_return_type_if_pack_has_an_emp
 
     TypeId functionType = arena.addType(FunctionTypeVar{argList, emptyTail});
 
-    if (FFlag::LuauFunctionReturnStringificationFixup)
+    CHECK("(string) -> string" == toString(functionType));
-        CHECK("(string) -> string" == toString(functionType));
-    else
-        CHECK("(string) -> (string)" == toString(functionType));
 }
 
 TEST_CASE_FIXTURE(Fixture, "no_parentheses_around_cyclic_function_type_in_union")

tests/TypeInfer.aliases.test.cpp

@@ -9,6 +9,7 @@ using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 LUAU_FASTFLAG(LuauNoMoreGlobalSingletonTypes)
+LUAU_FASTFLAG(LuauTypeMismatchInvarianceInError)
 
 TEST_SUITE_BEGIN("TypeAliases");
 
@@ -199,9 +200,15 @@ TEST_CASE_FIXTURE(Fixture, "generic_aliases")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    const char* expectedError = "Type '{ v: string }' could not be converted into 'T<number>'\n"
+    const char* expectedError;
-                                "caused by:\n"
+    if (FFlag::LuauTypeMismatchInvarianceInError)
-                                "  Property 'v' is not compatible. Type 'string' could not be converted into 'number'";
+        expectedError = "Type '{ v: string }' could not be converted into 'T<number>'\n"
+                        "caused by:\n"
+                        "  Property 'v' is not compatible. Type 'string' could not be converted into 'number' in an invariant context";
+    else
+        expectedError = "Type '{ v: string }' could not be converted into 'T<number>'\n"
+                        "caused by:\n"
+                        "  Property 'v' is not compatible. Type 'string' could not be converted into 'number'";
 
     CHECK(result.errors[0].location == Location{{4, 31}, {4, 44}});
     CHECK(toString(result.errors[0]) == expectedError);
@@ -220,11 +227,19 @@ TEST_CASE_FIXTURE(Fixture, "dependent_generic_aliases")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    const char* expectedError = "Type '{ t: { v: string } }' could not be converted into 'U<number>'\n"
+    const char* expectedError;
-                                "caused by:\n"
+    if (FFlag::LuauTypeMismatchInvarianceInError)
-                                "  Property 't' is not compatible. Type '{ v: string }' could not be converted into 'T<number>'\n"
+        expectedError = "Type '{ t: { v: string } }' could not be converted into 'U<number>'\n"
-                                "caused by:\n"
+                        "caused by:\n"
-                                "  Property 'v' is not compatible. Type 'string' could not be converted into 'number'";
+                        "  Property 't' is not compatible. Type '{ v: string }' could not be converted into 'T<number>'\n"
+                        "caused by:\n"
+                        "  Property 'v' is not compatible. Type 'string' could not be converted into 'number' in an invariant context";
+    else
+        expectedError = "Type '{ t: { v: string } }' could not be converted into 'U<number>'\n"
+                        "caused by:\n"
+                        "  Property 't' is not compatible. Type '{ v: string }' could not be converted into 'T<number>'\n"
+                        "caused by:\n"
+                        "  Property 'v' is not compatible. Type 'string' could not be converted into 'number'";
 
     CHECK(result.errors[0].location == Location{{4, 31}, {4, 52}});
     CHECK(toString(result.errors[0]) == expectedError);

tests/TypeInfer.annotations.test.cpp

@@ -7,8 +7,6 @@
 
 #include "doctest.h"
 
-LUAU_FASTFLAG(LuauIceExceptionInheritanceChange)
-
 using namespace Luau;
 
 TEST_SUITE_BEGIN("AnnotationTests");

tests/TypeInfer.builtins.test.cpp

@@ -684,20 +684,10 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    if (FFlag::DebugLuauDeferredConstraintResolution)
+    CHECK_EQ("any", toString(requireType("foo")));
-    {
+    CHECK_EQ("any", toString(requireType("bar")));
-        CHECK_EQ("string", toString(requireType("foo")));
+    CHECK_EQ("any", toString(requireType("baz")));
-        CHECK_EQ("*error-type*", toString(requireType("bar")));
+    CHECK_EQ("any", toString(requireType("quux")));
-        CHECK_EQ("*error-type*", toString(requireType("baz")));
-        CHECK_EQ("*error-type*", toString(requireType("quux")));
-    }
-    else
-    {
-        CHECK_EQ("any", toString(requireType("foo")));
-        CHECK_EQ("any", toString(requireType("bar")));
-        CHECK_EQ("any", toString(requireType("baz")));
-        CHECK_EQ("any", toString(requireType("quux")));
-    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail_and_string_head")
@@ -714,19 +704,13 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail_and_strin
     LUAU_REQUIRE_NO_ERRORS(result);
 
     if (FFlag::DebugLuauDeferredConstraintResolution)
-    {
         CHECK_EQ("string", toString(requireType("foo")));
-        CHECK_EQ("string", toString(requireType("bar")));
-        CHECK_EQ("*error-type*", toString(requireType("baz")));
-        CHECK_EQ("*error-type*", toString(requireType("quux")));
-    }
     else
-    {
         CHECK_EQ("any", toString(requireType("foo")));
-        CHECK_EQ("any", toString(requireType("bar")));
+
-        CHECK_EQ("any", toString(requireType("baz")));
+    CHECK_EQ("any", toString(requireType("bar")));
-        CHECK_EQ("any", toString(requireType("quux")));
+    CHECK_EQ("any", toString(requireType("baz")));
-    }
+    CHECK_EQ("any", toString(requireType("quux")));
 }
 
 TEST_CASE_FIXTURE(Fixture, "string_format_as_method")

tests/TypeInfer.classes.test.cpp

@@ -1,109 +1,18 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/BuiltinDefinitions.h"
+#include "Luau/Common.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
 
 #include "Fixture.h"
+#include "ClassFixture.h"
 
 #include "doctest.h"
 
 using namespace Luau;
 using std::nullopt;
 
-struct ClassFixture : BuiltinsFixture
+LUAU_FASTFLAG(LuauTypeMismatchInvarianceInError);
-{
-    ClassFixture()
-    {
-        TypeArena& arena = typeChecker.globalTypes;
-        TypeId numberType = typeChecker.numberType;
-
-        unfreeze(arena);
-
-        TypeId baseClassInstanceType = arena.addType(ClassTypeVar{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(baseClassInstanceType)->props = {
-            {"BaseMethod", {makeFunction(arena, baseClassInstanceType, {numberType}, {})}},
-            {"BaseField", {numberType}},
-        };
-
-        TypeId baseClassType = arena.addType(ClassTypeVar{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(baseClassType)->props = {
-            {"StaticMethod", {makeFunction(arena, nullopt, {}, {numberType})}},
-            {"Clone", {makeFunction(arena, nullopt, {baseClassInstanceType}, {baseClassInstanceType})}},
-            {"New", {makeFunction(arena, nullopt, {}, {baseClassInstanceType})}},
-        };
-        typeChecker.globalScope->exportedTypeBindings["BaseClass"] = TypeFun{{}, baseClassInstanceType};
-        addGlobalBinding(frontend, "BaseClass", baseClassType, "@test");
-
-        TypeId childClassInstanceType = arena.addType(ClassTypeVar{"ChildClass", {}, baseClassInstanceType, nullopt, {}, {}, "Test"});
-
-        getMutable<ClassTypeVar>(childClassInstanceType)->props = {
-            {"Method", {makeFunction(arena, childClassInstanceType, {}, {typeChecker.stringType})}},
-        };
-
-        TypeId childClassType = arena.addType(ClassTypeVar{"ChildClass", {}, baseClassType, nullopt, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(childClassType)->props = {
-            {"New", {makeFunction(arena, nullopt, {}, {childClassInstanceType})}},
-        };
-        typeChecker.globalScope->exportedTypeBindings["ChildClass"] = TypeFun{{}, childClassInstanceType};
-        addGlobalBinding(frontend, "ChildClass", childClassType, "@test");
-
-        TypeId grandChildInstanceType = arena.addType(ClassTypeVar{"GrandChild", {}, childClassInstanceType, nullopt, {}, {}, "Test"});
-
-        getMutable<ClassTypeVar>(grandChildInstanceType)->props = {
-            {"Method", {makeFunction(arena, grandChildInstanceType, {}, {typeChecker.stringType})}},
-        };
-
-        TypeId grandChildType = arena.addType(ClassTypeVar{"GrandChild", {}, baseClassType, nullopt, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(grandChildType)->props = {
-            {"New", {makeFunction(arena, nullopt, {}, {grandChildInstanceType})}},
-        };
-        typeChecker.globalScope->exportedTypeBindings["GrandChild"] = TypeFun{{}, grandChildInstanceType};
-        addGlobalBinding(frontend, "GrandChild", childClassType, "@test");
-
-        TypeId anotherChildInstanceType = arena.addType(ClassTypeVar{"AnotherChild", {}, baseClassInstanceType, nullopt, {}, {}, "Test"});
-
-        getMutable<ClassTypeVar>(anotherChildInstanceType)->props = {
-            {"Method", {makeFunction(arena, anotherChildInstanceType, {}, {typeChecker.stringType})}},
-        };
-
-        TypeId anotherChildType = arena.addType(ClassTypeVar{"AnotherChild", {}, baseClassType, nullopt, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(anotherChildType)->props = {
-            {"New", {makeFunction(arena, nullopt, {}, {anotherChildInstanceType})}},
-        };
-        typeChecker.globalScope->exportedTypeBindings["AnotherChild"] = TypeFun{{}, anotherChildInstanceType};
-        addGlobalBinding(frontend, "AnotherChild", childClassType, "@test");
-
-        TypeId vector2MetaType = arena.addType(TableTypeVar{});
-
-        TypeId vector2InstanceType = arena.addType(ClassTypeVar{"Vector2", {}, nullopt, vector2MetaType, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(vector2InstanceType)->props = {
-            {"X", {numberType}},
-            {"Y", {numberType}},
-        };
-
-        TypeId vector2Type = arena.addType(ClassTypeVar{"Vector2", {}, nullopt, nullopt, {}, {}, "Test"});
-        getMutable<ClassTypeVar>(vector2Type)->props = {
-            {"New", {makeFunction(arena, nullopt, {numberType, numberType}, {vector2InstanceType})}},
-        };
-        getMutable<TableTypeVar>(vector2MetaType)->props = {
-            {"__add", {makeFunction(arena, nullopt, {vector2InstanceType, vector2InstanceType}, {vector2InstanceType})}},
-        };
-        typeChecker.globalScope->exportedTypeBindings["Vector2"] = TypeFun{{}, vector2InstanceType};
-        addGlobalBinding(frontend, "Vector2", vector2Type, "@test");
-
-        TypeId callableClassMetaType = arena.addType(TableTypeVar{});
-        TypeId callableClassType = arena.addType(ClassTypeVar{"CallableClass", {}, nullopt, callableClassMetaType, {}, {}, "Test"});
-        getMutable<TableTypeVar>(callableClassMetaType)->props = {
-            {"__call", {makeFunction(arena, nullopt, {callableClassType, typeChecker.stringType}, {typeChecker.numberType})}},
-        };
-        typeChecker.globalScope->exportedTypeBindings["CallableClass"] = TypeFun{{}, callableClassType};
-
-        for (const auto& [name, tf] : typeChecker.globalScope->exportedTypeBindings)
-            persist(tf.type);
-
-        freeze(arena);
-    }
-};
 
 TEST_SUITE_BEGIN("TypeInferClasses");
 
@@ -521,6 +430,56 @@ TEST_CASE_FIXTURE(ClassFixture, "unions_of_intersections_of_classes")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(ClassFixture, "index_instance_property")
+{
+    ScopedFastFlag luauAllowIndexClassParameters{"LuauAllowIndexClassParameters", true};
+
+    CheckResult result = check(R"(
+        local function execute(object: BaseClass, name: string)
+            print(object[name])
+        end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ("Attempting a dynamic property access on type 'BaseClass' is unsafe and may cause exceptions at runtime", toString(result.errors[0]));
+}
+
+TEST_CASE_FIXTURE(ClassFixture, "index_instance_property_nonstrict")
+{
+    ScopedFastFlag luauAllowIndexClassParameters{"LuauAllowIndexClassParameters", true};
+
+    CheckResult result = check(R"(
+        --!nonstrict
+
+        local function execute(object: BaseClass, name: string)
+            print(object[name])
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(ClassFixture, "type_mismatch_invariance_required_for_error")
+{
+    CheckResult result = check(R"(
+type A = { x: ChildClass }
+type B = { x: BaseClass }
+
+local a: A
+local b: B = a
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+caused by:
+  Property 'x' is not compatible. Type 'ChildClass' could not be converted into 'BaseClass' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+caused by:
+  Property 'x' is not compatible. Type 'ChildClass' could not be converted into 'BaseClass')");
+}
+
 TEST_CASE_FIXTURE(ClassFixture, "callable_classes")
 {
     ScopedFastFlag luauCallableClasses{"LuauCallableClasses", true};

tests/TypeInfer.definitions.test.cpp

@@ -311,8 +311,6 @@ TEST_CASE_FIXTURE(Fixture, "definitions_documentation_symbols")
 
 TEST_CASE_FIXTURE(Fixture, "definitions_symbols_are_generated_for_recursively_referenced_types")
 {
-    ScopedFastFlag LuauPersistTypesAfterGeneratingDocSyms("LuauPersistTypesAfterGeneratingDocSyms", true);
-
     loadDefinition(R"(
         declare class MyClass
             function myMethod(self)

tests/TypeInfer.functions.test.cpp

@@ -230,8 +230,6 @@ TEST_CASE_FIXTURE(Fixture, "too_many_arguments")
 
 TEST_CASE_FIXTURE(Fixture, "too_many_arguments_error_location")
 {
-    ScopedFastFlag sff{"LuauArgMismatchReportFunctionLocation", true};
-
     CheckResult result = check(R"(
         --!strict
 
@@ -507,7 +505,9 @@ TEST_CASE_FIXTURE(Fixture, "complicated_return_types_require_an_explicit_annotat
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    const FunctionTypeVar* functionType = get<FunctionTypeVar>(requireType("most_of_the_natural_numbers"));
+    TypeId ty = requireType("most_of_the_natural_numbers");
+    const FunctionTypeVar* functionType = get<FunctionTypeVar>(ty);
+    REQUIRE_MESSAGE(functionType, "Expected function but got " << toString(ty));
 
     std::optional<TypeId> retType = first(functionType->retTypes);
     REQUIRE(retType);
@@ -1830,4 +1830,18 @@ TEST_CASE_FIXTURE(Fixture, "other_things_are_not_related_to_function")
     CHECK(5 == result.errors[3].location.begin.line);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_must_follow_in_overload_resolution")
+{
+    ScopedFastFlag luauTypeInferMissingFollows{"LuauTypeInferMissingFollows", true};
+
+    CheckResult result = check(R"(
+for _ in function<t0>():(t0)&((()->())&(()->()))
+end do
+_(_(_,_,_),_)
+end
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.generics.test.cpp

@@ -10,6 +10,7 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
+LUAU_FASTFLAG(LuauTypeMismatchInvarianceInError)
 
 using namespace Luau;
 
@@ -717,12 +718,24 @@ y.a.c = y
     )");
 
     LUAU_REQUIRE_ERRORS(result);
-    CHECK_EQ(toString(result.errors[0]),
+    if (FFlag::LuauTypeMismatchInvarianceInError)
-        R"(Type 'y' could not be converted into 'T<string>'
+    {
+        CHECK_EQ(toString(result.errors[0]),
+            R"(Type 'y' could not be converted into 'T<string>'
+caused by:
+  Property 'a' is not compatible. Type '{ c: T<string>?, d: number }' could not be converted into 'U<string>'
+caused by:
+  Property 'd' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    }
+    else
+    {
+        CHECK_EQ(toString(result.errors[0]),
+            R"(Type 'y' could not be converted into 'T<string>'
 caused by:
   Property 'a' is not compatible. Type '{ c: T<string>?, d: number }' could not be converted into 'U<string>'
 caused by:
   Property 'd' is not compatible. Type 'number' could not be converted into 'string')");
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "generic_type_pack_unification1")
@@ -1249,4 +1262,21 @@ instantiate(function(x: string) return "foo" end)
     CHECK_EQ("<a>(string) -> string", toString(tm1->givenType));
 }
 
+TEST_CASE_FIXTURE(Fixture, "bidirectional_checking_and_generalization_play_nice")
+{
+    CheckResult result = check(R"(
+        local foo = function(a)
+            return a()
+        end
+
+        local a = foo(function() return 1 end)
+        local b = foo(function() return "bar" end)
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK("number" == toString(requireType("a")));
+    CHECK("string" == toString(requireType("b")));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.intersectionTypes.test.cpp

@@ -185,7 +185,15 @@ TEST_CASE_FIXTURE(Fixture, "index_on_an_intersection_type_works_at_arbitrary_dep
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
-    CHECK_EQ("string & string", toString(requireType("r")));
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK_EQ("string", toString(requireType("r")));
+    }
+    else
+    {
+        CHECK_EQ("string & string", toString(requireType("r")));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "index_on_an_intersection_type_with_mixed_types")
@@ -199,7 +207,7 @@ TEST_CASE_FIXTURE(Fixture, "index_on_an_intersection_type_with_mixed_types")
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
-    CHECK_EQ("number & string", toString(requireType("r"))); // TODO(amccord): This should be an error.
+    CHECK_EQ("number & string", toString(requireType("r")));
 }
 
 TEST_CASE_FIXTURE(Fixture, "index_on_an_intersection_type_with_one_part_missing_the_property")
@@ -525,18 +533,16 @@ TEST_CASE_FIXTURE(Fixture, "intersection_of_tables_with_never_properties")
     ScopedFastFlag sffs[]{
         {"LuauSubtypeNormalizer", true},
         {"LuauTypeNormalization2", true},
+        {"LuauUninhabitedSubAnything", true},
     };
 
     CheckResult result = check(R"(
-        local x : { p : number?, q : never } & { p : never, q : string? }
+        local x : { p : number?, q : never } & { p : never, q : string? } -- OK
         local y : { p : never, q : never } = x -- OK
         local z : never = x -- OK
     )");
 
-    // TODO: this should not produce type errors, since never <: { p : never }
+    LUAU_REQUIRE_NO_ERRORS(result);
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK_EQ(toString(result.errors[0]), "Type '{| p: never, q: string? |} & {| p: number?, q: never |}' could not be converted into 'never'; none "
-                                         "of the intersection parts are compatible");
 }
 
 TEST_CASE_FIXTURE(Fixture, "overloaded_functions_returning_intersections")
@@ -848,7 +854,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatables_with_properties")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
-TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatable_with table")
+TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatable_with_table")
 {
     ScopedFastFlag sffs[]{
         {"LuauSubtypeNormalizer", true},
@@ -902,4 +908,37 @@ TEST_CASE_FIXTURE(Fixture, "CLI-44817")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "less_greedy_unification_with_intersection_types")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local function f(t): { x: number } & { x: string }
+            local x = t.x
+            return t
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("({| x: number |} & {| x: string |}) -> {| x: number |} & {| x: string |}", toString(requireType("f")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "less_greedy_unification_with_intersection_types_2")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local function f(t: { x: number } & { x: string })
+            return t.x
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("({| x: number |} & {| x: string |}) -> number & string", toString(requireType("f")));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.modules.test.cpp

@@ -11,6 +11,7 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
+LUAU_FASTFLAG(LuauTypeMismatchInvarianceInError)
 
 using namespace Luau;
 
@@ -408,7 +409,12 @@ local b: B.T = a
     CheckResult result = frontend.check("game/C");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'
+caused by:
+  Property 'x' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'
 caused by:
   Property 'x' is not compatible. Type 'number' could not be converted into 'string')");
 }
@@ -442,7 +448,12 @@ local b: B.T = a
     CheckResult result = frontend.check("game/D");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'
+caused by:
+  Property 'x' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'
 caused by:
   Property 'x' is not compatible. Type 'number' could not be converted into 'string')");
 }
@@ -462,4 +473,15 @@ return l0
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_anyify_variadic_return_must_follow")
+{
+    ScopedFastFlag luauTypeInferMissingFollows{"LuauTypeInferMissingFollows", true};
+
+    CheckResult result = check(R"(
+return unpack(l0[_])
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.operators.test.cpp

@@ -8,6 +8,7 @@
 #include "Luau/VisitTypeVar.h"
 
 #include "Fixture.h"
+#include "ClassFixture.h"
 
 #include "doctest.h"
 
@@ -817,6 +818,21 @@ TEST_CASE_FIXTURE(Fixture, "operator_eq_operands_are_not_subtypes_of_each_other_
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "operator_eq_completely_incompatible")
+{
+    ScopedFastFlag sff{"LuauIntersectionTestForEquality", true};
+
+    CheckResult result = check(R"(
+        local a: string | number = "hi"
+        local b: {x: string}? = {x = "bye"}
+
+        local r1 = a == b
+        local r2 = b == a
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
+}
+
 TEST_CASE_FIXTURE(Fixture, "refine_and_or")
 {
     CheckResult result = check(R"(
@@ -916,6 +932,31 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "expected_types_through_binary_or")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(ClassFixture, "unrelated_classes_cannot_be_compared")
+{
+    ScopedFastFlag sff{"LuauIntersectionTestForEquality", true};
+
+    CheckResult result = check(R"(
+        local a = BaseClass.New()
+        local b = UnrelatedClass.New()
+
+        local c = a == b
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "unrelated_primitives_cannot_be_compared")
+{
+    ScopedFastFlag sff{"LuauIntersectionTestForEquality", true};
+
+    CheckResult result = check(R"(
+        local c = 5 == true
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "mm_ops_must_return_a_value")
 {
     if (!FFlag::DebugLuauDeferredConstraintResolution)

tests/TypeInfer.provisional.test.cpp

@@ -170,24 +170,12 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "error_on_eq_metamethod_returning_a_type_othe
     CHECK_EQ("Metamethod '__eq' must return type 'boolean'", ge->message);
 }
 
-// Requires success typing to confidently determine that this expression has no overlap.
-TEST_CASE_FIXTURE(Fixture, "operator_eq_completely_incompatible")
-{
-    CheckResult result = check(R"(
-        local a: string | number = "hi"
-        local b: {x: string}? = {x = "bye"}
-
-        local r1 = a == b
-        local r2 = b == a
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
 // Belongs in TypeInfer.refinements.test.cpp.
-// We'll need to not only report an error on `a == b`, but also to refine both operands as `never` in the `==` branch.
+// We need refine both operands as `never` in the `==` branch.
 TEST_CASE_FIXTURE(Fixture, "lvalue_equals_another_lvalue_with_no_overlap")
 {
+    ScopedFastFlag sff{"LuauIntersectionTestForEquality", true};
+
     CheckResult result = check(R"(
         local function f(a: string, b: boolean?)
             if a == b then
@@ -198,7 +186,7 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_equals_another_lvalue_with_no_overlap")
         end
     )");
 
-    LUAU_REQUIRE_NO_ERRORS(result);
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
 
     CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "string");   // a == b
     CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "boolean?"); // a == b

tests/TypeInfer.refinements.test.cpp

@@ -8,6 +8,7 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAG(LuauTypeMismatchInvarianceInError)
 
 using namespace Luau;
 
@@ -35,6 +36,27 @@ std::optional<WithPredicate<TypePackId>> magicFunctionInstanceIsA(
     return WithPredicate<TypePackId>{booleanPack, {IsAPredicate{std::move(*lvalue), expr.location, tfun->type}}};
 }
 
+std::vector<ConnectiveId> dcrMagicRefinementInstanceIsA(MagicRefinementContext ctx)
+{
+    if (ctx.callSite->args.size != 1)
+        return {};
+
+    auto index = ctx.callSite->func->as<Luau::AstExprIndexName>();
+    auto str = ctx.callSite->args.data[0]->as<Luau::AstExprConstantString>();
+    if (!index || !str)
+        return {};
+
+    std::optional<DefId> def = ctx.dfg->getDef(index->expr);
+    if (!def)
+        return {};
+
+    std::optional<TypeFun> tfun = ctx.scope->lookupType(std::string(str->value.data, str->value.size));
+    if (!tfun)
+        return {};
+
+    return {ctx.connectiveArena->proposition(*def, tfun->type)};
+}
+
 struct RefinementClassFixture : BuiltinsFixture
 {
     RefinementClassFixture()
@@ -56,6 +78,7 @@ struct RefinementClassFixture : BuiltinsFixture
         TypePackId isARets = arena.addTypePack({typeChecker.booleanType});
         TypeId isA = arena.addType(FunctionTypeVar{isAParams, isARets});
         getMutable<FunctionTypeVar>(isA)->magicFunction = magicFunctionInstanceIsA;
+        getMutable<FunctionTypeVar>(isA)->dcrMagicRefinement = dcrMagicRefinementInstanceIsA;
 
         getMutable<ClassTypeVar>(inst)->props = {
             {"Name", Property{typeChecker.stringType}},
@@ -397,13 +420,21 @@ TEST_CASE_FIXTURE(Fixture, "truthy_constraint_on_properties")
         local t: {x: number?} = {x = 1}
 
         if t.x then
-            local foo: number = t.x
+            local t2 = t
+            local foo = t.x
         end
 
         local bar = t.x
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK("{| x: number? |} & {| x: ~(false?) |}" == toString(requireTypeAtPosition({4, 23})));
+        CHECK("(number?) & ~(false?)" == toString(requireTypeAtPosition({5, 26})));
+    }
+
     CHECK_EQ("number?", toString(requireType("bar")));
 }
 
@@ -442,12 +473,24 @@ TEST_CASE_FIXTURE(Fixture, "assign_table_with_refined_property_with_a_similar_ty
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK_EQ(R"(Type '{| x: number? |}' could not be converted into '{| x: number |}'
+
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+    {
+        CHECK_EQ(R"(Type '{| x: number? |}' could not be converted into '{| x: number |}'
+caused by:
+  Property 'x' is not compatible. Type 'number?' could not be converted into 'number' in an invariant context)",
+            toString(result.errors[0]));
+    }
+    else
+    {
+        CHECK_EQ(R"(Type '{| x: number? |}' could not be converted into '{| x: number |}'
 caused by:
   Property 'x' is not compatible. Type 'number?' could not be converted into 'number')",
-        toString(result.errors[0]));
+            toString(result.errors[0]));
+    }
 }
 
+
 TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_another_lvalue")
 {
     CheckResult result = check(R"(
@@ -464,8 +507,8 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_another_lvalue")
 
     if (FFlag::DebugLuauDeferredConstraintResolution)
     {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "((number | string)?) & (boolean?)"); // a == b
+        CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "((number | string)?) & unknown"); // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "((number | string)?) & (boolean?)"); // a == b
+        CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "(boolean?) & unknown");           // a == b
 
         CHECK_EQ(toString(requireTypeAtPosition({5, 33})), "((number | string)?) & unknown"); // a ~= b
         CHECK_EQ(toString(requireTypeAtPosition({5, 36})), "(boolean?) & unknown");           // a ~= b
@@ -496,7 +539,7 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_a_term")
 
     if (FFlag::DebugLuauDeferredConstraintResolution)
     {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "((number | string)?) & number");  // a == 1
+        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "((number | string)?) & unknown"); // a == 1
         CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "((number | string)?) & unknown"); // a ~= 1
     }
     else
@@ -548,8 +591,8 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_not_nil")
 
     if (FFlag::DebugLuauDeferredConstraintResolution)
     {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "((number | string)?) & ~nil"); // a ~= nil
+        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "((number | string)?) & ~nil");    // a ~= nil
-        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "((number | string)?) & nil");  // a == nil
+        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "((number | string)?) & unknown"); // a == nil
     }
     else
     {
@@ -573,8 +616,8 @@ TEST_CASE_FIXTURE(Fixture, "free_type_is_equal_to_an_lvalue")
     if (FFlag::DebugLuauDeferredConstraintResolution)
     {
         ToStringOptions opts;
-        CHECK_EQ(toString(requireTypeAtPosition({3, 33}), opts), "(string?) & a"); // a == b
+        CHECK_EQ(toString(requireTypeAtPosition({3, 33}), opts), "a & unknown");         // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 36}), opts), "(string?) & a"); // a == b
+        CHECK_EQ(toString(requireTypeAtPosition({3, 36}), opts), "(string?) & unknown"); // a == b
     }
     else
     {
@@ -628,8 +671,8 @@ TEST_CASE_FIXTURE(Fixture, "string_not_equal_to_string_or_nil")
         CHECK_EQ(toString(requireTypeAtPosition({6, 29})), "string & unknown");    // a ~= b
         CHECK_EQ(toString(requireTypeAtPosition({6, 32})), "(string?) & unknown"); // a ~= b
 
-        CHECK_EQ(toString(requireTypeAtPosition({8, 29})), "(string?) & string"); // a == b
+        CHECK_EQ(toString(requireTypeAtPosition({8, 29})), "string & unknown");    // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({8, 32})), "(string?) & string"); // a == b
+        CHECK_EQ(toString(requireTypeAtPosition({8, 32})), "(string?) & unknown"); // a == b
     }
     else
     {
@@ -1146,8 +1189,17 @@ TEST_CASE_FIXTURE(Fixture, "discriminate_from_truthiness_of_x")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    CHECK_EQ(R"({| tag: "exists", x: string |})", toString(requireTypeAtPosition({5, 28})));
+    if (FFlag::DebugLuauDeferredConstraintResolution)
-    CHECK_EQ(R"({| tag: "exists", x: string |} | {| tag: "missing", x: nil |})", toString(requireTypeAtPosition({7, 28})));
+    {
+        CHECK_EQ(R"(({| tag: "exists", x: string |} | {| tag: "missing", x: nil |}) & {| x: ~(false?) |})", toString(requireTypeAtPosition({5, 28})));
+        CHECK_EQ(
+            R"(({| tag: "exists", x: string |} | {| tag: "missing", x: nil |}) & {| x: ~~(false?) |})", toString(requireTypeAtPosition({7, 28})));
+    }
+    else
+    {
+        CHECK_EQ(R"({| tag: "exists", x: string |})", toString(requireTypeAtPosition({5, 28})));
+        CHECK_EQ(R"({| tag: "exists", x: string |} | {| tag: "missing", x: nil |})", toString(requireTypeAtPosition({7, 28})));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "discriminate_tag")
@@ -1159,17 +1211,57 @@ TEST_CASE_FIXTURE(Fixture, "discriminate_tag")
 
         local function f(animal: Animal)
             if animal.tag == "Cat" then
-                local cat: Cat = animal
+                local cat = animal
             elseif animal.tag == "Dog" then
-                local dog: Dog = animal
+                local dog = animal
             end
         end
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    CHECK_EQ("Cat", toString(requireTypeAtPosition({7, 33})));
+    if (FFlag::DebugLuauDeferredConstraintResolution)
-    CHECK_EQ("Dog", toString(requireTypeAtPosition({9, 33})));
+    {
+        CHECK_EQ(R"((Cat | Dog) & {| tag: "Cat" |})", toString(requireTypeAtPosition({7, 33})));
+        CHECK_EQ(R"((Cat | Dog) & {| tag: ~"Cat" |} & {| tag: "Dog" |})", toString(requireTypeAtPosition({9, 33})));
+    }
+    else
+    {
+        CHECK_EQ("Cat", toString(requireTypeAtPosition({7, 33})));
+        CHECK_EQ("Dog", toString(requireTypeAtPosition({9, 33})));
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "discriminate_tag_with_implicit_else")
+{
+    ScopedFastFlag sff{"LuauImplicitElseRefinement", true};
+
+    CheckResult result = check(R"(
+        type Cat = {tag: "Cat", name: string, catfood: string}
+        type Dog = {tag: "Dog", name: string, dogfood: string}
+        type Animal = Cat | Dog
+
+        local function f(animal: Animal)
+            if animal.tag == "Cat" then
+                local cat = animal
+            else
+                local dog = animal
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK_EQ(R"((Cat | Dog) & {| tag: "Cat" |})", toString(requireTypeAtPosition({7, 33})));
+        CHECK_EQ(R"((Cat | Dog) & {| tag: ~"Cat" |})", toString(requireTypeAtPosition({9, 33})));
+    }
+    else
+    {
+        CHECK_EQ("Cat", toString(requireTypeAtPosition({7, 33})));
+        CHECK_EQ("Dog", toString(requireTypeAtPosition({9, 33})));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "and_or_peephole_refinement")
@@ -1258,8 +1350,16 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "discriminate_from_isa_of_x")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    CHECK_EQ(R"({| tag: "Part", x: Part |})", toString(requireTypeAtPosition({5, 28})));
+    if (FFlag::DebugLuauDeferredConstraintResolution)
-    CHECK_EQ(R"({| tag: "Folder", x: Folder |})", toString(requireTypeAtPosition({7, 28})));
+    {
+        CHECK_EQ(R"(({| tag: "Folder", x: Folder |} | {| tag: "Part", x: Part |}) & {| x: Part |})", toString(requireTypeAtPosition({5, 28})));
+        CHECK_EQ(R"(({| tag: "Folder", x: Folder |} | {| tag: "Part", x: Part |}) & {| x: ~Part |})", toString(requireTypeAtPosition({7, 28})));
+    }
+    else
+    {
+        CHECK_EQ(R"({| tag: "Part", x: Part |})", toString(requireTypeAtPosition({5, 28})));
+        CHECK_EQ(R"({| tag: "Folder", x: Folder |})", toString(requireTypeAtPosition({7, 28})));
+    }
 }
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "typeguard_cast_free_table_to_vector")
@@ -1399,8 +1499,96 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "x_as_any_if_x_is_instance_elseif_x_is
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    CHECK_EQ("Folder", toString(requireTypeAtPosition({5, 28})));
+    if (FFlag::DebugLuauDeferredConstraintResolution)
-    CHECK_EQ("any", toString(requireTypeAtPosition({7, 28})));
+    {
+        CHECK_EQ("Folder & Instance & {-  -}", toString(requireTypeAtPosition({5, 28})));
+        CHECK_EQ("(~Folder | ~Instance) & {-  -} & never", toString(requireTypeAtPosition({7, 28})));
+    }
+    else
+    {
+        CHECK_EQ("Folder", toString(requireTypeAtPosition({5, 28})));
+        CHECK_EQ("any", toString(requireTypeAtPosition({7, 28})));
+    }
+}
+
+TEST_CASE_FIXTURE(RefinementClassFixture, "refine_param_of_type_instance_without_using_typeof")
+{
+    CheckResult result = check(R"(
+        local function f(x: Instance)
+            if x:IsA("Folder") then
+                local foo = x
+            elseif typeof(x) == "table" then
+                local foo = x
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK_EQ("Folder & Instance", toString(requireTypeAtPosition({3, 28})));
+        CHECK_EQ("Instance & ~Folder & never", toString(requireTypeAtPosition({5, 28})));
+    }
+    else
+    {
+        CHECK_EQ("Folder", toString(requireTypeAtPosition({3, 28})));
+        CHECK_EQ("never", toString(requireTypeAtPosition({5, 28})));
+    }
+}
+
+TEST_CASE_FIXTURE(RefinementClassFixture, "refine_param_of_type_folder_or_part_without_using_typeof")
+{
+    CheckResult result = check(R"(
+        local function f(x: Part | Folder)
+            if x:IsA("Folder") then
+                local foo = x
+            else
+                local foo = x
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK_EQ("(Folder | Part) & Folder", toString(requireTypeAtPosition({3, 28})));
+        CHECK_EQ("(Folder | Part) & ~Folder", toString(requireTypeAtPosition({5, 28})));
+    }
+    else
+    {
+        CHECK_EQ("Folder", toString(requireTypeAtPosition({3, 28})));
+        CHECK_EQ("Part", toString(requireTypeAtPosition({5, 28})));
+    }
+}
+
+TEST_CASE_FIXTURE(RefinementClassFixture, "isa_type_refinement_must_be_known_ahead_of_time")
+{
+    CheckResult result = check(R"(
+        local function f(x): Instance
+            if x:IsA("Folder") then
+                local foo = x
+            else
+                local foo = x
+            end
+
+            return x
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK_EQ("Instance", toString(requireTypeAtPosition({3, 28})));
+        CHECK_EQ("Instance", toString(requireTypeAtPosition({5, 28})));
+    }
+    else
+    {
+        CHECK_EQ("Instance", toString(requireTypeAtPosition({3, 28})));
+        CHECK_EQ("Instance", toString(requireTypeAtPosition({5, 28})));
+    }
 }
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "x_is_not_instance_or_else_not_part")
@@ -1526,4 +1714,18 @@ TEST_CASE_FIXTURE(Fixture, "else_with_no_explicit_expression_should_also_refine_
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "fuzz_filtered_refined_types_are_followed")
+{
+    ScopedFastFlag luauTypeInferMissingFollows{"LuauTypeInferMissingFollows", true};
+
+    CheckResult result = check(R"(
+local _
+do
+local _ = _ ~= _ or _ or _
+end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.tables.test.cpp

@@ -18,6 +18,7 @@ LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(LuauNoMoreGlobalSingletonTypes)
+LUAU_FASTFLAG(LuauTypeMismatchInvarianceInError)
 
 TEST_SUITE_BEGIN("TableTests");
 
@@ -2024,7 +2025,12 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERRORS(result);
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+caused by:
+  Property 'y' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
 caused by:
   Property 'y' is not compatible. Type 'number' could not be converted into 'string')");
 }
@@ -2043,7 +2049,14 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERRORS(result);
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+caused by:
+  Property 'b' is not compatible. Type 'AS' could not be converted into 'BS'
+caused by:
+  Property 'y' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
 caused by:
   Property 'b' is not compatible. Type 'AS' could not be converted into 'BS'
 caused by:
@@ -2063,7 +2076,14 @@ local c2: typeof(a2) = b2
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(2, result);
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'b1' could not be converted into 'a1'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'b1' could not be converted into 'a1'
+caused by:
+  Type '{ x: number, y: string }' could not be converted into '{ x: number, y: number }'
+caused by:
+  Property 'y' is not compatible. Type 'string' could not be converted into 'number' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'b1' could not be converted into 'a1'
 caused by:
   Type '{ x: number, y: string }' could not be converted into '{ x: number, y: number }'
 caused by:
@@ -2098,7 +2118,12 @@ TEST_CASE_FIXTURE(Fixture, "error_detailed_indexer_key")
     )");
 
     LUAU_REQUIRE_ERRORS(result);
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+caused by:
+  Property '[indexer key]' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
 caused by:
   Property '[indexer key]' is not compatible. Type 'number' could not be converted into 'string')");
 }
@@ -2114,7 +2139,12 @@ TEST_CASE_FIXTURE(Fixture, "error_detailed_indexer_value")
     )");
 
     LUAU_REQUIRE_ERRORS(result);
-    CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+    if (FFlag::LuauTypeMismatchInvarianceInError)
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
+caused by:
+  Property '[indexer value]' is not compatible. Type 'number' could not be converted into 'string' in an invariant context)");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Type 'A' could not be converted into 'B'
 caused by:
   Property '[indexer value]' is not compatible. Type 'number' could not be converted into 'string')");
 }
@@ -3261,7 +3291,7 @@ caused by:
 TEST_CASE_FIXTURE(Fixture, "a_free_shape_can_turn_into_a_scalar_if_it_is_compatible")
 {
     ScopedFastFlag sff{"LuauScalarShapeSubtyping", true};
-    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner", true}; // Changes argument from table type to primitive
+    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner2", true}; // Changes argument from table type to primitive
 
     CheckResult result = check(R"(
         local function f(s): string
@@ -3308,7 +3338,7 @@ caused by:
 TEST_CASE_FIXTURE(BuiltinsFixture, "a_free_shape_can_turn_into_a_scalar_directly")
 {
     ScopedFastFlag luauScalarShapeSubtyping{"LuauScalarShapeSubtyping", true};
-    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner", true};
+    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner2", true};
 
     CheckResult result = check(R"(
         local function stringByteList(str)
@@ -3394,7 +3424,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_has_a_side_effect")
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
-    CHECK(toString(requireType("foo")) == "{ @metatable { __add: (a, b) -> number }, {  } }");
+    CHECK(toString(requireType("foo")) == "{ @metatable { __add: <a, b>(a, b) -> number }, {  } }");
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "tables_should_be_fully_populated")
@@ -3413,4 +3443,43 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "tables_should_be_fully_populated")
     CHECK_EQ("{ x: *error-type*, y: number }", toString(requireType("t"), opts));
 }
 
+TEST_CASE_FIXTURE(Fixture, "fuzz_table_indexer_unification_can_bound_owner_to_string")
+{
+    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner2", true};
+
+    CheckResult result = check(R"(
+sin,_ = nil
+_ = _[_.sin][_._][_][_]._
+_[_] = _
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_table_extra_prop_unification_can_bound_owner_to_string")
+{
+    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner2", true};
+
+    CheckResult result = check(R"(
+l0,_ = nil
+_ = _,_[_.n5]._[_][_][_]._
+_._.foreach[_],_ = _[_],_._
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_typelevel_promote_on_changed_table_type")
+{
+    ScopedFastFlag luauScalarShapeUnifyToMtOwner{"LuauScalarShapeUnifyToMtOwner2", true};
+
+    CheckResult result = check(R"(
+_._,_ = nil
+_ = _.foreach[_]._,_[_.n5]._[_.foreach][_][_]._
+_ = _._
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.test.cpp

@@ -351,7 +351,7 @@ TEST_CASE_FIXTURE(Fixture, "check_expr_recursion_limit")
     CheckResult result = check(R"(("foo"))" + rep(":lower()", limit));
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK(nullptr != get<CodeTooComplex>(result.errors[0]));
+    CHECK_MESSAGE(nullptr != get<CodeTooComplex>(result.errors[0]), "Expected CodeTooComplex but got " << toString(result.errors[0]));
 }
 
 TEST_CASE_FIXTURE(Fixture, "globals")
@@ -1159,4 +1159,17 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "it_is_ok_to_have_inconsistent_number_of_retu
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "fuzz_free_table_type_change_during_index_check")
+{
+    ScopedFastFlag luauFollowInLvalueIndexCheck{"LuauFollowInLvalueIndexCheck", true};
+
+    CheckResult result = check(R"(
+local _ = nil
+while _["" >= _] do
+end
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.tryUnify.test.cpp

@@ -110,6 +110,68 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "incompatible_tables_are_preserved")
     CHECK_NE(*getMutable<TableTypeVar>(&tableOne)->props["foo"].type, *getMutable<TableTypeVar>(&tableTwo)->props["foo"].type);
 }
 
+TEST_CASE_FIXTURE(TryUnifyFixture, "uninhabited_intersection_sub_never")
+{
+    ScopedFastFlag sffs[]{
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        function f(arg : string & number) : never
+          return arg
+        end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(TryUnifyFixture, "uninhabited_intersection_sub_anything")
+{
+    ScopedFastFlag sffs[]{
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        function f(arg : string & number) : boolean
+          return arg
+        end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(TryUnifyFixture, "uninhabited_table_sub_never")
+{
+    ScopedFastFlag sffs[]{
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+        {"LuauUninhabitedSubAnything", true},
+    };
+
+    CheckResult result = check(R"(
+        function f(arg : { prop : string & number }) : never
+          return arg
+        end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(TryUnifyFixture, "uninhabited_table_sub_anything")
+{
+    ScopedFastFlag sffs[]{
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+        {"LuauUninhabitedSubAnything", true},
+    };
+
+    CheckResult result = check(R"(
+        function f(arg : { prop : string & number }) : boolean
+          return arg
+        end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_CASE_FIXTURE(TryUnifyFixture, "members_of_failed_typepack_unification_are_unified_with_errorType")
 {
     CheckResult result = check(R"(
@@ -299,4 +361,19 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "metatables_unify_against_shape_of_free_table
     CHECK_EQ(toString(state.errors[0]), expected);
 }
 
+TEST_CASE_FIXTURE(TryUnifyFixture, "fuzz_tail_unification_issue")
+{
+    ScopedFastFlag luauTxnLogTypePackIterator{"LuauTxnLogTypePackIterator", true};
+
+    TypePackVar variadicAny{VariadicTypePack{typeChecker.anyType}};
+    TypePackVar packTmp{TypePack{{typeChecker.anyType}, &variadicAny}};
+    TypePackVar packSub{TypePack{{typeChecker.anyType, typeChecker.anyType}, &packTmp}};
+
+    TypeVar freeTy{FreeTypeVar{TypeLevel{}}};
+    TypePackVar freeTp{FreeTypePack{TypeLevel{}}};
+    TypePackVar packSuper{TypePack{{&freeTy}, &freeTp}};
+
+    state.tryUnify(&packSub, &packSuper);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.typePacks.cpp

@@ -7,8 +7,6 @@
 
 #include "doctest.h"
 
-LUAU_FASTFLAG(LuauFunctionReturnStringificationFixup);
-
 using namespace Luau;
 
 TEST_SUITE_BEGIN("TypePackTests");
@@ -311,10 +309,7 @@ local c: Packed<string, number, boolean>
     auto ttvA = get<TableTypeVar>(requireType("a"));
     REQUIRE(ttvA);
     CHECK_EQ(toString(requireType("a")), "Packed<number>");
-    if (FFlag::LuauFunctionReturnStringificationFixup)
+    CHECK_EQ(toString(requireType("a"), {true}), "{| f: (number) -> number |}");
-        CHECK_EQ(toString(requireType("a"), {true}), "{| f: (number) -> number |}");
-    else
-        CHECK_EQ(toString(requireType("a"), {true}), "{| f: (number) -> (number) |}");
     REQUIRE(ttvA->instantiatedTypeParams.size() == 1);
     REQUIRE(ttvA->instantiatedTypePackParams.size() == 1);
     CHECK_EQ(toString(ttvA->instantiatedTypeParams[0], {true}), "number");
@@ -467,8 +462,6 @@ type I<S..., R...> = W<number, (string, S...), R...>
 
 TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit")
 {
-    ScopedFastFlag sff("LuauFunctionReturnStringificationFixup", true);
-
     CheckResult result = check(R"(
 type X<T...> = (T...) -> (T...)
 
@@ -492,8 +485,6 @@ type F = X<(string, ...number)>
 
 TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit_multi")
 {
-    ScopedFastFlag sff("LuauFunctionReturnStringificationFixup", true);
-
     CheckResult result = check(R"(
 type Y<T..., U...> = (T...) -> (U...)
 
@@ -1002,6 +993,10 @@ TEST_CASE_FIXTURE(Fixture, "unify_variadic_tails_in_arguments_free")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "type_packs_with_tails_in_vararg_adjustment")
 {
+    std::optional<ScopedFastFlag> sff;
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+        sff = {"LuauInstantiateInSubtyping", true};
+
     CheckResult result = check(R"(
         local function wrapReject<TArg, TResult>(fn: (self: any, ...TArg) -> ...TResult): (self: any, ...TArg) -> ...TResult
             return function(self, ...)
@@ -1017,4 +1012,46 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_packs_with_tails_in_vararg_adjustment")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "generalize_expectedTypes_with_proper_scope")
+{
+    ScopedFastFlag sff[] = {
+        {"DebugLuauDeferredConstraintResolution", true},
+        {"LuauInstantiateInSubtyping", true},
+    };
+
+    CheckResult result = check(R"(
+        local function f<TResult>(fn: () -> ...TResult): () -> ...TResult
+            return function()
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "fuzz_typepack_iter_follow")
+{
+    ScopedFastFlag luauTxnLogTypePackIterator{"LuauTxnLogTypePackIterator", true};
+
+    CheckResult result = check(R"(
+local _
+local _ = _,_(),_(_)
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_typepack_iter_follow_2")
+{
+    ScopedFastFlag luauTxnLogTypePackIterator{"LuauTxnLogTypePackIterator", true};
+
+    CheckResult result = check(R"(
+function test(name, searchTerm)
+    local found = string.find(name:lower(), searchTerm:lower())
+end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.unionTypes.test.cpp

@@ -729,4 +729,37 @@ TEST_CASE_FIXTURE(Fixture, "union_of_functions_with_mismatching_result_variadics
                                          "of the union options are compatible");
 }
 
+TEST_CASE_FIXTURE(Fixture, "less_greedy_unification_with_union_types")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local function f(t): { x: number } | { x: string }
+            local x = t.x
+            return t
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("({| x: number |} | {| x: string |}) -> {| x: number |} | {| x: string |}", toString(requireType("f")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "less_greedy_unification_with_union_types_2")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local function f(t: { x: number } | { x: string })
+            return t.x
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("({| x: number |} | {| x: string |}) -> number | string", toString(requireType("f")));
+}
+
 TEST_SUITE_END();

tests/VisitTypeVar.test.cpp

@@ -22,14 +22,7 @@ TEST_CASE_FIXTURE(Fixture, "throw_when_limit_is_exceeded")
 
     TypeId tType = requireType("t");
 
-    if (FFlag::LuauIceExceptionInheritanceChange)
+    CHECK_THROWS_AS(toString(tType), RecursionLimitException);
-    {
-        CHECK_THROWS_AS(toString(tType), RecursionLimitException);
-    }
-    else
-    {
-        CHECK_THROWS_AS(toString(tType), RecursionLimitException_DEPRECATED);
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "dont_throw_when_limit_is_high_enough")

tools/faillist.txt

@@ -14,9 +14,11 @@ AstQuery::getDocumentationSymbolAtPosition.overloaded_class_method
 AstQuery::getDocumentationSymbolAtPosition.overloaded_fn
 AstQuery::getDocumentationSymbolAtPosition.table_overloaded_function_prop
 AutocompleteTest.autocomplete_first_function_arg_expected_type
-AutocompleteTest.autocomplete_interpolated_string
+AutocompleteTest.autocomplete_interpolated_string_as_singleton
+AutocompleteTest.autocomplete_interpolated_string_constant
+AutocompleteTest.autocomplete_interpolated_string_expression
+AutocompleteTest.autocomplete_interpolated_string_expression_with_comments
 AutocompleteTest.autocomplete_oop_implicit_self
-AutocompleteTest.autocomplete_string_singleton_equality
 AutocompleteTest.autocomplete_string_singleton_escape
 AutocompleteTest.autocomplete_string_singletons
 AutocompleteTest.autocompleteProp_index_function_metamethod_is_variadic
@@ -25,9 +27,11 @@ AutocompleteTest.do_wrong_compatible_self_calls
 AutocompleteTest.keyword_methods
 AutocompleteTest.no_incompatible_self_calls
 AutocompleteTest.no_wrong_compatible_self_calls_with_generics
+AutocompleteTest.suggest_external_module_type
 AutocompleteTest.suggest_table_keys
 AutocompleteTest.type_correct_argument_type_suggestion
 AutocompleteTest.type_correct_expected_argument_type_pack_suggestion
+AutocompleteTest.type_correct_expected_argument_type_suggestion
 AutocompleteTest.type_correct_expected_argument_type_suggestion_optional
 AutocompleteTest.type_correct_expected_argument_type_suggestion_self
 AutocompleteTest.type_correct_expected_return_type_pack_suggestion
@@ -68,7 +72,6 @@ BuiltinTests.select_with_decimal_argument_is_rounded_down
 BuiltinTests.set_metatable_needs_arguments
 BuiltinTests.setmetatable_should_not_mutate_persisted_types
 BuiltinTests.sort_with_bad_predicate
-BuiltinTests.string_format_arg_count_mismatch
 BuiltinTests.string_format_as_method
 BuiltinTests.string_format_correctly_ordered_types
 BuiltinTests.string_format_report_all_type_errors_at_correct_positions
@@ -106,10 +109,10 @@ GenericsTests.generic_factories
 GenericsTests.generic_functions_should_be_memory_safe
 GenericsTests.generic_table_method
 GenericsTests.generic_type_pack_parentheses
-GenericsTests.generic_type_pack_unification2
 GenericsTests.higher_rank_polymorphism_should_not_accept_instantiated_arguments
 GenericsTests.infer_generic_function_function_argument
 GenericsTests.infer_generic_function_function_argument_overloaded
+GenericsTests.infer_generic_lib_function_function_argument
 GenericsTests.infer_generic_methods
 GenericsTests.infer_generic_property
 GenericsTests.instantiated_function_argument_names
@@ -117,9 +120,6 @@ GenericsTests.instantiation_sharing_types
 GenericsTests.no_stack_overflow_from_quantifying
 GenericsTests.reject_clashing_generic_and_pack_names
 GenericsTests.self_recursive_instantiated_param
-IntersectionTypes.index_on_an_intersection_type_with_mixed_types
-IntersectionTypes.index_on_an_intersection_type_with_property_guaranteed_to_exist
-IntersectionTypes.index_on_an_intersection_type_works_at_arbitrary_depth
 IntersectionTypes.no_stack_overflow_from_flattenintersection
 IntersectionTypes.select_correct_union_fn
 IntersectionTypes.should_still_pick_an_overload_whose_arguments_are_unions
@@ -151,6 +151,7 @@ ProvisionalTests.bail_early_if_unification_is_too_complicated
 ProvisionalTests.discriminate_from_x_not_equal_to_nil
 ProvisionalTests.do_not_ice_when_trying_to_pick_first_of_generic_type_pack
 ProvisionalTests.error_on_eq_metamethod_returning_a_type_other_than_boolean
+ProvisionalTests.free_options_cannot_be_unified_together
 ProvisionalTests.generic_type_leak_to_module_interface_variadic
 ProvisionalTests.greedy_inference_with_shared_self_triggers_function_with_no_returns
 ProvisionalTests.lvalue_equals_another_lvalue_with_no_overlap
@@ -164,15 +165,15 @@ ProvisionalTests.while_body_are_also_refined
 RefinementTest.apply_refinements_on_astexprindexexpr_whose_subscript_expr_is_constant_string
 RefinementTest.assert_a_to_be_truthy_then_assert_a_to_be_number
 RefinementTest.assert_non_binary_expressions_actually_resolve_constraints
+RefinementTest.assign_table_with_refined_property_with_a_similar_type_is_illegal
 RefinementTest.call_an_incompatible_function_after_using_typeguard
 RefinementTest.correctly_lookup_property_whose_base_was_previously_refined
 RefinementTest.correctly_lookup_property_whose_base_was_previously_refined2
-RefinementTest.discriminate_from_isa_of_x
-RefinementTest.discriminate_from_truthiness_of_x
 RefinementTest.discriminate_on_properties_of_disjoint_tables_where_that_property_is_true_or_false
 RefinementTest.discriminate_tag
 RefinementTest.else_with_no_explicit_expression_should_also_refine_the_tagged_union
 RefinementTest.falsiness_of_TruthyPredicate_narrows_into_nil
+RefinementTest.fuzz_filtered_refined_types_are_followed
 RefinementTest.index_on_a_refined_property
 RefinementTest.invert_is_truthy_constraint_ifelse_expression
 RefinementTest.is_truthy_constraint_ifelse_expression
@@ -181,7 +182,6 @@ RefinementTest.nonoptional_type_can_narrow_to_nil_if_sense_is_true
 RefinementTest.not_t_or_some_prop_of_t
 RefinementTest.refine_a_property_not_to_be_nil_through_an_intersection_table
 RefinementTest.refine_unknowns
-RefinementTest.truthy_constraint_on_properties
 RefinementTest.type_comparison_ifelse_expression
 RefinementTest.type_guard_can_filter_for_intersection_of_tables
 RefinementTest.type_guard_narrowed_into_nothingness
@@ -210,7 +210,6 @@ TableTests.defining_a_self_method_for_a_builtin_sealed_table_must_fail
 TableTests.defining_a_self_method_for_a_local_sealed_table_must_fail
 TableTests.dont_crash_when_setmetatable_does_not_produce_a_metatabletypevar
 TableTests.dont_hang_when_trying_to_look_up_in_cyclic_metatable_index
-TableTests.dont_leak_free_table_props
 TableTests.dont_quantify_table_that_belongs_to_outer_scope
 TableTests.dont_suggest_exact_match_keys
 TableTests.error_detailed_metatable_prop
@@ -240,6 +239,7 @@ TableTests.invariant_table_properties_means_instantiating_tables_in_assignment_i
 TableTests.invariant_table_properties_means_instantiating_tables_in_call_is_unsound
 TableTests.leaking_bad_metatable_errors
 TableTests.less_exponential_blowup_please
+TableTests.meta_add
 TableTests.meta_add_both_ways
 TableTests.meta_add_inferred
 TableTests.metatable_mismatch_should_fail
@@ -252,8 +252,6 @@ TableTests.only_ascribe_synthetic_names_at_module_scope
 TableTests.oop_indexer_works
 TableTests.oop_polymorphic
 TableTests.open_table_unification_2
-TableTests.pass_a_union_of_tables_to_a_function_that_requires_a_table
-TableTests.pass_a_union_of_tables_to_a_function_that_requires_a_table_2
 TableTests.persistent_sealed_table_is_immutable
 TableTests.prop_access_on_key_whose_types_mismatches
 TableTests.property_lookup_through_tabletypevar_metatable
@@ -268,6 +266,7 @@ TableTests.scalar_is_not_a_subtype_of_a_compatible_polymorphic_shape_type
 TableTests.shared_selfs
 TableTests.shared_selfs_from_free_param
 TableTests.shared_selfs_through_metatables
+TableTests.table_call_metamethod_basic
 TableTests.table_indexing_error_location
 TableTests.table_insert_should_cope_with_optional_properties_in_nonstrict
 TableTests.table_insert_should_cope_with_optional_properties_in_strict
@@ -323,6 +322,7 @@ TypeInfer.checking_should_not_ice
 TypeInfer.cli_50041_committing_txnlog_in_apollo_client_error
 TypeInfer.dont_report_type_errors_within_an_AstExprError
 TypeInfer.dont_report_type_errors_within_an_AstStatError
+TypeInfer.fuzz_free_table_type_change_during_index_check
 TypeInfer.globals
 TypeInfer.globals2
 TypeInfer.infer_assignment_value_types_mutable_lval
@@ -335,7 +335,6 @@ TypeInfer.tc_interpolated_string_with_invalid_expression
 TypeInfer.type_infer_recursion_limit_no_ice
 TypeInfer.type_infer_recursion_limit_normalizer
 TypeInferAnyError.for_in_loop_iterator_is_any2
-TypeInferAnyError.for_in_loop_iterator_is_error2
 TypeInferClasses.can_read_prop_of_base_class_using_string
 TypeInferClasses.class_type_mismatch_with_name_conflict
 TypeInferClasses.classes_without_overloaded_operators_cannot_be_added
@@ -351,8 +350,6 @@ TypeInferFunctions.cannot_hoist_interior_defns_into_signature
 TypeInferFunctions.dont_give_other_overloads_message_if_only_one_argument_matching_overload_exists
 TypeInferFunctions.dont_infer_parameter_types_for_functions_from_their_call_site
 TypeInferFunctions.duplicate_functions_with_different_signatures_not_allowed_in_nonstrict
-TypeInferFunctions.free_is_not_bound_to_unknown
-TypeInferFunctions.func_expr_doesnt_leak_free
 TypeInferFunctions.function_cast_error_uses_correct_language
 TypeInferFunctions.function_decl_non_self_sealed_overwrite_2
 TypeInferFunctions.function_decl_non_self_unsealed_overwrite
@@ -385,12 +382,11 @@ TypeInferLoops.for_in_loop
 TypeInferLoops.for_in_loop_error_on_factory_not_returning_the_right_amount_of_values
 TypeInferLoops.for_in_loop_with_next
 TypeInferLoops.for_in_with_generic_next
-TypeInferLoops.for_in_with_just_one_iterator_is_ok
 TypeInferLoops.loop_iter_metamethod_ok_with_inference
 TypeInferLoops.loop_iter_no_indexer_nonstrict
 TypeInferLoops.loop_iter_trailing_nil
+TypeInferLoops.properly_infer_iteratee_is_a_free_table
 TypeInferLoops.unreachable_code_after_infinite_loop
-TypeInferLoops.varlist_declared_by_for_in_loop_should_be_free
 TypeInferModules.custom_require_global
 TypeInferModules.do_not_modify_imported_types
 TypeInferModules.module_type_conflict
@@ -414,6 +410,8 @@ TypeInferOperators.compound_assign_mismatch_result
 TypeInferOperators.disallow_string_and_types_without_metatables_from_arithmetic_binary_ops
 TypeInferOperators.in_nonstrict_mode_strip_nil_from_intersections_when_considering_relational_operators
 TypeInferOperators.infer_any_in_all_modes_when_lhs_is_unknown
+TypeInferOperators.mm_comparisons_must_return_a_boolean
+TypeInferOperators.mm_ops_must_return_a_value
 TypeInferOperators.produce_the_correct_error_message_when_comparing_a_table_with_a_metatable_with_one_that_does_not
 TypeInferOperators.refine_and_or
 TypeInferOperators.typecheck_overloaded_multiply_that_is_an_intersection
@@ -427,16 +425,13 @@ TypeInferUnknownNever.assign_to_prop_which_is_never
 TypeInferUnknownNever.assign_to_subscript_which_is_never
 TypeInferUnknownNever.call_never
 TypeInferUnknownNever.dont_unify_operands_if_one_of_the_operand_is_never_in_any_ordering_operators
-TypeInferUnknownNever.index_on_union_of_tables_for_properties_that_is_never
 TypeInferUnknownNever.index_on_union_of_tables_for_properties_that_is_sorta_never
 TypeInferUnknownNever.math_operators_and_never
 TypeInferUnknownNever.type_packs_containing_never_is_itself_uninhabitable
 TypeInferUnknownNever.type_packs_containing_never_is_itself_uninhabitable2
 TypeInferUnknownNever.unary_minus_of_never
 TypePackTests.detect_cyclic_typepacks2
-TypePackTests.higher_order_function
 TypePackTests.pack_tail_unification_check
-TypePackTests.parenthesized_varargs_returns_any
 TypePackTests.type_alias_backwards_compatible
 TypePackTests.type_alias_default_export
 TypePackTests.type_alias_default_mixed_self
@@ -456,7 +451,6 @@ TypePackTests.type_alias_type_packs_nested
 TypePackTests.type_pack_type_parameters
 TypePackTests.unify_variadic_tails_in_arguments
 TypePackTests.unify_variadic_tails_in_arguments_free
-TypePackTests.varargs_inference_through_multiple_scopes
 TypePackTests.variadic_packs
 TypeSingletons.error_detailed_tagged_union_mismatch_bool
 TypeSingletons.error_detailed_tagged_union_mismatch_string
@@ -477,11 +471,8 @@ TypeSingletons.widening_happens_almost_everywhere_except_for_tables
 UnionTypes.error_detailed_optional
 UnionTypes.error_detailed_union_all
 UnionTypes.index_on_a_union_type_with_missing_property
-UnionTypes.index_on_a_union_type_with_mixed_types
 UnionTypes.index_on_a_union_type_with_one_optional_property
 UnionTypes.index_on_a_union_type_with_one_property_of_type_any
-UnionTypes.index_on_a_union_type_with_property_guaranteed_to_exist
-UnionTypes.index_on_a_union_type_works_at_arbitrary_depth
 UnionTypes.optional_assignment_errors
 UnionTypes.optional_call_error
 UnionTypes.optional_field_access_error