Sync to upstream/release/643 (#1408)

Pretty small release this week as well.

## New Solver
* We now unconditionally generalize functions with explicit generics
* Bugfixes for how we run builtin tests

## VM
* Fixed running Luau conformance tests in LUA_VECTOR_SIZE == 4
configuration

Internal Contributors:

Co-authored-by: Hunter Goldstein <hgoldstein@roblox.com>
Co-authored-by: James McNellis <jmcnellis@roblox.com>
Co-authored-by: Vighnesh Vijay <vvijay@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

---------

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

Analysis/src/Generalization.cpp

@@ -887,9 +887,6 @@ std::optional<TypeId> generalize(
     if (ty->owningArena != arena || ty->persistent)
         return ty;
 
-    if (const FunctionType* ft = get<FunctionType>(ty); ft && (!ft->generics.empty() || !ft->genericPacks.empty()))
-        return ty;
-
     FreeTypeSearcher fts{scope, cachedTypes};
     fts.traverse(ty);
 
@@ -912,8 +909,17 @@ std::optional<TypeId> generalize(
     FunctionType* ftv = getMutable<FunctionType>(ty);
     if (ftv)
     {
-        ftv->generics = std::move(gen.generics);
+        // If we're generalizing a function type, add any of the newly inferred
-        ftv->genericPacks = std::move(gen.genericPacks);
+        // generics to the list of existing generic types.
+        for (const auto g : std::move(gen.generics))
+        {
+            ftv->generics.push_back(g);
+        }
+        // Ditto for generic packs.
+        for (const auto gp : std::move(gen.genericPacks))
+        {
+            ftv->genericPacks.push_back(gp);
+        }
     }
 
     return ty;

Analysis/src/OverloadResolution.cpp

@@ -107,6 +107,7 @@ std::optional<ErrorVec> OverloadResolver::testIsSubtype(const Location& location
         case ErrorSuppression::NormalizationFailed:
             errors.emplace_back(location, NormalizationTooComplex{});
             // intentionally fallthrough here since we couldn't prove this was error-suppressing
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             errors.emplace_back(location, TypeMismatch{superTy, subTy});
             break;
@@ -136,6 +137,7 @@ std::optional<ErrorVec> OverloadResolver::testIsSubtype(const Location& location
         case ErrorSuppression::NormalizationFailed:
             errors.emplace_back(location, NormalizationTooComplex{});
             // intentionally fallthrough here since we couldn't prove this was error-suppressing
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             errors.emplace_back(location, TypePackMismatch{superTy, subTy});
             break;
@@ -301,6 +303,7 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
                 case ErrorSuppression::NormalizationFailed:
                     errors.emplace_back(argLocation, NormalizationTooComplex{});
                     // intentionally fallthrough here since we couldn't prove this was error-suppressing
+                    [[fallthrough]];
                 case ErrorSuppression::DoNotSuppress:
                     // TODO extract location from the SubtypingResult path and argExprs
                     switch (reason.variance)

Analysis/src/Simplify.cpp

@@ -141,6 +141,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     case Relation::Coincident:
         switch (b)
         {
@@ -155,6 +156,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     case Relation::Superset:
         switch (b)
         {
@@ -169,6 +171,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Superset;
         }
+        break;
     case Relation::Subset:
         switch (b)
         {
@@ -183,6 +186,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     case Relation::Intersects:
         switch (b)
         {
@@ -197,6 +201,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     }
 
     LUAU_UNREACHABLE();

Analysis/src/TypeChecker2.cpp

@@ -1378,7 +1378,7 @@ void TypeChecker2::visitCall(AstExprCall* call)
             break;
         case ErrorSuppression::NormalizationFailed:
             reportError(NormalizationTooComplex{}, call->func->location);
-            // fallthrough intentional
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             reportError(OptionalValueAccess{fnTy}, call->func->location);
         }
@@ -1582,7 +1582,7 @@ TypeId TypeChecker2::stripFromNilAndReport(TypeId ty, const Location& location)
             break;
         case ErrorSuppression::NormalizationFailed:
             reportError(NormalizationTooComplex{}, location);
-            // fallthrough intentional
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             reportError(OptionalValueAccess{ty}, location);
         }
@@ -1666,7 +1666,7 @@ void TypeChecker2::visit(AstExprIndexExpr* indexExpr, ValueContext context)
             break;
         case ErrorSuppression::NormalizationFailed:
             reportError(NormalizationTooComplex{}, indexExpr->location);
-            // fallthrough intentional
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             reportError(OptionalValueAccess{exprType}, indexExpr->location);
         }
@@ -2723,6 +2723,7 @@ void TypeChecker2::explainError(TypeId subTy, TypeId superTy, Location location,
         return;
     case ErrorSuppression::NormalizationFailed:
         reportError(NormalizationTooComplex{}, location);
+        break;
     case ErrorSuppression::DoNotSuppress:
         break;
     }
@@ -2741,6 +2742,7 @@ void TypeChecker2::explainError(TypePackId subTy, TypePackId superTy, Location l
         return;
     case ErrorSuppression::NormalizationFailed:
         reportError(NormalizationTooComplex{}, location);
+        break;
     case ErrorSuppression::DoNotSuppress:
         break;
     }

Analysis/src/TypeInfer.cpp

@@ -2751,7 +2751,7 @@ TypeId TypeChecker::checkRelationalOperation(
         if (lhsIsAny || rhsIsAny)
             return booleanType;
 
-        // Fallthrough here is intentional
+        [[fallthrough]];
     }
     case AstExprBinary::CompareLt:
     case AstExprBinary::CompareGt:

Ast/src/Parser.cpp

@@ -784,6 +784,7 @@ AstStat* Parser::parseAttributeStat()
             AstExpr* expr = parsePrimaryExpr(/* asStatement= */ true);
             return parseDeclaration(expr->location, attributes);
         }
+        [[fallthrough]];
     default:
         return reportStatError(
             lexer.current().location,

CLI/Require.cpp

@@ -204,7 +204,18 @@ void RequireResolver::substituteAliasIfPresent(std::string& path)
 {
     if (path.size() < 1 || path[0] != '@')
         return;
-    std::string potentialAlias = path.substr(1, path.find_first_of("\\/"));
+
+    // To ignore the '@' alias prefix when processing the alias
+    const size_t aliasStartPos = 1;
+
+    // If a directory separator was found, the length of the alias is the
+    // distance between the start of the alias and the separator. Otherwise,
+    // the whole string after the alias symbol is the alias.
+    size_t aliasLen = path.find_first_of("\\/");
+    if (aliasLen != std::string::npos)
+        aliasLen -= aliasStartPos;
+
+    const std::string potentialAlias = path.substr(aliasStartPos, aliasLen);
 
     // Not worth searching when potentialAlias cannot be an alias
     if (!Luau::isValidAlias(potentialAlias))

CMakeLists.txt

@@ -111,6 +111,7 @@ if(MSVC)
     list(APPEND LUAU_OPTIONS "/we4388") # Also signed/unsigned mismatch
 else()
     list(APPEND LUAU_OPTIONS -Wall) # All warnings
+    list(APPEND LUAU_OPTIONS -Wimplicit-fallthrough)
     list(APPEND LUAU_OPTIONS -Wsign-compare) # This looks to be included in -Wall for GCC but not clang
 endif()
 

Common/include/Luau/Common.h

@@ -20,6 +20,19 @@
 #define LUAU_DEBUGBREAK() __builtin_trap()
 #endif
 
+// LUAU_FALLTHROUGH is a C++11-compatible alternative to [[fallthrough]] for use in the VM library
+#if defined(__clang__) && defined(__has_warning)
+#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
+#define LUAU_FALLTHROUGH [[clang::fallthrough]]
+#else
+#define LUAU_FALLTHROUGH
+#endif
+#elif defined(__GNUC__) && __GNUC__ >= 7
+#define LUAU_FALLTHROUGH [[gnu::fallthrough]]
+#else
+#define LUAU_FALLTHROUGH
+#endif
+
 #if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 #define LUAU_BIG_ENDIAN
 #endif

VM/src/lstrlib.cpp

@@ -552,9 +552,9 @@ init: // using goto's to optimize tail recursion
                     }
                     break;
                 }
-                case '+': // 1 or more repetitions
+                case '+':             // 1 or more repetitions
-                    s++;  // 1 match already done
+                    s++;              // 1 match already done
-                          // go through
+                    LUAU_FALLTHROUGH; // go through
                 case '*': // 0 or more repetitions
                     s = max_expand(ms, s, p, ep);
                     break;
@@ -1480,7 +1480,8 @@ static int str_pack(lua_State* L)
             break;
         }
         case Kpadding:
-            luaL_addchar(&b, LUAL_PACKPADBYTE); // FALLTHROUGH
+            luaL_addchar(&b, LUAL_PACKPADBYTE);
+            LUAU_FALLTHROUGH;
         case Kpaddalign:
         case Knop:
             arg--; // undo increment

VM/src/ltable.cpp

@@ -659,7 +659,7 @@ const TValue* luaH_get(Table* t, const TValue* key)
         luai_num2int(k, n);
         if (luai_numeq(cast_num(k), nvalue(key))) // index is int?
             return luaH_getnum(t, k);             // use specialized version
-                                                  // else go through
+        LUAU_FALLTHROUGH;                         // else go through
     }
     default:
     {

tests/Conformance.test.cpp

@@ -133,7 +133,12 @@ static int lua_vector_cross(lua_State* L)
     const float* a = luaL_checkvector(L, 1);
     const float* b = luaL_checkvector(L, 2);
 
+#if LUA_VECTOR_SIZE == 4
+    lua_pushvector(L, a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0], 0.0f);
+#else
     lua_pushvector(L, a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]);
+#endif
+
     return 1;
 }
 
@@ -144,15 +149,25 @@ static int lua_vector_index(lua_State* L)
 
     if (strcmp(name, "Magnitude") == 0)
     {
+#if LUA_VECTOR_SIZE == 4
+        lua_pushnumber(L, sqrtf(v[0] * v[0] + v[1] * v[1] + v[2] * v[2] + v[3] * v[3]));
+#else
         lua_pushnumber(L, sqrtf(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]));
+#endif
         return 1;
     }
 
     if (strcmp(name, "Unit") == 0)
     {
+#if LUA_VECTOR_SIZE == 4
+        float invSqrt = 1.0f / sqrtf(v[0] * v[0] + v[1] * v[1] + v[2] * v[2] + v[3] * v[3]);
+
+        lua_pushvector(L, v[0] * invSqrt, v[1] * invSqrt, v[2] * invSqrt, v[3] * invSqrt);
+#else
         float invSqrt = 1.0f / sqrtf(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
 
         lua_pushvector(L, v[0] * invSqrt, v[1] * invSqrt, v[2] * invSqrt);
+#endif
         return 1;
     }
 

tests/Fixture.cpp

@@ -3,6 +3,7 @@
 
 #include "Luau/AstQuery.h"
 #include "Luau/BuiltinDefinitions.h"
+#include "Luau/Common.h"
 #include "Luau/Constraint.h"
 #include "Luau/ModuleResolver.h"
 #include "Luau/NotNull.h"
@@ -25,6 +26,7 @@ static const char* mainModuleName = "MainModule";
 LUAU_FASTFLAG(LuauSolverV2);
 LUAU_FASTFLAG(DebugLuauFreezeArena);
 LUAU_FASTFLAG(DebugLuauLogSolverToJsonFile)
+LUAU_FASTFLAG(LuauDCRMagicFunctionTypeChecker);
 
 extern std::optional<unsigned> randomSeed; // tests/main.cpp
 
@@ -150,6 +152,8 @@ const Config& TestConfigResolver::getConfig(const ModuleName& name) const
 
 Fixture::Fixture(bool freeze, bool prepareAutocomplete)
     : sff_DebugLuauFreezeArena(FFlag::DebugLuauFreezeArena, freeze)
+    // In tests, we *always* want to register the extra magic functions for typechecking `string.format`.
+    , sff_LuauDCRMagicFunctionTypeChecker(FFlag::LuauDCRMagicFunctionTypeChecker, true)
     , frontend(
           &fileResolver,
           &configResolver,

tests/Fixture.h

@@ -99,6 +99,7 @@ struct Fixture
     TypeId requireExportedType(const ModuleName& moduleName, const std::string& name);
 
     ScopedFastFlag sff_DebugLuauFreezeArena;
+    ScopedFastFlag sff_LuauDCRMagicFunctionTypeChecker;
 
     TestFileResolver fileResolver;
     TestConfigResolver configResolver;

tests/IrLowering.test.cpp

@@ -937,6 +937,7 @@ bb_bytecode_0:
     );
 }
 
+#if LUA_VECTOR_SIZE == 3
 TEST_CASE("FastcallTypeInferThroughLocal")
 {
     CHECK_EQ(
@@ -1045,6 +1046,7 @@ bb_bytecode_1:
 )"
     );
 }
+#endif
 
 TEST_CASE("LoadAndMoveTypePropagation")
 {
@@ -1115,6 +1117,7 @@ bb_bytecode_4:
     );
 }
 
+#if LUA_VECTOR_SIZE == 3
 TEST_CASE("ArgumentTypeRefinement")
 {
     CHECK_EQ(
@@ -1152,6 +1155,7 @@ bb_bytecode_0:
 )"
     );
 }
+#endif
 
 TEST_CASE("InlineFunctionType")
 {
@@ -1422,6 +1426,7 @@ bb_2:
     );
 }
 
+#if LUA_VECTOR_SIZE == 3
 TEST_CASE("UnaryTypeResolve")
 {
     CHECK_EQ(
@@ -1443,6 +1448,7 @@ end
 )"
     );
 }
+#endif
 
 TEST_CASE("ForInManualAnnotation")
 {

tests/RequireByString.test.cpp

@@ -436,6 +436,12 @@ TEST_CASE_FIXTURE(ReplWithPathFixture, "RequirePathWithParentAlias")
     assertOutputContainsAll({"true", "result from other_dependency"});
 }
 
+TEST_CASE_FIXTURE(ReplWithPathFixture, "RequirePathWithAliasPointingToDirectory")
+{
+    std::string path = getLuauDirectory(PathType::Relative) + "/tests/require/with_config/src/directory_alias_requirer";
+    runProtectedRequire(path);
+    assertOutputContainsAll({"true", "result from subdirectory_dependency"});
+}
 
 TEST_CASE_FIXTURE(ReplWithPathFixture, "RequireAliasThatDoesNotExist")
 {

tests/ToString.test.cpp

@@ -843,7 +843,7 @@ TEST_CASE_FIXTURE(Fixture, "pick_distinct_names_for_mixed_explicit_and_implicit_
 
     if (FFlag::LuauSolverV2)
     {
-        CHECK("<a>(a, 'b) -> ()" == toString(requireType("foo")));
+        CHECK("<a>(a, unknown) -> ()" == toString(requireType("foo")));
     }
     else
         CHECK("<a, b>(a, b) -> ()" == toString(requireType("foo")));

tests/TypeInfer.builtins.test.cpp

@@ -9,7 +9,6 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2);
-LUAU_FASTFLAG(LuauDCRMagicFunctionTypeChecker);
 
 TEST_SUITE_BEGIN("BuiltinTests");
 
@@ -793,8 +792,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail_and_strin
 
 TEST_CASE_FIXTURE(Fixture, "string_format_as_method")
 {
-    ScopedFastFlag sff{FFlag::LuauDCRMagicFunctionTypeChecker, true};
-
     CheckResult result = check("local _ = ('%s'):format(5)");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -807,7 +804,6 @@ TEST_CASE_FIXTURE(Fixture, "string_format_as_method")
 
 TEST_CASE_FIXTURE(Fixture, "string_format_use_correct_argument")
 {
-    ScopedFastFlag sff{FFlag::LuauDCRMagicFunctionTypeChecker, true};
     CheckResult result = check(R"(
         local _ = ("%s"):format("%d", "hello")
     )");
@@ -819,7 +815,6 @@ TEST_CASE_FIXTURE(Fixture, "string_format_use_correct_argument")
 
 TEST_CASE_FIXTURE(Fixture, "string_format_use_correct_argument2")
 {
-    ScopedFastFlag sff{FFlag::LuauDCRMagicFunctionTypeChecker, true};
     CheckResult result = check(R"(
         local _ = ("%s %d").format("%d %s", "A type error", 2)
     )");
@@ -878,7 +873,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "debug_info_is_crazy")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "aliased_string_format")
 {
-    ScopedFastFlag sff{FFlag::LuauDCRMagicFunctionTypeChecker, true};
     CheckResult result = check(R"(
         local fmt = string.format
         local s = fmt("%d", "oops")
@@ -938,7 +932,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "select_on_variadic")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "string_format_report_all_type_errors_at_correct_positions")
 {
-    ScopedFastFlag sff{FFlag::LuauDCRMagicFunctionTypeChecker, true};
     CheckResult result = check(R"(
         ("%s%d%s"):format(1, "hello", true)
         string.format("%s%d%s", 1, "hello", true)

tests/TypeInfer.generics.test.cpp

@@ -7,6 +7,7 @@
 
 #include "Fixture.h"
 
+#include "ScopedFlags.h"
 #include "doctest.h"
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping);
@@ -1419,10 +1420,19 @@ TEST_CASE_FIXTURE(Fixture, "apply_type_function_nested_generics3")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "quantify_functions_with_no_generics")
+{
+    CheckResult result = check(R"(
+        function foo(f, x)
+            return f(x)
+        end
+    )");
+
+    CHECK("<a, b...>((a) -> (b...), a) -> (b...)" == toString(requireType("foo")));
+}
+
 TEST_CASE_FIXTURE(Fixture, "quantify_functions_even_if_they_have_an_explicit_generic")
 {
-    ScopedFastFlag sff{FFlag::LuauSolverV2, false};
-
     CheckResult result = check(R"(
         function foo<X>(f, x: X)
             return f(x)
@@ -1432,6 +1442,17 @@ TEST_CASE_FIXTURE(Fixture, "quantify_functions_even_if_they_have_an_explicit_gen
     CHECK("<X, a...>((X) -> (a...), X) -> (a...)" == toString(requireType("foo")));
 }
 
+TEST_CASE_FIXTURE(Fixture, "no_extra_quantification_for_generic_functions")
+{
+    CheckResult result = check(R"(
+        function foo<X, Y>(f : (X) -> Y, x: X)
+            return f(x)
+        end
+    )");
+
+    CHECK("<X, Y>((X) -> Y, X) -> Y" == toString(requireType("foo")));
+}
+
 TEST_CASE_FIXTURE(Fixture, "do_not_always_instantiate_generic_intersection_types")
 {
     ScopedFastFlag sff{FFlag::LuauSolverV2, false};
@@ -1535,6 +1556,19 @@ TEST_CASE_FIXTURE(Fixture, "missing_generic_type_parameter")
     REQUIRE(get<UnknownSymbol>(result.errors[1]));
 }
 
+TEST_CASE_FIXTURE(Fixture, "generic_implicit_explicit_name_clash")
+{
+    ScopedFastFlag _{FFlag::LuauSolverV2, true};
+
+    auto result = check(R"(
+        function apply<a>(func, argument: a)
+            return func(argument)
+        end
+    )");
+
+    CHECK("<a, b...>((a) -> (b...), a) -> (b...)" == toString(requireType("apply")));
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "generic_type_functions_work_in_subtyping")
 {
     ScopedFastFlag sff{FFlag::LuauSolverV2, false};

tests/TypeInfer.provisional.test.cpp

@@ -1310,9 +1310,7 @@ TEST_CASE_FIXTURE(Fixture, "we_cannot_infer_functions_that_return_inconsistently
     if (FFlag::LuauSolverV2)
     {
         LUAU_CHECK_ERROR_COUNT(2, result);
-
+        CHECK("<T>({T}, unknown) -> number" == toString(requireType("find_first")));
-        // The second argument should be unknown.  CLI-111111
-        CHECK("<T>({T}, 'b) -> number" == toString(requireType("find_first")));
     }
     else
     {

tests/require/with_config/src/.luaurc

@@ -1,6 +1,7 @@
 {
     "paths": ["../ProjectLuauLibraries"],
     "aliases": {
-        "dep": "dependency"
+        "dep": "dependency",
+        "subdir": "subdirectory"
     }
 }

tests/require/with_config/src/directory_alias_requirer.luau

@@ -0,0 +1 @@
+return(require("@subdir/subdirectory_dependency"))

tests/require/with_config/src/subdirectory/subdirectory_dependency.luau

@@ -0,0 +1 @@
+return {"result from subdirectory_dependency"}