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Fix #2134: Instantiate generics in expected function types before sub… #2140

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Fix #2134: Instantiate generics in expected function types before sub… #2140

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4cb4792
Fix #2134: Instantiate generics in expected function types before sub…
Definisi Dec 9, 2025
4caa6a4
Fix: Add polarity parameter to freshTypePack call
Definisi Dec 9, 2025
63eb60a
Fix: Only instantiate generics when argument has its own generics
Definisi Dec 9, 2025
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33 changes: 33 additions & 0 deletions Analysis/src/ConstraintSolver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1814,6 +1814,39 @@ bool ConstraintSolver::tryDispatch(const FunctionCheckConstraint& c, NotNull<con
TypeId expectedArgTy = follow(expectedArgs[i + typeOffset]);
AstExpr* expr = unwrapGroup(c.callSite->args.data[i]);

// If the expected type is a function type whose signature contains generics from the calling function,
// and the actual argument is a lambda with its own generics, instantiate the calling function's generics
// with fresh types to avoid conflicts with the actual type's generics.
const auto lambdaExpr = expr->as<AstExprFunction>();
bool argHasGenerics = lambdaExpr && (lambdaExpr->generics.size > 0 || lambdaExpr->genericPacks.size > 0);

if (get<FunctionType>(expectedArgTy) && ContainsGenerics::hasGeneric(expectedArgTy, NotNull{&genericTypesAndPacks}) && argHasGenerics)
{
DenseHashMap<TypeId, TypeId> freshReplacements{nullptr};
DenseHashMap<TypePackId, TypePackId> freshReplacementPacks{nullptr};

for (auto generic : ftv->generics)
{
if (auto gty = get<GenericType>(follow(generic)))
{
freshReplacements[generic] = freshType(arena, builtinTypes, constraint->scope, Polarity::Mixed);
trackInteriorFreeType(constraint->scope, freshReplacements[generic]);
}
}

for (auto genericPack : ftv->genericPacks)
{
freshReplacementPacks[genericPack] = arena->freshTypePack(constraint->scope, Polarity::Mixed);
trackInteriorFreeTypePack(constraint->scope, freshReplacementPacks[genericPack]);
}

Replacer freshReplacer{arena, std::move(freshReplacements), std::move(freshReplacementPacks)};
if (auto instantiated = freshReplacer.substitute(expectedArgTy))
{
expectedArgTy = *instantiated;
}
}

PushTypeResult result =
pushTypeInto(c.astTypes, c.astExpectedTypes, NotNull{this}, constraint, NotNull{&u2}, NotNull{&subtyping}, expectedArgTy, expr);

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