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Filter return type inferences by constraint applicability (#58910)

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Mateusz Burzyński
2025-12-03 18:46:59 +01:00
committed by GitHub
parent 5026c6675c
commit 28fbc0a1ef
13 changed files with 890 additions and 3 deletions
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16
src/compiler/checker.ts
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@@ -27576,10 +27576,20 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
const constraint = getConstraintOfTypeParameter(inference.typeParameter);
if (constraint) {
const instantiatedConstraint = instantiateType(constraint, context.nonFixingMapper);
if (!inferredType || !context.compareTypes(inferredType, getTypeWithThisArgument(instantiatedConstraint, inferredType))) {
// If the fallback type satisfies the constraint, we pick it. Otherwise, we pick the constraint.
inference.inferredType = fallbackType && context.compareTypes(fallbackType, getTypeWithThisArgument(instantiatedConstraint, fallbackType)) ? fallbackType : instantiatedConstraint;
if (inferredType) {
const constraintWithThis = getTypeWithThisArgument(instantiatedConstraint, inferredType);
if (!context.compareTypes(inferredType, constraintWithThis)) {
// If we have a pure return type inference, we may succeed by removing constituents of the inferred type
// that aren't assignable to the constraint type (pure return type inferences are speculation anyway).
const filteredByConstraint = inference.priority === InferencePriority.ReturnType ? filterType(inferredType, t => !!context.compareTypes(t, constraintWithThis)) : neverType;
inferredType = !(filteredByConstraint.flags & TypeFlags.Never) ? filteredByConstraint : undefined;
}
}
if (!inferredType) {
// If the fallback type satisfies the constraint, we pick it. Otherwise, we pick the constraint.
inferredType = fallbackType && context.compareTypes(fallbackType, getTypeWithThisArgument(instantiatedConstraint, fallbackType)) ? fallbackType : instantiatedConstraint;
}
inference.inferredType = inferredType;
}
clearActiveMapperCaches();
}