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Improve contextual types inferred from return types

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This commit is contained in:
Anders Hejlsberg
2025-06-22 16:08:02 -04:00
parent 479285d0ac
commit 1b13408834
2 changed files with 8 additions and 4 deletions
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6
src/compiler/checker.ts
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@@ -26727,7 +26727,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
}
if (!inference.isFixed) {
const candidate = propagationType || source;
if (candidate === blockedStringType) {
// ReturnMapper inferences are used only for contextual types. We exclude `any` and `unknown` types
// that might otherwise swallow other useful inferences.
if (candidate === blockedStringType || candidate.flags & TypeFlags.AnyOrUnknown && priority & InferencePriority.ReturnMapper) {
return;
}
if (inference.priority === undefined || priority < inference.priority) {
@@ -35698,7 +35700,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
// type parameters for which the inferences are being made.
const returnContext = createInferenceContext(signature.typeParameters!, signature, context.flags);
const returnSourceType = instantiateType(contextualType, outerContext && createOuterReturnMapper(outerContext));
inferTypes(returnContext.inferences, returnSourceType, inferenceTargetType);
inferTypes(returnContext.inferences, returnSourceType, inferenceTargetType, InferencePriority.ReturnMapper);
context.returnMapper = some(returnContext.inferences, hasInferenceCandidates) ? getMapperFromContext(cloneInferredPartOfContext(returnContext)) : undefined;
}
}

6
src/compiler/types.ts
View File

@@ -7103,9 +7103,10 @@ export const enum InferencePriority {
LiteralKeyof = 1 << 8, // Inference made from a string literal to a keyof T
NoConstraints = 1 << 9, // Don't infer from constraints of instantiable types
AlwaysStrict = 1 << 10, // Always use strict rules for contravariant inferences
MaxValue = 1 << 11, // Seed for inference priority tracking
ReturnMapper = 1 << 11, // Inferring for return mapper
MaxValue = 1 << 12, // Seed for inference priority tracking
PriorityImpliesCombination = ReturnType | MappedTypeConstraint | LiteralKeyof, // These priorities imply that the resulting type should be a combination of all candidates
PriorityImpliesCombination = ReturnType | ReturnMapper | MappedTypeConstraint | LiteralKeyof, // These priorities imply that the resulting type should be a combination of all candidates
Circularity = -1, // Inference circularity (value less than all other priorities)
}
@@ -7129,6 +7130,7 @@ export const enum InferenceFlags {
NoDefault = 1 << 0, // Infer silentNeverType for no inferences (otherwise anyType or unknownType)
AnyDefault = 1 << 1, // Infer anyType (in JS files) for no inferences (otherwise unknownType)
SkippedGenericFunction = 1 << 2, // A generic function was skipped during inference
NoUnknownInference = 1 << 3,
}
/**