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Merge pull request #12640 from Microsoft/mappedTypesSecondaryInferences

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Classify mapped type inferences as secondary
This commit is contained in:
Anders Hejlsberg
2016-12-04 07:02:51 -08:00
committed by GitHub
parent f61a22478a 970c4aa4f7
commit 23992ba106
8 changed files with 178 additions and 4 deletions
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5
src/compiler/checker.ts
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@@ -8706,12 +8706,15 @@ namespace ts {
if (constraintType.flags & TypeFlags.Index) {
// We're inferring from some source type S to a homomorphic mapped type { [P in keyof T]: X },
// where T is a type variable. Use inferTypeForHomomorphicMappedType to infer a suitable source
// type and then infer from that type to T.
// type and then make a secondary inference from that type to T. We make a secondary inference
// such that direct inferences to T get priority over inferences to Partial<T>, for example.
const index = indexOf(typeVariables, (<IndexType>constraintType).type);
if (index >= 0 && !typeInferences[index].isFixed) {
const inferredType = inferTypeForHomomorphicMappedType(source, <MappedType>target);
if (inferredType) {
inferiority++;
inferFromTypes(inferredType, typeVariables[index]);
inferiority--;
}
}
return;