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This commit is contained in:
Anders Hejlsberg 2019-01-18 14:47:58 -08:00
parent c809002bd3
commit 0b366ce751
1 changed files with 20 additions and 1 deletions
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21
src/compiler/checker.ts
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@ -17715,12 +17715,28 @@ namespace ts {
if (contextualType && maybeTypeOfKind(contextualType, TypeFlags.Instantiable)) {
const returnMapper = (<InferenceContext>getContextualMapper(node)).returnMapper;
if (returnMapper) {
return mapType(contextualType, t => t.flags & TypeFlags.Instantiable ? instantiateType(t, returnMapper) : t);
return instantiateInstantiableTypes(contextualType, returnMapper);
}
}
return contextualType;
}
// This function is similar to instantiateType, except (a) that it only instantiates types that
// are classified as instantiable (i.e. it doesn't instantiate object types), and (b) it performs
// no reductions on instantiated union types.
function instantiateInstantiableTypes(type: Type, mapper: TypeMapper): Type {
if (type.flags & TypeFlags.Instantiable) {
return instantiateType(type, mapper);
}
if (type.flags & TypeFlags.Union) {
getUnionType(map((<UnionType>type).types, t => instantiateInstantiableTypes(t, mapper)), UnionReduction.None);
}
if (type.flags & TypeFlags.Intersection) {
getIntersectionType(map((<IntersectionType>type).types, t => instantiateInstantiableTypes(t, mapper)));
}
return type;
}
/**
* Woah! Do you really want to use this function?
*
@ -22963,6 +22979,9 @@ namespace ts {
const checkMode = contextualMapper === identityMapper ? CheckMode.SkipContextSensitive :
contextualMapper ? CheckMode.Inferential : CheckMode.Contextual;
const type = checkExpression(node, checkMode);
// We strip literal freshness when an appropriate contextual type is present such that contextually typed
// literals always preserve their literal types (otherwise they might widen during type inference). An alternative
// here would be to not mark contextually typed literals as fresh in the first place.
const result = maybeTypeOfKind(type, TypeFlags.Literal) && isLiteralOfContextualType(type, instantiateContextualType(contextualType, node)) ?
getRegularTypeOfLiteralType(type) : type;
context.contextualType = saveContextualType;