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Properly construct replacement mapper in mapped type instantiation

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This commit is contained in:
Anders Hejlsberg
2017-01-09 09:11:09 -08:00
parent 5b075ff924
commit 9441555778
1 changed files with 7 additions and 4 deletions
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11
src/compiler/checker.ts
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@@ -6564,6 +6564,12 @@ namespace ts {
return mapper;
}
function createReplacementMapper(source: Type, target: Type, baseMapper: TypeMapper) {
const mapper: TypeMapper = t => t === source ? target : baseMapper(t);
mapper.mappedTypes = baseMapper.mappedTypes;
return mapper;
}
function cloneTypeParameter(typeParameter: TypeParameter): TypeParameter {
const result = <TypeParameter>createType(TypeFlags.TypeParameter);
result.symbol = typeParameter.symbol;
@@ -6662,10 +6668,7 @@ namespace ts {
if (typeVariable !== mappedTypeVariable) {
return mapType(mappedTypeVariable, t => {
if (isMappableType(t)) {
const replacementMapper = createUnaryTypeMapper(typeVariable, t);
const combinedMapper = mapper.mappedTypes && mapper.mappedTypes.length === 1 ? replacementMapper : combineTypeMappers(replacementMapper, mapper);
combinedMapper.mappedTypes = mapper.mappedTypes;
return instantiateMappedObjectType(type, combinedMapper);
return instantiateMappedObjectType(type, createReplacementMapper(typeVariable, t, mapper));
}
return t;
});