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Merge pull request #28965 from Microsoft/simplifyIndexedAccess

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Simplify indexed access types applied to mapped types
This commit is contained in:
Anders Hejlsberg
2018-12-11 17:56:03 -08:00
committed by GitHub
parent 5ab24ed7e0 c3a93944aa
commit fecbdb68bd
10 changed files with 120 additions and 36 deletions
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19
src/compiler/checker.ts
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@@ -9686,26 +9686,15 @@ namespace ts {
// If the object type is a mapped type { [P in K]: E }, where K is generic, instantiate E using a mapper
// that substitutes the index type for P. For example, for an index access { [P in K]: Box<T[P]> }[X], we
// construct the type Box<T[X]>. We do not further simplify the result because mapped types can be recursive
// and we might never terminate.
// construct the type Box<T[X]>.
if (isGenericMappedType(objectType)) {
return type.simplified = substituteIndexedMappedType(objectType, type);
}
if (objectType.flags & TypeFlags.TypeParameter) {
const constraint = getConstraintOfTypeParameter(objectType as TypeParameter);
if (constraint && isGenericMappedType(constraint)) {
return type.simplified = substituteIndexedMappedType(constraint, type);
}
const mapper = createTypeMapper([getTypeParameterFromMappedType(objectType)], [type.indexType]);
const templateMapper = combineTypeMappers(objectType.mapper, mapper);
return type.simplified = mapType(instantiateType(getTemplateTypeFromMappedType(objectType), templateMapper), getSimplifiedType);
}
return type.simplified = type;
}
function substituteIndexedMappedType(objectType: MappedType, type: IndexedAccessType) {
const mapper = createTypeMapper([getTypeParameterFromMappedType(objectType)], [type.indexType]);
const templateMapper = combineTypeMappers(objectType.mapper, mapper);
return instantiateType(getTemplateTypeFromMappedType(objectType), templateMapper);
}
function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode | PropertyName, missingType = accessNode ? errorType : unknownType): Type {
if (objectType === wildcardType || indexType === wildcardType) {
return wildcardType;