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Properly handle constraints for types like (T & { [x: string]: D })[K]

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This commit is contained in:
Anders Hejlsberg
2017-08-02 11:54:29 -07:00
parent b2ba275f23
commit caea4f3a50
1 changed files with 51 additions and 1 deletions
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52
src/compiler/checker.ts
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@@ -5900,6 +5900,10 @@ namespace ts {
}
function getConstraintOfIndexedAccess(type: IndexedAccessType) {
const transformed = getTransformedIndexedAccessType(type);
if (transformed) {
return transformed;
}
const baseObjectType = getBaseConstraintOfType(type.objectType);
const baseIndexType = getBaseConstraintOfType(type.indexType);
return baseObjectType || baseIndexType ? getIndexedAccessType(baseObjectType || type.objectType, baseIndexType || type.indexType) : undefined;
@@ -5971,11 +5975,18 @@ namespace ts {
return stringType;
}
if (t.flags & TypeFlags.IndexedAccess) {
const transformed = getTransformedIndexedAccessType(<IndexedAccessType>t);
if (transformed) {
return getBaseConstraint(transformed);
}
const baseObjectType = getBaseConstraint((<IndexedAccessType>t).objectType);
const baseIndexType = getBaseConstraint((<IndexedAccessType>t).indexType);
const baseIndexedAccess = baseObjectType && baseIndexType ? getIndexedAccessType(baseObjectType, baseIndexType) : undefined;
return baseIndexedAccess && baseIndexedAccess !== unknownType ? getBaseConstraint(baseIndexedAccess) : undefined;
}
if (isGenericMappedType(t)) {
return emptyObjectType;
}
return t;
}
}
@@ -7610,7 +7621,44 @@ namespace ts {
false;
}
function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode) {
// Return true if the given type is a non-generic object type with a string index signature and no
// other members.
function isStringIndexOnlyType(type: Type) {
if (type.flags & TypeFlags.Object && !isGenericMappedType(type)) {
const t = resolveStructuredTypeMembers(<ObjectType>type);
return t.properties.length === 0 &&
t.callSignatures.length === 0 && t.constructSignatures.length === 0 &&
t.stringIndexInfo && !t.numberIndexInfo;
}
return false;
}
// Given an indexed access type T[K], if T is an intersection containing one or more generic types and one or
// more object types with only a string index signature, e.g. '(U & V & { [x: string]: D })[K]', return a
// transformed type of the form '(U & V)[K] | D'. This allows us to properly reason about higher order indexed
// access types with default property values as expressed by D.
function getTransformedIndexedAccessType(type: IndexedAccessType): Type {
const objectType = type.objectType;
if (objectType.flags & TypeFlags.Intersection && isGenericObjectType(objectType) && some((<IntersectionType>objectType).types, isStringIndexOnlyType)) {
const regularTypes: Type[] = [];
const stringIndexTypes: Type[] = [];
for (const t of (<IntersectionType>objectType).types) {
if (isStringIndexOnlyType(t)) {
stringIndexTypes.push(getIndexTypeOfType(t, IndexKind.String));
}
else {
regularTypes.push(t);
}
}
return getUnionType([
getIndexedAccessType(getIntersectionType(regularTypes), type.indexType),
getIntersectionType(stringIndexTypes)
]);
}
return undefined;
}
function getIndexedAccessType(objectType: Type, indexType: Type, accessNode?: ElementAccessExpression | IndexedAccessTypeNode): Type {
// If the object type is a mapped type { [P in K]: E }, where K is generic, we 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]>.
@@ -18662,6 +18710,8 @@ namespace ts {
}
function checkIndexedAccessType(node: IndexedAccessTypeNode) {
checkSourceElement(node.objectType);
checkSourceElement(node.indexType);
checkIndexedAccessIndexType(getTypeFromIndexedAccessTypeNode(node), node);
}