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Replace replaceable indexed accesses early to reuse cache entries #62822

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Replace replaceable indexed accesses early to reuse cache entries #62822

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27 changes: 10 additions & 17 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -14663,23 +14663,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
inferredProp.declarations = prop.declarations;
inferredProp.links.nameType = getSymbolLinks(prop).nameType;
inferredProp.links.propertyType = getTypeOfSymbol(prop);
if (
type.constraintType.type.flags & TypeFlags.IndexedAccess
&& (type.constraintType.type as IndexedAccessType).objectType.flags & TypeFlags.TypeParameter
&& (type.constraintType.type as IndexedAccessType).indexType.flags & TypeFlags.TypeParameter
) {
// A reverse mapping of `{[K in keyof T[K_1]]: T[K_1]}` is the same as that of `{[K in keyof T]: T}`, since all we care about is
// inferring to the "type parameter" (or indexed access) shared by the constraint and template. So, to reduce the number of
// type identities produced, we simplify such indexed access occurences
const newTypeParam = (type.constraintType.type as IndexedAccessType).objectType;
const newMappedType = replaceIndexedAccess(type.mappedType, type.constraintType.type as ReplaceableIndexedAccessType, newTypeParam);
inferredProp.links.mappedType = newMappedType as MappedType;
inferredProp.links.constraintType = getIndexType(newTypeParam) as IndexType;
}
else {
inferredProp.links.mappedType = type.mappedType;
inferredProp.links.constraintType = type.constraintType;
}
inferredProp.links.mappedType = type.mappedType;
inferredProp.links.constraintType = type.constraintType;
members.set(prop.escapedName, inferredProp);
}
setStructuredTypeMembers(type, members, emptyArray, emptyArray, indexInfos);
Expand Down Expand Up @@ -26370,6 +26355,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
* variable T[P] (i.e. we treat the type T[P] as the type variable we're inferring for).
*/
function inferTypeForHomomorphicMappedType(source: Type, target: MappedType, constraint: IndexType): Type | undefined {
// A reverse mapping of `{[K in keyof T[K_1]]: T[K_1]}` is the same as that of `{[K in keyof T]: T}`, since all we care about is
// inferring to the "type parameter" (or indexed access) shared by the constraint and template. So, to reduce the number of
// type identities produced, we simplify such indexed access occurences
if (constraint.type.flags & TypeFlags.IndexedAccess) {
const newTypeParam = (constraint.type as IndexedAccessType).objectType;
target = replaceIndexedAccess(target, constraint.type as ReplaceableIndexedAccessType, newTypeParam) as MappedType;
constraint = getIndexType(newTypeParam) as IndexType;
}
const cacheKey = source.id + "," + target.id + "," + constraint.id;
if (reverseHomomorphicMappedCache.has(cacheKey)) {
return reverseHomomorphicMappedCache.get(cacheKey);
Expand Down
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