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Cache substitution types (#30775) #30905

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Cache substitution types (#30775) #30905

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7 changes: 7 additions & 0 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,7 @@ namespace ts {
const literalTypes = createMap<LiteralType>();
const indexedAccessTypes = createMap<IndexedAccessType>();
const conditionalTypes = createMap<Type>();
const substitutionTypes = createMap<SubstitutionType>();
const evolvingArrayTypes: EvolvingArrayType[] = [];
const undefinedProperties = createMap<Symbol>() as UnderscoreEscapedMap<Symbol>;

Expand Down Expand Up @@ -8870,9 +8871,15 @@ namespace ts {
if (substitute.flags & TypeFlags.AnyOrUnknown) {
return typeVariable;
}
const id = `${getTypeId(typeVariable)}>${getTypeId(substitute)}`;
const cached = substitutionTypes.get(id);
if (cached) {
return cached;
}
const result = <SubstitutionType>createType(TypeFlags.Substitution);
result.typeVariable = typeVariable;
result.substitute = substitute;
substitutionTypes.set(id, result);
return result;
}

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2 changes: 1 addition & 1 deletion tests/baselines/reference/inlinedAliasAssignableToConstraintSameAsAlias.types
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Expand Up @@ -31,7 +31,7 @@ class A {
>z : A[]

whereRelated< // Works // Type is same as A1, but is not assignable to type A
>whereRelated : <RF extends RelationFields = RelationFields, N extends "x" | "y" | "z" = "x" | "y" | "z", A1 extends A = RF[N] extends A[] ? RF[N][0] : never, A2 extends A = ShouldA<RF, N>>() => number
>whereRelated : <RF extends RelationFields = RelationFields, N extends "x" | "y" | "z" = "x" | "y" | "z", A1 extends A = RF[N] extends A[] ? RF[N][0] : never, A2 extends A = RF[N] extends A[] ? RF[N][0] : never>() => number

RF extends RelationFields = RelationFields,
N extends Name = Name,
Expand Down