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Add optionality to mapped type substitutions based on existence of an optional modifiers prop #57493

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Add optionality to mapped type substitutions based on existence of an optional modifiers prop #57493

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12 changes: 11 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -18514,10 +18514,20 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
return !!(getUnionType([intersectTypes(type1, type2), neverType]).flags & TypeFlags.Never);
}

function hasOptionalModifiersProperty(mappedType: MappedType) {
const modifiersType = getApparentType(getModifiersTypeFromMappedType(mappedType));
if (!(modifiersType.flags & TypeFlags.Object)) {
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TODO: might also have to handle intersection (that's what isWeakType is doing) and I need to recheck behavior with unions

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recheck behavior with union types later

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@Mateusnasciment Please try to keep comments actionable and on-topic

return false;
}
const properties = resolveStructuredTypeMembers(modifiersType as ObjectType).properties;
return some(properties, p => !!(p.flags & SymbolFlags.Optional));
}

function substituteIndexedMappedType(objectType: MappedType, index: Type) {
const mapper = createTypeMapper([getTypeParameterFromMappedType(objectType)], [index]);
const templateMapper = combineTypeMappers(objectType.mapper, mapper);
return instantiateType(getTemplateTypeFromMappedType(objectType.target as MappedType || objectType), templateMapper);
const type = instantiateType(getTemplateTypeFromMappedType(objectType.target as MappedType || objectType), templateMapper);
return addOptionality(type, /*isProperty*/ true, hasOptionalModifiersProperty(objectType));
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TODO: this should get the list of known optional properties and check if index is assignable to that, if the substitution happens using a known non-optional property then the optionality shouldn't be added

}

function getIndexedAccessType(objectType: Type, indexType: Type, accessFlags = AccessFlags.None, accessNode?: ElementAccessExpression | IndexedAccessTypeNode | PropertyName | BindingName | SyntheticExpression, aliasSymbol?: Symbol, aliasTypeArguments?: readonly Type[]): Type {
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6 changes: 5 additions & 1 deletion tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
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Expand Up @@ -31,9 +31,10 @@ keyofAndIndexedAccess2.ts(68,3): error TS2322: Type 'number' is not assignable t
'number' is assignable to the constraint of type 'T[K]', but 'T[K]' could be instantiated with a different subtype of constraint 'number'.
keyofAndIndexedAccess2.ts(108,5): error TS2322: Type '123' is not assignable to type 'Type[K]'.
Type 'number' is not assignable to type 'never'.
keyofAndIndexedAccess2.ts(115,21): error TS2313: Type parameter 'Q' has a circular constraint.


==== keyofAndIndexedAccess2.ts (23 errors) ====
==== keyofAndIndexedAccess2.ts (24 errors) ====
function f1(obj: { a: number, b: 0 | 1, c: string }, k0: 'a', k1: 'a' | 'b', k2: 'a' | 'b' | 'c') {
obj[k0] = 1;
obj[k0] = 2;
Expand Down Expand Up @@ -205,6 +206,9 @@ keyofAndIndexedAccess2.ts(108,5): error TS2322: Type '123' is not assignable to
type StrictExtract<T, U> = T extends U ? U extends T ? T : never : never;
type StrictExclude<T, U> = T extends StrictExtract<T, U> ? never : T;
type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
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I'm not sure what's the best strategy to avoid circularity here. I didn't look into it yet. I'm hitting the 🛌 but maybe somebody would chime in with some suggestions in the meantime ;p

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2313: Type parameter 'Q' has a circular constraint.
!!! related TS2751 keyofAndIndexedAccess2.ts:116:36: Circularity originates in type at this location.
type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;

// Repros from #30938
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