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Fixed an issue with optionality not being stripped from generic mapped types on indexed access #59921

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Fixed an issue with optionality not being stripped from generic mapped types on indexed access #59921

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6 changes: 3 additions & 3 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -19103,9 +19103,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
const mapper = createTypeMapper([getTypeParameterFromMappedType(objectType)], [index]);
const templateMapper = combineTypeMappers(objectType.mapper, mapper);
const instantiatedTemplateType = instantiateType(getTemplateTypeFromMappedType(objectType.target as MappedType || objectType), templateMapper);
const isOptional = getMappedTypeOptionality(objectType) > 0 || (isGenericType(objectType) ?
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In the given repro the immediate modifiers type has -? for which getMappedTypeOptionality returns -1. So the first condition was not satisfied and the compiler proceeded to compute getCombinedMappedTypeOptionality. This time it was called with the modifiers type and not the original object type. Since that was a mapped type too it got its modifiers type etc.

Essentially this was skipping the outermost mapped type modifiers in this scenario - the ones that were supposed strip the optionality.

getCombinedMappedTypeOptionality(getModifiersTypeFromMappedType(objectType)) > 0 :
couldAccessOptionalProperty(objectType, index));
const isOptional = isGenericType(objectType) ?
getCombinedMappedTypeOptionality(objectType) > 0 :
getMappedTypeOptionality(objectType) > 0 || couldAccessOptionalProperty(objectType, index);
return addOptionality(instantiatedTemplateType, /*isProperty*/ true, isOptional);
}

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20 changes: 20 additions & 0 deletions tests/baselines/reference/genericMappedTypeOptionalityModifier1.errors.txt
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@@ -0,0 +1,20 @@
genericMappedTypeOptionalityModifier1.ts(10,9): error TS2322: Type 'undefined' is not assignable to type 'RequiredValues'.


==== genericMappedTypeOptionalityModifier1.ts (1 errors) ====
// https://github.com/microsoft/TypeScript/issues/59902

const example = <T extends string>() => {
type SomeOptional = { [key in T]?: 1 };

type AllRequired = { [key in keyof SomeOptional]-?: 1 };

type RequiredValues = AllRequired[keyof AllRequired];

const x: RequiredValues = undefined; // error
~
!!! error TS2322: Type 'undefined' is not assignable to type 'RequiredValues'.

return x;
};

34 changes: 34 additions & 0 deletions tests/baselines/reference/genericMappedTypeOptionalityModifier1.symbols
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//// [tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts] ////

=== genericMappedTypeOptionalityModifier1.ts ===
// https://github.com/microsoft/TypeScript/issues/59902

const example = <T extends string>() => {
>example : Symbol(example, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 5))
>T : Symbol(T, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 17))

type SomeOptional = { [key in T]?: 1 };
>SomeOptional : Symbol(SomeOptional, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 41))
>key : Symbol(key, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 25))
>T : Symbol(T, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 17))

type AllRequired = { [key in keyof SomeOptional]-?: 1 };
>AllRequired : Symbol(AllRequired, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 41))
>key : Symbol(key, Decl(genericMappedTypeOptionalityModifier1.ts, 5, 24))
>SomeOptional : Symbol(SomeOptional, Decl(genericMappedTypeOptionalityModifier1.ts, 2, 41))

type RequiredValues = AllRequired[keyof AllRequired];
>RequiredValues : Symbol(RequiredValues, Decl(genericMappedTypeOptionalityModifier1.ts, 5, 58))
>AllRequired : Symbol(AllRequired, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 41))
>AllRequired : Symbol(AllRequired, Decl(genericMappedTypeOptionalityModifier1.ts, 3, 41))

const x: RequiredValues = undefined; // error
>x : Symbol(x, Decl(genericMappedTypeOptionalityModifier1.ts, 9, 7))
>RequiredValues : Symbol(RequiredValues, Decl(genericMappedTypeOptionalityModifier1.ts, 5, 58))
>undefined : Symbol(undefined)

return x;
>x : Symbol(x, Decl(genericMappedTypeOptionalityModifier1.ts, 9, 7))

};

35 changes: 35 additions & 0 deletions tests/baselines/reference/genericMappedTypeOptionalityModifier1.types
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//// [tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts] ////

=== genericMappedTypeOptionalityModifier1.ts ===
// https://github.com/microsoft/TypeScript/issues/59902

const example = <T extends string>() => {
>example : <T extends string>() => { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
> : ^ ^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
><T extends string>() => { type SomeOptional = { [key in T]?: 1 }; type AllRequired = { [key in keyof SomeOptional]-?: 1 }; type RequiredValues = AllRequired[keyof AllRequired]; const x: RequiredValues = undefined; // error return x;} : <T extends string>() => { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
> : ^ ^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

type SomeOptional = { [key in T]?: 1 };
>SomeOptional : { [key in T]?: 1 | undefined; }
> : ^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^

type AllRequired = { [key in keyof SomeOptional]-?: 1 };
>AllRequired : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }
> : ^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

type RequiredValues = AllRequired[keyof AllRequired];
>RequiredValues : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
> : ^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

const x: RequiredValues = undefined; // error
>x : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
> : ^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>undefined : undefined
> : ^^^^^^^^^

return x;
>x : { [key_1 in keyof { [key in T]?: 1 | undefined; }]-?: 1; }[T]
> : ^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

};

16 changes: 16 additions & 0 deletions tests/cases/compiler/genericMappedTypeOptionalityModifier1.ts
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// @strict: true
// @noEmit: true

// https://github.com/microsoft/TypeScript/issues/59902

const example = <T extends string>() => {
type SomeOptional = { [key in T]?: 1 };

type AllRequired = { [key in keyof SomeOptional]-?: 1 };

type RequiredValues = AllRequired[keyof AllRequired];

const x: RequiredValues = undefined; // error

return x;
};