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Allow parameters to be contextually-typed based on contextual rest instantiated using return mapper #62341

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Allow parameters to be contextually-typed based on contextual rest instantiated using return mapper #62341

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f3691a3
Allow parameters to be contextually-typed based on contextual rest in…
Andarist Aug 27, 2025
37499a8
fix filename typo
Andarist Aug 27, 2025
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4 changes: 3 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -39547,7 +39547,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
inferFromAnnotatedParametersAndReturn(signature, contextualSignature, inferenceContext!);
const restType = getEffectiveRestType(contextualSignature);
if (restType && restType.flags & TypeFlags.TypeParameter) {
instantiatedContextualSignature = instantiateSignature(contextualSignature, inferenceContext!.nonFixingMapper);
const info = find(inferenceContext!.inferences, info => info.typeParameter === restType);
const mapper = combineTypeMappers(info && !hasInferenceCandidates(info) ? inferenceContext!.returnMapper : undefined, inferenceContext!.nonFixingMapper);
instantiatedContextualSignature = instantiateSignature(contextualSignature, mapper);
}
}
instantiatedContextualSignature ||= inferenceContext ?
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42 changes: 42 additions & 0 deletions .../baselines/reference/contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.symbols
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@@ -0,0 +1,42 @@
//// [tests/cases/compiler/contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts] ////

=== contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts ===
// https://github.com/microsoft/TypeScript/issues/62336

declare function call<T>(fn: (a: string, b: T) => unknown): (b: T) => unknown;
>call : Symbol(call, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 0, 0))
>T : Symbol(T, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 22))
>fn : Symbol(fn, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 25))
>a : Symbol(a, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 30))
>b : Symbol(b, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 40))
>T : Symbol(T, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 22))
>b : Symbol(b, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 61))
>T : Symbol(T, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 22))

declare function fn<Args extends any[]>(
>fn : Symbol(fn, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 78))
>Args : Symbol(Args, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 4, 20))

fn: (...args: Args) => unknown,
>fn : Symbol(fn, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 4, 40))
>args : Symbol(args, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 5, 7))
>Args : Symbol(Args, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 4, 20))

): (...args: Args) => unknown;
>args : Symbol(args, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 6, 4))
>Args : Symbol(Args, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 4, 20))

call(
>call : Symbol(call, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 0, 0))

fn(function (a, b: number) {
>fn : Symbol(fn, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 2, 78))
>a : Symbol(a, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 9, 15))
>b : Symbol(b, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 9, 17))

a; // string
>a : Symbol(a, Decl(contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts, 9, 15))

}),
);

56 changes: 56 additions & 0 deletions tests/baselines/reference/contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.types
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@@ -0,0 +1,56 @@
//// [tests/cases/compiler/contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts] ////

=== contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts ===
// https://github.com/microsoft/TypeScript/issues/62336

declare function call<T>(fn: (a: string, b: T) => unknown): (b: T) => unknown;
>call : <T>(fn: (a: string, b: T) => unknown) => (b: T) => unknown
> : ^ ^^ ^^ ^^^^^
>fn : (a: string, b: T) => unknown
> : ^ ^^ ^^ ^^ ^^^^^
>a : string
> : ^^^^^^
>b : T
> : ^
>b : T
> : ^

declare function fn<Args extends any[]>(
>fn : <Args extends any[]>(fn: (...args: Args) => unknown) => (...args: Args) => unknown
> : ^ ^^^^^^^^^ ^^ ^^ ^^^^^

fn: (...args: Args) => unknown,
>fn : (...args: Args) => unknown
> : ^^^^ ^^ ^^^^^
>args : Args
> : ^^^^

): (...args: Args) => unknown;
>args : Args
> : ^^^^

call(
>call( fn(function (a, b: number) { a; // string }),) : (b: number) => unknown
> : ^ ^^^^^^^^^^^^^
>call : <T>(fn: (a: string, b: T) => unknown) => (b: T) => unknown
> : ^ ^^ ^^ ^^^^^

fn(function (a, b: number) {
>fn(function (a, b: number) { a; // string }) : (a: string, b: number) => unknown
> : ^^^^^^^^^^^^^^^^^^^^^^^^^^
>fn : <Args extends any[]>(fn: (...args: Args) => unknown) => (...args: Args) => unknown
> : ^ ^^^^^^^^^ ^^ ^^ ^^^^^
>function (a, b: number) { a; // string } : (a: string, b: number) => void
> : ^ ^^^^^^^^^^ ^^ ^^^^^^^^^
>a : string
> : ^^^^^^
>b : number
> : ^^^^^^

a; // string
>a : string
> : ^^^^^^

}),
);

16 changes: 16 additions & 0 deletions tests/cases/compiler/contextuallyTypeParametersUsingInstantiatedRestReturnMapper1.ts
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@@ -0,0 +1,16 @@
// @strict: true
// @noEmit: true

// https://github.com/microsoft/TypeScript/issues/62336

declare function call<T>(fn: (a: string, b: T) => unknown): (b: T) => unknown;

declare function fn<Args extends any[]>(
fn: (...args: Args) => unknown,
): (...args: Args) => unknown;

call(
fn(function (a, b: number) {
a; // string
}),
);
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