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Fixed signature caching issue caused by reentrant signature checking #64077

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6705198
Port "Reuse cached resolved signatures early"
Andarist Aug 23, 2026
2198dcc
Prevent self-contextual return inference and restore diagnostics for …
Andarist Aug 28, 2026
00c2075
add extra test
Andarist Aug 28, 2026
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3 changes: 2 additions & 1 deletion tsc/internal/checker/checker.go
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Expand Up @@ -29795,7 +29795,8 @@ func (c *Checker) getContextualReturnType(functionDecl *ast.Node, contextFlags C
// Otherwise, if the containing function is contextually typed by a function type with exactly one call signature
// and that call signature is non-generic, return statements are contextually typed by the return type of the signature
signature := c.getContextualSignatureForFunctionLikeDeclaration(functionDecl)
if signature != nil && !c.isResolvingReturnTypeOfSignature(signature) {
// A function's own inferred return type must not become contextual evidence for its body.
if signature != nil && signature != c.getSignatureFromDeclaration(functionDecl) && !c.isResolvingReturnTypeOfSignature(signature) {
returnType := c.getReturnTypeOfSignature(signature)
functionFlags := ast.GetFunctionFlags(functionDecl)
if functionFlags&ast.FunctionFlagsGenerator != 0 {
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48 changes: 48 additions & 0 deletions tsc/internal/fourslash/tests/quickInfoGenericDefaultInReentrantCallResolution_test.go
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@@ -0,0 +1,48 @@
package fourslash_test

import (
"testing"

"github.com/microsoft/TypeScript/tsc/internal/fourslash"
"github.com/microsoft/TypeScript/tsc/internal/testutil"
)

func TestQuickInfoGenericDefaultInReentrantCallResolution(t *testing.T) {
t.Parallel()
const content = `// @target: es2015
// @strict: true
declare function fetcher<D>(cfg: unknown): Promise<D>;
type Routes<R> = R extends "x" ? { IN: { v: number }; OUT: string } : never;
function executeFetch<R extends string, T = Routes<R>>(
route: R,
body?: T extends Record<"IN", any> ? T["IN"] : never,
) {
return fetcher<T extends Record<"OUT", any> ? T["OUT"] : T>({ route, body });
}
declare function useCallback<T extends Function>(cb: T, deps: unknown[]): T;
export const /*callback*/cb = useCallback((data: { v: number }) => {
return executeFetch("x", /*argument*/data);
}, []);
export const check: Promise<string> = cb({ v: 1 });`
for _, first := range []string{"callback", "argument", "diagnostics"} {

@Andarist Mateusz Burzyński (Andarist) Aug 28, 2026

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In here, I just make sure the cached signatures stay the same regardless of the order of the LSP requests

t.Run(first, func(t *testing.T) {
t.Parallel()
defer testutil.RecoverAndFail(t, "Panic on fourslash test")
f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
defer done()
callbackInfo := "const cb: (data: {\n v: number;\n}) => Promise<string>"
argumentInfo := "(parameter) data: {\n v: number;\n}"
switch first {
case "callback":
f.VerifyQuickInfoAt(t, "callback", callbackInfo, "")
case "argument":
f.VerifyQuickInfoAt(t, "argument", argumentInfo, "")
case "diagnostics":
f.VerifyNoErrors(t)
}
f.VerifyQuickInfoAt(t, "callback", callbackInfo, "")
f.VerifyQuickInfoAt(t, "argument", argumentInfo, "")
f.VerifyNoErrors(t)
})
}
}
114 changes: 114 additions & 0 deletions tsc/testdata/baselines/reference/compiler/genericDefaultInReentrantCallResolution.symbols
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//// [tests/cases/compiler/genericDefaultInReentrantCallResolution.ts] ////

=== genericDefaultInReentrantCallResolution.ts ===
// https://github.com/microsoft/TypeScript/issues/63949

declare function fetcher<D>(cfg: unknown): Promise<D>;
>fetcher : Symbol(fetcher, Decl(genericDefaultInReentrantCallResolution.ts, 0, 0))
>D : Symbol(D, Decl(genericDefaultInReentrantCallResolution.ts, 2, 25))
>cfg : Symbol(cfg, Decl(genericDefaultInReentrantCallResolution.ts, 2, 28))
>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
>D : Symbol(D, Decl(genericDefaultInReentrantCallResolution.ts, 2, 25))

type Routes<R> = R extends "x" ? { IN: { v: number }; OUT: string } : never;
>Routes : Symbol(Routes, Decl(genericDefaultInReentrantCallResolution.ts, 2, 54))
>R : Symbol(R, Decl(genericDefaultInReentrantCallResolution.ts, 4, 12))
>R : Symbol(R, Decl(genericDefaultInReentrantCallResolution.ts, 4, 12))
>IN : Symbol(IN, Decl(genericDefaultInReentrantCallResolution.ts, 4, 34))
>v : Symbol(v, Decl(genericDefaultInReentrantCallResolution.ts, 4, 40))
>OUT : Symbol(OUT, Decl(genericDefaultInReentrantCallResolution.ts, 4, 53))

function executeFetch<R extends string, T = Routes<R>>(
>executeFetch : Symbol(executeFetch, Decl(genericDefaultInReentrantCallResolution.ts, 4, 76))
>R : Symbol(R, Decl(genericDefaultInReentrantCallResolution.ts, 6, 22))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 6, 39))
>Routes : Symbol(Routes, Decl(genericDefaultInReentrantCallResolution.ts, 2, 54))
>R : Symbol(R, Decl(genericDefaultInReentrantCallResolution.ts, 6, 22))

route: R,
>route : Symbol(route, Decl(genericDefaultInReentrantCallResolution.ts, 6, 55))
>R : Symbol(R, Decl(genericDefaultInReentrantCallResolution.ts, 6, 22))

body?: T extends Record<"IN", any> ? T["IN"] : never,
>body : Symbol(body, Decl(genericDefaultInReentrantCallResolution.ts, 7, 13))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 6, 39))
>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 6, 39))

) {
return fetcher<T extends Record<"OUT", any> ? T["OUT"] : T>({ route, body });
>fetcher : Symbol(fetcher, Decl(genericDefaultInReentrantCallResolution.ts, 0, 0))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 6, 39))
>Record : Symbol(Record, Decl(lib.es5.d.ts, --, --))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 6, 39))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 6, 39))
>route : Symbol(route, Decl(genericDefaultInReentrantCallResolution.ts, 10, 65))
>body : Symbol(body, Decl(genericDefaultInReentrantCallResolution.ts, 10, 72))
}

declare function useCallback<T extends Function>(cb: T, deps: unknown[]): T;
>useCallback : Symbol(useCallback, Decl(genericDefaultInReentrantCallResolution.ts, 11, 1))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 13, 29))
>Function : Symbol(Function, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
>cb : Symbol(cb, Decl(genericDefaultInReentrantCallResolution.ts, 13, 49))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 13, 29))
>deps : Symbol(deps, Decl(genericDefaultInReentrantCallResolution.ts, 13, 55))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 13, 29))

export const cb = useCallback((data: { v: number }) => {
>cb : Symbol(cb, Decl(genericDefaultInReentrantCallResolution.ts, 15, 12))
>useCallback : Symbol(useCallback, Decl(genericDefaultInReentrantCallResolution.ts, 11, 1))
>data : Symbol(data, Decl(genericDefaultInReentrantCallResolution.ts, 15, 31))
>v : Symbol(v, Decl(genericDefaultInReentrantCallResolution.ts, 15, 38))

return executeFetch("x", data);
>executeFetch : Symbol(executeFetch, Decl(genericDefaultInReentrantCallResolution.ts, 4, 76))
>data : Symbol(data, Decl(genericDefaultInReentrantCallResolution.ts, 15, 31))

}, []);

export const check: Promise<string> = cb({ v: 1 });
>check : Symbol(check, Decl(genericDefaultInReentrantCallResolution.ts, 19, 12))
>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --))
>cb : Symbol(cb, Decl(genericDefaultInReentrantCallResolution.ts, 15, 12))
>v : Symbol(v, Decl(genericDefaultInReentrantCallResolution.ts, 19, 42))

// https://github.com/microsoft/TypeScript/issues/63949#issuecomment-5400383233

declare function request<T = { input: { value: number }; output: string }>(
>request : Symbol(request, Decl(genericDefaultInReentrantCallResolution.ts, 19, 51))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 23, 25))
>input : Symbol(input, Decl(genericDefaultInReentrantCallResolution.ts, 23, 30))
>value : Symbol(value, Decl(genericDefaultInReentrantCallResolution.ts, 23, 39))
>output : Symbol(output, Decl(genericDefaultInReentrantCallResolution.ts, 23, 56))

body?: T extends { input: unknown } ? T["input"] : never,
>body : Symbol(body, Decl(genericDefaultInReentrantCallResolution.ts, 23, 75))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 23, 25))
>input : Symbol(input, Decl(genericDefaultInReentrantCallResolution.ts, 24, 22))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 23, 25))

): T extends { output: unknown } ? T["output"] : T;
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 23, 25))
>output : Symbol(output, Decl(genericDefaultInReentrantCallResolution.ts, 25, 14))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 23, 25))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 23, 25))

declare function identity<T>(callback: T): T;
>identity : Symbol(identity, Decl(genericDefaultInReentrantCallResolution.ts, 25, 51))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 27, 26))
>callback : Symbol(callback, Decl(genericDefaultInReentrantCallResolution.ts, 27, 29))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 27, 26))
>T : Symbol(T, Decl(genericDefaultInReentrantCallResolution.ts, 27, 26))

identity((data: { value: number }) =>
>identity : Symbol(identity, Decl(genericDefaultInReentrantCallResolution.ts, 25, 51))
>data : Symbol(data, Decl(genericDefaultInReentrantCallResolution.ts, 29, 10))
>value : Symbol(value, Decl(genericDefaultInReentrantCallResolution.ts, 29, 17))

request(data),
>request : Symbol(request, Decl(genericDefaultInReentrantCallResolution.ts, 19, 51))
>data : Symbol(data, Decl(genericDefaultInReentrantCallResolution.ts, 29, 10))

);

96 changes: 96 additions & 0 deletions tsc/testdata/baselines/reference/compiler/genericDefaultInReentrantCallResolution.types
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//// [tests/cases/compiler/genericDefaultInReentrantCallResolution.ts] ////

=== genericDefaultInReentrantCallResolution.ts ===
// https://github.com/microsoft/TypeScript/issues/63949

declare function fetcher<D>(cfg: unknown): Promise<D>;
>fetcher : <D>(cfg: unknown) => Promise<D>
>cfg : unknown

type Routes<R> = R extends "x" ? { IN: { v: number }; OUT: string } : never;
>Routes : Routes<R>
>IN : { v: number; }
>v : number
>OUT : string

function executeFetch<R extends string, T = Routes<R>>(
>executeFetch : <R extends string, T = Routes<R>>(route: R, body?: T extends Record<"IN", any> ? T["IN"] : never) => Promise<T extends Record<"OUT", any> ? T["OUT"] : T>

route: R,
>route : R

body?: T extends Record<"IN", any> ? T["IN"] : never,
>body : (T extends Record<"IN", any> ? T["IN"] : never) | undefined

) {
return fetcher<T extends Record<"OUT", any> ? T["OUT"] : T>({ route, body });
>fetcher<T extends Record<"OUT", any> ? T["OUT"] : T>({ route, body }) : Promise<T extends Record<"OUT", any> ? T["OUT"] : T>
>fetcher : <D>(cfg: unknown) => Promise<D>
>{ route, body } : { route: R; body: (T extends Record<"IN", any> ? T["IN"] : never) | undefined; }
>route : R
>body : (T extends Record<"IN", any> ? T["IN"] : never) | undefined
}

declare function useCallback<T extends Function>(cb: T, deps: unknown[]): T;
>useCallback : <T extends Function>(cb: T, deps: unknown[]) => T
>cb : T
>deps : unknown[]

export const cb = useCallback((data: { v: number }) => {
>cb : (data: { v: number; }) => Promise<string>
>useCallback((data: { v: number }) => { return executeFetch("x", data);}, []) : (data: { v: number; }) => Promise<string>
>useCallback : <T extends Function>(cb: T, deps: unknown[]) => T
>(data: { v: number }) => { return executeFetch("x", data);} : (data: { v: number; }) => Promise<string>
>data : { v: number; }
>v : number

return executeFetch("x", data);
>executeFetch("x", data) : Promise<string>
>executeFetch : <R extends string, T = Routes<R>>(route: R, body?: T extends Record<"IN", any> ? T["IN"] : never) => Promise<T extends Record<"OUT", any> ? T["OUT"] : T>
>"x" : "x"
>data : { v: number; }

}, []);
>[] : never[]

export const check: Promise<string> = cb({ v: 1 });
>check : Promise<string>
>cb({ v: 1 }) : Promise<string>
>cb : (data: { v: number; }) => Promise<string>
>{ v: 1 } : { v: number; }
>v : number
>1 : 1

// https://github.com/microsoft/TypeScript/issues/63949#issuecomment-5400383233

declare function request<T = { input: { value: number }; output: string }>(
>request : <T = { input: { value: number; }; output: string; }>(body?: T extends { input: unknown; } ? T["input"] : never) => T extends { output: unknown; } ? T["output"] : T
>input : { value: number; }
>value : number
>output : string

body?: T extends { input: unknown } ? T["input"] : never,
>body : (T extends { input: unknown; } ? T["input"] : never) | undefined
>input : unknown

): T extends { output: unknown } ? T["output"] : T;
>output : unknown

declare function identity<T>(callback: T): T;
>identity : <T>(callback: T) => T
>callback : T

identity((data: { value: number }) =>
>identity((data: { value: number }) => request(data),) : (data: { value: number; }) => string
>identity : <T>(callback: T) => T
>(data: { value: number }) => request(data) : (data: { value: number; }) => string
>data : { value: number; }
>value : number

request(data),
>request(data) : string
>request : <T = { input: { value: number; }; output: string; }>(body?: T extends { input: unknown; } ? T["input"] : never) => T extends { output: unknown; } ? T["output"] : T
>data : { value: number; }

);

16 changes: 16 additions & 0 deletions ...elines/reference/compiler/reentrantCallDoesNotReuseInapplicableCachedSignature.errors.txt
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reentrantCallDoesNotReuseInapplicableCachedSignature.ts(6,20): error TS2345: Argument of type '(a: string) => string' is not assignable to parameter of type '(a: string) => number'.
Type 'string' is not assignable to type 'number'.


==== reentrantCallDoesNotReuseInapplicableCachedSignature.ts (1 errors) ====
declare const example: (f: (a: string) => number) => string;

const f = (a: string) => g();

const g = () => {
return example(f);
~
!!! error TS2345: Argument of type '(a: string) => string' is not assignable to parameter of type '(a: string) => number'.
!!! error TS2345: Type 'string' is not assignable to type 'number'.
};

22 changes: 22 additions & 0 deletions ...baselines/reference/compiler/reentrantCallDoesNotReuseInapplicableCachedSignature.symbols
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//// [tests/cases/compiler/reentrantCallDoesNotReuseInapplicableCachedSignature.ts] ////

=== reentrantCallDoesNotReuseInapplicableCachedSignature.ts ===
declare const example: (f: (a: string) => number) => string;
>example : Symbol(example, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 0, 13))
>f : Symbol(f, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 0, 24))
>a : Symbol(a, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 0, 28))

const f = (a: string) => g();
>f : Symbol(f, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 2, 5))
>a : Symbol(a, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 2, 11))
>g : Symbol(g, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 4, 5))

const g = () => {
>g : Symbol(g, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 4, 5))

return example(f);
>example : Symbol(example, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 0, 13))
>f : Symbol(f, Decl(reentrantCallDoesNotReuseInapplicableCachedSignature.ts, 2, 5))

};

26 changes: 26 additions & 0 deletions ...a/baselines/reference/compiler/reentrantCallDoesNotReuseInapplicableCachedSignature.types
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//// [tests/cases/compiler/reentrantCallDoesNotReuseInapplicableCachedSignature.ts] ////

=== reentrantCallDoesNotReuseInapplicableCachedSignature.ts ===
declare const example: (f: (a: string) => number) => string;
>example : (f: (a: string) => number) => string
>f : (a: string) => number
>a : string

const f = (a: string) => g();
>f : (a: string) => string
>(a: string) => g() : (a: string) => string
>a : string
>g() : string
>g : () => string

const g = () => {
>g : () => string
>() => { return example(f);} : () => string

return example(f);
>example(f) : string
>example : (f: (a: string) => number) => string
>f : (a: string) => string

};

8 changes: 4 additions & 4 deletions tsc/testdata/baselines/reference/conformance/intraExpressionInferencesJsx.types
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Expand Up @@ -143,10 +143,10 @@ const Component = <T extends Animations>({
>func : () => { a: true; }

return {
>{ a: true, } : { a: true; }

@Andarist Mateusz Burzyński (Andarist) Aug 28, 2026

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I think those are correct, the inferred signature here includes boolean and then that object became checked with that as its contextual part so a true literal became here contextually-typed by a boolean and that makes it to retain the true type (instead of widening to boolean)

>{ a: true, } : { a: boolean; }

a: true,
>a : true
>a : boolean
>true : true

};
Expand Down Expand Up @@ -192,10 +192,10 @@ const Component = <T extends Animations>({
>() => { return { a: true, }; } : () => { a: true; }

return {
>{ a: true, } : { a: true; }
>{ a: true, } : { a: boolean; }

a: true,
>a : true
>a : boolean
>true : true

};
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2 changes: 1 addition & 1 deletion tsc/testdata/baselines/reference/conformance/neverReturningFunctions1.types
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Expand Up @@ -591,7 +591,7 @@ const Component = registerComponent('test-component', {
>parse : () => boolean[]

return [true];
>[true] : true[]
>[true] : boolean[]
>true : true
}
},
Expand Down
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