🤖 Pick PR #59121 (Fixed regression in signature insta...) into release-5.5 (#59204)

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

Author: TypeScript Bot

src/compiler/checker.ts

@@ -15942,7 +15942,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function createSignatureTypeMapper(signature: Signature, typeArguments: readonly Type[] | undefined): TypeMapper {
-        return createTypeMapper(signature.typeParameters!, typeArguments);
+        return createTypeMapper(sameMap(signature.typeParameters!, tp => tp.mapper ? instantiateType(tp, tp.mapper) : tp), typeArguments);
     }
 
     function getErasedSignature(signature: Signature): Signature {

tests/baselines/reference/excessiveStackDepthFlatArray.types

@@ -1,7 +1,7 @@
 //// [tests/cases/compiler/excessiveStackDepthFlatArray.ts] ////
 
 === Performance Stats ===
-Instantiation count: 1,000
+Instantiation count: 1,000 -> 2,500
 
 === index.tsx ===
 interface MiddlewareArray<T> extends Array<T> {}

tests/baselines/reference/genericCallInferenceConditionalType1.symbols

@@ -0,0 +1,39 @@
+//// [tests/cases/compiler/genericCallInferenceConditionalType1.ts] ////
+
+=== genericCallInferenceConditionalType1.ts ===
+// https://github.com/microsoft/TypeScript/issues/59108
+
+declare const f: <T>(f: (x: T) => unknown) => (x: T) => unknown;
+>f : Symbol(f, Decl(genericCallInferenceConditionalType1.ts, 2, 13))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 2, 18))
+>f : Symbol(f, Decl(genericCallInferenceConditionalType1.ts, 2, 21))
+>x : Symbol(x, Decl(genericCallInferenceConditionalType1.ts, 2, 25))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 2, 18))
+>x : Symbol(x, Decl(genericCallInferenceConditionalType1.ts, 2, 47))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 2, 18))
+
+declare const g: <T extends unknown>(x: { foo: T }) => unknown;
+>g : Symbol(g, Decl(genericCallInferenceConditionalType1.ts, 3, 13))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 3, 18))
+>x : Symbol(x, Decl(genericCallInferenceConditionalType1.ts, 3, 37))
+>foo : Symbol(foo, Decl(genericCallInferenceConditionalType1.ts, 3, 41))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 3, 18))
+
+const h = f(g);
+>h : Symbol(h, Decl(genericCallInferenceConditionalType1.ts, 5, 5))
+>f : Symbol(f, Decl(genericCallInferenceConditionalType1.ts, 2, 13))
+>g : Symbol(g, Decl(genericCallInferenceConditionalType1.ts, 3, 13))
+
+type FirstParameter<T> = T extends (x: infer P) => unknown ? P : unknown;
+>FirstParameter : Symbol(FirstParameter, Decl(genericCallInferenceConditionalType1.ts, 5, 15))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 7, 20))
+>T : Symbol(T, Decl(genericCallInferenceConditionalType1.ts, 7, 20))
+>x : Symbol(x, Decl(genericCallInferenceConditionalType1.ts, 7, 36))
+>P : Symbol(P, Decl(genericCallInferenceConditionalType1.ts, 7, 44))
+>P : Symbol(P, Decl(genericCallInferenceConditionalType1.ts, 7, 44))
+
+type X = FirstParameter<typeof h>["foo"];
+>X : Symbol(X, Decl(genericCallInferenceConditionalType1.ts, 7, 73))
+>FirstParameter : Symbol(FirstParameter, Decl(genericCallInferenceConditionalType1.ts, 5, 15))
+>h : Symbol(h, Decl(genericCallInferenceConditionalType1.ts, 5, 5))
+

tests/baselines/reference/genericCallInferenceConditionalType1.types

@@ -0,0 +1,45 @@
+//// [tests/cases/compiler/genericCallInferenceConditionalType1.ts] ////
+
+=== genericCallInferenceConditionalType1.ts ===
+// https://github.com/microsoft/TypeScript/issues/59108
+
+declare const f: <T>(f: (x: T) => unknown) => (x: T) => unknown;
+>f : <T>(f: (x: T) => unknown) => (x: T) => unknown
+>  : ^ ^^ ^^                 ^^^^^                 
+>f : (x: T) => unknown
+>  : ^ ^^ ^^^^^       
+>x : T
+>  : ^
+>x : T
+>  : ^
+
+declare const g: <T extends unknown>(x: { foo: T }) => unknown;
+>g : <T extends unknown>(x: { foo: T; }) => unknown
+>  : ^ ^^^^^^^^^       ^^ ^^           ^^^^^       
+>x : { foo: T; }
+>  : ^^^^^^^ ^^^
+>foo : T
+>    : ^
+
+const h = f(g);
+>h : <T extends unknown>(x: { foo: T; }) => unknown
+>  : ^ ^^^^^^^^^       ^^ ^^^^^^^^^ ^^^^^^^^       
+>f(g) : <T extends unknown>(x: { foo: T; }) => unknown
+>     : ^ ^^^^^^^^^       ^^ ^^^^^^^^^ ^^^^^^^^       
+>f : <T>(f: (x: T) => unknown) => (x: T) => unknown
+>  : ^ ^^ ^^                 ^^^^^                 
+>g : <T extends unknown>(x: { foo: T; }) => unknown
+>  : ^ ^^^^^^^^^       ^^ ^^           ^^^^^       
+
+type FirstParameter<T> = T extends (x: infer P) => unknown ? P : unknown;
+>FirstParameter : FirstParameter<T>
+>               : ^^^^^^^^^^^^^^^^^
+>x : P
+>  : ^
+
+type X = FirstParameter<typeof h>["foo"];
+>X : unknown
+>  : ^^^^^^^
+>h : <T extends unknown>(x: { foo: T; }) => unknown
+>  : ^ ^^^^^^^^^       ^^ ^^^^^^^^^ ^^^^^^^^       
+

tests/cases/compiler/genericCallInferenceConditionalType1.ts

@@ -0,0 +1,13 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/59108
+
+declare const f: <T>(f: (x: T) => unknown) => (x: T) => unknown;
+declare const g: <T extends unknown>(x: { foo: T }) => unknown;
+
+const h = f(g);
+
+type FirstParameter<T> = T extends (x: infer P) => unknown ? P : unknown;
+
+type X = FirstParameter<typeof h>["foo"];