Add regression test

Author: ahejlsberg

tests/baselines/reference/conditionalTypes2.errors.txt

@@ -326,4 +326,10 @@ tests/cases/conformance/types/conditional/conditionalTypes2.ts(75,12): error TS2
     declare function gg<T>(f: (x: Foo3<T>) => void): void;
     type Foo3<T> = T extends number ? { n: T } : { x: T };
     gg(ff);
+    
+    // Repro from 39364
+    
+    type StringOrNumber<T extends () => any> = [ReturnType<T>] extends [string] ? string : number;
+    
+    type Test = StringOrNumber<() => number>;  // number
 

tests/baselines/reference/conditionalTypes2.js

@@ -237,6 +237,12 @@ declare function ff(x: Foo3<string>): void;
 declare function gg<T>(f: (x: Foo3<T>) => void): void;
 type Foo3<T> = T extends number ? { n: T } : { x: T };
 gg(ff);
+
+// Repro from 39364
+
+type StringOrNumber<T extends () => any> = [ReturnType<T>] extends [string] ? string : number;
+
+type Test = StringOrNumber<() => number>;  // number
 
 
 //// [conditionalTypes2.js]
@@ -477,3 +483,5 @@ declare type Foo3<T> = T extends number ? {
 } : {
     x: T;
 };
+declare type StringOrNumber<T extends () => any> = [ReturnType<T>] extends [string] ? string : number;
+declare type Test = StringOrNumber<() => number>;

tests/baselines/reference/conditionalTypes2.symbols

@@ -841,3 +841,15 @@ gg(ff);
 >gg : Symbol(gg, Decl(conditionalTypes2.ts, 234, 43))
 >ff : Symbol(ff, Decl(conditionalTypes2.ts, 230, 2))
 
+// Repro from 39364
+
+type StringOrNumber<T extends () => any> = [ReturnType<T>] extends [string] ? string : number;
+>StringOrNumber : Symbol(StringOrNumber, Decl(conditionalTypes2.ts, 237, 7))
+>T : Symbol(T, Decl(conditionalTypes2.ts, 241, 20))
+>ReturnType : Symbol(ReturnType, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(conditionalTypes2.ts, 241, 20))
+
+type Test = StringOrNumber<() => number>;  // number
+>Test : Symbol(Test, Decl(conditionalTypes2.ts, 241, 94))
+>StringOrNumber : Symbol(StringOrNumber, Decl(conditionalTypes2.ts, 237, 7))
+

tests/baselines/reference/conditionalTypes2.types

@@ -527,3 +527,11 @@ gg(ff);
 >gg : <T>(f: (x: Foo3<T>) => void) => void
 >ff : (x: { x: string; }) => void
 
+// Repro from 39364
+
+type StringOrNumber<T extends () => any> = [ReturnType<T>] extends [string] ? string : number;
+>StringOrNumber : StringOrNumber<T>
+
+type Test = StringOrNumber<() => number>;  // number
+>Test : number
+

tests/cases/conformance/types/conditional/conditionalTypes2.ts

@@ -239,3 +239,9 @@ declare function ff(x: Foo3<string>): void;
 declare function gg<T>(f: (x: Foo3<T>) => void): void;
 type Foo3<T> = T extends number ? { n: T } : { x: T };
 gg(ff);
+
+// Repro from 39364
+
+type StringOrNumber<T extends () => any> = [ReturnType<T>] extends [string] ? string : number;
+
+type Test = StringOrNumber<() => number>;  // number