swc/crates/swc_ecma_parser/tests/tsc/genericCallWithGenericSignatureArguments3.ts

// When a function expression is inferentially typed (section 4.9.3) and a type assigned to a parameter in that expression references type parameters for which inferences are being made, 
// the corresponding inferred type arguments to become fixed and no further candidate inferences are made for them.

function foo<T>(x: T, a: (x: T) => T, b: (x: T) => T) {
    var r: (x: T) => T;
    return r;
}

var r1 = foo('', (x: string) => '', (x: Object) => null); // any => any
var r1ii = foo('', (x) => '', (x) => null); // string => string
var r2 = foo('', (x: string) => '', (x: Object) => ''); // string => string
var r3 = foo(null, (x: Object) => '', (x: string) => ''); // Object => Object
var r4 = foo(null, (x) => '', (x) => ''); // any => any
var r5 = foo(new Object(), (x) => '', (x) => ''); // Object => Object

enum E { A }
enum F { A }

var r6 = foo(E.A, (x: number) => E.A, (x: F) => F.A); // number => number 


function foo2<T, U>(x: T, a: (x: T) => U, b: (x: T) => U) {
    var r: (x: T) => U;
    return r;
}

var r8 = foo2('', (x) => '', (x) => null); // string => string
var r9 = foo2(null, (x) => '', (x) => ''); // any => any
var r10 = foo2(null, (x: Object) => '', (x: string) => ''); // Object => Object

var x: (a: string) => boolean;
var r11 = foo2(x, (a1: (y: string) => string) => (n: Object) => 1, (a2: (z: string) => string) => 2); // error
var r12 = foo2(x, (a1: (y: string) => boolean) => (n: Object) => 1, (a2: (z: string) => boolean) => 2); // error