Type arguments are not being inferred correctly from method group

[hez2010]

Version Used: .NET 8

Steps to Reproduce:

var foo = new Foo();
Bar(foo.A<int, int, int, int>); // <--- error
Bar(ReturnMySelf(foo.A<int, int, int, int>)); // <--- ok

void Bar<T1, T2, T3, TResult>(Func<T1, T2, T3, TResult> func) {}
T ReturnMySelf<T>(T x) => x;

class Foo { public extern TResult A<T1, T2, T3, TResult>(T1 a, T2 b, T3 c); }

It's too weird that you just return the type itself and then it gets inferred.

Expected Behavior:

The compiler can infer the type arguments in both two Bar calls.

Actual Behavior:

Only the second call Bar(ReturnMySelf(foo.A<int, int, int, int>)) can infer the type arguments correctly.

[huoyaoyuan]

I believe this is a language issue, natural type of method group doesn't employ such inference.

[jcouv]

Yes, I think this is currently by-design. We have a csharplang proposal to make this work.
Note: the current workaround would be to use a lambda Bar((int x, int y, int z) => foo.A<int, int, int, int>(x, y, z));.