Clang rejects valid program when using function call operator

[ranaanoop]

The following valid program is rejected by clang: Demo

struct A {
    A() {}
    A(A&&) = default;
    void f(this A) {}
    void operator() (this A) {}
};

int main() {
    A{}.f(); // ok
    A{}();   // Clang rejects while gcc and msvc accepts 
}

As per over.call, the expression A{}() is equivalent to(interpreted as) A{}.operator()() which clang accepts.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Anoop Rana (ranaanoop)

The following valid program is rejected by clang: [Demo](https://godbolt.org/z/rK5W6G7K8) ``` struct A { A() {} A(A&&) = default; void f(this A) {} void operator() (this A) {} };

int main() {
A{}.f(); // ok
A{}(); // Clang rejects while gcc and msvc accepts
}

As per [over.call](https://eel.is/c++draft/over.call#<!-- -->1.sentence-5), the expression `A{}()` is equivalent to(interpreted as) `A{}.operator()()` which [clang accepts](https://godbolt.org/z/eTc6b6TYq).
</details>

[shafik]

This looks like a clang bug: https://godbolt.org/z/TK7KeEWjG

[zygoloid]

For some reason, the this A parameter is being copied from the A{} prvalue -- the parameter should be initialized directly with the prvalue instead.