clang: regression - erroneous warning when calling `[[nodiscard]]` `static` function through a `std::forward`

[elbeno]

This code:

#include <utility>

struct A {
    [[nodiscard]] static auto f() {
        return 42;
    }
};

template <typename T>
auto f(T &&t) {
    return std::forward<T>(t).f();
}

auto b = f(A{}) == 42;

https://godbolt.org/z/cxGvxM9bn

Provokes a warning:

<source>:11:12: warning: ignoring return value of function declared with 'nodiscard' attribute [-Wunused-result]
   11 |     return std::forward<T>(t).f();
      |            ^~~~~~~~~~~~~~~ ~
<source>:14:10: note: in instantiation of function template specialization 'f<A>' requested here
   14 | auto b = f(A{}) == 42;
      |          ^
1 warning generated.

This seems to be a regression from clang-19.

This happens when:

• the function called is static
• we are calling it through member syntax with an object that is std::forward-ed

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Ben Deane (elbeno)

This code: ```cpp #include <utility>

struct A {
[[nodiscard]] static auto f() {
return 42;
}
};

template <typename T>
auto f(T &&t) {
return std::forward<T>(t).f();
}

auto b = f(A{}) == 42;

https://godbolt.org/z/cxGvxM9bn

Provokes a warning:
```console
<source>:11:12: warning: ignoring return value of function declared with 'nodiscard' attribute [-Wunused-result]
   11 |     return std::forward<T>(t).f();
      |            ^~~~~~~~~~~~~~~ ~
<source>:14:10: note: in instantiation of function template specialization 'f<A>' requested here
   14 | auto b = f(A{}) == 42;
      |          ^
1 warning generated.

This seems to be a regression from clang-19.

This happens when:

• the function called is static
• we are calling it through member syntax with an object that is std::forward-ed