Spurious -Wbitfield-enum-conversion warning when using signed enum in a bit-field

[brevzin]

Short reproduction:

#include <cstdint>

enum class E : int8_t {
    sell = -1,
    buy = +1,
    other = 0
};

struct Data {
    E e : 8;
    int padding : 24 = 0;
};

struct Aux {
    E e;
};

auto make_data(Aux const& aux) -> Data {
    return Data{.e=aux.e};
}

The warning I get from clang (under -Wconversion) is:

<source>:19:20: warning: assigning value of signed enum type 'E' to unsigned bit-field 'e'; negative enumerators of enum 'E' will be converted to positive values [-Wbitfield-enum-conversion]
   19 |     return Data{.e=aux.e};
      |                    ^
<source>:10:5: note: consider making the bit-field type signed
   10 |     E e : 8;
      |     ^

But the bit-field type is signed. And I can't write signed E either.

[AaronBallman]

Closing as this is fixed on trunk already: https://godbolt.org/z/MWofc1xv8