[Bug c++/123091] New: `operator auto` should be rejected

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123091

            Bug ID: 123091
           Summary: `operator auto` should be rejected
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 94404
  Target Milestone: ---

After https://wg21.link/CWG1670, `auto operator` becomes invalid and should be
rejected.
That is:
```
  struct S {
    operator auto() { return 0; }
  };
```

Should be invalid.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94404
[Bug 94404] [meta-bug] C++ core issues