[Bug c++/107256] New: Contradictory circular noexcept-specifier is accepted

[de34 at live dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107256

            Bug ID: 107256
           Summary: Contradictory circular noexcept-specifier is accepted
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: de34 at live dot cn
  Target Milestone: ---

This code snipet is currently accepted by gcc while the noexcept-specifier
cannot be meaningful.

struct Weird {
    static void f() noexcept(!noexcept(Weird::f())) {}
};

Godbolt link: https://godbolt.org/z/hqnha3aPd

The code was rejected by gcc 9 and earlier versions, but with a seemly
incorrect reason (error: incomplete type 'Weird' used in nested name
specifier). According to CWG DR 1330 and current wording in [class.mem.general]
/7, the noexcept-specifier establishes a complete-class context, so Weird is
complete inside it.