[Bug c++/108456] New: attribute deprecated on enum doesn't warn

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108456

            Bug ID: 108456
           Summary: attribute deprecated on enum doesn't warn
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

In this test:

struct S {
  enum [[deprecated]] E { D };
};

int main()
{
  auto a1 = S::D;
  auto a2 = S::E::D;
}

we emit a -Wdeprecated-declarations warning only for a2 but not a1, whereas
clang++ warns for a1 too (twice, in fact).  I suppose we want a warning there
as well.

C++20 using enum test:

enum class [[deprecated]] E { X };

int main()
{
    using enum E;
    auto a = X;
}

clang++ warns but g++ doesn't.