[Bug c++/102004] New: The opaque-enum-declaration whose enum-head-name contains a nest-name-specifier should be permitted in an explicit specialization

[xmh970252187 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102004

            Bug ID: 102004
           Summary: The opaque-enum-declaration whose enum-head-name
                    contains a nest-name-specifier should be permitted in
                    an explicit specialization
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xmh970252187 at gmail dot com
  Target Milestone: ---

template<class T>
struct A{
    enum C:T;
};
template<>
enum A<int>::C:int;


This explicit specialization should be accepted by comfort implementations.
Since the standard only says that  

> If the enum-head-name of an opaque-enum-declaration contains a 
> nested-name-specifier, the declaration shall be an explicit specialization.  

Clang accepts this example while GCC rejects it with the diagnosis
"opaque-enum-specifier must use a simple identifier". 
https://godbolt.org/z/zYG4sYbK6