[Bug c++/96116] New: GCC accepts "enum struct/class" in reference to enumeration

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96116

            Bug ID: 96116
           Summary: GCC accepts "enum struct/class" in reference to
                    enumeration
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

Hi,all.

This code, might be an invalid code, but GCC accepts it.

$cat test.cc
using alias1 = enum struct E1;
using alias2 = enum class E2;

While in clang:
$clang++ test.cc
test.cc:1:21: error: reference to enumeration must use 'enum' not 'enum struct'
[-Welaborated-enum-class]
using alias1 = enum struct E1;
                    ^~~~~~~
test.cc:2:21: error: reference to enumeration must use 'enum' not 'enum class'
[-Welaborated-enum-class]
using alias2 = enum class E2;
                    ^~~~~~
2 errors generated.


Here is a related bug report in llvm:
https://bugs.llvm.org/show_bug.cgi?id=46603

They suggested that ""enum class" can only be used when defining an enumeration
or as part of a standalone forward declaration"

Versions from 6.1 to trunk behave the same. So is this an invalid code for GCC?

Thanks,
Haoxin