[Bug libstdc++/106839] New: Library traits need to handle array of incomplete type with unknown bound

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106839

            Bug ID: 106839
           Summary: Library traits need to handle array of incomplete type
                    with unknown bound
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

This should be valid:

#include <type_traits>
struct Inc;
static_assert( ! std::is_empty_v<Inc[]> );
static_assert( ! std::is_pod_v<Inc[]> );
static_assert( ! std::is_polymorphic_v<Inc[]> );
static_assert( ! std::is_abstract_v<Inc[]> );

However, before r13-25 the front-end rejected it. For the release branches, the
library needs to workaround this.