[Bug c++/104578] New: [12 Regression] accepts invalid partial template specialization, non-type template argument depends on a template parameter

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104578

            Bug ID: 104578
           Summary: [12 Regression] accepts invalid partial  template
                    specialization, non-type template argument depends on
                    a template parameter
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

While looking into PR 104567, I just happened upon some code which is rejected
by before GCC 12, MSVC, clang and ICC. I suspect it is invalid code as all
other compilers besides the trunk reject it for a similar reasons.
Take:
template <typename _TAny, int value = _TAny::param>
struct s{};

template <typename _TAny>
struct s<_TAny, _TAny::param>
{
  typedef int type;
};
struct checked_type
{
    static const int param = 0;
};

s<checked_type>::type  t;

int main()
{
    return t;
}
----- CUT ----
clang reports:
<source>:5:17: error: type of specialized non-type template argument depends on
a template parameter of the partial specialization
struct s<_TAny, _TAny::param>
                ^~~~~
<source>:14:18: error: no type named 'type' in 's<checked_type, 0>'
s<checked_type>::type  t;
~~~~~~~~~~~~~~~~~^

MSVC reports:
<source>(8): error C2753: 's<_TAny,_TAny::param>': partial specialization
cannot match argument list for primary template

ICC reports:
<source>(5): error: the template argument list of the partial specialization
includes a nontype argument whose type depends on a template parameter
  struct s<_TAny, _TAny::param>
         ^

GCC 11.2.0 reports:
<source>:5:8: error: template argument '_TAny::param' involves template
parameter(s)
    5 | struct s<_TAny, _TAny::param>
      |        ^~~~~~~~~~~~~~~~~~~~~~

GCC 12 accepts this for all levels of the C++ standard.