[Bug c++/106143] New: Add fix-it for missing ::value on trait with std::integral_constant base

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106143

            Bug ID: 106143
           Summary: Add fix-it for missing ::value on trait with
                    std::integral_constant base
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

#include <type_traits>
static_assert( std::is_void<void>, "void is void is void" );
constexpr bool b = std::is_void<void>;

v.C:2:34: error: expected primary-expression before ',' token
    2 | static_assert( std::is_void<void>, "void is void is void" );
      |                                  ^
v.C:3:38: error: expected primary-expression before ';' token
    3 | constexpr bool b = std::is_void<void>;
      |                                      ^

I do this all the time: forget to take the ::value of the trait and just use
the type itself. The diagnostic could be improved for this case, by detecting
that the type has a base that is a specialization of std::integral_constant and
suggesting adding ::value as a fix-it:

v.C:2:34: error: expected primary-expression before ',' token
    2 | static_assert( std::is_void<void>, "void is void is void" );
      |                                  ^
      |                                  ::value
v.C:3:38: error: expected primary-expression before ';' token
    3 | constexpr bool b = std::is_void<void>;
      |                                      ^
      |                                      ::value