[Bug c++/104567] SFINAE check failure with trying to access member field on the default template argument for a function

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104567

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |12.0

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
A testcase that shows the bug is a lot more useful than one that needs
something uncommented to show the bug.

template <typename _TAny, char const* value = _TAny::param>
constexpr bool has_char_static_param(int)
    { return true; }

template <typename _TAny>
constexpr bool has_char_static_param(...)
    { return false; }

struct works1
{
    constexpr static char param[] = "param";
};

struct works2
{
    constexpr static int param = 0;
};

struct fails
{
    char const* param; // not static
};

static_assert(has_char_static_param<works1>(0), "");
static_assert(!has_char_static_param<works2>(0), "");
static_assert(!has_char_static_param<fails>(0), "");  // FAILS