[Bug c++/104567] New: SFINAE check failure starting gcc 4.7.1 and up with -std=c++11

[Bug c++/104567] New: SFINAE check failure starting gcc 4.7.1 and up with -std=c++11

[armenchik at mail dot ru]

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

            Bug ID: 104567
           Summary: SFINAE check failure starting gcc 4.7.1 and up with
                    -std=c++11
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: armenchik at mail dot ru
  Target Milestone: ---

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 checked_type
{
    constexpr static char param[] = "param"; // <- everything works fine
    //constexpr static int param = 0; // <- sfinae works fine, fails static
assert
    //int param; // <- sfinae fails! reporting error during param substitution
    //char const* param; // <- sfinae fails again as above
};

int main()
{
    static_assert(has_char_static_param<checked_type>(0), "check failed");
    return 0;
}

[Bug c++/104567] SFINAE check failure starting gcc 4.7.1 and up with -std=c++11

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|https://godbolt.org/z/eGc9s |
                   |n6GM                        |

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://godbolt.org/z/eGc9sn6GM

[Bug c++/104567] SFINAE check failure with trying to access member field

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |4.1.2, 4.6.4
   Last reconfirmed|                            |2022-02-16
            Summary|SFINAE check failure        |SFINAE check failure with
                   |starting gcc 4.7.1 and up   |trying to access member
                   |with -std=c++11             |field

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually it has always failed.
Here is a C++98 testcase which shows the issue even with GCC 4.1.2:
template <typename _TAny, char const* value = _TAny::param>
bool has_char_static_param(int)
    { return true; }

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

struct checked_type
{
    int param;
};

int main()
{
    int t = has_char_static_param<checked_type>(0);
    return t;
}

[Bug c++/104567] SFINAE check failure with trying to access member field

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.1.2                       |4.4.7

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Oh I forgot default template arguments for function calls only came to be part
of C++11.

[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]

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