[Bug c++/110513] New: Invalid use of incomplete type std::bool_constant inside requires expression

[Bug c++/110513] New: Invalid use of incomplete type std::bool_constant inside requires expression

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110513

            Bug ID: 110513
           Summary: Invalid use of incomplete type std::bool_constant
                    inside requires expression
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

The following program


#include <type_traits>

struct B {
    bool b = true;
};

// ok everywhere
static_assert( std::bool_constant<B{}.b>{}() );

// error in GCC
static_assert( requires() { std::bool_constant<B{}.b>{}(); } );


is accepted in Clang and MSVC, but GCC complains


<source>:11:56: error: invalid use of incomplete type
'std::bool_constant<B{}.b>'
   11 | static_assert( requires() { std::bool_constant<B{}.b>{}(); } );
      |                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
In file included from <source>:1:
/opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/type_traits:62:12: note:
declaration of 'std::bool_constant<B{}.b>'
   62 |     struct integral_constant
      |            ^~~~~~~~~~~~~~~~~


Online demo: https://gcc.godbolt.org/z/csKanbM88

[Bug c++/110513] Invalid use of incomplete type std::bool_constant inside requires expression

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110513

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-07-01
     Ever confirmed|0                           |1
           Keywords|                            |rejects-valid

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
```
template<bool a>
struct bool_const1 
{
  typedef bool T;
  static constexpr T value = a;
  constexpr T operator()(){return value;}
};

struct B {
    bool b = true;
};

// ok everywhere
static_assert( bool_const1<B{}.b>{}() );

// error in GCC
static_assert( requires() { bool_const1<B{}.b>{}(); } );
```

[Bug c++/110513] Invalid use of incomplete type std::bool_constant inside requires expression

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110513

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced slightly more:
```
template<bool a>
struct bool_const1 {};

struct B {
    bool b = true;
};

// error in GCC
static_assert( requires() { bool_const1<B{}.b>{}; } );
```

[Bug c++/110513] Invalid use of incomplete type std::bool_constant inside requires expression

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110513

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The underlaying problem here is most likely the same issue as the one in PR
94332 .

[Bug c++/110513] Invalid use of incomplete type std::bool_constant inside requires expression

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110513

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ed at catmur dot uk

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 111016 has been marked as a duplicate of this bug. ***