[Bug c++/107605] New: GCC rejects valid program involving std::bind and requires

[Bug c++/107605] New: GCC rejects valid program involving std::bind and requires

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107605

            Bug ID: 107605
           Summary: GCC rejects valid program involving std::bind and
                    requires
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlame646 at gmail dot com
  Target Milestone: ---

The following valid program(afaik) is rejected by gcc but accepted by clang.
Demo: https://godbolt.org/z/bdMfKE41n

```
template <typename T>                                                           
class myclass {                                                                 
public:                                                                         

  void func(const T&) requires true
  {
     std::cout << "true";
  }

  void func(const T&) requires false
  {
     std::cout << "false";
  }
};                                                                              


int main(){                                                                     

  myclass<int> obj;                                                             
  auto mylambda = std::bind(&myclass<int>::func, &obj, 5); //accepted by clang
rejected by gcc
  mylambda();                                                                   

} 
```
The error says:

```
error: no matching function for call to 'bind(<unresolved overloaded function
type>, myclass<int>*, int)'
   24 |   auto mylambda = std::bind(&myclass<int>::func, &obj, 5); //accepted
by clang rejected by gcc
```

This has been discussed here:
https://stackoverflow.com/questions/74385849/clang-accepts-program-involving-requires-constraint-while-gcc-and-msvc-rejects-i

[Bug c++/107605] GCC rejects valid program involving std::bind and requires

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107605

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |rejects-valid
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-11-10

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This has nothing to do with std::bind.

extern "C" int puts(const char*);

template <typename T>
class myclass {
public:

  void func(const T&) requires true
  {
     puts("true");
  }

  void func(const T&) requires false
  {
     puts("false");
  }
};                                                                              

auto mylambda = &myclass<int>::func;

req.C:18:32: error: unable to deduce ‘auto’ from ‘& myclass<int>::func’
   18 | auto mylambda = &myclass<int>::func;
      |                                ^~~~
req.C:18:32: note:   couldn’t deduce template parameter ‘auto’


I think there's an existing bug about this.

[Bug c++/107605] GCC rejects valid program involving requires-clause

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107605

Jason Liam <jlame646 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|GCC rejects valid program   |GCC rejects valid program
                   |involving std::bind and     |involving requires-clause
                   |requires                    |

--- Comment #2 from Jason Liam <jlame646 at gmail dot com> ---
(In reply to Jonathan Wakely from comment #1)
> This has nothing to do with std::bind.
> 


Yes i know this has nothing to do with `std::bind`. For example, I created the
following demo that reproduces the same error without std::bind. See demo:
https://godbolt.org/z/K6jKqsGx5  . I also mentioned the same in one of my
comments here:
https://stackoverflow.com/questions/74385849/clang-accepts-program-involving-requires-constraint-while-gcc-and-msvc-rejects-i/74386905#comment131319278_74385849
.  I've edited the title of this bug.

```
template <typename T>                                                           
class myclass {                                                                 
public:                                                                         

  void func(const T&) requires true
  {
     std::cout << "true";
  }

  void func(const T&) requires false
  {
     std::cout << "false";
  }
};      
template<typename T>                                                            
void bar(T&& )
{

}

int main(){                                                                     

  myclass<int> obj; 
  bar(&myclass<int>::func); //accepted by clang but rejected by gcc and msvc    

}  
```

[Bug c++/107605] GCC rejects valid program involving requires-clause

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107605

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jason Liam from comment #2)
> Yes i know this has nothing to do with `std::bind`.

OK, good. You reported a bug with std::bind in the title, and std::bind in the
example. I'm providing the necessary analysis in the bug report and a reduced
example. You don't need to get defensive about it.

 For example, I created
> the following demo that reproduces the same error without std::bind. See
> demo: https://godbolt.org/z/K6jKqsGx5

Nice. That wasn't provided in the bug report. So I added the information here.

If you don't want us to analyse your bug report and add detail to it, don't
bother reporting it!

[Bug c++/107605] constraint on a member function does causes ambigious and not allowing forming a pointer to the function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107605

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|101603                      |
            Summary|GCC rejects valid program   |constraint on a member
                   |involving requires-clause   |function does causes
                   |                            |ambigious and not allowing
                   |                            |forming a pointer to the
                   |                            |function

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
At first I thought it was a pointer to member function issue but nope it is not
as the following happens too but we need to have have the class as a template
rather than the function:
extern "C" int puts(const char*);

template <typename T>
class myclass {
public:

  static void func(const T&) requires true
  {
     puts("true");
  }

  static void func(const T&) requires false
  {
     puts("false");
  }
};                                                                              

auto mylambda = &myclass<int>::func;


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101603
[Bug 101603] [meta-bug] pointer to member functions issues

[Bug c++/107605] constraint on a member function does causes ambigious and not allowing forming a pointer to the function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107605

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
            Summary|constraint on a member      |constraint on a member
                   |function gives ambiguous    |function does causes
                   |error when forming a        |ambigious and not allowing
                   |pointer to the function     |forming a pointer to the
                   |                            |function
             Status|NEW                         |RESOLVED

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 80637.

*** This bug has been marked as a duplicate of bug 80637 ***