[Bug c++/109136] New: [concepts] initializer_list constructor constraint should require static_cast for explicit conversion operator

[Bug c++/109136] New: [concepts] initializer_list constructor constraint should require static_cast for explicit conversion operator

[ldalessandro at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109136

            Bug ID: 109136
           Summary: [concepts] initializer_list constructor constraint
                    should require static_cast for explicit conversion
                    operator
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ldalessandro at gmail dot com
  Target Milestone: ---

The following concept should fail the static_assert, but passes (I should need
a static_cast here).

```
    #include <initializer_list>

    template <class From, class To>
    concept implicit_convertible_to = requires(From x) { 
        std::initializer_list<To>{ x }; 
    };

    struct foo {
        explicit operator int();
    };

    static_assert(implicit_convertible_to<foo, int>);

```

Live: https://godbolt.org/z/GffP9f8o7

[Bug c++/109136] initializer_list constructor constraint and explicit conversion operator

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109136

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[concepts] initializer_list |initializer_list
                   |constructor constraint      |constructor constraint and
                   |should require static_cast  |explicit conversion
                   |for explicit conversion     |operator
                   |operator                    |

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This has nothing to do with concepts really:
```

#include <initializer_list>

struct foo {
explicit operator int();
};

template <class From, class To>
void f(From x)
{
  std::initializer_list<To>{ x };
}
void g()
{
  f<foo, int>(foo{});
}
```
GCC accepts the above example but clang rejects it.

[Bug c++/109136] initializer_list constructor and explicit conversion operator

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109136

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=85577

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It might be the case GCC is the only one implementing
https://cplusplus.github.io/CWG/issues/2137.html .