[Bug c++/114625] New: requires { T{}; } wrongly accepted when T{} is ill-formed

[Bug c++/114625] New: requires { T{}; } wrongly accepted when T{} is ill-formed

[ted at lyncon dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

            Bug ID: 114625
           Summary: requires { T{}; } wrongly accepted when T{} is
                    ill-formed
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ted at lyncon dot se
  Target Milestone: ---

This program compiles but I'd expect both `static_assert`s to refuse it since
`d x{};` is invalid.
```
#include <concepts>

template<class T>
concept default_initializable =
    std::constructible_from<T> &&
    requires { T{}; } &&
    requires { ::new T; };

struct b { explicit b(auto...) {} };
struct d : b {};

int main() {
    static_assert(default_initializable<d>);
    static_assert(std::default_initializable<d>);
    //d x{}; // ERROR
}
```

[Bug c++/114625] requires { T{}; } wrongly accepted when T{} is ill-formed while in concept

[ted at lyncon dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

Ted Lyngmo <ted at lyncon dot se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|requires { T{}; } wrongly   |requires { T{}; } wrongly
                   |accepted when T{} is        |accepted when T{} is
                   |ill-formed                  |ill-formed while in concept
                 CC|                            |ted at lyncon dot se

--- Comment #1 from Ted Lyngmo <ted at lyncon dot se> ---
The assertion correctly fails with this though:
```
static_assert(requires { d{}; });
```

[Bug c++/114625] requires { T{}; } wrongly accepted when T{} is ill-formed while in concept

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-04-07

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/114625] requires { T{}; } wrongly returns false when T{} is ill-formed while in concept

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94885

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Non-concepts testcase:

struct b { explicit b(); };
struct d : b {};

template<class T, class = decltype(T{})> void f(int) = delete;
template<class T> void f(...);

int main() {
  f<d>(0);
}

This seems related to PR94885 / r11-20-g30da2906ac5217, maybe Marek would be
interested.

[Bug c++/114625] requires { T{}; } wrongly returns false when T{} is ill-formed while in concept

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Thanks.  Probably GCC 15 work.

[Bug c++/114625] requires { T{}; } wrongly returns false when T{} is ill-formed while in concept

[ted at lyncon dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

--- Comment #5 from Ted Lyngmo <ted at lyncon dot se> ---
@Andrew, the title change seems wrong. It wrongly returns true when T{} is
ill-formed.

[Bug c++/114625] requires { T{}; } wrongly returns true when T{} is ill-formed while in concept/decltype

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114625

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|requires { T{}; } wrongly   |requires { T{}; } wrongly
                   |returns false when T{} is   |returns true when T{} is
                   |ill-formed while in concept |ill-formed while in
                   |                            |concept/decltype

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Ted Lyngmo from comment #5)
> @Andrew, the title change seems wrong. It wrongly returns true when T{} is
> ill-formed.

Sorry you are correct. I have corrected the summary.