[Bug c++/115594] New: requires expression permits arrays of voids

[Bug c++/115594] New: requires expression permits arrays of voids

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115594

            Bug ID: 115594
           Summary: requires expression permits arrays of voids
           Product: gcc
           Version: 14.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

This program
```
template<typename T>
concept C = requires(T t[2]) {
    t;
};

static_assert(!C<void>);
```
seems valid because arrays of voids are not allowed, and it is accepted by
Clang and MSVC. But in GCC static_assert evaluates to opposite value. Online
demo: https://gcc.godbolt.org/z/nM8Mj8qrb

[Bug c++/115594] requires expression permits arrays of voids

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115594

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The interesting thing is the reason why clang outputs:
<source>:2:25: note: because 't' would be invalid: array has incomplete element
type 'void'


Is not exactly correct as if you change void to being a incomplete type:
struct A;

static_assert(C<A>);

it is accepted by all compilers ...

[Bug c++/115594] requires expression permits arrays of voids

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115594

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a dup of bug 24664.

[Bug c++/115594] requires expression permits arrays of voids

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115594

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Yes it is a dup.

The following should also be rejected but currently is not:
```
  template<class T, class T1 = int*(T[5])> int f(T*);
  int j=f<void>(nullptr);
```

Basically function arguments (including concepts "arguments") decay too early
for arrays to pointers.

*** This bug has been marked as a duplicate of bug 24664 ***