[Bug c++/103564] New: type-requirement that names a constructor should fail

[johelegp at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103564

            Bug ID: 103564
           Summary: type-requirement that names a constructor should fail
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johelegp at gmail dot com
                CC: johelegp at gmail dot com
  Target Milestone: ---

See https://godbolt.org/z/8dr9oG4Y1.

```C++
template<class T> concept C =
  requires { typename T::base; };

struct base { };

static_assert(C<base>);
```

Clang rejects with:
```
<source>:6:1: error: static_assert failed
static_assert(C<base>);
^             ~~~~~~~
<source>:6:15: note: because 'base' does not satisfy 'C'
static_assert(C<base>);
              ^
<source>:2:26: note: because 'typename T::base' would be invalid: ISO C++
specifies that qualified reference to 'base' is a constructor name rather than
a type in this context, despite preceding 'typename' keyword
  requires { typename T::base; };
                         ^
1 error generated.
```