[Bug c++/94186] New: compiler incorrectly accepts a requires clause with predicate of non-bool type

[akrzemi1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94186

            Bug ID: 94186
           Summary: compiler incorrectly accepts a requires clause with
                    predicate of non-bool type
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: akrzemi1 at gmail dot com
  Target Milestone: ---

The following program should fail to compile in C++20 because the type of the
predicate in requires-clause is not bool. 

```
template <typename T>
struct is_small
{
  enum { value = sizeof(T) <= 4 };
};

template <typename T>
  requires is_small<T>::value
void fun(T) {} 

template <typename T>
void fun(T) {} 

int main()
{
  fun(1);  // expected hard compiler error
}
```