[Bug c++/96830] GCC does not complain template-head containing requires clause

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96830

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
G++ still accepts this version, though EDG and Clang reject it:

template<typename T> concept C = requires { typename T::value_type; };

template<C Container>
class Foo {
public:
    void func();
};

template<typename Container>
void Foo<Container>::func()
{}


$ edg --c++20 -c 96830.C
"96830.C", line 10: error: template argument list must match the parameter list
  void Foo<Container>::func()
       ^

1 error detected in the compilation of "96830.C".

$ clang++ -std=c++2a -c 96830.C
96830.C:9:10: error: type constraint differs in template redeclaration
template<typename Container>
         ^
96830.C:3:10: note: previous template declaration is here
template<C Container>
         ^
1 error generated.