The following code attempts to partially specialize a class using a concept and add a method to the specialization, but it is rejected by clang 11.0.0:
#include <concepts>
template <typename T> // note: previous template declaration is here
struct S {};
template <std::integral T>
struct S<T>
{
void f();
};
template <std::integral T> // error: type constraint differs in template redeclaration
void S<T>::f()
{
}
clang gives the error message:
<source>:14:16: error: type constraint differs in template redeclaration
template <std::integral T>
^
<source>:3:11: note: previous template declaration is here
template <typename T>
(see https://godbolt.org/z/Wv1ojK). Why is this code wrong? Or is this a bug in clang? (FWIW, this code is accepted by gcc trunk and by MSVC 19.28, although that's no guarantee of correctness.)