https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102412
Bug ID: 102412
Summary: Template argument deduction fails when using concept
as defaulted non-type template parameter
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: joeloser93 at gmail dot com
Target Milestone: ---
When using a defaulted non-type template parameter whose value is from a
concept, GCC is unable to deduce the template correctly when calling the
function template. Clang accepts this code and it should be valid.
```
#include <concepts>
template<class T, class U>
concept different_from = not std::is_same_v<T, U>;
template<class T, auto B = different_from<T, int>>
void f() {}
template<class T, auto B = not std::is_same_v<T, int>>
void g() {}
int main() {
f<double>(); // fails to compile
g<double>(); // compiles
}
```
See it live at https://godbolt.org/z/n1zrzGPoq
