https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102660
Bug ID: 102660
Summary: Valid template default parameter of a friend function
is rejected
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fchelnokov at gmail dot com
Target Milestone: ---
This is a presumably valid program:
```
struct A{
template<int R>
friend void show();
private:
int c;
};
template<int R = decltype(A{}.c){0} >
void show(){
}
int main(){
show<>();
}
```
It is accepted by Clang, MSVC, but rejected in GCC, which complains about
default parameter of R (asking for forward declaration of the function). Demo:
https://gcc.godbolt.org/z/q1r1a9Ycn
Related discussion: https://stackoverflow.com/q/69341936/7325599
