[Bug c++/117422] Error: template parameter was not declared in this scope

[nerd.cpp at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117422

--- Comment #7 from Jesse Williamson <nerd.cpp at gmail dot com> ---
Revisiting this, I don't think it's a bug-- but perhaps a more specific error
message could have saved some confusion. 

See update: https://godbolt.org/z/sePdf4bvv

...adding scope resolution to the friend declaration in the class appears to
produce the correct match, so I'm thinking that the unqualified version was
causing the compiler to treat it as a forward declaration of a class member
rather than a free function:

template <typename T>
void f(T x) {}

/* Note: same error with:
void f(auto x) {}
*/

struct {
void f(int); 
friend void ::f<>(int); // <--- remove :: to see non-bug
} foo;