On Fri, 29 Sept 2023 at 12:48, Vladimir Grigoriev via Std-Discussion <std-discussion@lists.isocpp.org> wrote:
In the C++23 Standard there is written (11.9.4 Friends):
 
«11 If a friend declaration appears in a local class (11.6) and the name specified is an unqualified name, a prior declaration is looked up without considering scopes that are outside the innermost enclosing non-class scope. For a friend function declaration, if there is no prior declaration, the program is ill-formed. For a friend class declaration, if there is no prior declaration, the class that is specified belongs to the innermost enclosing non-class scope, but if it is subsequently referenced, its name is not found by name lookup until a matching declaration is provided in the innermost enclosing non-class scope.»
 
and there is also provided an example (I have simplified it)
 
void f()
{
    extern void b();
 
    class A
    {
        friend void b(); // OK
    };
}
In this case a question arises: How can the friend function b access an object of the local class A? The name A is not visible outside the block scope of the function f.

It can become visible via a deduced return type.
 
 If it is possible can anybody provide an example of such a function? 

auto f() {
    extern int b();
    class A {
        friend int b(); // OK
        int i = 1;
    };
    return A();
}
int b() { return f().i; }

Note that gcc rejects; this is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101356 .