[Bug c++/97531] New: Improve type/non-type declaration diagnostic

[mpolacek at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97531

            Bug ID: 97531
           Summary: Improve type/non-type declaration diagnostic
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

For this:

struct A { };
struct B { B(A); };

void
fn ()
{
  B(A()); // extern struct B A (void);
  A a;
}

we issue:
q.C: In function ‘void fn()’:
q.C:8:4: error: expected ‘;’ before ‘a’
    8 |   A a;
      |    ^~
      |    ;

Eh, what?

clang++:
q.C:8:3: error: must use 'struct' tag to refer to type 'A' in this scope
  A a;
  ^
  struct 
q.C:7:5: note: struct 'A' is hidden by a non-type declaration of 'A' here
  B(A()); // extern struct B A (void);
    ^