[Bug c++/85105] New: missing -Wignored-qualifiers with const decltype

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85105

            Bug ID: 85105
           Summary: missing -Wignored-qualifiers with const decltype
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Both const qualifiers in the program below are ignored but GCC only issues
-Wignored-qualifiers for the first.  A warning for the second instance would be
even more useful since the author may be assuming that r2 declares a const
reference to int when it in fact declares a non-const reference.

$ cat u.C && gcc -S -Wall -Wextra -Wpedantic -Wuseless-cast u.C
const int f ();   // -Wignored-qualifiers (good)

extern int &r1;

const decltype (r1) r2 = r1;   // missing -Wignored-qualifiers
u.C:1:1: warning: type qualifiers ignored on function return type
[-Wignored-qualifiers]
 const int f ();   // -Wignored-qualifiers (good)
 ^~~~~