[Bug c++/61596] New: -Wunused-local-typedefs warns incorrectly on a typedef that's referenced indirectly

[thakis at chromium dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61596

            Bug ID: 61596
           Summary: -Wunused-local-typedefs warns incorrectly on a typedef
                    that's referenced indirectly
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thakis at chromium dot org

-Wunused-local-typedefs warns that the typedef in line "XXX" is unused, but
it's used in line "YYY":

auto f() {
  struct S {
    typedef int t; // XXX
  };
  return S();
}
void g() {
  auto x = f();
  decltype(x)::t y; // YYY
}

/example.cpp: In function ‘auto f()’:

2 : warning: typedef ‘f()::S::t’ locally defined but not used
[-Wunused-local-typedefs]

struct S { typedef int t; };

^

(This is with 4.9.0. Testcase from Richard Smith.)