[Bug c++/63872] New: -Wunused-local-typedefs warns incorrectly on a typedef that's referenced from a template

[Bug c++/63872] New: -Wunused-local-typedefs warns incorrectly on a typedef that's referenced from a template

[thakis at chromium dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63872

            Bug ID: 63872
           Summary: -Wunused-local-typedefs warns incorrectly on a typedef
                    that's referenced from a template
           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

$ cat test2.cc
typedef char YesType;
struct NoType { YesType dummy[2]; };

template <typename T>
struct ShouldAbortOnSelfReset {
  template <typename U>
  static NoType Test(const typename U::AllowSelfReset*);

  template <typename U>
  static YesType Test(...);

  static const bool value = sizeof(Test<T>(0)) == sizeof(YesType);
};

template<class T>
struct Foo {
  void reset() {
    ShouldAbortOnSelfReset<T>::value;
  }
};

void f() {
  struct NoOpDeleter {
    typedef void AllowSelfReset;
    inline void operator()(int*) {}
  };

  Foo<NoOpDeleter> f;
  f.reset();
}

$ ~/gcc482prefix/bin/gcc -c test2.cc -std=c++11 -Wall
test2.cc: In function ‘void f()’:
test2.cc:24:18: warning: typedef ‘f()::NoOpDeleter::AllowSelfReset’ locally
defined but not used [-Wunused-local-typedefs]
     typedef void AllowSelfReset;
                  ^
test2.cc: In instantiation of ‘void Foo<T>::reset() [with T =
f()::NoOpDeleter]’:
test2.cc:29:11:   required from here


Warning on this is very dangerous, since removing the typedef will change the
meaning of the code but it's still going to compile.

This is with 4.8.2, but it also happens in gcc 4.9.
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From: "richard at netbsd dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/63779] g++ 4.9 generates invalid object provoking a GOT relative relocation must reference a local symbol linker error on SunOS
Date: Fri, 14 Nov 2014 16:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc779

--- Comment #2 from Richard PALO <richard at netbsd dot org> ---
Sorry. Given the size, I'll use the following directory for any information
needed: http://www.netbsd.org/~richard/xulrunner31-g++-issue/

Index of /~richard/xulrunner31-g++-issue

    Parent Directory
    MediaDecoderReader.cpp
    MediaDecoderReader.h
    MediaDecoderReader.ii
    MediaDecoderReader.o
    MediaDecoderReader.o.gkd
    MediaDecoderReader.s
    ld-debug.txt.gz

I included the gzip'd output of the link with:
LD_OPTIONS=-Dfiles,detail,reloc,got,sections,output=ld-debug.txt

Anything else useful to provide?

[Bug c++/63872] -Wunused-local-typedefs warns incorrectly on a typedef that's referenced from a template

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63872

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-11-14
            Version|unknown                     |4.8.2
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
That's just a bug, a typedef defined at class scope is not a local typedef,
even if it's in a local class.

[Bug c++/63872] -Wunused-local-typedefs warns incorrectly on a typedef that's referenced from a template

[thakis at chromium dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63872

--- Comment #2 from thakis at chromium dot org ---
I think warning on unused typedefs in local classes is generally a useful
feature, not a bug. The bug here is that it's warning on a typedef in a local
class that is being used.