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From: "ppluzhnikov at google dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/59295] New: useless warning: 'Bar' is already a friend of 'Foo' [enabled by default]
Date: Tue, 26 Nov 2013 00:02:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59295

            Bug ID: 59295
           Summary: useless warning: 'Bar' is already a friend of 'Foo'
                    [enabled by default]
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com

Google ref: b/11542609

Using trunk gcc:
g++ (GCC) 4.9.0 20131125 (experimental)

/// -- cut ---
class Foo {
 friend class Bar;
 friend class Bar;
};
/// -- cut ---


g++ -c t.cc
t.cc:3:15: warning: 'Bar' is already a friend of 'Foo' [enabled by default]
  friend class Bar;
               ^

This warning is purely stylistic -- no possible bug could happen when this
warning is disabled.

It is also not suppressable :-(

In actual code, both friend declarations come from macro expansion, and are
somewhat hard to get rid of.