[Bug c++/39159] New: unhelpful attribute warning on matching declaration after definition

[Bug c++/39159] New: unhelpful attribute warning on matching declaration after definition

[sebor at roguewave dot com]

gcc 4.3 issues a warning for the declaration of struct A below despite the
attribute on the declaration being consistent with that on the definition and
thus benign. While the warning is valuable in cases where the attributes
between the declaration and the definition do not match, it is not useful in
benign cases such as the one below. In these cases the warning makes applying
the attribute difficult in existing C++ libraries that rely heavily but not
completely on forward declarations and that also already make use of the Visual
C++ __declspec(dllexport) feature or the Sun C++ __global or __protected
specifiers, neither of which warns about such benign cases.

$ cat t.C && g++ -c t.C
struct __attribute__ ((visibility ("default"))) A { };
struct __attribute__ ((visibility ("default"))) A;
t.C:2: warning: type attributes ignored after type is already defined


-- 
           Summary: unhelpful attribute warning on matching declaration
                    after definition
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sebor at roguewave dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39159

[Bug c++/39159] unhelpful attribute warning on matching declaration after definition

[sebor at roguewave dot com]

------- Comment #1 from sebor at roguewave dot com  2009-02-12 17:02 -------
In addition, as the test case below shows, the warning is issued inconsistently
between classes and functions, suggesting that the instance of the warning on
the class declaration on line 2 might be a bug rather than a feature:

$ cat -n t.C && g++ -dumpversion && g++ -c t.C
     1  struct __attribute__ ((visibility ("default"))) A { };
     2  struct __attribute__ ((visibility ("default"))) A;
     3
     4  void __attribute__ ((visibility ("default"))) foo () { }
     5  void __attribute__ ((visibility ("default"))) foo ();
4.3.1
t.C:2: warning: type attributes ignored after type is already defined


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39159

[Bug c++/39159] unhelpful attribute warning on matching declaration after definition

[jj at chaosbits dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39159

Jesper Juhl <jj at chaosbits dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jj at chaosbits dot net

--- Comment #2 from Jesper Juhl <jj at chaosbits dot net> ---
I've run into this as well with GCC 4.8.2 - it's rather annoying.

[Bug c++/39159] unhelpful attribute warning on matching declaration after definition

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39159

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-08-16
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Confirmed.

Perhaps it is not hard to fix. Just look how it is handled for functions.
Probably it is at the same place as this:

  void __attribute__ ((visibility ("default"))) foo () { }
  void __attribute__ ((visibility ("hidden"))) foo ();

pr39159.C:4:49: warning: ‘void foo()’: visibility attribute ignored because it
conflicts with previous declaration [-Wattributes]
   void __attribute__ ((visibility ("default"))) foo () { }
                                                 ^
pr39159.C:4:49: note: previous declaration of ‘void foo()’

and see if you can implement the same thing for types, probably at the point
where the " type attributes ignored" warning is given.
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Subject: [Bug c++/57466] [DR 1584] Argument deduction fails for 'const T*' when T is function type
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idW466

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Still working on this.