[Bug libstdc++/56468] New: Clang exposes bug with unexpected forward-declaration of type_info

[Bug libstdc++/56468] New: Clang exposes bug with unexpected forward-declaration of type_info

[d.frey at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

             Bug #: 56468
           Summary: Clang exposes bug with unexpected forward-declaration
                    of type_info
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: d.frey@gmx.de


The following program fails to compile with Clang++ 3.2:

#include <typeinfo>
#include <exception>

const char* get_name( const std::exception_ptr eptr )
{
  return eptr.__cxa_exception_type()->name();
}

int main() {}

The output in the shell is:

$ g++-4.7 -std=c++0x -O3 -Wall -Wextra t.cc -o t
$ clang++-3.2 -std=c++0x -O3 -Wall -Wextra t.cc -o t
t.cc:6:37: error: member access into incomplete type 'const class type_info'
  return eptr.__cxa_exception_type()->name();
                                    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/exception_ptr.h:144:19:
note: forward declaration of
      'std::__exception_ptr::type_info'
      const class type_info*
                  ^
1 error generated.
$

The problem is that <typeinfo> includes <exception> before it forward-declares
std::type_info. In <exception>, type_info is used in the context of
std::__exception_ptr, thus Clang generates an implicit forward-declaration for
std::__exception_ptr::type_info and, when used in the above code, consequently
fails.

Further discussion has taken place at <http://stackoverflow.com/q/15098174>.

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-02-26
     Ever Confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-26 23:22:23 UTC ---
Something like this should fix it

--- a/libstdc++-v3/libsupc++/exception_ptr.h
+++ b/libstdc++-v3/libsupc++/exception_ptr.h
@@ -44,6 +44,8 @@ extern "C++" {

 namespace std 
 {
+  class type_info;
+
   /**
    * @addtogroup exceptions
    * @{
@@ -141,7 +143,7 @@ namespace std
       operator==(const exception_ptr&, const exception_ptr&)
        _GLIBCXX_USE_NOEXCEPT __attribute__ ((__pure__));

-      const class type_info*
+      const std::type_info*
       __cxa_exception_type() const _GLIBCXX_USE_NOEXCEPT
        __attribute__ ((__pure__));
     };

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-27 07:35:56 UTC ---
Is that something g++ should diagnose too?
Or is this because init_rtti_processing forward declares std::type_info class
automatically?

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-02-27 09:33:27 UTC ---
It's because of the implicit declaration of std::type_info, G++ correctly
diagnoses similar cases with altered namespace names or type names, it only
happens for std::type_info.  I see no harm in adding an explicit declaration to
the libstdc++ header so it works with clang and other compilers that don't
declare std::type_info automatically.

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[d.frey at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #4 from Daniel Frey <d.frey at gmx dot de> 2013-02-28 16:14:41 UTC ---
(In reply to comment #1)

I think the first line you added is enough, as evidenced by my "fix" referenced
in the Stack Overflow discussion (see link above). But the second line won't
hurt either.

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-16 20:01:27 UTC ---
Author: redi
Date: Sat Mar 16 20:01:16 2013
New Revision: 196709

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196709
Log:
    PR libstdc++/56468
    * libsupc++/exception_ptr.h (type_info): Declare.

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/libsupc++/exception_ptr.h

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-16 20:22:57 UTC ---
Author: redi
Date: Sat Mar 16 20:22:40 2013
New Revision: 196711

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196711
Log:
    PR libstdc++/56468
    * libsupc++/exception_ptr.h (type_info): Declare.

Modified:
    branches/gcc-4_7-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_7-branch/libstdc++-v3/libsupc++/exception_ptr.h

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |redi at gcc dot gnu.org
                   |gnu.org                     |
   Target Milestone|---                         |4.7.3

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-16 20:23:58 UTC ---
Fixed on trunk and 4.7 branch so far, the fix will also be done for 4.8.1

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #8 from Steven Bosscher <steven at gcc dot gnu.org> 2013-03-16 23:46:08 UTC ---
(In reply to comment #7)
> Fixed on trunk and 4.7 branch so far, the fix will also be done for 4.8.1

It's unusual for a bug to be fixed for a previous release and for trunk,
but not on the latest release. Isn't this worth applying to GCC 4.8.0
also? The patch looks safe and simple enough...

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-17 11:35:55 UTC ---
Yeah, I think this patch is fine even for 4.8.0, and there is no need to do
another RC for that.

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-17 14:10:46 UTC ---
Author: redi
Date: Sun Mar 17 14:10:39 2013
New Revision: 196749

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196749
Log:
    PR libstdc++/56468
    * libsupc++/exception_ptr.h (type_info): Declare.

Modified:
    branches/gcc-4_8-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_8-branch/libstdc++-v3/libsupc++/exception_ptr.h

[Bug libstdc++/56468] Clang exposes bug with unexpected forward-declaration of type_info

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56468

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-17 14:11:44 UTC ---
OK, thanks, guys, this is done then.