[Bug c++/33518] unused code changes the result of name lookup

["bangerth at dealii dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #2 from bangerth at dealii dot org  2007-09-23 18:09 -------
This indeed looks like a bug. Take this:
---------------------
#include <iterator>

namespace M {
  struct A {};
  using std::distance;
}

namespace N
{
  template <class> struct S {};
  class Q : S<M::A> {};
  int distance(Q,Q);
}

int i = distance (N::Q(), N::Q());
----------------
I would expect this to compile: all arguments to the call to distance()
have associated namespace N, so we would expect that the compiler finds
N::distance. However, apparently, gcc also performs the derived-to-base
conversion to find S<M::A> and concludes that namespace M is also
associated from where it tries to use std::distance and gives the error

g/x> c++ -c y.cc
/usr/include/c++/4.1.2/bits/stl_iterator_base_types.h: In instantiation of
'std::iterator_traits<N::Q>':
y.cc:15:   instantiated from here
/usr/include/c++/4.1.2/bits/stl_iterator_base_types.h:129: error: no type named
'iterator_category' in 'class N::Q'
/usr/include/c++/4.1.2/bits/stl_iterator_base_types.h:130: error: no type named
'value_type' in 'class N::Q'
/usr/include/c++/4.1.2/bits/stl_iterator_base_types.h:131: error: no type named
'difference_type' in 'class N::Q'
/usr/include/c++/4.1.2/bits/stl_iterator_base_types.h:132: error: no type named
'pointer' in 'class N::Q'
/usr/include/c++/4.1.2/bits/stl_iterator_base_types.h:133: error: no type named
'reference' in 'class N::Q'

It shouldn't be hard to produce a wrong-code bug from this.

If someone wants to beat me to producing something without the include
file, feel free...

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-09-23 18:09:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33518