[Bug c++/33518] invalid Koenig lookup

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

------- Comment #3 from bangerth at dealii dot org  2007-09-23 18:23 -------
This actually turns out to be a serious bug in several different ways.

Here's self-contained code:
-------------------
namespace X {
  template<typename T> struct H { typedef typename T::type type; };

  template<typename T> typename H<T>::type foo(T);
}

namespace M {
  struct A {};
  using X::foo;
}

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

int i = foo (N::Q());
---------------------
We get this:
g/x> c++ -c y.ii
y.ii: In instantiation of 'X::H<N::Q>':
y.ii:18:   instantiated from here
y.ii:2: error: no type named 'type' in 'class N::Q'


Note that in the call to foo, all arguments have associated namespace
N, so X::foo shouldn't be considered. The fact that we do is bug 1.

Bug 2 is that even if we consider X::foo, we should realize that the
return type of X::foo can't be instantiated for this template argument,
since X::H<T>::type doesn't exist. That we don't silently give up means
that we aren't doing SFINAE right.

I'll try to come up with a wrong-code version of this in a minute.

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
            Summary|unused code changes the     |invalid Koenig lookup
                   |result of name lookup       |


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