------- Comment #2 from mmitchel at gcc dot gnu dot org 2007-03-23 00:50
-------
This code in lookup_template_class:
- /* Consider an example where a template template parameter declared as
-
- template <class T, class U = std::allocator<T> > class TT
-
- The template parameter level of T and U are one level larger than
- of TT. To proper process the default argument of U, say when an
- instantiation `TT<int>' is seen, we need to build the full
- arguments containing {int} as the innermost level. Outer levels,
- available when not appearing as default template argument, can be
- obtained from `current_template_args ()'.
-
- Suppose that TT is later substituted with std::vector. The above
- instantiation is `TT<int, std::allocator<T> >' with TT at
- level 1, and T at level 2, while the template arguments at level 1
- becomes {std::vector} and the inner level 2 is {int}. */
-
- if (current_template_parms)
- arglist = add_to_template_args (current_template_args (), arglist);
is simply bogus; the current template arguments have nothing to do with the
situation. It is this code which causes the crash.
I believe that the correct change is to remove that code and to make template
parameters for template template parameters restart at level 1. So, in:
template <template <typename T> class A>
class B {};
both T and A have level 1. (Right now, T has level 2.)
T should have level 1 because, when instantiating A, that's what make sense.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30897
