Re: [Bug c++/40092] -std=gnu++0x expansion pattern fails with error about derived template instead of actual template

[Larry Evans <cppljevans at suddenlink dot net>]

On 05/14/09 20:19, cppljevans at suddenlink dot net wrote:
> ------- Comment #4 from cppljevans at suddenlink dot net  2009-05-15 01:19 -------
> Created an attachment (id=17869)
>  --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17869&action=view)
> Much simpler code showing problem
>
> Code has #defines which can be enabled or disabled to 
> show or hide bug.

The same error occurs with snapshot:

ftp://gcc.gnu.org/pub/gcc/snapshots/4.4-20090519/gcc-4.4-20090519.tar.bz2

The error message is from gcc/cp/pt.c:2692.  I suspect there's some
problem in find_parameter_packs_r used as arg a few lines up as:

  cp_walk_tree (&arg, &find_parameter_packs_r, &ppd, ppd.visited);

I've tried using gdb stepping to see where the problem is; however,
it's so hard to understand the tree structure and which type of
tree is supposed to be valid with a given TREE_CODE(t), that I
haven't had much success yet.

Help on how to debug this would be appreciated.