Re: [PATCH] PRs c++/51239, c++/51180 - Better support for unbound alias template specialization

[Jason Merrill <jason at redhat dot com>]

Hmm.  I know I'm the one that suggested this approach, but I think I'm 
uncomfortable with this minimal change, since code for handling 
BOUND_TEMPLATE_TEMPLATE_PARM expects to be able to get a 
TEMPLATE_TYPE_PARM_INDEX out of it, and that won't work for the alias 
template use.

So I'd like to rename BOUND_TEMPLATE_TEMPLATE_PARM to something more 
generic, perhaps TEMPLATE_ID_TYPE, that just takes a template and args. 
 So existing uses of BOUND_TEMPLATE_TEMPLATE_PARM would be replaced 
with a TEMPLATE_ID_TYPE around a TEMPLATE_TEMPLATE_PARM.

At that point it probably makes sense to replace the use of 
TEMPLATE_ID_EXPR in TYPENAME_TYPE with TEMPLATE_ID_TYPE.

Does this make sense?  Sorry to make more work for you.

Also, rather than pass back unknown_nb_args_p from 
coerce_template_parms, let's make it a predicate next to 
any_dependent_template_arguments_p and then use it in both places.  And 
change the name; it took me a little while to realize that "nb" is short 
for "number".

Thanks,
Jason