Re: [PATCH] PR c++/50852 - loose template parameter comparison

[Jason Merrill <jason at redhat dot com>]

Sorry for the delay in getting back to you on this; I just keep thinking 
there has to be a better way to deal with this issue than this 
increasingly complex fixup machinery.

The basic problem we're dealing with is that two typedefs from different 
contexts are considered identical for the purpose of template argument 
comparison, and we are leaving them in non-type template arguments, so 
when we look for a pre-existing specialization one typedef gets replaced 
by the other, which breaks.

The fixup stuff is a solution to the problem of typedefs with 
incompatible template parameters leading to crashes, but it seems to me 
that this is just a symptom of the problem of replacing one typedef with 
another, and we should attack that underlying problem instead.  That 
problem is also visible when the typedefs have different names and an 
error message ends up talking about the wrong one.

It seems to me that the way to do this is to strip typedefs from 
non-type arguments like strip_typedefs does for types.  Did we try this 
before?

Ideal would be to treat a specialization using the typedef-using 
arguments as a typedef to the specialization using the canonical 
arguments, but that could follow on later.

Jason