Re: PR c++/30195

[Jason Merrill <jason at redhat dot com>]

On 10/24/2011 05:53 PM, Fabien Chêne wrote:
> After looking into it a bit more, I now see things differently. The
> target_decl is in fact put into the CLASSTYPE_METHOD_VEC at
> instantiation time, via handle_using_decl, with the correct access.

Great.

> The problem is that while parsing the template (before instantiating),
> it is not yet there and an error is immediately raised.

Ah, I see.  We need lookup_member to find the USING_DECL, but if we're 
skipping function USING_DECLs in lookup_field_1 and they aren't in 
CLASSTYPE_METHOD_VEC in templates, we don't find it either way.

> I only see three solutions:
> 1) perform an additional lookup for using declarations that designate
> functions in lookup_fnfields_slot to find something even if the
> CLASSTYPE_METHOD_VEC is empty (what I implemented in the previous
> patch)
> 2) inhibate the lookup error at some point.
> 3) put the decl into the CLASSTYPE_METHOD_VEC before instantiation

> Honestly, I don't know if 2) is realistic, and how to implement it as well ...
> 3) seems complicated: in finish_member_declaration, we must put away
> the decl into TYPE_FIELDS or TYPE_METHODS, but we would like to put
> the target_decl into TYPE_METHODS (and call add_method), and at the
> same time put its  using decl into TYPE_FIELDS... I don't know if it
> can theoretically work, but having try it, I think it would need many
> adjustments.

I think #3 is the way to go.  Isn't that what happens in non-templates? 
 We don't try to instantiate the CLASSTYPE_METHOD_VEC, we build up a 
whole new one from the decl list, so having it in both places shouldn't 
be a problem for instantiation.

Jason