Re: [C++ PATCH] PR c++/45114 - Support alias templates

[Jason Merrill <jason@redhat.com>]

On 11/05/2011 07:36 PM, Dodji Seketeli wrote:
> +#define TYPE_DECL_NAMES_ALIAS_TEMPLATE_P(NODE)                         \

This doesn't seem to be needed anymore.

> +dump_alias_template_specialization (tree t, int flags)
> +{
> +  gcc_assert (alias_template_specialization_p (t));
> +
> +  if (CLASS_TYPE_P (t))
> +    dump_aggr_type (t, flags);
> +  else
> +    {
> +      tree name;
> +      name = TYPE_IDENTIFIER (t);
> +      pp_cxx_tree_identifier (cxx_pp, name);
> +      dump_template_parms (TYPE_TEMPLATE_INFO (t),
> +                          /*primary=*/false,
> +                          flags & ~TFF_TEMPLATE_HEADER);
> +    }

Why do you treat class and non-class aliases differently?  In both cases 
I think we want alias specializations to be printed as 
scope::name<args>.  We don't want to print 'class' since such a 
specialization cannot be used in an elaborated-type-specifier. 
7.1.6.3/2: "If the identifier resolves to a typedef-name or
the simple-template-id resolves to an alias template specialization, the 
elaborated-type-specifier is ill-formed."

> +      if (alias_template_specialization_p (t))
> +       {
> +         dump_alias_template_specialization (t, flags);
> +         return;
> +       }
> +      else if ((flags & TFF_CHASE_TYPEDEF)
> +              || DECL_SELF_REFERENCE_P (decl)
> +              || (!flag_pretty_templates
> +                  && DECL_LANG_SPECIFIC (decl) && DECL_TEMPLATE_INFO (decl)))
>         t = strip_typedefs (t);

The order of these two should be reversed.  We want TFF_CHASE_TYPEDEF 
and -fno-pretty-templates to strip alias-templates as well as 
non-template typedefs.

> -  /* If the next keyword is `namespace', we have a
> +  /* If the next keyword is `namespace', we have either a
>       namespace-alias-definition.  */

This change seems unintended.

> +      if (!(type_decl != NULL_TREE
> +           && TREE_CODE (type_decl) == TYPE_DECL
> +           && TYPE_DECL_ALIAS_P (type_decl)
> +           && DECL_TEMPLATE_INSTANTIATION (type_decl)))
> +       cp_parser_simulate_error (parser);

I think the TYPE_DECL_ALIAS_P and DECL_TEMPLATE_INSTANTIATION checks 
should be an assert instead; at this point any TYPE_DECL we get should 
satisfy those.

> -         || (TYPE_P (t) && TYPE_DECL_ALIAS_P (TYPE_NAME (t)))
> +         || (TYPE_P (t)
> +             && TYPE_NAME (t)
> +             && TREE_CODE (TYPE_NAME (t)) == TYPE_DECL
> +             && TYPE_DECL_ALIAS_P (TYPE_NAME (t)))

In C++ I think a non-null TYPE_NAME is always a TYPE_DECL.

>> Why not set r here, as for the other cases?
> Because I'd like to handle alias declarations even for cases handled
> by the other cases where, r is end up being NULL.

Hmm.  With this code we end up substituting into a non-template alias 
declaration at file scope.  I think if you check 
alias_template_specialization_p before checking for class/function scope 
that should handle the cases you need.

Jason