Re: [Patch] [C++0x] Support decltype-specifier as start of nested-name-specifier. (Bug 6709)

[Jason Merrill <jason@redhat.com>]

Now that we're in stage 1 again, I'd like to get your decltype changes 
integrated.  Sorry I didn't respond sooner.

On 01/20/2011 11:51 AM, Adam Butcher wrote:
> The attached patch attempts to resolve bug
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=6709  Allowing
> decltype(expr) to appear as the start of a nested-name-specifier.
>
> However there is something wrong.  Although it parses fine, the
> resulting tree seems to be treated as if it were dependent on a template
> parameter.  An additional 'typename' prefix is required to get the
> desired behaviour.
>
> Although this seems to work for many scenarios, the resulting tree
> seems to be treated as dependent (in the sense of dependent on a
> template parameter) even when used outside of a template.  For
> instance:
>
>    struct X {};
>    struct Y { typedef X Inner; enum { E = 7 }; };
>    Y y;
>    decltype(y)::Inner x;          // error: 'Inner' does not name a type

It's not that it's treated as dependent; the patch to 
cp_parser_simple_type parses the nested-name-specifier, then discards it 
and doesn't rewind the input stream, so the later call to 
cp_parser_nested_name_specifier doesn't see it and it's as though the 
"decltype(y)::" didn't exist.

I think you want to arrange to skip the lower calls to 
cp_parser_global_scope_opt and cp_parser_nested_name_specifier in this case.

Do you have tests for your decltype patches?

Jason