[cxx-abi-dev] namespace-qualified unresolved-names

[John McCall]

On Apr 29, 2011, at 2:41 PM, David Vandevoorde wrote:
> On Apr 24, 2011, at 2:22 AM, John McCall wrote:
>> Consider the following:
>> 
>> namespace ns {
>>   int foo(int);
>>   short foo(short);
>> }
>> 
>> template <typename T> auto forward_foo(T t) -> decltype(ns::foo(t)) {
>>   return ns::foo(t);
>> }
>> 
>> short test(short x) { return forward_foo(x); }
>> 
>> gcc-4.6 mangles forward_foo<short> as:
>> _Z11forward_fooIsEDTcl3foofp_EET_
>> 
>> This seems obviously wrong:  the qualifier has completely disappeared,
>> and this now looks like an unqualified call.  I believe the correct
>> mangling falls under the fourth production for <unresolved-name>:
>> <unresolved-name> ::= [gs] sr <unresolved-qualifier-level>+ E <base-unresolved-name>
>> In that case, the mangling should be:
>> _Z11forward_fooIsEDTclsr2nsE3foofp_EET_
>> 
>> Right?
> 
> Yes.  (That's what we produce.)

Okay.  It seems to me that this should be made more explicit in the document.
If we're all in agreement, then I suggest the following wording:

Strike the sentence reading:
  Similarly, an <unresolved-qualifier-level> may encode a known class type.
After the next sentence (beginning "That production is also used..."), insert:
  The mangling of an <unresolved-name> always follows the structure
  of the source, even when it can be resolved wholly or in part to a known
  entity.  All names in an <unresolved-name>, except names of template
  parameters, names appearing in a <decltype>, and names appearing in
  the <template-args> of a <simple-id>, are mangled as if completely
  unresolved;  this includes names of namespaces, namespace aliases,
  types, typedefs, type aliases, templates, template aliases, and so on.

We may also want to put some of these examples in the following
examples section.

Incidentally, while I was drafting this, I realized I had no idea how we're
supposed to mangle unresolved names starting with template-ids
where the template name is a template template parameter, e.g.
  template <template <class> temp> void foo(decltype(temp<int>::bar()) x);

I would suggest tweaking <unresolved-type> like so:
  <unresolved-type> ::= <template-param> [ <template-args>]
This should be unambiguous because I believe nothing
following an <unresolved-type> can start with an I, although I am
a bit worried about <destructor-name>.  But note that it's important
to express this in <destructor-name>, too!

John.