Re: [C++ Patch] Improve grokdeclarator error

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

On 30/09/19 20:46, Jason Merrill wrote:
> On Mon, Sep 30, 2019 at 6:54 AM Paolo Carlini <paolo.carlini@oracle.com> wrote:
> > On 28/09/19 04:05, Jason Merrill wrote:
> > > On 9/26/19 3:39 PM, Paolo Carlini wrote:
> > > > +template void foo<int>(  // { dg-error "15:template-id .foo<int>.
> > > > used as a declarator" }
> > > That's a strange diagnostic message; there's nothing wrong with using
> > > a template-id as a declarator.  Why are we even calling grokdeclarator
> > > when we hit EOF in the middle of the declarator?
> > It's indeed a weird situation. Note, by the way, that for
> >
> > template void foo<int>;
> >
> > we end up giving the same diagnostic, only, the location was already fine.
> >
> > Anyway, to explain why I say weird, clang believes it's dealing with an
> > explicit instantiation:
> >
> > explicit instantiation of 'foo' does not refer to a function template,
> > variable template, member function, member class, or static data member
> >
> > whereas EDG gives:
> >
> > declaration is incompatible with function template "void foo<<unnamed>>()"
> >
> > I *think* what we are issuing is closer in spirit to the latter, we
> > don't get fooled into thinking it's an instantiation and we say that as
> > a declaration doesn't work either. See what I mean?
> Well, it is an explicit instantiation, the problem (as EDG says) is
> that the instantiation declaration doesn't match the template.

Definitely it doesn't.

> > Removing completely
> > the diagnostic code doesn't seem fine either because we end up with very
> > confusing wordings like
> >
> > variable or field declared void
> >
> > or worse we mention variable templates, depending on the type (I already
> > mentioned this).
> Any thought about my question about why we're calling grokdeclarator
> in the first place?

Yes. If you look at cp_parser_explicit_instantiation, clearly 
cp_parser_declarator doesn't return a cp_error_declarator and in such 
cases we always call grokdeclarator. Do you think we should error out 
here instead, much earlier? Currently grokdeclarator does quite a bit of 
work before the diagnostic.

Paolo..