C++ PATCH for c++/79817 - attribute deprecated on namespace

[Jason Merrill]

On Thu, Aug 22, 2019 at 11:01 AM Nathan Sidwell <nathan@acm.org> wrote:
>
> On 8/20/19 9:03 PM, Marek Polacek wrote:
>
> > and in cp_parser_nested_name_specifier_opt we simply don't know if we're
> > dealing with a function decl.  Calling cp_warn_deprecated_use_scopes from
> > cp_parser_type_specifier resulted int duplicated diagnostics so that one
> > is out too.  So I did the following which doesn't seem too bad.
>
> >
> > diff --git gcc/cp/decl.c gcc/cp/decl.c
> > index 08b7baa40e0..46ad0271f7b 100644
> > --- gcc/cp/decl.c
> > +++ gcc/cp/decl.c
> > @@ -10791,6 +10791,7 @@ grokdeclarator (const cp_declarator *declarator,
> >     cp_warn_deprecated_use (type);
> >     if (type && TREE_CODE (type) == TYPE_DECL)
> >       {
> > +      cp_warn_deprecated_use_scopes (DECL_CONTEXT (type));
>
> CP_DECL_CONTEXT would be clearer, here and elsewhere.
>
> >     /* Do warn about using typedefs to a deprecated class.  */
> > diff --git gcc/cp/decl2.c gcc/cp/decl2.c
> > index a32108f9d16..d6f407d7aef 100644
> > --- gcc/cp/decl2.c
> > +++ gcc/cp/decl2.c
> > @@ -5407,6 +5407,23 @@ cp_warn_deprecated_use (tree decl, tsubst_flags_t complain)
> >     return warned;
> >   }
> >
> > +/* Like above, but takes into account outer scopes.  */
> > +
> > +void
> > +cp_warn_deprecated_use_scopes (tree ns)
>
> Do we need to walk non-namespace scopes here?  can we just bail if NS is
> not a namespace?  if can legitimately not be a namespace, calling it NS
> is confusing :)

It seems like it can be a class in some cases, and I would want to
warn about deprecated classes named in a nested-name-specifier.  Did
we not already warn about that?

I agree that the parameter name is confusing.

> > +{
> > +  while (ns
> > +      && ns != error_mark_node
> > +      && ns != global_namespace)
> > +    {
> > +      cp_warn_deprecated_use (ns);
> > +      if (TYPE_P (ns))
> ... and does this ever trigger?
>
> > +     ns = CP_TYPE_CONTEXT (ns);
> > +      else
> > +     ns = CP_DECL_CONTEXT (ns);
> > +    }
> > +}
>
> I always worry about such recursive lookups.  NAMESPACE_DECL has so many
> spare flags, could we take one to say 'is, or contained in, deprecated',
> and thus know whether we can bail early.  And stop at the first
> deprecated one -- though not sure why someone would deprecate more than
> one namespace in a nest.  thoughts?

I can imagine deprecating an inner namespace and later deprecating an
outer namespace, but I don't think it's important to warn about more
than one in that case.

Jason