Re: C++ PATCH for c++/88184, ICE when treating name as template-name

[Jason Merrill <jason@redhat.com>]

OK.
On Tue, Dec 4, 2018 at 12:27 PM Marek Polacek <polacek@redhat.com> wrote:
>
> On Thu, Nov 29, 2018 at 04:03:50PM -0500, Jason Merrill wrote:
> > On 11/29/18 1:28 PM, Marek Polacek wrote:
> > > On Wed, Nov 28, 2018 at 10:34:11PM -0500, Jason Merrill wrote:
> > > > On 11/28/18 10:48 AM, Marek Polacek wrote:
> > > > > Since P0846R0 was implemented, a name will be treated as a template-name when
> > > > > it is an unqualified-id followed by a < and name lookup finds either one or
> > > > > more functions or finds nothing, in order to potentially cause ADL to be performed.
> > > > >
> > > > > In this case, we had
> > > > >
> > > > >     f<T> ();
> > > > >
> > > > > where we'd found a decl for f (not a TEMPLATE_DECL) and < follows.
> > > >
> > > >  From the backtrace in the PR, it seems as though we're treating f<T> as
> > > > non-dependent, which is wrong.  type_dependent_expression_p only looks at
> > > > the arguments of a TEMPLATE_ID_EXPR if it has unknown_type_node, so we
> > > > probably want to give it that type.
> > >
> > > That was my first attempt but it was crashing everywhere, so I abandoned it.
> > > But I was setting unknown_type_node in cp_parser_template_name whereas this
> > > patch sets it in cp_parser_postfix_expression, which works and is arguably
> > > better because it reuses the diagnostic in finish_call_expr.
> >
> > Would it work for lookup_template_function to always use unknown_type_node?
>
> Luckily, that seems to work!  I wish I'd thought of that, I like fixing bugs by
> simplifying code.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-12-04  Marek Polacek  <polacek@redhat.com>
>
>         PR c++/88184 - ICE when treating name as template-name.
>         * pt.c (lookup_template_function): Always build the TEMPLATE_ID_EXPR
>         with unknown_type_node.
>
>         * g++.dg/cpp2a/fn-template17.C: New test.
>         * g++.dg/cpp2a/fn-template18.C: New test.
>
> diff --git gcc/cp/pt.c gcc/cp/pt.c
> index a0d899f594b..78addc6c1c2 100644
> --- gcc/cp/pt.c
> +++ gcc/cp/pt.c
> @@ -9068,8 +9068,6 @@ add_pending_template (tree d)
>  tree
>  lookup_template_function (tree fns, tree arglist)
>  {
> -  tree type;
> -
>    if (fns == error_mark_node || arglist == error_mark_node)
>      return error_mark_node;
>
> @@ -9090,11 +9088,7 @@ lookup_template_function (tree fns, tree arglist)
>        return fns;
>      }
>
> -  type = TREE_TYPE (fns);
> -  if (TREE_CODE (fns) == OVERLOAD || !type)
> -    type = unknown_type_node;
> -
> -  return build2 (TEMPLATE_ID_EXPR, type, fns, arglist);
> +  return build2 (TEMPLATE_ID_EXPR, unknown_type_node, fns, arglist);
>  }
>
>  /* Within the scope of a template class S<T>, the name S gets bound
> diff --git gcc/testsuite/g++.dg/cpp2a/fn-template17.C gcc/testsuite/g++.dg/cpp2a/fn-template17.C
> new file mode 100644
> index 00000000000..f0d24107682
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp2a/fn-template17.C
> @@ -0,0 +1,21 @@
> +// PR c++/88184
> +// { dg-do compile }
> +// { dg-options "-std=c++2a -fchecking=2" }
> +
> +namespace A
> +{
> +  void f ();
> +}
> +
> +using A::f;
> +
> +template <typename T> void g ()
> +{
> +  f<T> (); // { dg-error "no matching function for call" }
> +}
> +
> +void
> +fn ()
> +{
> +  g<int>();
> +}
> diff --git gcc/testsuite/g++.dg/cpp2a/fn-template18.C gcc/testsuite/g++.dg/cpp2a/fn-template18.C
> new file mode 100644
> index 00000000000..7fe5e89ace3
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp2a/fn-template18.C
> @@ -0,0 +1,23 @@
> +// PR c++/88184
> +// { dg-do compile }
> +// { dg-options "-std=c++2a -fchecking=2" }
> +
> +namespace A
> +{
> +  void f ();
> +  void f (int);
> +  void f (int, int);
> +}
> +
> +using A::f;
> +
> +template <typename T> void g ()
> +{
> +  f<T> (); // { dg-error "no matching function for call" }
> +}
> +
> +void
> +fn ()
> +{
> +  g<int>();
> +}