OK.
On Wed, Feb 15, 2017 at 12:30 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> On Wed, Feb 15, 2017 at 11:56:30AM -0500, Jason Merrill wrote:
>> On Tue, Feb 14, 2017 at 3:13 PM, Jakub Jelinek <ja...@redhat.com> wrote:
>> > The following testcase fails, because while we have the nodiscard
>> > attribute on the template, we actually never propagate it to the
>> > instantiation, which is where it is checked (I'm really surprised about
>> > this).
>>
>> Normally we propagate attributes when instantiating the class; see the
>> call to apply_late_template_attributes in
>> instantiate_class_template_1. I'm not sure why that wouldn't be
>
> Yes, instantiate_class_template_1 calls apply_late_template_attributes,
> but that actually does nothing if there are no dependent attributes.
> If there are any, it sets TYPE_ATTRIBUTES (or DECL_ATTRIBUTES) to
> a copy of the attributes list, removes all the dependent attributes
> from there and calls cplus_decl_attributes on the late attrs (after
> tsubst_attribute them). So setting {TYPE,DECL}_ATTRIBUTES to the
> attributes list unmodified if there are no dependent ones matches
> the behavior for non-dependent ones if there is at least one dependent.
>
> So, does the following patch look better?
>
> 2017-02-15 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/79502
> * pt.c (apply_late_template_attributes): If there are
> no dependent attributes, set *p to attributes.
>
> * g++.dg/cpp1z/nodiscard4.C: New test.
>
> --- gcc/cp/pt.c.jj 2017-02-14 09:23:49.000000000 +0100
> +++ gcc/cp/pt.c 2017-02-15 18:21:45.581055915 +0100
> @@ -10113,6 +10113,8 @@ apply_late_template_attributes (tree *de
>
> cplus_decl_attributes (decl_p, late_attrs, attr_flags);
> }
> + else
> + *p = attributes;
> }
>
> /* Perform (or defer) access check for typedefs that were referenced
> --- gcc/testsuite/g++.dg/cpp1z/nodiscard4.C.jj 2017-02-15 18:11:33.281135469
> +0100
> +++ gcc/testsuite/g++.dg/cpp1z/nodiscard4.C 2017-02-15 18:11:33.281135469
> +0100
> @@ -0,0 +1,14 @@
> +// PR c++/79502
> +// { dg-do compile { target c++11 } }
> +
> +template<typename>
> +struct [[nodiscard]] missiles {};
> +
> +missiles<void> make() { return {}; }
> +missiles<void> (*fnptr)() = make;
> +
> +int main()
> +{
> + make(); // { dg-warning "ignoring returned value of type" }
> + fnptr(); // { dg-warning "ignoring returned value of type" }
> +}
>
>
> Jakub
