Re: C++ PATCH to suppress bogus -Wunused warning for parameter packs (PR c++/68965)

[Jason Merrill <jason at redhat dot com>]

On 01/13/2016 05:52 PM, Marek Polacek wrote:
> On Wed, Jan 13, 2016 at 03:33:27PM -0500, Jason Merrill wrote:
> > On 01/13/2016 11:50 AM, Marek Polacek wrote:
> > > So to quash that -Wunused-parameter warning, I decided to set TREE_USED at the
> > > place where we create those #xs parameters.
> >
> > Won't that cause false negatives when the parameter pack is never mentioned
> > in the function?
>
> You mean that e.g. for
>
> auto fn = [](auto&&... xs)
> {
> };
>
> int
> main ()
> {
>    fn (1, 2, 3);
> }
>
> we won't print
> z.cc:1:24: warning: unused parameter 'xs' [-Wunused-parameter]
> anymore?  Unfortunately, we don't print that even without the patch :(.

But we do currently print

wa.C:1:24: warning: unused parameter ‘xs#0’ [-Wunused-parameter]
wa.C:1:24: warning: unused parameter ‘xs#1’ [-Wunused-parameter]
wa.C:1:24: warning: unused parameter ‘xs#2’ [-Wunused-parameter]

for that testcase, and I think your patch would remove this warning as well.

Jason