Re: Change default level for -Wimplicit-fallthrough

[Jakub Jelinek <jakub at redhat dot com>]

On Thu, Nov 03, 2016 at 01:55:33PM +0100, Markus Trippelsdorf wrote:
> On 2016.11.03 at 13:32 +0100, Jakub Jelinek wrote:
> > On Thu, Nov 03, 2016 at 01:22:11PM +0100, Bernd Schmidt wrote:
> > > On 11/03/2016 12:58 PM, Jakub Jelinek wrote:
> > > >On Thu, Nov 03, 2016 at 12:51:15PM +0100, Bernd Schmidt wrote:
> > > >>I'm concerned about the number of false positives for this warning, and
> > > >>judging by previous discussions, I'm not alone in this. This patch limits it
> > > >>to level 1 (any comment before the case label disables the warning) for
> > > >>cases where the user specified no explicit level. It'll still generate
> > > >>enough noise that people will be aware of it and can choose whether to use a
> > > >>higher level or not.
> > > >>
> > > >>Bootstrapped and tested on x86_64-linux. Ok?
> > > >
> > > >I disagree, I'm ok with changing it to 2, but 1 is too much.
> > > 
> > > Well, we have data from our own sources where we had to "fix" lots of
> > > perfectly good code, and also from the Linux kernel. From an earlier
> > > discussion:
> > 
> > That data wasn't really convincing on this.  All it proved is that most of
> > the cases are (likely) deliberate fall-throughs without any comment
> > whatsoever, the rest is in the noise.  As one needs to deal with those
> > where comments are missing altogether, dealing with the noise is acceptable.
> 
> Without Bernd's patch to set the default to 1 you will drown in false
> positives once you start using gcc-7 to build a whole distro. On my
> Gentoo test box anything but level 1 is simply unacceptable, because you
> will miss important other warnings in the -Wimplicit-fallthrough noise
> otherwise.

That is really strange.  First of all, most of packages aren't compiled with
-Wextra/-W.  And in those that are, are you sure that that no comment at all
for the implicit fallthroughs isn't significantly more common than the
set of comments that are accepted by -Wimplicit-fallthrough=1 and not
accepted by -Wimplicit-fallthrough=2?

	Jakub