On Wed, Oct 12, 2016 at 12:34:45AM +0200, Bernd Schmidt wrote:
> On 10/11/2016 11:52 PM, Jakub Jelinek wrote:
> >The following patch introduces difference warning levels for
> >-Wimplicit-fallthrough warning, so projects can choose if they want to
> >honor only attributes (-Wimplicit-fallthrough=5), or what kind of comments.
> >=4 is very picky and accepts only very small amount of comments, =3 is what
> >we had before this patch, =2 looks case insensitively for falls?[
> >\t-]*thr(u|ough)
> >anywhere in the comment, =1 accepts any comment, =0 is the same as
> >-Wno-implicit-fallthrough - disables the warning.
> >
> >Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> I think this is ok, and thank you very much for doing this.
>
> >The patch keeps as the default the current forms, I'm not against changing
> >it to =2 if there is consensus on it, but would strongly prefer doing that
> >incrementally, as e.g. we'll need to adjust the testsuite for that, and
> >perhaps also use =3 as the warning for gcc bootstraps when we are already =3
> >mode clear.
>
> It's a discussion we should have, but I agree it should be done
> incrementally. I would argue for =1 as the default.
>
> > * c.opt (Wextra): Add as C/C++/ObjC/ObjC++ option.
> > (Wimplicit-fallthrough=): Enable for these languages by -Wextra.
>
> This bit looks like it does a bit more magic than is immediately obvious.
> Could you elaborate how this works?
It is all magic to get it working correctly, took me a while to figure it
out. The thing is that EnabledBy doesn't support the positive and negative
arguments (and after all, -Wimplicit-fallthrough doesn't make much sense to
be enabled for non-C family of languages from -Wextra), so it needs
LangEnabledBy. But, LangEnabledBy will not work if the option doesn't have
a corresponding language mask, so I had to add that mask to it, otherwise
C_handle_option_auto, CXX_handle_option_auto etc. wouldn't be called for
that option.
E.g. fortran/lang.opt already had:
Wcompare-reals
Fortran Warning Var(warn_compare_reals) LangEnabledBy(Fortran,Wextra)
Warn about equality comparisons involving REAL or COMPLEX expressions.
and to be able to do that also had:
Wextra
Fortran Warning
; Documented in common
-Wall which has far more LangEnabledBy uses is even not defined in
common.opt, only in the FE *.opt files. Wunused is another option
that is similarly copied/extended in c.opt, so that it can be used
in LangEnabledBy and can also have its own LangEnabledBy.
Jakub
