Re: [PATCH RFC] c-family: make -fno-permissive upgrade pedwarns

[Richard Biener <richard.guenther@gmail.com>]

On Mon, May 15, 2023 at 3:56 PM Jason Merrill <jason@redhat.com> wrote:
>
> On 5/15/23 03:32, Richard Biener wrote:
> > On Fri, May 12, 2023 at 10:54 PM Jason Merrill via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >> In the context of the recent discussion, it occurred to me that this semantic
> >> would be useful, but currently there is no easy way to access it.  Bikeshedding
> >> welcome; the use of this flag is a bit odd, but it has the advantage of being
> >> accepted without error going back at least to 4.3.
> >>
> >> -- 8< --
> >>
> >> Currently there is no flag to use to upgrade all currently-enabled pedwarns
> >> from warning to error.  -pedantic-errors also enables the -Wpedantic
> >> pedwarns, while -Werror=pedantic uselessly makes only the -Wpedantic
> >> pedwarns errors.
> >>
> >> I suggest that since -fpermissive lowers some diagnostics from error to
> >> warning, -fno-permissive could do the reverse.
> >
> > Hmm, but that makes '-fno-permissive' different from '-fpermissive
> > -fno-permissive'?
> > What about '-fpermissive -fno-permissive -fno-permissive' then?
> >
> > So I think over-loading -fno-permissive with differen semantics from negating
> > the option is bad.
>
> Fair enough.  Any other thoughts?  It occurs to me now that it is
> already possible to specify this behavior with -pedantic-errors
> -Wno-pedantic, maybe that's sufficient if a bit cumbersome.

I guess so.  Maybe the -fpermissive documentation could hint at
that for this case?

Richard.

> >> gcc/ChangeLog:
> >>
> >>          * doc/invoke.texi: Document -fno-permissive.
> >>
> >> gcc/c-family/ChangeLog:
> >>
> >>          * c.opt (fpermissive): Accept in C and ObjC as well.
> >>          * c-opts.cc (c_common_post_options): -fno-permissive sets
> >>          global_dc->pedantic_errors.
> >> ---
> >>   gcc/doc/invoke.texi    | 7 +++++++
> >>   gcc/c-family/c.opt     | 2 +-
> >>   gcc/c-family/c-opts.cc | 4 ++++
> >>   3 files changed, 12 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> >> index b92b8576027..6198df14382 100644
> >> --- a/gcc/doc/invoke.texi
> >> +++ b/gcc/doc/invoke.texi
> >> @@ -3438,11 +3438,18 @@ issue.  Currently, the only such diagnostic issued by G++ is the one for
> >>   a name having multiple meanings within a class.
> >>
> >>   @opindex fpermissive
> >> +@opindex fno-permissive
> >>   @item -fpermissive
> >>   Downgrade some diagnostics about nonconformant code from errors to
> >>   warnings.  Thus, using @option{-fpermissive} allows some
> >>   nonconforming code to compile.
> >>
> >> +Conversely, @option{-fno-permissive} can be used to upgrade some
> >> +diagnostics about nonconformant code from warnings to errors.  This
> >> +differs from @option{-pedantic-errors} in that the latter also implies
> >> +@option{-Wpedantic}; this option does not enable additional
> >> +diagnostics, only upgrades the severity of those that are enabled.
> >> +
> >>   @opindex fno-pretty-templates
> >>   @opindex fpretty-templates
> >>   @item -fno-pretty-templates
> >> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> >> index 3333cddeece..07165d2bbe8 100644
> >> --- a/gcc/c-family/c.opt
> >> +++ b/gcc/c-family/c.opt
> >> @@ -2075,7 +2075,7 @@ C ObjC C++ ObjC++
> >>   Look for and use PCH files even when preprocessing.
> >>
> >>   fpermissive
> >> -C++ ObjC++ Var(flag_permissive)
> >> +C ObjC C++ ObjC++ Var(flag_permissive)
> >>   Downgrade conformance errors to warnings.
> >>
> >>   fplan9-extensions
> >> diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
> >> index c68a2a27469..1973c068d59 100644
> >> --- a/gcc/c-family/c-opts.cc
> >> +++ b/gcc/c-family/c-opts.cc
> >> @@ -1021,6 +1021,10 @@ c_common_post_options (const char **pfilename)
> >>     SET_OPTION_IF_UNSET (&global_options, &global_options_set,
> >>                         flag_delete_dead_exceptions, true);
> >>
> >> +  if (!global_options_set.x_flag_pedantic_errors
> >> +      && global_options_set.x_flag_permissive)
> >> +    global_dc->pedantic_errors = !flag_permissive;
> >> +
> >>     if (cxx_dialect >= cxx11)
> >>       {
> >>         /* If we're allowing C++0x constructs, don't warn about C++98
> >>
> >> base-commit: 62c4d34ec005e95f000ffabd34da440dc62ac346
> >> --
> >> 2.31.1
> >>
> >
>