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

[Jason Merrill <jason@redhat.com>]

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.

>> 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
>>
>