Re: [PATCH v2] cpp/c: Add -Wexpansion-to-defined

["Manuel López-Ibáñez" <lopezibanez@gmail.com>]

On 10 August 2016 at 15:44, Paolo Bonzini <bonzini@gnu.org> wrote:
>
>
> On 10/08/2016 16:42, Manuel López-Ibáñez wrote:
>> > > My only fear is that people not using -Wpedantic nor -pedantic-errors
>> > > expect that GNU extensions work. This is a GNU extension that defines
>> > > something that is undefined according to ISO. Enabling the warning
>> > > with -Wextra is just annoying those people who may not care about
>> > > other compilers.
>> >
>> > I think this warning falls in the same category as
>> > -Wshift-negative-value.  (In fact I dislike -Wshift-negative-value a
>> > lot, and would put that one under -Wpedantic only).
>>
>> It is not the same category. One is compile-time UB and the other is
>> runtime UB. See:
>> https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01551.html
>> and https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01529.html
>
> Right---what I meant is it's the same kind of "annoying for people who
> expect that GNU extensions work" warning.

Oh, I agree. I'm just mentioning what the current definition/behavior
is (and documenting it here:
https://gcc.gnu.org/wiki/DiagnosticsGuidelines FWIW), not what I think
should be.

Perhaps we need something like -Wextra-pedantic, for things that are
undefined by ISO C but defined by GNU. Thus, they would not trigger
pedwarns and no error with -pedantic-errors.

Or we need to split -Wpedantic into -Wpedantic-pedwarns and
-Wpedantic-nopedwarns (with better names). This way -pedantic-errors
would be equivalent to -Werror=pedantic-pedwarns +
-Werror=pedwarns-not-controlled-by-pedantic.

i find -pedantic-errors too out of place with the rest of -W* options.

Manuel.