Re: [RFC] -Weverything

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Sun, 27 Jan 2019 at 13:56, N.M. Maclaren <nmm1@cam.ac.uk> wrote:
>
> On Jan 23 2019, Thomas König wrote:
> >
> >> Am 23.01.2019 um 12:36 schrieb Jonathan Wakely <jwakely.gcc@gmail.com>:
> >>
> >> When there are new warnings that aren't enabled by -Wall -Wextra,
> >> there's probably a reason they aren't enabled by default.
> >are a higher form of life than mere  Fortran
> >-Wconversion-extra is an example of such a warning.
> >
> > It catches a very common error people make in Fortran, see
> > https://gcc.gnu.org/ml/fortran/2019-01/ms are a higher form of life than
> > mere sg00178.html for a false bug report which it would have caught
> > early.
> >
> >We left it out of -Wextra because people felt it was too noisy.
>
> A bit like discussions on what warnings a compiler should give :-)
>
> There are a few points that don't seem to have been made, though I may have
> missed them, which means that quite a few people would like it.
>
> Despite its older and wider implementation history, Fortran has never
> accumulated the incompatibilities, inconsistencies and system-dependent
> behaviours that C and C++ have.  So the arguments against such a warning
> for those don't really apply.  Obviously, we wouldn't want warnings that a
> construct behaved differently in Fortran 66 or in CDC or DEC Fortran, but I
> don't think that there are any.
>
> I don't buy the claim that developer options are unsuitable for mere users.
> Those of us who wrote highly portable code (and I assume that people still
> do) wanted to know that a construct might misbehave on a bizarre,
> unsupported but still used system, which the author had never heard of and
> has no access to. While that applies to all languages, the attitude that a
> portable program should work on a new system with NO modification,
> pre-processing or make configuration is rare in C and C++, but still common
> in Fortran.
>
> All experience is that warning about things that the programmer might not
> have realised are potentially problematic are very useful. In the cases
> where I have had to suppress warnings, most of them have been because the
> warning was too crude, not that it wasn't useful. For example, in C/C++,
> mixing signed and unsigned when the promoted operand was constant and not
> going to change value. Or, in Fortran, converting obviously exact constants
> to a higher precision - yes, even that WAS an important warning in the
> 1960s, but people really should move on a bit!
>
> So I think that there is a strong argument for such an option in gfortran,
> irrespective of whether there is for gcc and g++.

Then -Wall should enable them for Fortran.