[RFC] -Weverything

[N.M. Maclaren]

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++.


Regards,
Nick Maclaren.