[Python-Dev] what environment variable should contain compiler warning suppression flags?

[Brett Cannon]

On Sat, Jun 26, 2010 at 16:37, M.-A. Lemburg <mal at egenix.com> wrote:
> Brett Cannon wrote:
>> On Wed, Jun 23, 2010 at 14:53, Brett Cannon <brett at python.org> wrote:
>>> I finally realized why clang has not been silencing its warnings about
>>> unused return values: I have -Wno-unused-value set in CFLAGS which
>>> comes before OPT (which defines -Wall) as set in PY_CFLAGS in
>>> Makefile.pre.in.
>>>
>>> I could obviously set OPT in my environment, but that would override
>>> the default OPT settings Python uses. I could put it in EXTRA_CFLAGS,
>>> but the README says that's for stuff that tweak binary compatibility.
>>>
>>> So basically what I am asking is what environment variable should I
>>> use? If CFLAGS is correct then does anyone have any issues if I change
>>> the order of things for PY_CFLAGS in the Makefile so that CFLAGS comes
>>> after OPT?
>>>
>>
>> Since no one objected I swapped the order in r82259. In case anyone
>> else uses clang to compile Python, this means that -Wno-unused-value
>> will now work to silence the warning about unused return values that
>> is caused by some macros. Probably using -Wno-empty-body is also good
>> to avoid all the warnings triggered by the UCS4 macros in cjkcodecs.
>
> I think you need to come up with a different solution and revert
> the change...
>
> OPT has historically been the only variable to use for
> adjusting the Python C compiler settings.

Just found the relevant section in the README.

>
> As the name implies this was usually used to adjust the
> optimizer settings, including raising the optimization level
> from the default or disabling it.

It meant optional to me, not optimization. I hate abbreviations sometimes.

>
> With your change CFLAGS will always override OPT and thus
> any optimization definitions made in OPT will no longer
> have an effect.

That was the point; OPT defines defaults through configure.in and I
simply wanted to add to those instead of having OPT completely
overwritten by me.

>
> Note that CFLAGS defines -O2 on many platforms.

So then wouldn't that mean they want that to be the optimization
level? Or is the historical reason that default exists is so that some
default exists but to expect the application to override as desired?

>
> In your particular case, you should try setting OPT to
> "... -Wno-unused-value ..." (ie. replace -Wall with your
> setting).

So what is CFLAGS for then? ``configure -h`` says it's for "C compiler
flags"; that's extremely ambiguous. And it doesn't help that OPT is
not mentioned by ``configure -h`` as that is what I have always gone
by to know what flags are available for compilation.

-Brett

>
> --
> Marc-Andre Lemburg
> eGenix.com
>
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