CLN/BUILD: Fix clang warnings on build

[TomAugspurger]

Here's the output from the current master. I could try to clean some of the warnings up someday if there's any interest; a decent excuse to look through the source code.

A lot of the warnings look similar:

• deprecated numpy API
• warning: static variable 'PyArray_API' is used in an inline function with external linkage [-Wstatic-in-inline]
• warning: comparison of constant -1 with expression of type 'PANDAS_DATETIMEUNIT' is always true
• warning: format specifies type 'long' but the argument has type 'long long' [-Wformat]
• various unused functions

What do things look like with gcc (and whatever windows uses)?

[cpcloud]

1. Deprecated NumPy API is on all system AFAIK
2. Not sure
3. Looks like it could potentially lead to a bug and should be fixed or at least documented.
4. Format string warning that would be nice to get rid of.
5. Unused functions/variables are probably okay to remove unless they're from Cython, which you can't really control. I would expect most compilers remove dead code, so this isn't that big of a deal.

[jtratner]

Also, klib may create unused functions because of macros...

[jtratner]

btw - you can see what the build warnings are on Travis too (just expand the build part of the build summary)

[ghost]

@jreback, numpy is moving on, should we put effort into moving pandas into 1.7 cleanliness?
is it delicate or just tedious?

[jreback]

I have no idea.....scipy/numpy builds are not clean themselves....does it bother anyone?

[ghost]

aesthetically? a little bit. there are increasingly more warnings related
to compiling pandas or running the tests. a dose of anti-entropy wouldn't
hurt, but it's not actually damaging.

[jreback]

would take someone whom is more familiar with the build process and some time

[jreback]

so we prob want to have this as an option, but just passing -w in compilation of extensions basically suppresses almost everything: https://travis-ci.org/jreback/pandas/jobs/115105866

What we could do is have an option to turn this on/off (default on). any thoughts

@TomAugspurger @jorisvandenbossche @wesm

[wesm]

If we are not already, we should definitely set -Wno-unused-function as Cython generates a lot of warnings barf on clang. Compiler warnings are good but not if they're for some Cython issues that we can't fix ourselves, so I'd be in favor of manually suppressing the ones that are causing the most issues (or fixing the underlying problems if any)

[jreback]

@wesm that looks like a nice compromise (between using '-w' which removes everything). Ok will push that.

[jreback]

not bad on linux, a bit more on osx. Note that we are now building osx on Travis (for 1 build / 3.5)

[jbrockmendel]

I think this can be closed. Numpy/cython are discussing making the deprecated-API warnings suppressable. Other than that there’s not much else to be done.