I'm not sure that is a robust way to do compiler detection, since I'm not sure the platform module and distutils agree.

I'd suggest instead to do in the top-level setup.py:

def get_build_ext_override():
    from numpy.distutils.commands.build_ext import build_ext as old_build_ext
    class build_ext(old_build_ext):
        def build_extension(self, ext):
            <add compiler flags to ext.extra_compile_args here>
            old_build_ext.build_extension(self, ext)
    return build_ext
...

def setup_package():
...
    metadata = dict(
...
        cmdclass={"sdist": sdist_checked,
            'build_ext': get_build_ext_override()},
...

to override just the compiler flags used when building the extensions. This is what @peterbell10 did for Scipy, and I guess it should also work here.

The design of distutils is again a problem here that makes solutions hacky.

The CI run with gcc 4.8 agrees that it is not enough to add the flag for pocketfft and random, we need it for all c-extensions.

Turns out we need to override both build_clib and build_ext

the build with gcc 4.8 passes.

Will this correctly apply the flag for the configtest stuff too?

It won't apply to configtest I think, as that's done by an earlier config command, but not sure if the flag is necessary there. Might also be possible to override the config command here.

Thanks Matti. I don't think the config tests need the flag, but it may be worth tracking down the call in case that changes in the future.