Incorporate Fedora's distutil patch

[hroncok]

See pypa/setuptools#2896 (comment)

[hroncok]

This is a proof of concept. It has not been tested and Fedra's old Pythons currently don't set this attribute.

[jaraco]

Thanks for this. For Debian and pkgsrc, I've been instead of incorporating the patches, creating hooks where platforms can provide their customizations. Let me take this example and illustrate what I have in mind.

[jaraco]

With this latest change, Fedora would include on the Python path a module, _distutils_system_mod containing:

"""
Patch distutils to mangle the prefix when not a virtualenv.

Sets self.prefix to sys.prefix + local/ unless RPM build.
"""

import os
import sysconfig
import distutils.command.install


rpm_build = 'RPM_BUILD_ROOT' in os.environ
if sysconfig._distutils_mangle_rpm_prefix and not rpm_build:
    distutils.command.install.install._prefix_addition = "/local"

Because the module is only available in the system environment, it doesn't need to do virtualenv detection (I hope). And because it's only available on platforms that introduce it, the _distutils_mangle_rpm_prefix can be known to be present (also an assumption).

Still, I think the general concept holds, and it gives Fedora more ownership over the behavior.

WDYT?

[hroncok]

Because the module is only available in the system environment

How so? Where would we put it if not to the stdlib which is always available? Even if we put it to site-packages, it will be available in virtual environments configured to see them.

OTOH _distutils_mangle_rpm_prefix does not need to exist at all, it was introduced here as a way to let distutils know we want to do that. With this hook, we are already doing that.

[jaraco]

Because the module is only available in the system environment

How so? Where would we put it if not to the stdlib which is always available? Even if we put it to site-packages, it will be available in virtual environments configured to see them.

That's fine. I'd welcome any number of gates (restore virtualenv check) as needed if it's not possible to place the hook in such a context that it's only present when needed.

OTOH _distutils_mangle_rpm_prefix does not need to exist at all, it was introduced here as a way to let distutils know we want to do that. With this hook, we are already doing that.

Sounds good. And of course, Fedora has full control over the behavior.

[hroncok]

I've included this in https://github.com/hroncok/setuptools/tree/local-distutils-fedora-addition for easier testing.

[hroncok]

This seems to work reliably.

[hroncok]

Here's the Fedora patch I've tried this with:

hroncok/cpython@a9ab687#diff-d593bd299ba58e440ba411ffa0640ccd9d20d518b0cf2644ed4bdb75a82a3e70

[jaraco]

Sounds good. Since you're not using _distutils_system_mod, I've removed the change to the comment authorizing that use. Is there anything else you want to see before rolling out this change?

[jaraco]

I'm going to go ahead and roll this out. We can iterate more if needed.

[hroncok]

Thanks.