KeyError when scheme hacks encounter missing purelib.

setuptools version

v59.8.0

Python version

3.8.12

OS

Ubuntu 21.04

Additional environment information

No response

Description

Until recently, kombu was using some code like this hack to copy data files into the module directory.

Now we're seeing this error:

Traceback (most recent call last):
File "setup.py", line 60, in
scheme['data'] = scheme['purelib']
KeyError: 'purelib'

Because in v59.8.0 osx_framework_user was added to INSTALL_SCHEMES and it doesn't defined the purelib part of the dict.

Should that new osx_framework_user have purelib defined? If it's not necessary, maybe it's best these old hacks break and requiring changing code to use MANIFEST.in like this other SO post suggests?: https://stackoverflow.com/a/1857436

Expected behavior

That new osx_framework_user in INSTALL_SCHEMES should have purelib defined?

How to Reproduce

Run:

from distutils.command.install import INSTALL_SCHEMES

for scheme in list(INSTALL_SCHEMES.values()):
    scheme['data'] = scheme['purelib']

on v59.8.0

Output

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
KeyError: 'purelib'

Code of Conduct

• I agree to follow the PSF Code of Conduct

Start with distutils.command.install.INSTALL_SCHEMES and reproduce the KeyError using the Python snippet in the issue on setuptools v59.8.0. Inspect the osx_framework_user scheme and determine whether its missing purelib entry should be defined; done means the reproduction no longer raises the reported KeyError or the expected compatibility behavior is documented.