bpo-34032: Add platlibdir as an option for distinguishing /usr/lib and /usr/lib64

[mcepl]

Build system has been modified to allow /usr/lib64 as well as /usr/lib into install path as well as to the search path for the Linux distributions which distinguish between 32bit and 64bit libraries.

https://bugs.python.org/issue34032

@vstinner , @doko42 , who else?

[vstinner]

The new "platlibdir" variable should be documented in Doc/library/sysconfig.rst:
https://docs.python.org/dev/library/sysconfig.html#installation-paths

You have to add it to the list, and also add a ".. versionchanged:: 3.8 (...)" markup to document the change.

IMHO it's worth it to also add a second NEWS entry for the sysconfig change (new "platlibdir" variable).

[vstinner]

Can you mention the new --with-custom-platlibdir= configure option somewhere?

Nitpick: I would write "32 bit and 64 bit libraries" ;-) (or "32-bit and 64-bit libraries")

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[vstinner]

The OpenSUSE patch only changes the "unix_prefix" scheme, but the Fedora patch also changes the 'unix_home' scheme. To be honest, I don't understand well this change.

[mcepl]

Hmm, this pull request fails on AppVeyor with:

======================================================================
ERROR: test_user_site (distutils.tests.test_install.InstallTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\distutils\tests\test_install.py", line 114, in test_user_site
    cmd.ensure_finalized()
  File "C:\projects\cpython\lib\distutils\cmd.py", line 107, in ensure_finalized
    self.finalize_options()
  File "C:\projects\cpython\lib\distutils\command\install.py", line 330, in finalize_options
    self.create_home_path()
  File "C:\projects\cpython\lib\distutils\command\install.py", line 536, in create_home_path
    if path.startswith(home) and not os.path.isdir(path):
AttributeError: 'NoneType' object has no attribute 'startswith'
----------------------------------------------------------------------
Ran 246 tests in 32.131s
FAILED (errors=1, skipped=24)
test test_distutils failed

and with

test_user_similar (test.test_sysconfig.TestSysConfig) ... test test_sysconfig failed
ERROR
======================================================================
ERROR: test_get_path (test.test_sysconfig.TestSysConfig)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_sysconfig.py", line 100, in test_get_path
    res = get_path(name, scheme)
  File "C:\projects\cpython\lib\sysconfig.py", line 506, in get_path
    return get_paths(scheme, vars, expand)[name]
  File "C:\projects\cpython\lib\sysconfig.py", line 496, in get_paths
    return _expand_vars(scheme, vars)
  File "C:\projects\cpython\lib\sysconfig.py", line 170, in _expand_vars
    res[key] = os.path.normpath(_subst_vars(value, vars))
  File "C:\projects\cpython\lib\sysconfig.py", line 151, in _subst_vars
    raise AttributeError('{%s}' % var) from None
AttributeError: {'installed_base'}
======================================================================
ERROR: test_user_similar (test.test_sysconfig.TestSysConfig)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\projects\cpython\lib\test\test_sysconfig.py", line 267, in test_user_similar
    global_path = get_path(name, 'posix_prefix')
  File "C:\projects\cpython\lib\sysconfig.py", line 506, in get_path
    return get_paths(scheme, vars, expand)[name]
  File "C:\projects\cpython\lib\sysconfig.py", line 496, in get_paths
    return _expand_vars(scheme, vars)
  File "C:\projects\cpython\lib\sysconfig.py", line 170, in _expand_vars
    res[key] = os.path.normpath(_subst_vars(value, vars))
  File "C:\projects\cpython\lib\sysconfig.py", line 151, in _subst_vars
    raise AttributeError('{%s}' % var) from None
AttributeError: {'installed_base'}
----------------------------------------------------------------------
Ran 21 tests in 0.084s

Hmm, I guess this whole thing should be limited just to Unix (non-Windows, non-Mac) systems, right?

[Fak3]

Was this superseded by #11755 ?

[vstinner]

I merged PR #18381 instead which is very similar. Thanks @mcepl for helping on PR #18381.