Allow opt-in and opt-out of distutils adoption at run time with...

Allow opt-in and opt-out of distutils adoption at run time with SETUPTOOLS_USE_DISTUTILS environment variable.

changelog.d/2232.misc.patch

+In preparation for re-enabling a local copy of distutils, Setuptools now honors an environment variable, SETUPTOOLS_USE_DISTUTILS. If set to 'stdlib' (current default), distutils will be used from the standard library. If set to 'local' (default in a imminent backward-incompatible release), the local copy of distutils will be used.

setuptools/__init__.py

@@ -4,7 +4,7 @@ import os
 import functools
 
 # Disabled for now due to: #2228, #2230
-# import setuptools.distutils_patch  # noqa: F401
+import setuptools.distutils_patch  # noqa: F401
 
 import distutils.core
 import distutils.filelist

setuptools/distutils_patch.py

@@ -23,9 +23,10 @@ def clear_distutils():
 
 def enabled():
     """
-    Provide an escape hatch for environments wishing to opt out.
+    Allow selection of distutils by environment variable.
     """
-    return 'SETUPTOOLS_DISTUTILS_ADOPTION_OPT_OUT' not in os.environ
+    which = os.environ.get('SETUPTOOLS_USE_DISTUTILS', 'stdlib')
+    return which == 'local'
 
 
 def ensure_local_distutils():