Move all but a small shim in override into _distutils_hack

1 files changed, 51 insertions, 0 deletions

diff --git a/_distutils_hack/__init__.py b/_distutils_hack/__init__.py
index 3ad70100..a8638344 100644
--- a/_distutils_hack/__init__.py
+++ b/_distutils_hack/__init__.py
@@ -1,5 +1,11 @@
 import sys
 import os
+import re
+import importlib
+import warnings
+
+
+is_pypy = '__pypy__' in sys.builtin_module_names
 
 
 def enabled():
@@ -10,6 +16,51 @@ def enabled():
     return which == 'local'
 
 
+def warn_distutils_present():
+    if 'distutils' not in sys.modules:
+        return
+    if is_pypy and sys.version_info < (3, 7):
+        # PyPy for 3.6 unconditionally imports distutils, so bypass the warning
+        # https://foss.heptapod.net/pypy/pypy/-/blob/be829135bc0d758997b3566062999ee8b23872b4/lib-python/3/site.py#L250
+        return
+    warnings.warn(
+        "Distutils was imported before Setuptools. This usage is discouraged "
+        "and may exhibit undesirable behaviors or errors. Please use "
+        "Setuptools' objects directly or at least import Setuptools first.")
+
+
+def clear_distutils():
+    if 'distutils' not in sys.modules:
+        return
+    warnings.warn("Setuptools is replacing distutils.")
+    mods = [name for name in sys.modules if re.match(r'distutils\b', name)]
+    for name in mods:
+        del sys.modules[name]
+
+
+def ensure_local_distutils():
+    clear_distutils()
+    distutils = importlib.import_module('setuptools._distutils')
+    distutils.__name__ = 'distutils'
+    sys.modules['distutils'] = distutils
+
+    # sanity check that submodules load as expected
+    core = importlib.import_module('distutils.core')
+    assert '_distutils' in core.__file__, core.__file__
+
+
+def do_override():
+    """
+    Ensure that the local copy of distutils is preferred over stdlib.
+
+    See https://github.com/pypa/setuptools/issues/417#issuecomment-392298401
+    for more motivation.
+    """
+    warn_distutils_present()
+    if enabled():
+        ensure_local_distutils()
+
+
 class DistutilsMetaFinder:
     def find_spec(self, fullname, path, target=None):
         if path is not None or fullname != "distutils":