Bypass .pth loader when distutils is loaded from pip. Workaround for pypa/pip#8761.

_distutils_hack/__init__.py

@@ -3,6 +3,7 @@ import os
 import re
 import importlib
 import warnings
+import inspect
 
 
 is_pypy = '__pypy__' in sys.builtin_module_names
@@ -66,7 +67,7 @@ def do_override():
 
 class DistutilsMetaFinder:
     def find_spec(self, fullname, path, target=None):
-        if path is not None or fullname != "distutils":
+        if path is not None or fullname != "distutils" or self._bypass():
             return None
 
         return self.get_distutils_spec()
@@ -84,6 +85,16 @@ class DistutilsMetaFinder:
 
         return importlib.util.spec_from_loader('distutils', DistutilsLoader())
 
+    def _bypass(self):
+        """
+        Suppress the import of distutils from setuptools when running under pip.
+        See pypa/pip#8761 for rationale.
+        """
+        return any(
+            level.frame.f_globals['__name__'].startswith('pip.')
+            for level in inspect.stack(context=False)
+        )
+
 
 DISTUTILS_FINDER = DistutilsMetaFinder()