Suppress distutils replacement when building or testing CPython. Fixes …

…#2965. Fixes #3007.

_distutils_hack/__init__.py

@@ -89,6 +89,9 @@ def find_spec(self, fullname, path, target=None):
         return method()
 
     def spec_for_distutils(self):
+        if self.is_cpython():
+            return
+
         import importlib
         import importlib.abc
         import importlib.util
@@ -118,6 +121,14 @@ def exec_module(self, module):
             'distutils', DistutilsLoader(), origin=mod.__file__
         )
 
+    @staticmethod
+    def is_cpython():
+        """
+        Suppress supplying distutils for CPython (build and tests).
+        Ref #2965 and #3007.
+        """
+        return os.path.isfile('pybuilddir.txt')
+
     def spec_for_pip(self):
         """
         Ensure stdlib distutils when running under pip.
@@ -135,9 +146,9 @@ def spec_for_setuptools(self):
         a stubbed spec to represent setuptools being present
         without invoking any behavior.
 
-        Workaround for pypa/get-pip#137.
+        Workaround for pypa/get-pip#137. Ref #2993.
         """
-        if not self.is_get_pip():
+        if not self.is_script('get-pip'):
             return
 
         import importlib
@@ -166,14 +177,11 @@ def pip_imported_during_build(cls):
             for frame, line in traceback.walk_stack(None)
         )
 
-    @classmethod
-    def is_get_pip(cls):
-        """
-        Detect if get-pip is being invoked. Ref #2993.
-        """
+    @staticmethod
+    def is_script(name):
         try:
             import __main__
-            return os.path.basename(__main__.__file__) == 'get-pip.py'
+            return os.path.basename(__main__.__file__) == f'{name}.py'
         except AttributeError:
             pass
 

changelog.d/3031.misc.rst

@@ -0,0 +1 @@
+Suppress distutils replacement when building or testing CPython.