When pip is imported as part of a build, leave distutils patched.

_distutils_hack/__init__.py

@@ -92,9 +92,22 @@ def spec_for_pip(self):
         Ensure stdlib distutils when running under pip.
         See pypa/pip#8761 for rationale.
         """
+        if self.pip_imported_during_build():
+            return
         clear_distutils()
         self.spec_for_distutils = lambda: None
 
+    @staticmethod
+    def pip_imported_during_build():
+        """
+        Detect if pip is being imported in a build script. Ref #2355.
+        """
+        import traceback
+        return any(
+            frame.f_globals['__file__'].endswith('setup.py')
+            for frame, line in traceback.walk_stack(None)
+        )
+
 
 DISTUTILS_FINDER = DistutilsMetaFinder()
 

changelog.d/2355.change.rst

@@ -0,0 +1 @@
+When pip is imported as part of a build, leave distutils patched.