Replace condition to patch distutils.dist.log

changelog.d/3709.misc.rst

@@ -0,0 +1,2 @@
+Fix condition to patch ``distutils.dist.log`` to only apply when using
+``distutils`` from the stdlib.

setuptools/logging.py

@@ -1,4 +1,5 @@
 import sys
+import inspect
 import logging
 import distutils.log
 from . import monkey
@@ -22,7 +23,7 @@ def configure():
     handlers = err_handler, out_handler
     logging.basicConfig(
         format="{message}", style='{', handlers=handlers, level=logging.DEBUG)
-    if hasattr(distutils.log, 'Log'):
+    if inspect.ismodule(distutils.dist.log):
         monkey.patch_func(set_threshold, distutils.log, 'set_threshold')
         # For some reason `distutils.log` module is getting cached in `distutils.dist`
         # and then loaded again when patched,

setuptools/tests/test_logging.py

@@ -1,4 +1,6 @@
+import inspect
 import logging
+import os
 
 import pytest
 
@@ -34,3 +36,18 @@ def test_verbosity_level(tmp_path, monkeypatch, flag, expected_level):
     log_level = logger.getEffectiveLevel()
     log_level_name = logging.getLevelName(log_level)
     assert log_level_name == expected_level
+
+
+def test_patching_does_not_cause_problems():
+    # Ensure `dist.log` is only patched if necessary
+
+    import setuptools.logging
+    from distutils import dist
+
+    setuptools.logging.configure()
+
+    if os.getenv("SETUPTOOLS_USE_DISTUTILS", "local").lower() == "local":
+        # Modern logging infra, no problematic patching.
+        assert isinstance(dist.log, logging.Logger)
+    else:
+        assert inspect.ismodule(dist.log)