Emit a warning when an older version of importlib_metadata is detected to give users better guidance when this condition is present. Ref #3452.bugfix/3452-warn

1 files changed, 27 insertions, 0 deletions

diff --git a/setuptools/_importlib.py b/setuptools/_importlib.py
index 819bf5d3..d1970bdc 100644
--- a/setuptools/_importlib.py
+++ b/setuptools/_importlib.py
@@ -34,11 +34,38 @@ def disable_importlib_metadata_finder(metadata):
         sys.meta_path.remove(item)
 
 
+def check_old_importlib_metadata(metadata):
+    """
+    Warn the user if an old importlib_metadata is present and might
+    cause problems.
+
+    Workaround for #3452. Remove this check after 2022-12-31.
+    """
+    try:
+        version = metadata.version('importlib_metadata')
+        parsed = tuple(map(int, version.split('.')))
+    except Exception:
+        return
+
+    if parsed > (4, 3):
+        return
+
+    msg = (
+        "`importlib_metadata` version is incompatible with the stdlib "
+        "importlib.metadata and may cause problems if plugins import "
+        "importlib_metadata. See pypa/setuptools#3452 for details. "
+        "Consider updating to importlib_metadata 4.3 or later."
+    )
+    import warnings
+    warnings.warn(msg)
+
+
 if sys.version_info < (3, 10):
     from setuptools.extern import importlib_metadata as metadata
     disable_importlib_metadata_finder(metadata)
 else:
     import importlib.metadata as metadata  # noqa: F401
+    check_old_importlib_metadata(metadata)
 
 
 if sys.version_info < (3, 9):