confit: Improve deprecation warning

Show the actual origin of the import statement, cf. #4024

beets/util/confit.py

@@ -16,7 +16,13 @@
 import confuse
 
 import warnings
-warnings.warn("beets.util.confit is deprecated; use confuse instead")
+warnings.warn(
+    "beets.util.confit is deprecated; use confuse instead",
+    # Show the location of the `import confit` statement as the warning's
+    # source, rather than this file, such that the offending module can be
+    # identified easily.
+    stacklevel=2,
+)
 
 # Import everything from the confuse module into this module.
 for key, value in confuse.__dict__.items():

test/test_util.py

@@ -182,6 +182,21 @@ class PathTruncationTest(_common.TestCase):
         self.assertEqual(p, 'abcde/f.ext')
 
 
+class ConfitDeprecationTest(_common.TestCase):
+    def test_confit_deprecattion_warning_origin(self):
+        """Test that importing `confit` raises a warning.
+
+        In addition, ensure that the warning originates from the actual
+        import statement, not the `confit` module.
+        """
+        # See https://github.com/beetbox/beets/discussions/4024
+        with self.assertWarns(UserWarning) as w:
+            import beets.util.confit  # noqa: F401
+
+        self.assertIn(__file__, w.filename)
+        self.assertNotIn("confit.py", w.filename)
+
+
 def suite():
     return unittest.TestLoader().loadTestsFromName(__name__)