Legacy plugin copy not copying properties. (#6101)

The recently introduces `data_source_mismatch_penalty` property in the MetadataPlugin
class was not copied in the backwards compatibility layer. This PR
introduces a fixes this such that `cached_properties` are copied to
legacy metadata plugins.

This also includes a test for the expected behavior.

See also [beetcamp
issue](https://github.com/snejus/beetcamp/issues/85#issuecomment-3399273892).

beets/plugins.py

@@ -22,7 +22,7 @@ import re
 import sys
 import warnings
 from collections import defaultdict
-from functools import wraps
+from functools import cached_property, wraps
 from importlib import import_module
 from pathlib import Path
 from types import GenericAlias
@@ -192,12 +192,23 @@ class BeetsPlugin(metaclass=abc.ABCMeta):
             stacklevel=3,
         )
 
+        method: property | cached_property[Any] | Callable[..., Any]
         for name, method in inspect.getmembers(
             MetadataSourcePlugin,
-            predicate=lambda f: (
-                inspect.isfunction(f)
-                and f.__name__ not in MetadataSourcePlugin.__abstractmethods__
-                and not hasattr(cls, f.__name__)
+            predicate=lambda f: (  # type: ignore[arg-type]
+                (
+                    isinstance(f, (property, cached_property))
+                    and not hasattr(
+                        BeetsPlugin,
+                        getattr(f, "attrname", None) or f.fget.__name__,  # type: ignore[union-attr]
+                    )
+                )
+                or (
+                    inspect.isfunction(f)
+                    and f.__name__
+                    and not getattr(f, "__isabstractmethod__", False)
+                    and not hasattr(BeetsPlugin, f.__name__)
+                )
             ),
         ):
             setattr(cls, name, method)

docs/changelog.rst

@@ -22,6 +22,8 @@ For packagers:
 
 - Fixed dynamic versioning install not disabled for source distribution builds.
   :bug:`6089`
+- Fixed issue with legacy metadata plugins not copying properties from the base
+  class.
 
 Other changes:
 

test/autotag/test_distance.py

@@ -11,6 +11,7 @@ from beets.autotag.distance import (
 )
 from beets.library import Item
 from beets.metadata_plugins import MetadataSourcePlugin, get_penalty
+from beets.plugins import BeetsPlugin
 from beets.test.helper import ConfigMixin
 
 _p = pytest.param
@@ -310,8 +311,13 @@ class TestDataSourceDistance:
             def candidates(self, *args, **kwargs): ...
             def item_candidates(self, *args, **kwargs): ...
 
-        class OriginalPlugin(TestMetadataSourcePlugin):
-            pass
+        # We use BeetsPlugin here to check if our compatibility layer
+        # for pre 2.4.0 MetadataPlugins is working as expected
+        # TODO: Replace BeetsPlugin with TestMetadataSourcePlugin in v3.0.0
+        with pytest.deprecated_call():
+
+            class OriginalPlugin(BeetsPlugin):
+                data_source = "Original"
 
         class OtherPlugin(TestMetadataSourcePlugin):
             @property
@@ -332,6 +338,7 @@ class TestDataSourceDistance:
         [
             _p("Original", "Original", 0.5, 1.0, True, MATCH, id="match"),
             _p("Original", "Other", 0.5, 1.0, True, MISMATCH, id="mismatch"),
+            _p("Other", "Original", 0.5, 1.0, True, MISMATCH, id="mismatch"),
             _p("Original", "unknown", 0.5, 1.0, True, MISMATCH, id="mismatch-unknown"),  # noqa: E501
             _p("Original", None, 0.5, 1.0, True, MISMATCH, id="mismatch-no-info"),  # noqa: E501
             _p(None, "Other", 0.5, 1.0, True, MISMATCH, id="mismatch-no-original-multiple-sources"),  # noqa: E501

test/test_plugins.py

@@ -523,3 +523,23 @@ class TestImportPlugin(PluginMixin):
         assert "PluginImportError" not in caplog.text, (
             f"Plugin '{plugin_name}' has issues during import."
         )
+
+
+class TestDeprecationCopy:
+    # TODO: remove this test in Beets 3.0.0
+    def test_legacy_metadata_plugin_deprecation(self):
+        """Test that a MetadataSourcePlugin with 'legacy' data_source
+        raises a deprecation warning and all function and properties are
+        copied from the base class.
+        """
+        with pytest.warns(DeprecationWarning, match="LegacyMetadataPlugin"):
+
+            class LegacyMetadataPlugin(plugins.BeetsPlugin):
+                data_source = "legacy"
+
+        # Assert all methods are present
+        assert hasattr(LegacyMetadataPlugin, "albums_for_ids")
+        assert hasattr(LegacyMetadataPlugin, "tracks_for_ids")
+        assert hasattr(LegacyMetadataPlugin, "data_source_mismatch_penalty")
+        assert hasattr(LegacyMetadataPlugin, "_extract_id")
+        assert hasattr(LegacyMetadataPlugin, "get_artist")