From 670c300625b0dd7ef7a5c62c3ae2106ed5dfbf15 Mon Sep 17 00:00:00 2001
From: Sebastian Mohr <sebastian@mohrenclan.de>
Date: Tue, 14 Oct 2025 17:15:02 +0200
Subject: [PATCH] Fixed issue with legacy plugin copy not copying properties.
 Also added test for it

---
 beets/plugins.py     | 25 +++++++++++++++----------
 docs/changelog.rst   |  2 ++
 test/test_plugins.py | 20 ++++++++++++++++++++
 3 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/beets/plugins.py b/beets/plugins.py
index a8e803efd..9c7a93b7f 100644
--- a/beets/plugins.py
+++ b/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
@@ -192,15 +192,20 @@ class BeetsPlugin(metaclass=abc.ABCMeta):
             stacklevel=3,
         )
 
-        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__)
-            ),
-        ):
-            setattr(cls, name, method)
+        abstracts = MetadataSourcePlugin.__abstractmethods__
+
+        for name, method in inspect.getmembers(MetadataSourcePlugin):
+            # Skip if already defined in the subclass
+            if hasattr(cls, name) or name in abstracts:
+                continue
+
+            # Copy functions, methods, and properties
+            if (
+                inspect.isfunction(method)
+                or inspect.ismethod(method)
+                or isinstance(method, cached_property)
+            ):
+                setattr(cls, name, method)
 
     def __init__(self, name: str | None = None):
         """Perform one-time plugin setup."""
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 6d08d6bdb..88c157ec5 100644
--- a/docs/changelog.rst
+++ b/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:
 
diff --git a/test/test_plugins.py b/test/test_plugins.py
index df338f924..07bbf0966 100644
--- a/test/test_plugins.py
+++ b/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")