Do not force load musicbrainz, add a test to show the behaviour

beets/config_default.yaml

@@ -6,8 +6,7 @@ statefile: state.pickle
 
 # --------------- Plugins ---------------
 
-plugins: []
+plugins: [musicbrainz]
-disabled_plugins: []
 
 pluginpath: []
 

beets/plugins.py

@@ -417,20 +417,18 @@ def get_plugin_names() -> list[str]:
     beets.config.add({"disabled_plugins": []})
     disabled_plugins = set(beets.config["disabled_plugins"].as_str_seq())
     # TODO: Remove in v3.0.0
-    if "musicbrainz" not in plugins and "musicbrainz" not in disabled_plugins:
+    mb_enabled = beets.config["musicbrainz"].flatten().get("enabled")
+    if mb_enabled:
         deprecate_for_user(
             log,
-            "Automatic loading of 'musicbrainz' plugin",
+            "'musicbrainz.enabled' configuration option",
             "'plugins' configuration to explicitly add 'musicbrainz'",
         )
-
+        if "musicbrainz" not in plugins:
-    enabled = beets.config["musicbrainz"].flatten().get("enabled")
+            plugins.append("musicbrainz")
-    if enabled is not None:
+    elif mb_enabled is False:
         deprecate_for_user(log, "'musicbrainz.enabled' configuration option")
-    if enabled is False:
         disabled_plugins.add("musicbrainz")
-    else:
-        plugins.append("musicbrainz")
 
     return [p for p in plugins if p not in disabled_plugins]
 

test/test_plugins.py

@@ -543,3 +543,39 @@ class TestDeprecationCopy:
         assert hasattr(LegacyMetadataPlugin, "data_source_mismatch_penalty")
         assert hasattr(LegacyMetadataPlugin, "_extract_id")
         assert hasattr(LegacyMetadataPlugin, "get_artist")
+
+
+class TestMusicBrainzPluginLoading:
+    @pytest.fixture(autouse=True)
+    def config(self):
+        _config = config
+        _config.sources = []
+        _config.read(user=False, defaults=True)
+        return _config
+
+    def test_default(self):
+        assert "musicbrainz" in plugins.get_plugin_names()
+
+    def test_other_plugin_enabled(self, config):
+        config["plugins"] = ["anything"]
+
+        assert "musicbrainz" not in plugins.get_plugin_names()
+
+    def test_deprecated_enabled(self, config, caplog):
+        config["plugins"] = ["anything"]
+        config["musicbrainz"]["enabled"] = True
+
+        assert "musicbrainz" in plugins.get_plugin_names()
+        assert (
+            "musicbrainz.enabled' configuration option is deprecated"
+            in caplog.text
+        )
+
+    def test_deprecated_disabled(self, config, caplog):
+        config["musicbrainz"]["enabled"] = False
+
+        assert "musicbrainz" not in plugins.get_plugin_names()
+        assert (
+            "musicbrainz.enabled' configuration option is deprecated"
+            in caplog.text
+        )