feat(lastgenre): cleanup_existing

Introduce a new lastgenre `cleanup_existing` flag.

It handles the case where canonicalization is desired on existing tags.
The new logic triggers if:
- `force`: False
- `cleanup_existing: True

Depending on whether `whitelist: True` or `canonical: True`, the genres
are then canonicalized and/or whitelisting is applied

Author: Nukesor

beetsplug/lastgenre/__init__.py

@@ -111,6 +111,7 @@ def default_configuration() -> dict[str, Any]:
             "count": 1,
             "fallback": None,
             "canonical": False,
+            "cleanup_existing": False,
             "source": "album",
             "force": False,
             "keep_existing": False,
@@ -397,7 +398,19 @@ def _try_resolve_stage(
         genres = self._get_existing_genres(obj)
 
         if genres and not self.config["force"]:
-            # Without force pre-populated tags are returned as-is.
+            # Without force, but cleanup_existing enabled, we attempt
+            # to canonicalize pre-populated tags before returning them.
+            # If none are found, we use the fallback (if set).
+            if self.config["cleanup_existing"]:
+                keep_genres = [g.lower() for g in genres]
+                if result := _try_resolve_stage("original", keep_genres, []):
+                    return result
+
+                # Return fallback string (None if not set).
+                return self.config["fallback"].get(), "fallback"
+
+            # If cleanup_existing is not set, the pre-populated tags are
+            # returned as-is.
             return genres, "keep any, no-force"
 
         if self.config["force"]:

docs/changelog.rst

@@ -114,6 +114,8 @@ been dropped.
 New features
 ~~~~~~~~~~~~
 
+- :doc:`plugins/lastgenre`: Added ``cleanup_existing`` configuration flag to
+  allow whitelist canonicalization of existing genres.
 - :doc:`plugins/fetchart`: Added config setting for a fallback cover art image.
 - :doc:`plugins/ftintitle`: Added argument for custom feat. words in ftintitle.
 - :doc:`plugins/ftintitle`: Added album template value ``album_artist_no_feat``.

docs/plugins/lastgenre.rst

@@ -170,6 +170,11 @@ file. The available options are:
 - **canonical**: Use a canonicalization tree. Setting this to ``yes`` will use a
   built-in tree. You can also set it to a path, like the ``whitelist`` config
   value, to use your own tree. Default: ``no`` (disabled).
+- **cleanup_existing**: This option only takes effect with ``force: no``,
+  Setting this to ``yes`` will result in cleanup of existing genres. That
+  includes canonicalization and whitelisting, if enabled. If no matching genre
+  can be determined, the ``fallback`` is used instead. Default: ``no``
+  (disabled).
 - **count**: Number of genres to fetch. Default: 1
 - **fallback**: A string to use as a fallback genre when no genre is found
   ``or`` the original genre is not desired to be kept (``keep_existing: no``).

test/plugins/test_lastgenre.py

@@ -306,6 +306,30 @@ def test_sort_by_depth(self):
             },
             (["Jazzin"], "album, any"),
         ),
+        # Canonicalize original genre when force is **off** and
+        # whitelist, canonical and cleanup_existing are on.
+        # "Cosmic Disco" is not in the default whitelist, thus gets resolved "up" in the
+        # tree to "Disco" and "Electronic".
+        (
+            {
+                "force": False,
+                "keep_existing": False,
+                "source": "artist",
+                "whitelist": True,
+                "canonical": True,
+                "cleanup_existing": True,
+                "prefer_specific": False,
+                "count": 10,
+            },
+            ["Cosmic Disco"],
+            {
+                "artist": [],
+            },
+            (
+                ["Disco", "Electronic"],
+                "keep + original, whitelist",
+            ),
+        ),
         # fallback to next stages until found
         (
             {