feat(lastgenre): canonicalize_existing

Introduce a new lastgenre `canonicalize_existing` flag.

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

Author: Nukesor

beetsplug/lastgenre/__init__.py

@@ -106,6 +106,7 @@ def __init__(self) -> None:
                 "count": 1,
                 "fallback": None,
                 "canonical": False,
+                "canonicalize_existing": False,
                 "source": "album",
                 "force": False,
                 "keep_existing": False,
@@ -399,6 +400,24 @@ def _try_resolve_stage(
         genres = self._get_existing_genres(obj)
 
         if genres and not self.config["force"]:
+            # Without force and whitelisting + canonicalize_existing, we attempt
+            # to canonicalize pre-populated tags before returning them.
+            # If none are found, we use the fallback.
+            if (
+                self.config["whitelist"]
+                and self.config["canonical"]
+                and self.config["canonicalize_existing"]
+            ):
+                keep_genres = [g.lower() for g in genres]
+                if result := _try_resolve_stage("original", keep_genres, []):
+                    return result
+                elif fallback := self.config["fallback"].get():
+                    # Return fallback string.
+                    return fallback, "fallback"
+                else:
+                    # No fallback configured.
+                    return None, "fallback unconfigured"
+
             # Without force pre-populated tags are returned as-is.
             label = "keep any, no-force"
             if isinstance(obj, library.Item):

docs/changelog.rst

@@ -12,6 +12,8 @@ been dropped.
 
 New features:
 
+- :doc:`plugins/lastgenre`: Added ``canonicalize_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

@@ -171,6 +171,11 @@ 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).
+- **canonicalize_existing**: This option only takes effect with ``force: no``,
+  ``canonical: yes`` and ``whitelist: yes``.
+  Setting this to ``yes`` will result in attempted canonicalization of existing
+  genres. If this fails, the ``fallback`` is used isntead.
+  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

@@ -302,6 +302,29 @@ def test_sort_by_depth(self):
             },
             ("Jazzin", "album, any"),
         ),
+        # 5.1 - Canonicalize original genre when force is **off** and
+        # whitelist, canonical and canonicalize_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,
+                "canonicalize_existing": True,
+                "prefer_specific": False,
+            },
+            "Cosmic Disco",
+            {
+                "artist": [],
+            },
+            (
+                "Disco, Electronic",
+                "keep + original, whitelist",
+            ),
+        ),
         # 6 - fallback to next stages until found
         (
             {