Allow selecting either tags or genres in the includes, defaulting to genres

Genres is a filtered list based on what musicbrainz considers a genre,
tags are all the user-submitted tags. [1]

1. https://musicbrainz.org/doc/MusicBrainz_API#:~:text=Since%20genres%20are,!).

Also apply suggestions from code review

Co-authored-by: Šarūnas Nejus <snejus@protonmail.com>

beetsplug/musicbrainz.py

@@ -90,6 +90,7 @@ RELEASE_INCLUDES = list(
         "isrcs",
         "url-rels",
         "release-rels",
+        "genres",
         "tags",
     }
     & set(musicbrainzngs.VALID_INCLUDES["release"])
@@ -370,6 +371,10 @@ def _merge_pseudo_and_actual_album(
 
 
 class MusicBrainzPlugin(MetadataSourcePlugin):
+    @cached_property
+    def genres_field(self) -> str:
+        return f"{config['musicbrainz']['genres_tag'].get()}-list"
+
     def __init__(self):
         """Set up the python-musicbrainz-ngs module according to settings
         from the beets configuration. This should be called at startup.
@@ -382,6 +387,7 @@ class MusicBrainzPlugin(MetadataSourcePlugin):
                 "ratelimit": 1,
                 "ratelimit_interval": 1,
                 "genres": False,
+                "genres_tag": "genre",
                 "external_ids": {
                     "discogs": False,
                     "bandcamp": False,
@@ -723,8 +729,8 @@ class MusicBrainzPlugin(MetadataSourcePlugin):
 
         if self.config["genres"]:
             sources = [
-                release["release-group"].get("tag-list", []),
-                release.get("tag-list", []),
+                release["release-group"].get(self.genres_field, []),
+                release.get(self.genres_field, []),
             ]
             genres: Counter[str] = Counter()
             for source in sources:

docs/changelog.rst

@@ -13,6 +13,8 @@ been dropped.
 New features:
 
 - :doc:`plugins/ftintitle`: Added argument for custom feat. words in ftintitle.
+- :doc:`plugins/musicbrainz`: Allow selecting tags or genres to populate the
+  genres tag.
 - :doc:`plugins/ftintitle`: Added argument to skip the processing of artist and
   album artist are the same in ftintitle.
 - :doc:`plugins/play`: Added `$playlist` marker to precisely edit the playlist

docs/plugins/musicbrainz.rst

@@ -32,6 +32,7 @@ Default
         ratelimit_interval: 1.0
         extra_tags: []
         genres: no
+        genres_tag: genre
         external_ids:
             discogs: no
             bandcamp: no
@@ -136,6 +137,12 @@ Default
     ``beatport_album_id``, ``deezer_album_id``, ``tidal_album_id``). On re-imports
     existing data will be overwritten.
 
+.. conf:: _genres_tag
+    :default: genres
+
+    Either ``genres`` or ``tags``. Specify ``genres`` to use just musicbrainz genres and
+    ``tags`` to use all user-supplied musicbrainz tags.
+
 .. include:: ./shared_metadata_source_config.rst
 
 .. _building search indexes: https://musicbrainz.org/doc/Development/Search_server_setup