lastgenre: Album to item genre fallback

In case individual track sources are enabled but no genre could be
fetched from last.fm, fall back to the album's genre (only if that is
not the fallback genre already).

Author: JOJ0

beetsplug/lastgenre/__init__.py

@@ -582,15 +582,25 @@ def lastgenre_func(lib, opts, args):
                         if "track" in self.sources:
                             item_genre, label = self._get_genre(item)
 
-                            if not item_genre:
+                            # Fallback to album genre if required
+                            if (
+                                not item_genre
+                                or item_genre == self.config["fallback"].get()
+                                and album.genre
+                                and album.genre != self.config["fallback"].get()
+                            ):
+                                item_genre = album.genre
+                                label = "inherit from album"
+
+                            if item_genre:
+                                self._apply_item_genre(item, label, item_genre)
+                                if write:
+                                    item.try_write()
+                            else:
                                 self._log.info(
                                     'No genre found for track "{0.title}"',
                                     item,
                                 )
-                            else:
-                                self._apply_item_genre(item, label, item.genre)
-                                if write:
-                                    item.try_write()
 
             else:
                 # Just query single tracks or singletons
@@ -614,6 +624,17 @@ def imported(self, session, task):
             if "track" in self.sources:
                 for item in album.items():
                     item_genre, label = self._get_genre(item)
+
+                    # Fallback to album genre if required
+                    if (
+                        not item_genre
+                        or item_genre == self.config["fallback"].get()
+                        and album.genre
+                        and album.genre != self.config["fallback"].get()
+                    ):
+                        item_genre = album.genre
+                        label = "inherit from album"
+
                     self._apply_item_genre(item, label, item_genre)
 
         else: