AcoustidPlugin.candidates returns a list of lists

[jayme-github]

I'm not sure if this is the right spot to fix the problem but for me it looks like "def candidates(..)" should always return a list of AlbumInfo objects. As "_album_for_id" (at least in my case) returns a list, AcoustidPlugin.candidates should extend the result instead of appending it (but maybe this needs a more general fix?):

diff --git a/beetsplug/chroma.py b/beetsplug/chroma.py
index 3b2731a..14003d9 100644
--- a/beetsplug/chroma.py
+++ b/beetsplug/chroma.py
@@ -129,7 +129,7 @@ class AcoustidPlugin(plugins.BeetsPlugin):
         for relid in _all_releases(items):
             album = hooks._album_for_id(relid)
             if album:
-                albums.append(album)
+                albums.extend(album)

         log.debug('acoustid album candidates: %i' % len(albums))
         return albums```

[sampsyo]

Ah, thanks for spotting this. There are a few other places where this needs to be addressed also (c.f. ack _album_for_id). This was broken by #291.

I think I'd like to change hooks._album_for_id back to returning a single (MusicBrainz) match. A separate function (maybe the plural form?) will get matches from all sources. This will also avoid confusing situations (as in mbsync and missing) where plugins should not provide matches.

[sampsyo]

Ah, I see that @mrmachine, in ee0c00708b30333e5a5415a8b7f4ab7d0b43dd11, has already addressed many of these cases. Still thinking about adapting the interface, however.

[sampsyo]

Should be all fixed as of 4624f65ce3c77e4ec8472c2878c9eceedb9e348b.