After some more tries, and giving it some more thought:
I found a release that has a guest performer entered separately as a guest per instrument.
(Ben Cullum performing on two instruments as a guest)
That ends up displaying perfectly with the ‘Standardise performers’ plugin and my script.
But when a performer has one entry with more than one instrument gathered together with ‘guest’ checked, only the first instrument credit will have ‘guest’ prevailed.
The same happens with ‘additional’.
Dann Huff is credited as ‘additional acoustic guitar and electric guitar’ in one combined entry.
With the ‘Standardise performers’ plugin, the ‘additional’ attribute only shows for the first instrument:
additional acoustic guitar: Dann Huff
electric guitar: Dann Huff
So, some observations for now:
There are releases in the MusicBrainz database that have ‘messy’ and/or inconsistent entries for artists being a guest or not.
where Omar Hakim is both a ‘guest’, and a non-guest (regular) performer.
Since the guest attribute relates to a person (while ‘additional’ relates to an instrument/role), it might be good if there was some mechanism on the MB data entry webpage that prevents a performer being entered as being both a guest and a non-guest for a release.
(or at least have it trigger some alert like ‘are you sure?’)
Picard doesn’t seem to do anything ‘wrong’.
It just copies a tag such as: ‘additional acoustic guitar and electric guitar: Dann Huff’ verbatim, so you will not even consider if ‘additional’ relates to only the first instrument, or to both instruments.
The ‘Standardise performers’ plugin will create separate lines for the instrument roles, and will show the checked attributes only for the first instrument.
for the ‘guest’ attribute that is most likely always incorrect. (a person is a guest, or he is not)
so ‘guest’ should be appended to both lines.
for the ‘additional’ attribute it will depend on how an editor has entered it in MusicBrainz’ database:
If a performer played two additional instruments, and the editor entered both instruments under the same performer relationship using the ‘additional’ checkbox, the second instrument will not be labeled as additional using the plugin.
If an editor created two separate entries for these instruments, checking ‘additional’ for both entries, it will end up displaying correct.
If a performer plays an additional instrument besides his main instrument (e.g. the vocalist playing additional percussion), the editor should always be creating two separate entries, and not one for both instruments.
I have no editing experience (yet), so my knowledge and insights are quite limited concerning on that matter, but allow me a suggestion:
Would it be an idea to make a change to the way these attributes are entered in the database?
- The attribute ‘guest’ would be a checkbox next to the performer’s name, and would label all contributions from that performer as being a guest.
- The attribute ‘additional’ would be a checkbox next to each instrument (or role, in case of e.g. ‘recording engineer’).
So you could e.g. leave ‘additional’ unchecked for ‘vocals’, and check it for ‘percussion’, or leave ‘additional’ unchecked for ‘producer’, and check it for ‘recording engineer’.
Does this make sense? And is it feasible?