Functional changes for display_artist on 3NF schema

[Rouzax]

Summary

Ports the functional display_artist changes onto your 3NF contributor_display schema, as discussed in PR #20.

• Replace tag swap with capture-before-defer: extracts display strings from ALBUMARTIST/ARTIST without mutating tag values. Fixes scenario 3 data loss.
• Rescan path: updateOrCreateBase and _postCheckAttributes now populate display_contributor on track update, not just fresh scan.
• Track-level display: populates tracks.display_contributor and contributor_track_display junction table for ARTIST/TRACKARTIST roles. Queries return track-level display_artist via aliased JOINs.
• Preference gate: usePluralArtistTags (default OFF). When ON, ALBUMARTISTS/ARTISTS entries replace singular tags for contributor creation.
• FTS indexing: display names indexed in fulltext search via contributor_display JOINs.
• Helper extraction: _getOrCreateDisplayContributor reuses the lookup/insert pattern across _newTrack, _postCheckAttributes, and both album/track paths.

Schema is untouched. All changes work with your contributor_display table, integer FK columns, and junction tables as-is.

Supersedes #20 (flat-column approach).

Test plan

• Fresh scan with pref OFF: contributor_display populated, albums.display_contributor set, API returns display_artist
• Fresh scan with pref ON: individual contributors created from plural tags, no joined-string contributor rows
• Rescan after retag: display_contributor updates on existing tracks
• FTS search for display string (e.g. "Chick Corea & Gary Burton") finds album
• Smoketest and verifyStrings pass

[darrell-k]

The new setting is not sticking when I try to change it to enabled. Probably needs adding to the list of prefs in Slim/Web/Settings/Server/Behavior.pm

You should also add a $prefs->setchange rule to trigger the rescan.

[darrell-k]

I forgot to push schema_clear.sql to the branch. Done now.

[darrell-k]

This is not working. example tags:

ALBUMARTIST: Bill Evans Trio with Scott LaFaro & Paul Motian
ALBUMARTISTS: Bill Evans; Bill Evans Trio; Scott LaFaro; Paul Motian

Results in only a single contributor being created "Bill Evans Trio with Scott LaFaro & Paul Motian" (I forced the new pref to "1").

[darrell-k]

Probably because $attributes->{ALBUMARTISTS} is not an array?

[Rouzax]

Good catch. The code assumed an arrayref but ALBUMARTISTS arrives as a scalar when written as a single semicolon-joined field (e.g. "Bill Evans; Scott LaFaro"). Fixed by routing through splitTag which handles both arrayrefs (pass-through) and scalars (splits on the configured splitList separator). Added a test fixture (fixture 23) that writes scalar plural tags to catch this going forward.

[Rouzax]

Fixed in the latest push (00cc68c -> 81b63ba):

1. Pref not sticking: added usePluralArtistTags to the prefs list in Slim/Web/Settings/Server/Behavior.pm.
2. Rescan trigger: added to the setChange wipecache list in Slim/Utils/Prefs.pm so toggling the pref triggers a rescan.
3. Scalar plural tags: the code assumed ALBUMARTISTS/ARTISTS would always be an arrayref (true for Vorbis multi-value, but not for a single field with semicolons). Now routes through splitTag which handles both arrayrefs and scalar strings. Also improved the description text to be clearer for non-technical users.

Rebased onto your schema_clear.sql commit as well.

[darrell-k]

@Rouzax Thanks, I'm going to merge this, and the Material Skin PR and offer it to the forum for further testing.