lastgenre: Improve original fallback (better use of aliases and count)

[JOJ0]

Description

When _get_genre runs with force, whitelist and canonicalization enabled, as a last resort it tries to fall back to the original genres. Of course this stage normalizes, canonicalizes, does all the stuff it's supposed to when resolving the stage. That also includes reducing genres to the configured count. Now in that case that could reduce the list of genres and is not exactly what a fall back to what we had before should look like.

This PR changes the stage as follows:

We don't run through _try_resolve_stage instantly because we want to make sure the count setting doesn't kick out anything prematurely! We then apply whitelist checks and return if something valid is found.

The very last resort action is kept as we had it already: Use keep_genres (the lowercased originals) to canonicalize and hope that now we find a whitelisted parent genre.

Note: Requires #6474

To Do

• Documentation. (Not required IMO)
• Changelog.
• Tests. (We might want to add some, need to check)

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.67%. Comparing base (e2f60a5) to head (389148e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@                       Coverage Diff                        @@
##           lastgenre_refactor_get_genre    #6890      +/-   ##
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- Coverage                         75.67%   75.67%   -0.01%     
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  Files                               163      163              
  Lines                             21418    21418              
  Branches                           3385     3384       -1     
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- Hits                              16209    16208       -1     
- Misses                             4410     4411       +1     
  Partials                            799      799              

Files with missing lines	Coverage Δ
beetsplug/lastgenre/__init__.py	81.59% <100.00%> (+0.34%)	⬆️

... and 1 file with indirect coverage changes

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[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[Copilot]

Pull request overview

PR make lastgenre original-genre fallback better when force + keep_existing + whitelist (+ canonical) is on. Goal is: do alias normalize + whitelist check without _resolve_genres path that can apply count too early, then only do canonical-parent fallback as last resort.

Changes:

• Change “original fallback” stage to alias-normalize originals, then run whitelist/ignore filtering directly (no _try_resolve_stage yet).
• Keep existing canonicalized-parent fallback via _try_resolve_stage(...) when nothing survives whitelist after aliasing.
• Update docstring to describe new fallback order.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (1)

beetsplug/lastgenre/init.py:517

• grug see new logic to avoid count dropping good original genres before whitelist. grug want regression test so this not break later. add pytest case where force+keep_existing+whitelist+canonical and count=1, existing genres has non-whitelisted first then whitelisted later, and expect "original fallback" returns whitelisted one (not lost to early count).

        # We do not run through try_resolve_stage yet because count could drop
        # existing genres, but we still apply aliases before whitelist
        # filtering.
        normalized = [
            norm if norm != g.lower() else g
            for g in genres
            if (norm := normalize_genre(self._log, self.alias_patterns, g))
        ]