lastgenre: Refactor _get_genre

[JOJ0]

Description

The monolithic _get_genre method was broken down into several private instance methods and refactored for readability. The contract is kept and is already well tested (test_get_genre)

• Core Helpers - were moved from within _get_genre to a reusable instance method and a cached_property:

  • _try_resolve_stage: Handles the canonicalization and logging of genres for a specific stage.
  • fallback: Provides the configured fallback genre. Is used as a last resort in _try_resolve_existing_genres and when _get_genre couldn't find any genre in any stage at all.

• Lookup Stages - some were complex enough to deserve their own instance method for readability, some stay inline in _get_genre:

  • _try_resolve_existing_genres: Manages the initial check for pre-existing genres and the cleanup_existing logic when force is disabled.
  • track stage: stays inline
  • album stage: indentical to track stage, but not worth moving / deduplication doesn't buy much (see subsequent PR though)
  • _fetch_artist_stage: Fetches and resolves artist-level genres, including multi-valued album artists and "Various Artists" logic.
  • _fetch_va_genres: specifically handles the plurality logic for "Various Artists" albums.

• Fallbacks:

  • _try_resolve_original_fallback: Handles the "keep_existing" logic that attempts to use/canonicalize originally present genres if no new ones are found.

Make sure to also look at subsequent PR's:

• lastgenre: Improve original fallback (better use of aliases and count) #6890
• lastgenre: Album stage fall back to multi-valued albumartists #6893

To Do

• Documentation
• Changelog. (Not required, refactor only)
• Tests (_get_genre was already well covered and the signature of the method was kept)

[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

❌ Patch coverage is 74.35897% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.11%. Comparing base (5406ed7) to head (87633a8).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beetsplug/lastgenre/__init__.py	74.35%	11 Missing and 9 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6474      +/-   ##
==========================================
+ Coverage   76.06%   76.11%   +0.04%     
==========================================
  Files         163      163              
  Lines       21146    21151       +5     
  Branches     3334     3334              
==========================================
+ Hits        16085    16099      +14     
+ Misses       4273     4264       -9     
  Partials      788      788              

Files with missing lines	Coverage Δ
beetsplug/lastgenre/__init__.py	86.06% <74.35%> (+3.43%)	⬆️

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[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[JOJ0]

@semohr @snejus @henry-oberholtzer @Serene-Arc anyone care to review a no-op refactor-only PR? :-) Thanks :-)

[JOJ0]

Thanks @snejus that was great feedback! 👍 I think I addressed all of it.

[JOJ0]

Hi @snejus, thanks for the approval. Did two more tiny things: Fixed mypy errors, accidentally applied GenresWithLable alias to _fetch_artist_stage which is slightly different. Fixed another 2-line docstring/comment (below type alias CanonTree).