Fixes a bug where existing tags were set to None, if they weren't whitelisted, but an whitelisted canonicalized parent existed up the tree.
In all other cases, the original genres are canonicalized and considered for the final genre, except in the keep_existing logic branch.
This PR fixes the issue and results in the expected behavior for this combination of options.
For the bug to trigger several conditions had to be met:
- Canonicalization is enabled and a whitelist is specified.
- `force` and `keep_existing` are set. Meaning, that Lastfm is queried for a genre, but the existing genres are still left around when none are found online.
- A release with a non-whitelisted genre exists, but that genre has a whitelisted genre parent up the tree.
- That very release has no genre on lastfm.
This is rather convoluted, but stay with me :D
What would happen is the following:
- `keep_genres` is set to the existing genres, as `force` and `keep_existing` is set.
- Genres for `track`/`album`/`artist` aren't found for this release, as they don't exist in lastfm.
- Then the `keep_existing` logic is entered.
- The old logic only checks if the existing genres have an **exact** match for the whitelist. In contrast to all other code branches, we don't do the `_try_resolve_stage` in case there's no direct match, resulting in no match.
- We continue to the fallback logic, which returns the fallback (`None` in my case)
This patch results in one last try to resolve the existing genres when `keep_existing` is set, which includes canonicalization (if enabled).
- Handle list-valued fields when grouping for --field/--equal-chance to avoid
"TypeError: unhashable type: 'list'" (e.g., artists).
- Sort items by the grouping key before building groups so equal-chance
permutation preserves the same item set as `beet list`, only randomized.
- Add Tool type alias and SUPPORTED_FORMATS_BY_TOOL class variable
- Refactor __init__ to use shutil.which() and set cmd_name early
- Simplify format_supported() to use dictionary lookup
