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FeatureSet cleanup: simplify over-complex type-system remnants in compatibility_hints.py #659

@tobixen

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@tobixen

⚠️ This comment is AI-generated (Claude Sonnet 4.6 via Claude Code) on behalf of tobixen

The FeatureSet class in caldav/compatibility_hints.py was written with a more ambitious vision than what ended up being needed. A review of all its methods found several items that can be simplified or removed. Details are documented in docs/design/TODO_COMPATIBILITY_HINTS.md.

Summary of findings

1. Dead/buggy bool branch in _convert_node
The else branch for non-server-feature types has inverted logic (not node.get('enable') returns True when enable=False) and is unreachable in practice — no caller uses is_supported(bool) on client-feature or server-peculiarity features. Should be replaced with an AssertionError to surface accidental misuse.

2. Possibly redundant _derive_from_subfeatures call in is_supported
For features with no dots, the method is called twice in the same lookup path (once in the loop body, once in the post-loop block). Needs careful review to confirm if one call is truly redundant.

3. _old_flags migration (ongoing)
Already marked ## TODO: remove this when it can be removed. ~12 server config dicts still carry old_flags lists. Each needs to be translated into new-style dotted features, then the shim code can be deleted.

4. feature_tree / _dots_to_tree can be simplified
Builds and caches a full nested-dict tree only to answer one-level subfeature lookups in find_feature. Can be replaced with a one-liner list comprehension, eliminating both methods.

5. _collapse_key carries vestigial enable/observed fields
These slots exist for the complex type vision but collapse is only ever called on server-feature nodes. Simplify to just return feature_dict.get('support').

6. copyFeatureSet should be renamed copy_feature_set
Inconsistent camelCase already noted with a TODO comment. No external callers; safe rename.

Suggested order

  • Items 3 and 6 are independent and safe to do first.
  • Items 1, 2, 4, 5 are interrelated around the type-system simplification and are best tackled together.

⚠️ This comment is AI-generated (Claude Sonnet 4.6 via Claude Code) on behalf of tobixen

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