This is an RFC.

• Alternative to / supersedes Refactor SearchContainer filtering operation and fix potential flaws #5154
• Will help address Search container is flawed in multiple ways osu#18003 if merged
• Required for further work on mod select search box game-side

Contents

IHasFilterableChildren is removed; hierarchical lookups now leverage IContainerEnumerable<T>

This is the same as in the original PR. Rather than rely on IHasFilterableChildren to descend down complex hierarchies for filtering purposes, IContainerEnumerable<T>.Children is used, which results in less boilerplate as you don't need to remember to implement it whenever needed.

IConditionalFilterable (?) is introduced

At first I tried to resurrect the aforementioned PR rather than rewrite, but the invalidation issues pointed out therein ended up being caused by a fatal contradiction in its logic that I describe in more detail here. As a result, this PR takes a different, explicit approach of introducing a new IConditionalFilterable interface.

The name is bad, I know (suggestions welcome), but the gist of it is that upon implementing IConditionalFilterable, you get one extra bindable to play with. If the value of said bindable is true, then the item is included in textual search as usual. If it is false, however, it - and its entire subtree - is excluded from further search on the premise that the item does not meet external criteria. In practical terms, you would set it to false when you want to hide some items inside a SearchContainer because they're unavailable due to other settings, which is precisely the use case that needs fixing game-side.

A branch for game-side adjustments for this framework change, that end up fixing ppy/osu#18003, is available for preview at https://github.com/ppy/osu/compare/master...bdach:filtering-framework-change-adjustments?expand=1.

I also recommend examining the commit messages of d0d90e9 and b790cd3.