Hierarchy navigation sidebar performance

[strogonoff]

The hierarchy sidebar (the topmost button on bottom left, after JS loads) is sluggish.

Not only it is slow when you use it, but you will find that hiding it (just by clicking the button again) or switching to another sidebar (e.g., search) will make browsing experience outside of the sidebar much faster, too.

The hierarchy sidebar uses Adobe Spectrum’s tree view component, which as they say themselves is currently in alpha/beta version and under active development. This may have to do with it being not optimized, unlike the rest of the library.

There are two options:

• Dig into Spectrum’s tree component and understand why it is slow; fix it in a fork and use the fork until it’s fixed upstream (maybe even contribute a PR to them? but note that Adobe requires signing a contributor agreement for that).
• Make a custom tree view component based on Spectrum/Aria primitives. It probably won’t have the full-blown accessibility support that Spectrum boasts for its components, but it could work in meantime. It’s not that difficult, we just need to manage offsets according to hierarchy levels, and collapsed/expanded states. Ideally, our custom component should stick to the same API as Spectrum’s tree component, so that we can swap them out.