Persistent List View: Improve interplay with the other left-side sidebars

[Copons]

This issue is about the Persistent List View experiment (#28637), currently only available in the Site Editor.

Currently, Navigation, Inserter, and List View sidebars are alternative between each others: opening one will close the other.

Given the Persistent List View is supposed to be persistent, we might want to find a better interaction between the three sidebars.

Possible solutions:

1. Remember if the List View was open when opening another sidebar, so that closing that will automatically reopen the List View.
2. Keep the List View open besides one of the other sidebars (Inserter and Navigation will remain alternative between each other).
3. Split horizontally the secondary sidebar, so that Inserter and List View can be open at the same time, occupying half (or a resizeable portion) of the sidebar slot.

[mtias]

It's persistent while it's opened, but opening another left sidebar (like the inserter) should close it. I don't think it needs to be remembered and opened again. Once it's closed (either by closing directly or opening another) it's closed for good. The other parallel is the block inspector and the global styles sidebar on the right.

[jameskoster]

Agreed for now.

In the future it might be fun to explore the split sidebar idea though:

I'm curious about the idea of being able to drag blocks from the Inserter directly in to List View.

[shaunandrews]

It's persistent while it's opened, but opening another left sidebar (like the inserter) should close it.

I can understand this logic at certain viewports, but if I have a sufficiently wide viewport this is just restrictive for no reason.

I've been trying to build a theme with the site editor, and I often jump between templates as I'm going; With this decision, its incredibly frustrating that I can't have both my list of templates and the list of blocks on the current template open at the same time.

[yscik]

What do you think about making this sidebar available for plugins too? We have a few use cases where it would make sense to have some controls be more prominent & easier to discover than what a sidebar shared with block settings allows.

It would be great to have an API exposed to query what's open, or even a <PluginSidebar> prop to register stuff to the secondary sidebar slot.

[mtias]

Plugins can already use PluginSidebar as a slot.

With this decision, its incredibly frustrating that I can't have both my list of templates and the list of blocks on the current template open at the same time.

@shaunandrews I think this is different. The W sidebar is the main core navigation, and should not interact with inner sidebars on the editor. The ones I mean should not stack are the block inserter and the list view as they occupy the same plane.

[annezazu]

In watching a video of a person using the Site Editor, it's mentioned a desire to have both list view and the inserter open at the same time. For larger screen sizes, this is worth considering, perhaps in the same way we're looking at the future of the Site Editor with a more layered approach like this:

We could reuse a similar design approach to have both open at once.