Dataviews: Add a way to view and browse subcategories

[jarekmorawski]

Data views like templates can get quite complex. WooCommerce is one of a few plugins that comes with multiple patterns, many of which may be difficult for users to find because they're currently displayed all at once without additional filtering. In this issue, I'm proposing a simple solution for making it possible to have subfolders in data views.

Why
Many admin pages like post categories have subcategories and we need a way to navigate them in the new wp-admin. Additionally, new features like views make it possible for users to build custom areas and we may want to prepare the UX for making it possible to group those by user role, subject, or more.

How

• Folders can have subfolders. Users can navigate between levels similar to menu items in the main navigation.
• Folders with branches use different icons to differentiate them from leaves.
• Each subfolder has an All view that displays all items inside. It's the default view selected when the user enters a subfolder.
• Navigation items in the data views have slightly tweaked metrics to allocate the additional chevron.
• [Nice to have] We display breadcrumbs in the header to make jumping to a specific level easy.

sublayers.mov

[jameskoster]

The breadcrumbs might need more thought in terms of placement, but generally I think this looks like a good starting point.

How would the indentation of the count work when there are no subcategories at all? The 'Template parts' section looks a little unintentional.

[jarekmorawski]

The breadcrumbs might need more thought in terms of placement, but generally I think this looks like a good starting point.

I looked at other placements and styles, but it was either too prominent (when put in a smaller font above the screen title) or too easy to miss (when placed in a bar at the bottom of the screen, like in the editor). Happy to explore this further later on or make it a future improvement (if used here, it'd have to apply to other screens, including nav pages).

How would the indentation of the count work when there are no subcategories at all?

We'd remove the ident, but then the layout would shift between drilldown levels. We'd try moving the counts closer to the item name, like so: