Tab Bar Navigation preview

[boscojwho]

Tab Bar Navigation Preview

TL;DR: Try and see if any bug(s) make it totally unusable...plez 🥹

Feature
Users can use the tab bar to navigate back, scroll to top, and show the sidebar.

Discussion
The implementation allows for two types of tab bar navigation actions:

• System dismiss action (i.e. "go back" when used on a NavigationStack).
• Auxiliary action, which is loosely defined as any other action that does not involve the system dismiss action.
  ~ Examples include "scroll to top", "focus of search bar", etc. Technically, we could even make it scroll up to each parent comment in ExpandedPost (not that that makes sense =P).
  ~ This auxiliary action is implemented as a () -> Bool closure where you can define multiple "auxiliary sub-actions" by returning true. The tab bar navigator will continue to call into this closure until it returns false.

Implementation Notes
Initially, this feature was implemented by programmatically manipulating a tab's corresponding navigation path.

Unfortunately, this approach is problematic because the navigation path is immediately updated at the beginning of the "go back" animation. While that animation is in-flight, users can initiate further calls that trigger programmatic navigation path manipulation. When that happens, the navigation stack/path data state and UI state become de-synced, and results in some unexpected behaviour when attempting to further manipulate that navigation path.

This revised implementation uses the environment's dismiss action to trigger go back navigation, which means the we let the system deal with coordinating between data state and UI state on a navigation path/stack.

However, this approach has the downside of requiring us to access the DismissAction on each top-level view that can be presented on a navigation stack. is a wrapper around the older, deprecated PresentationMode

Additional Notes
This revision also handles the following use cases:

• Tab bar navigation still works if user peeks at previous view using drag gesture, then cancels that action.
• Rapidly tapping on tab to trigger tab bar navigation.

Customization
Currently, there is no option to customize this behaviour. It could make sense to offer one or more of the following options:

1. Use system behaviour (i.e. always pop to root, then scroll to top).
2. Go back per page until root page, then scroll to top (then focus on search bar, if API available), and finally pop to sidebar (and scroll to top in sidebar).
3. Same as 3, but scroll to top on every page.
4. Turn off entirely.

Todo

• Check for iOS 17 regressions
• Add ability to focus on search bar (only available on iOS 17)
• Review sidebar behaviour on iPad.
• Clean up API for enabling tab bar navigation (Ideally one-liners, to make it easy to switch to programmatic navigation path manipulation if/when Apple improves that API for our use case.)
• Documentation

Known Issues

• Haptic feedback may trigger even if action is ignored because animation is in-flight, causing confusion for users.
• Haptic feedback is always on.
• Haptic feedback doesn't play in sidebar.