Re-present sheet, popover and fullscreen when identity changes.

[tgrapperon]

EDIT: I made a booboo and the branch of #76 was deleted and the PR closed, so I'm opening the same PR again with a new branch.

This is a WIP PR that implement a solution to #75.
I still need to implement the confirmation dialog part and fix existential opening on older versions of Swift. A few remarks:

• sheet modifiers were annotated @MainActor, but .popover and .fullScreenCover weren't, so I removed this annotation for .sheet. I can implement the other alternative if needed.
• I removed the Team ID from the Standups example.
• Fact's id from CaseStudies is now only based on the number instead of the number + the description to avoid unwanted presentations when the description is updated.[Edit, I need to fix the saved facts list too]

[tgrapperon]

I don't know if alert and confirmationDialog should follow the same treatment. According to my tests, SwiftUI doesn't represent the alert/dialog if the presenting value changes, and any interaction with a button closes the alert/dialog.

With the current implementation, .sheet, .fullScreenCover and .popover are re-presented if the presentation identity changes. This presentation identity is:

• The id: ID value if the presented value is Identifiable.
• The value's type otherwise, annotated with the enum's case tag if it applies.

I'm not really sure if we should use the enum's case tag for optionals. The PR can be easily modified to only tag non-optional enums and let the optionality be handled by the binding upstream.

The issue with the current implementation is that there is no built-in way to opt-out of this behavior, and I'm not really sure how to implement one without touching the API or adding a new protocol. One workaround would be to wrap the presented value in an Identifiable wrapper that returns a constant id (but I don't think such wrapper should ship with the library).

[stephencelis]

@tgrapperon Thanks for looking into this! I won't have time to look right away, but did want to let you know that we encountered the following issue when exploring this in TCA the other day:

https://gist.github.com/mbrandonw/f8b94957031160336cac6898a919cbb7#file-fb11975674-md

Basically, re-presenting a sheet causes dismissal hooks to fail, and we need to use onDisappear on the sheet content to workaround.

There is even more puzzling behavior with popovers, where dismissal fires for the re-presented popover before it's even initially presented. We haven't found workarounds for this yet, if there are any.

We haven't checked full screen covers...hopefully they're free of SwiftUI bugs... 😬

[Muhammed9991]

Is this still being worked on?

[dlewandaDK]

Following up here, my team would benefit from this fix becoming part of the product. We are maintaining a local implementation that is similar to this one, but would much rather lean on a first-party solution that has broader acceptance.