[Stats Revamp] Fix crash after backgrounding app from Stats screen

[staskus]

Fixes #20006

Description

We call this method when the app is in the background, which causes the crash. This method is called in the background since traidCollectionDidChange method is triggered when apps go into background. This issue is only reproducible when there's Total Likes and Total Comments cards with guide text when going into background. That's why it wasn't found before.

It's concerning since we used a failable try? initializer.

Fixing the issue by checking if app is not in the background before rebuilding NSAttributedString with html.

Testing instructions

Case 1:

1. Install app version 21.6 or above (e.g. from trunk or TestFlight)
2. Log in to an open Stats, Total Likes / Total Comments card should be visible that has guide informational text
3. Background the app
4. The app shouldn't crash

Regression Notes

1. Potential unintended areas of impact

None

2. What I did to test those areas of impact (or what existing automated tests I relied on)

None

3. What automated tests I added (or what prevented me from doing so)

None

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Images & Videos

[wpmobilebot]

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• Then installing the build number pr20008-609edd9 on your iPhone

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[wpmobilebot]

You can test the changes in Jetpack from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr20008-609edd9 on your iPhone

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[guarani]

Thank you for the fix! I reproduced this on release/21.6 on a physical device (it doesn't seem to happen on sims) and then verified the bug isn't reproducible on this branch.

I found a few mentions of similar bugs, see #12554 and #12519, but no clear solution.

Those PRs mention a fix that works but prevents the system from capturing a screenshot of the app in both light & dark mode as the app transitions to the background. I'm actually not sure if the system still does this. As an app is backgrounded, it's still showing animations in motion, so I think the app switcher keeps the apps "running" (i.e. it doesn't show screenshots anymore).

Feel free to merge this as-is. In the meantime, are there any downsides you see to this fix?

[guarani]

It's concerning since we used a failable try? initializer.

Apple's docs say this about Swift and Obj-C exceptions:

In Swift, you can recover from errors passed using Cocoa’s error pattern, as described above in Catch Errors. However, there’s no safe way to recover from Objective-C exceptions in Swift. To handle Objective-C exceptions, write Objective-C code that catches exceptions before they reach any Swift code.

So it looks like this internal exception (which could be an Apple bug) can't be caught by Swift.

[staskus]

@guarani thanks for testing!

Those PRs mention a fix that works but prevents the system from capturing a screenshot of the app in both light & dark mode as the app transitions to the background

So interesting, couldn't resist testing it immediately. It does look like the app switcher "screenshots" are not perfect and the guide text appears in the wrong color. NSAttributedStrings are a bit challenging because of this reason.

Simulator.Screen.Recording.-.iPhone.14.-.2023-01-26.at.21.55.59.mp4

are there any downsides you see to this fix?

If you look at the video, the guide text reappears after coming back from the background. I'm thinking if a better solution would be to add this != .background check inside traitCollectionDidChange method, then we would avoid rebuilding guildText when background. It would look this way:

Simulator.Screen.Recording.-.iPhone.14.-.2023-01-26.at.22.03.27.mp4

[guarani]

Thanks for sharing those videos. In the first video, it's noticeable how the card changes in size due to the guide text being re-added. I agree that the second video where the card does not change size is much better (the guide color changing isn't very noticeable).
If you want to merge as-is to get this fix in the beta, that's OK. If you'd rather make the change first, feel free to ping folks to get a review if needed because I'll be away tomorrow. 🙇