Audit + investigate use of withCheckedContinuation and withCheckedThrowingContinuation

[data-sync-user]

Related to 12/5/24 incident.

We should audit our use of withCheckedContinuation in Firefox iOS. We have some Sentry crashes which may be related, example: https://mozilla.sentry.io/issues/6115735470/?environment=Production&environment=production&project=6176941&query=is%3Aunresolved withCheckedContinuation&referrer=issue-stream&statsPeriod=7d&stream_index=0

These crashes only appear to impact iOS 18.x users so far.

For additional context also please see onboarding crash incident doc: https://docs.google.com/document/d/1DL5vMCO-g9z0ezoVfbm4WSd2p-6dMpybwUXjGmWXF3k/edit?tab=t.0

Related PRs:

• Fix PR for incident that caused a crash loop during onboarding
  • https://github.com/mozilla-mobile/firefox-ios/pull/23596
• NotificationManager
  • https://github.com/mozilla-mobile/firefox-ios/pull/23679
  • Tested a workaround for v135 where we just used the unsafe version of the continuation (rather than checked) to see if that works
• Pocket fetchStories
  • https://github.com/mozilla-mobile/firefox-ios/pull/23680
• JumpBackInDataAdaptor
  • https://github.com/mozilla-mobile/firefox-ios/pull/23678
  • NOTE: This was a continuation that did NOT use a URLSession (or, in fact, any real asynchronous code!)
• DefaultHTMLDataRequest
  • https://github.com/mozilla-mobile/firefox-ios/pull/23862
• Kingfisher 8 migration and continuation removals:
  • https://github.com/mozilla-mobile/firefox-ios/pull/23920
  • https://github.com/mozilla-mobile/firefox-ios/pull/23921

Related Tickets:

• Incident onboarding crash: https://mozilla-hub.atlassian.net/browse/FXIOS-10811
• https://mozilla-hub.atlassian.net/browse/FXIOS-10911
• Follow up to using “unsafe” version of continuations for v135: https://mozilla-hub.atlassian.net/browse/FXIOS-9889
• Crash at startup with Kingfisher image processing https://mozilla-hub.atlassian.net/browse/FXIOS-10940
  • We determined there were continuations, so we migrated to the new version of Kingfisher and removed those continuations… but Kingfisher itself uses continuations under the hood for its async/await methods

┆Issue is synchronized with this Jira Task

[data-sync-user]

➤ Isabella commented:

This is a very strange bug that makes me think there’s something wrong on Apple’s side that suddenly our code is not working for iOS 18 users. The crashes are only on iOS18 devices.

FYI we’re not the only people running into issues with iOS18 global with* methods:

• App is crashing when using "withCheckedContinuation" in Xcode 15 beta 5 - https://developer.apple.com/forums/thread/761580?answerId=803930022#803930022 ( https://developer.apple.com/forums/thread/761580?answerId=803930022#803930022 )

  • Other reports for xcode 16+

• Some more possibly related discussion here: https://forums.swift.org/t/global-with-concurrency-functions-crash-on-catalyst-designed-for-ipad-on-macos/74823/15 ( https://forums.swift.org/t/global-with-concurrency-functions-crash-on-catalyst-designed-for-ipad-on-macos/74823/15|smart-link )

Some people worked around an earlier similar issue by changing to use unsafe version (e.g. withUnsafeContinuation)

Reference: swiftlang/swift#76218 (comment) ( https://github.com/swiftlang/swift/pull/76218#issuecomment-2375423832|smart-link )

[data-sync-user]

➤ Isabella commented:

QA Test Notes:

A few fixes lumped under this ticket. Please test for regressions in the following areas:

• Related to PR fix Bug 1094306 - Add a database class for Bookmarks #1: Bugfix FXIOS-10832 Possible workaround for FXIOS-10832 withCheckedContinuation crash in JumpBackInDataAdaptor #23678 ( Bugfix FXIOS-10832 Possible workaround for FXIOS-10832 withCheckedContinuation crash in JumpBackInDataAdaptor #23678 )

  • Jump Back In / Synced Tabs
  • Synced credit cards

• Related to PR fix Share to more stuff #2: Bugfix FXIOS-10832 Test workaround for withCheckedContinuation crash in NotificationManager #23679 ( Bugfix FXIOS-10832 Test workaround for withCheckedContinuation crash in NotificationManager #23679 )

  • Fresh install, user accepts push notifications, is able to receive notifications in the app
  • App can receive notifications when backgrounded
  • App can detect when notifications are disabled
  • Settings > Notifications > toggling Sync works as expected

• Related to PR fix Bug 1094195 - (ios) Integrate the login viewcontroller #3: Bugfix FXIOS-10832 - Made pocket provider fetchStories to be async to fix withCheckedContinuation crash #23680 ( Bugfix FXIOS-10832 - Made pocket provider fetchStories to be async to fix withCheckedContinuation crash #23680 ) (FYI Nishant Bhasin )

  • Test pocket stories load as expected