Crashes on iOS 16 after updating IGListKit from 4.0.0 to 5.0.0

[aleksanderlorenc-lw]

Hello, After we updated IGListKit to 5.0.0 we started observing crashes related to laying out cells in collection views.

Fatal Exception: NSInternalInconsistencyException
Height of item 0 in section 0 (100 pt) must be less than or equal to container (0 pt) accounting for section insets {0, 0, 0, 0}. Delegate class: _TtC9AppNameP33_3252A8D0199CBA1CE0F628B039E44F6B26IconImageSectionController

Trace

          Fatal Exception: NSInternalInconsistencyException
0  CoreFoundation                 0xa248 __exceptionPreprocess
1  libobjc.A.dylib                0x17a68 objc_exception_throw
2  Foundation                     0x546958 -[NSMutableDictionary(NSMutableDictionary) initWithContentsOfFile:]
3  AppName                      0x242eba0 -[IGListCollectionViewLayout _calculateLayoutIfNeeded] + 543 (IGListCollectionViewLayout.mm:543)
4  UIKitCore                      0x76828 -[UICollectionViewData _prepareToLoadData]
5  UIKitCore                      0x444020 -[UICollectionViewData validateLayoutInRect:]
6  UIKitCore                      0x29ac8 -[UICollectionView layoutSubviews]
7  UIKitCore                      0x4cec -[UIView(CALayerDelegate) layoutSublayersOfLayer:]
8  QuartzCore                     0xa4e8 CA::Layer::layout_if_needed(CA::Transaction*)
9  UIKitCore                      0xd2ae8 -[UIView(Hierarchy) layoutBelowIfNeeded]
10 UIKitCore                      0x4f33e4 __47-[UICollectionViewAnimation startWithAnimator:]_block_invoke
11 UIKitCore                      0x316d0 +[UIView(Animation) performWithoutAnimation:]
12 UIKitCore                      0xa3668 -[UICollectionViewAnimation startWithAnimator:]
13 UIKitCore                      0x707948 -[UICollectionView _startViewAnimationsWithContext:oldVisibleViews:reorderedViewAttributesTable:viewAnimator:viewAnimationsCompletedDispatchGroup:]
14 UIKitCore                      0x4e2df0 __102-[UICollectionView _updateWithItems:tentativelyForReordering:propertyAnimator:collectionViewAnimator:]_block_invoke_2
15 UIKitCore                      0xd0af0 +[UIView _setupAnimationWithDuration:delay:view:options:factory:animations:start:animationStateGenerator:completion:]
16 UIKitCore                      0xa3da8 +[UIView(UIViewAnimationWithBlocks) animateWithDuration:delay:options:animations:completion:]
17 UIKitCore                      0x3145e8 -[UICollectionView _updateWithItems:tentativelyForReordering:propertyAnimator:collectionViewAnimator:]
18 UIKitCore                      0x3135a8 -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:collectionViewAnimator:]
19 UIKitCore                      0x27111c -[UICollectionView _performBatchUpdates:completion:invalidationContext:tentativelyForReordering:animator:animationHandler:]
20 AppName                      0x24298f0 __43-[IGListBatchUpdateTransaction _applyDiff:]_block_invoke.9 + 190 (IGListBatchUpdateTransaction.m:190)
21 UIKitCore                      0x316d0 +[UIView(Animation) performWithoutAnimation:]
22 AppName                      0x2429614 -[IGListBatchUpdateTransaction _applyDiff:] + 192 (IGListBatchUpdateTransaction.m:192)
23 AppName                      0x24291c8 -[IGListBatchUpdateTransaction _didDiff:onBackground:] + 155 (IGListBatchUpdateTransaction.m:155)
24 AppName                      0x2428df4 -[IGListBatchUpdateTransaction _diff] + 124 (IGListBatchUpdateTransaction.m:124)
25 AppName                      0x24262d8 -[IGListAdapterUpdater update] + 124 (IGListAdapterUpdater.m:124)
26 AppName                      0x24260f0 __44-[IGListAdapterUpdater _queueUpdateIfNeeded]_block_invoke + 73 (IGListAdapterUpdater.m:73)

These crashes didn't occur on iOS 17 and 18.

I've gone through the changelist checking commit by commit when the regression started, and it seems this commit is at fault: 032e1b0 - namely the change which removes the if with an early return, which guarded the diff from happening.

On iOS 16 in our case the collection view's window seems to be nil, which is why the if was triggering, whereas on 17 and 18 the window was not nil.

To give some more context, for this collection view we are not laying out the view. If we lay it out explicitly, the crash is no longer there. On 4.0.0 the code inside the if laid out the view, however, but since that is gone the crashes started happening.

I'm thinking whether we should guarantee the view is already laid out for IGListKit?

Thank you in advance

[TimOliver]

Hey @aleksanderlorenc-lw!

Sorry to hear that v5 started introducing this crash issue. Looking at Maxime's explanation in that commit, the check was removed since it was causing a lot of thrash to occur that was impacting performance.

Certainly in recent versions of iOS, IGListKit has had to change its behaviour to match Apple's changes to UICollectionView. Namely, a lot of the original UICollectionView behaviour was to do a complete reload whenever invalid state was detected, but that's being slowly replaced with straight up crashes/exceptions to encourage developers to work out why the state was invalid and to properly fix those issues.

I definitely think you should add a check in your code to confirm if the view is laid out like you proposed, but if you're interested, it might also be great if we could build a similar check into IGListKit to also catch those sorts of issues for others!

What do you think?

[aleksanderlorenc-lw]

Hey @TimOliver, from our side we have made sure the view is always laid out before starting IGListKit work and additionally we are dropping iOS 16 soon, so the issue should be gone. Not really sure how much of the users would have a similar case, but maybe a simple debug assert telling the users the view should be laid out at that point would be helpful