Crash when adding a section before view appears

[JosephDuffy]

Describe the bug

When adding a section to a ComposedSectionProvider in a viewDidLoad after the CollectionCoordinator has been set as the delegate but before the view has appeared the coordinator will fatalError in elementsProvider(for:) with error Fatal error: No UI configuration available for section 2.

To Reproduce

1. Checkout https://github.com/composed-swift/Composed-Demo/tree/ComposedSectionProvider-crash-example
2. Uncomment https://github.com/composed-swift/Composed-Demo/blob/ComposedSectionProvider-crash-example/Composed-Demo/Collection/PeopleCollectionViewController.swift#L20

Expected behavior

Should not crash

Environment

• OS Version: iOS 13.5, iOS 14 beta 7
• Library Version: 1.0.2
• Device: iPhone 8 Simulator

Additional context

The crash is triggered by collectionView.performBatchUpdates, but the closure is never executed so prepareSections never gets a chance to be called.

[shaps80]

Any suggested fix? I kinda get the issue, but I'm not sure off-hand the most appropriate fix. Seems we'd need to know somehow that its 'detached'? Or perhaps I'm misunderstand the issue?

[shaps80]

Is this resolved from the PR I just merged related to performBatchUpdates or is this a separate issue?

[JosephDuffy]

Is this resolved from the PR I just merged related to performBatchUpdates or is this a separate issue?

I tried the change but it didn't fix this. It could be something similar though so worth thinking about.