Weird crash on iOS 15

[buscarini]

I'm seeing this crash when running on a device with iOS 15. It seems more like a bug with the code generated by the compiler, but I haven't been able to find much info on the Internet. Has anyone encountered this? Any workaround? I have tried to disable bitcode, optimizations, but it crashes anyway.

[tgrapperon]

In my experience, these weird crashes (that are happening where they shouldn't) are caused by a stack overflow. It can happen easily when using TCA, as the State can end up being a huge struct value that lives almost entirely on the stack.
Maybe you can try to box a few of your child states (you can convert them as a computed property to the first value of a one-value array (which stores its values on the heap) to quickly check if it helps, or use a proper boxing property wrapper). You may find more information here and here for example.

It may be something else, but that's what I'd try first in this case. Deleting DerivedData may also be an option if you have doubts about your compiler-generated code.

[tgrapperon]

BTW, looking at the StackTrace again, and I'm maybe reading it wrong, but it looks like you're observing some quite complex data (AppState>TabState>HomeModel>SelectionState) through a ViewStore. If this is indeed the case, this is not optimal performance-wise. As it is unlikely that your UI will need access to all the AppState at this level, you should maybe consider scoping your store to an intermediate ViewState that exposes only the bare minimum to construct the UI.

If this is not a stack overflow, the issue seems related to the equatability of SelectionState. Maybe you can build two SelectionState values at launch and see if it crashes too when you compare them.

But as @jaanussiim said, it is faster to clean the build folder at first, as it requires no code change. If this doesn't solve the issue, and SelectionState is failing to compare in isolation, the next level is deleting DerivedData. If you do this, you should quit Xcode first. You will also need to "Xcode>Package>Reset Package Cache" when you launch it back.

[jaanussiim]

I usually see this when changing the state object in module/package between runs. Quick 'Clean Build Folder' resolves it.

I would blame Xcode. May be related to the new experimental build system in Xcode 13.2.

Working with smaller feature modules helps to reduce recompiling needed.

[buscarini]

Thanks all. Yes, I saw that there was a view store inspecting the whole app state, and optimized that away. I got rid of some code and this crash went away. Probably it's due to a stack overflow, as @tgrapperon suggested; I discarded it initially because the stack didn't seem that large to me, but it might be related.