Sorted SwiftUI List Crashes iOS 14.2 App

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Created Nov ’20

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Ran into a challenging EXC_BAD_ACCESS iOS app crash that provides no real information on the culprit within my code. Tried Zombie Objects to no avail.

After some extensive trial and error, the issue seems to point to using a sorted and sectioned SwiftUI List pulled from a CoreData FetchRequest.

If I change from a List to a ScrollView/VStack, things work just fine without any other code changes. (Obviously not preferred since I'll lose native swipe-to-delete, etc).

Using the same List code, the issue didn't exist in iOS 13 nor did it seem to exist in earlier iOS 14 versions.

Some code snippets below showing how I'm handing the FetchRequest, Sort/Sectioning by date, and ultimate display. Also included a snippet of the crash log.

If anyone's run into a similar issue or has some insight, it would be appreciated. Wondering if the true root cause is an OS-level bug since the problem didn't exist before.

Fetch Request:

Code Block  @FetchRequest(entity: StoredTrip.entity(), sortDescriptors: [
        NSSortDescriptor(keyPath: \StoredTrip.blockStart, ascending: true)]) var storedTrips: FetchedResults<StoredTrip>

Sorting:

Code Block func update(_ result : FetchedResults<StoredTrip>)-> [[StoredTrip]] {
	return Dictionary(grouping: result){ (element : StoredTrip) in
		dateFormatter.string(from: element.blockStart!)
	}.values.sorted() { $0[0].blockStart! > $1[0].blockStart! }
}

Display:

Code Block List {
	ForEach(update(storedTrips), id: \.self)  { (section: [StoredTrip]) in
		Section(header: Text( self.dateFormatter.string(from: section[0].blockStart!)).padding(.top,2).padding(.bottom,2)) {
			ForEach(section, id: \.self) { trip in
				ListItem(trip: trip).environmentObject(self.dataStorage)
			}
		}
	}
}

Code Block OS Version:          iPhone OS 14.2.1 (18B121)
Release Type:        User
Baseband Version:    1.14.06
Report Version:      104
Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x0000000000000008
VM Region Info: 0x8 is not in any region.  Bytes before following region: 4333666296
      REGION TYPE                 START - END      [ VSIZE] PRT/MAX SHRMOD  REGION DETAIL
      UNUSED SPACE AT START
--->  
      TEXT                   1024e8000-10251c000 [  208K] r-x/r-x SM=COW  ....app/***
Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [1171]
Triggered by Thread:  0
Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   AttributeGraph                	0x00000001aa77b91c AG::AttributeID::size+ 92444 () const + 44
1   AttributeGraph                	0x00000001aa76f604 AG::Graph::add_indirect_attribute+ 42500 (AG::Subgraph&, AG::AttributeID, unsigned long, std::1::optional<unsigned long>, bool) + 140
2   AttributeGraph                	0x00000001aa781d80 (anonymous namespace)::create_indirect_attribute+ 118144 (unsigned int, std::__1::optional<unsigned long>) + 80
3   SwiftUI                       	0x00000001890a3c0c partial apply for thunk for @callee_guaranteed () -> + 9710604 (@unowned IndirectAttribute<A>) + 32
4   SwiftUI                       	0x00000001890a3a1c closure #1 in AGSubgraphRef.apply<A>+ 9710108 (_:) + 72
5   SwiftUI                       	0x00000001890a3810 Attribute.makeReusable+ 9709584 (indirectMap:) + 276

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