Thanks Ziqiao. I filed the report. It's FB16712454.

Oh here's a direct link to the zip file instead of a shared folder. https://www.icloud.com/iclouddrive/022QsLMXmVHAU2lAcuj4XuV4w#MigrationSample

Trying different things with my project, I discovered that the problem only occurs when CloudKit syncing is enabled. Turning off syncing by passing cloudKitDatabase: .none to ModelConfiguration or by unchecking the CloudKit option in Signing & Capabilities makes the problem go away. But then of course iCloud syncing doesn't work. Makes sense considering the error message I get. I was able to reproduce the problem easily with a new project based on the SwiftData Xcode template. I don't think it's doing anything out of the ordinary but I'm looking forward to find out. The project can be found here: https://www.icloud.com/iclouddrive/0a5WkBaQRA1N-FOLGjKukV8Ag#MigrationSample There are actually two projects, one for schema v1 and one for schema v2. To reproduce the error I get: Open the MigrationSampleV1 project, build and run. In the running app, create some data. Open the MigrationSampleV2 project, build and run. Expected result: The migration kicks in and the app opens. Actual result: A crash occurs before the migration's didMigrate.

Thanks Ziqiao, I will take a look at the code sample you pointed to and try to come up with a reduction that I can share. Either way I'll report back.

A couple other things I noticed. First, the crash occurs between the calls to willMigrate and didMigrate. Second, if I try to run the app again after the crash then it runs fine, albeit with the new property being nil since didMigrate didn't execute, but this seems to suggest that the crash occurs downstream from the new schema version being applied to the database.

Such a weird bug. Still happening two years later with iOS 16.4. struct ContentView: View { var body: some View { NavigationView { List { NavigationLink("Go to detail view") { Text("Detail view") .toolbar { ToolbarItem(placement: .bottomBar) { Button(action: { print("tap") }) { Image(systemName: "square.and.arrow.up") } } } } } } // Without this, toolbar is either empty or doesn't appear in detail view .navigationViewStyle(.stack) } }

Done, thanks!