Runtime crash from SwiftUI.State and variadic types from Xcode 27 Beta 3

Question

Created 3w

Replies 5

Boosts 0

Participants 2

I am seeing a weird crash from Xcode 27 Beta 3 when building a variadic type DynamicProperty that also needs SwiftUI.State. This does not crash from Xcode 26.

Here is a repro:

import SwiftUI

struct Repeater<each Input>: DynamicProperty {
  @State private var storage = Storage()

  private var input: (repeat each Input)

  init(_ input: repeat each Input) {
    self.input = (repeat each input)
  }
}

extension Repeater {
  final class Storage {
    
  }
}

@main
struct CrashDemoApp: App {
  private var repeater = Repeater(1)
  
  var body: some Scene {
    WindowGroup {
      EmptyView()
    }
  }
}

Here is the crash:

Thread 1 Queue : com.apple.main-thread (serial)
#0	0x000000019a93aec0 in swift::TargetMetadata<swift::InProcess>::isCanonicalStaticallySpecializedGenericMetadata ()
#1	0x000000019a946b38 in performOnMetadataCache<swift::MetadataResponse, swift_checkMetadataState::CheckStateCallbacks> ()
#2	0x000000019a8c85f0 in swift_checkMetadataState ()
#3	0x00000001004a2c78 in type metadata completion function for Repeater ()
#4	0x000000019a94cfe4 in swift::GenericCacheEntry::tryInitialize ()
#5	0x000000019a94c870 in swift::MetadataCacheEntryBase<swift::GenericCacheEntry, void const*>::doInitialization ()
#6	0x000000019a94f820 in swift::LockingConcurrentMap<swift::GenericCacheEntry, swift::LockingConcurrentMapStorage<swift::GenericCacheEntry, (unsigned short)14>>::getOrInsert<swift::MetadataCacheKey, swift::MetadataRequest&, swift::TargetTypeContextDescriptor<swift::InProcess> const*&, void const* const*&> ()
#7	0x000000019a93c714 in _swift_getGenericMetadata ()
#8	0x00000001004a4190 in __swift_instantiateGenericMetadata ()
#9	0x00000001004a2a5c in type metadata accessor for Repeater ()
#10	0x00000001004a5094 in type metadata accessor for Repeater<Pack{Int}> ()
#11	0x00000001004a4fcc in type metadata completion function for CrashDemoApp ()
#12	0x000000019a9543bc in swift::MetadataCacheEntryBase<(anonymous namespace)::SingletonMetadataCacheEntry, int>::doInitialization ()
#13	0x000000019a8d2ae0 in swift_getSingletonMetadata ()
#14	0x00000001004a479c in type metadata accessor for CrashDemoApp ()
#15	0x00000001004a473c in static CrashDemoApp.$main() ()
#16	0x00000001004a4a34 in main ()
#17	0x0000000186e47e00 in start ()

Here is a repo to demo:

https://github.com/vanvoorden/2026-07-17

Please let me know if you have any ideas about that. Thanks!

Answer 1

vanvoorden OP

3w

This is still broken for me in Xcode 27 Beta 4. :(

Answer 2

vanvoorden OP

2w

Here is a version that crashes without the State macro:

struct Repeater<each Input> {
  private var __storage = SwiftUICore.State._makeStorage({
    Storage()
  })
  
  private var input: (repeat each Input)

  init(_ input: repeat each Input) {
    self.input = (repeat each input)
  }
}

Answer 3

vanvoorden OP

2w

Another repro:

struct Repeater<each Input> {
  private var __storage = LazyState(initialValue: {
    Storage()
  })

  private var input: (repeat each Input)

  init(_ input: repeat each Input) {
    self.input = (repeat each input)
  }
}

Using classic State does not crash:

struct Repeater<each Input> {
  private var __storage = State(initialValue: Storage())

  private var input: (repeat each Input)

  init(_ input: repeat each Input) {
    self.input = (repeat each input)
  }
}

And for some reason I can build from LazyState if I do not save my parameter pack to a stored instance variable:

struct Repeater<each Input> {
  private var __storage = LazyState(initialValue: {
    Storage()
  })

  init(_ input: repeat each Input) { }
}

It also turns out I can also use LazyState if I declare the stored parameter pack variable before I declare the LazyState variable:

struct Repeater<each Input> {
  private var input: (repeat each Input)

  private var __storage = LazyState(initialValue: {
    Storage()
  })

  init(_ input: repeat each Input) {
    self.input = (repeat each input)
  }
}

That one does not crash.

Answer 4

vanvoorden OP

1d

This is still broken for me from Xcode 27 beta 5. But it looks like we did patch a fix on 6.4.^1

Answer 5

DTS Engineer OP

Apple

17h

@vanvoorden Could you please file a bug report using Feedback Assistant with the sample code that reproduces this issue? Please post the Feedback ID here once you have it.