Xcode produces a lot of "Cannot form key path that captures non-sendable type..." warnings when using sheet(unwrapping:)

[SwiftDevDennis]

Hey 👋, I love this package and what it can do in combination with CasePaths! Makes the code so much nicer and easier to maintain. Thanks a lot for all your hard work!

I've been using it pretty extensively in an app I'm building and it is working flawlessly. The only thing that is strange is a growing set of warnings that Xcode produces:

Cannot form key path that captures non-sendable type 'KeyPath<Presentation.AllCasePaths, AnyCasePath<Presentation, Void>>'
Generic class 'KeyPath' does not conform to the 'Sendable' protocol

I have dozens of those accumulated in my project and I'm not sure how to get rid of them, assuming that's even possible (if I remember correctly, KeyPaths and Sendable currently don't go so well together in Swift).

It seems that this kind of warning appears for each sheet(unwrapping:) modifier in the project, like:

@CasePathable
enum Presentation: Sendable {
  case test
}
// ...
@State var presentation: Presentation?
// ...
.sheet(unwrapping: $presentation.test) { _ in
  Text("Sheet")
}

Funnily enough, the warning is only produced when you're not in the file (that's probably some strange Xcode bug). You have to go to a different file and compile for the waning to appear.

I have created a minimal example (see below) that produces this error (at least for me). I use Xcode 15.2 with the Concurrency Checker set to "Complete".

One "fix" I have found is this:

extension KeyPath: @unchecked Sendable {}

But that feels wrong 😅

Have you encountered this warning before? If so, is there a nicer workaround than an @unchecked Sendable on KeyPath? Or is this something we have to wait for Swift to fix in the future? I haven't really found any discussions or issues on this topic. Maybe I'm also just doing something wrong 😄

Demo Project

Just go to App.swift and compile.

CasePathsWarningDemo.zip

Full Code

App.swift

import SwiftUI

@main
struct CasePathsWarningDemoApp: App {
  var body: some Scene {
    WindowGroup {
      ContentView()
    }
  }
}

ContentView.swift

import CasePaths
import SwiftUI
import SwiftUINavigation

@CasePathable
enum Presentation: Sendable { // I also tried removing Sendable here
  case test
}

struct ContentView: View {
  @State var destination: Presentation?

  var body: some View {
    Color.clear
      .sheet(unwrapping: $destination.test) { _ in
        Text("Sheet")
      }
  }
}

[mbrandonw]

Hi @SwiftDevDennis, this is a limitation of Swift currently, and a recently accepted proposal will fix the issue. For now you can ignore those warnings.

Since this is not an issue with the library I am going to convert it to a discussion. Feel free to follow up with any questions over there. Oops sorry, this is already a discussion! I thought it was an issue.

[SwiftDevDennis]

Ah, perfect, that's great to hear :) Thanks!

[sri-sundhed]

HI @mbrandonw
We just ran in to the issue mentioned above during our efforts to update our codebase to be Swift 6 compliant. Should we just ignore these warnings and expect them to go away with a future release of Swift?

[mbrandonw]

Hi @sri-sundhed, these warnings/errors are fixed as of Xcode 16, Swift 6 and the newest version of the library. Are you using an older version of any of these things?

[jshier]

For a full fix of KeyPath-related Sendable warnings you'll need to enable the "Infer Sendable for Methods and Key Path Literals" upcoming feature in Xcode, or move right to Swift 6 mode.