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.

[sri-sundhed]

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?

We are still using Swift 5.10 with additional options set to get warnings about what will break when we migrate to Swift 6. So supposedly these warnings will not be errors, but completely disappear, when we do the real upgrade...