Custom Environment Values and Non-Sendable Errors

I have a following code. I use the Environment(.showMessage) in my SwiftUI view only to show and hide views. When I compile this code with Swift 6 I get the error (shown at the end).

struct ShowMessageAction {
    typealias Action = (String, MessageType) -> ()
    let action: Action
    func callAsFunction(_ message: String, _ messageType: MessageType = .error) {
        action(message, messageType)
    }
}

extension EnvironmentValues {
    @Entry var showMessage = ShowMessageAction { _, _ in }
}

    Static property 'defaultValue' is not concurrency-safe because non-'Sendable' type 'ShowMessageAction' may have shared mutable state. 

What can I do in this situation?

UPDATE 1:

I made the change but now MyProductListScreen is complaining.

      NavigationStack {
//Call to main actor-isolated initializer 'init()' in a synchronous // nonisolated context
                    MyProductListScreen()
                }

MyProductListScreen

    struct MyProductListScreen: View {
        
// It complains about showMessage. 
        @Environment(\.showMessage) private var showMessage
        @Environment(ProductStore.self) private var productStore
        @State private var isPresented: Bool = false
        @AppStorage("userId") private var userId: Int?

SOLUTION:

I ended up marking my destination property in AppScreen with @MainActor.

 @MainActor
    @ViewBuilder
    var destination: some View {
        switch self {
            case .home:
            NavigationStack {
                ProductListScreen()
            }
            case .myProducts:
            NavigationStack {
                MyProductListScreen()
                        .requiresAuthentication()
            }

>Solution :

This is very much related to how the @Entry macro generates the defaultValue property (See also my answer here).

@Entry in your current code generates

static let defaultValue = ShowMessageAction { _, _ in }

which is considered not safe because ShowMessageAction is not Sendable (See also SE-0412).

We would like defaultValue to be a computed property, so there is no global state. i.e.

static var defaultValue: ShowMessageAction { 
    ShowMessageAction { _, _ in } 
}

@Entry can generate this if you specify the type of the property explicitly.

@Entry var showMessage: ShowMessageAction = .init { _, _ in }

It is impossible for @Entry to generate a computed property without an explicit type, because a computed property needs an explicit type annotation, but macros cannot know the type of an arbitrary expression like ShowMessageAction { _, _ in }.