Allow wrapping screens to guarantee a described view controller

Author: kyleve

WorkflowUI/Sources/Screen/AnyContentContainerScreen/AnyContentContainerScreen.swift

@@ -0,0 +1,49 @@
+//
+//  AnyContentContainerScreen.swift
+//  WorkflowUI
+//
+//  Created by Kyle Van Essen on 9/26/22.
+//
+
+import Foundation
+
+///
+///
+public struct AnyContentContainerScreen: Screen {
+    public let content: AnyScreen
+
+    public init<ScreenType: Screen>(_ content: ScreenType) {
+        if let content = content as? Self {
+            self = content
+        } else {
+            self.content = content.asAnyScreen()
+        }
+    }
+
+    // MARK: Screen
+
+    public func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        let description = content.viewControllerDescription(environment: environment)
+
+        return ViewControllerDescription(
+            /// The inner `DescribedViewController` will respect `performInitialUpdate` from
+            /// the nested screen – so our value should always be false.
+            performInitialUpdate: false,
+            type: DescribedViewController.self,
+            build: {
+                DescribedViewController(description: description)
+            },
+            update: { vc in
+                vc.update(description: description)
+            }
+        )
+    }
+}
+
+extension Screen {
+    ///
+    ///
+    public func inContainerScreen() -> AnyContentContainerScreen {
+        AnyContentContainerScreen(self)
+    }
+}

WorkflowUI/Sources/ViewControllerDescription/DescribedViewController.swift

@@ -18,6 +18,8 @@
 
     import UIKit
 
+    /// Displays the backing `ViewControllerDescription` for a given `Screen`.
+    ///
     public final class DescribedViewController: UIViewController {
         var currentViewController: UIViewController
 
@@ -63,7 +65,11 @@
         }
 
         public func update<S: Screen>(screen: S, environment: ViewEnvironment) {
-            update(description: screen.viewControllerDescription(environment: environment))
+            if let screen = screen as? AnyContentContainerScreen {
+                update(description: screen.content.viewControllerDescription(environment: environment))
+            } else {
+                update(description: screen.viewControllerDescription(environment: environment))
+            }
         }
 
         override public func viewDidLoad() {