Support eager navigation destination resolution

Examples/CaseStudies/UIKit/ErasedNavigationStackController.swift

@@ -81,6 +81,10 @@ private class NumberFeatureViewController: UIViewController {
     self.number = number
     super.init(nibName: nil, bundle: nil)
     title = "Feature \(number)"
+
+    navigationDestination(for: String.self) { string in
+      StringFeatureViewController(string: string)
+    }
   }
   required init?(coder: NSCoder) {
     fatalError("init(coder:) has not been implemented")
@@ -89,10 +93,6 @@ private class NumberFeatureViewController: UIViewController {
     super.viewDidLoad()
     view.backgroundColor = .systemBackground
 
-    navigationDestination(for: String.self) { string in
-      StringFeatureViewController(string: string)
-    }
-
     let numberButton = UIButton(
       type: .system,
       primaryAction: UIAction { [weak self] _ in
@@ -137,6 +137,10 @@ private class StringFeatureViewController: UIViewController {
     self.string = string
     super.init(nibName: nil, bundle: nil)
     title = "Feature '\(string)'"
+
+    navigationDestination(for: Bool.self) { bool in
+      BoolFeatureViewController(bool: bool)
+    }
   }
   required init?(coder: NSCoder) {
     fatalError("init(coder:) has not been implemented")
@@ -145,10 +149,6 @@ private class StringFeatureViewController: UIViewController {
     super.viewDidLoad()
     view.backgroundColor = .systemBackground
 
-    navigationDestination(for: Bool.self) { bool in
-      BoolFeatureViewController(bool: bool)
-    }
-
     let numberButton = UIButton(
       type: .system,
       primaryAction: UIAction { [weak self] _ in

Examples/CaseStudiesTests/NavigationPathTests.swift

@@ -483,6 +483,59 @@ final class NavigationPathTests: XCTestCase {
     await assertEventuallyNoDifference(path.elements, [.eager(1), .eager("Hello"), .eager(true)])
   }
 
+  @MainActor
+  func testPushMultipleFeaturesAtOnce_InitRegisteredNavigationDestination() async throws {
+    @UIBinding var path = UINavigationPath()
+    let nav = NavigationStackController(path: $path) {
+      InitRootViewController()
+    }
+    try await setUp(controller: nav)
+
+    let root = nav.viewControllers[0]
+    withUITransaction(\.uiKit.disablesAnimations, true) {
+      root.traitCollection.push(value: 2)
+      root.traitCollection.push(value: "Hello")
+      root.traitCollection.push(value: true)
+    }
+
+    await assertEventuallyEqual(nav.viewControllers.count, 4, timeout: 2)
+    await assertEventuallyNoDifference(
+      nav.values,
+      [2, "Hello", true] as [AnyHashable]
+    )
+    await assertEventuallyNoDifference(
+      path.elements,
+      [.eager(2), .eager("Hello"), .eager(true)]
+    )
+  }
+
+  @MainActor
+  func testDeepLink_InitRegisteredNavigationDestination() async throws {
+    var initialPath = UINavigationPath()
+    initialPath.append(1)
+    initialPath.append("Hello")
+    initialPath.append(true)
+    @UIBinding var path = initialPath
+
+    let nav = NavigationStackController(path: $path) {
+      UIViewController()
+    }
+    nav.navigationDestination(for: Int.self) { int in
+      InitIntegerViewController(value: int)
+    }
+    try await setUp(controller: nav)
+
+    await assertEventuallyEqual(nav.viewControllers.count, 4, timeout: 2)
+    await assertEventuallyNoDifference(
+      nav.values,
+      [1, "Hello", true] as [AnyHashable]
+    )
+    await assertEventuallyNoDifference(
+      path.elements,
+      [.eager(1), .eager("Hello"), .eager(true)]
+    )
+  }
+
   @MainActor
   func testRegisterNavigationDestinationTypeMultipleTimes_LastOneWins() async throws {
     @UIBinding var path = UINavigationPath()
@@ -625,6 +678,43 @@ private final class BoolViewController: UIViewController, _ValueViewController {
   }
 }
 
+private final class InitRootViewController: UIViewController {
+  override func viewDidLoad() {
+    super.viewDidLoad()
+    navigationDestination(for: Int.self) { int in
+      InitIntegerViewController(value: int)
+    }
+  }
+}
+
+private final class InitIntegerViewController: UIViewController, _ValueViewController {
+  let value: Int
+  init(value: Int) {
+    self.value = value
+    super.init(nibName: nil, bundle: nil)
+    navigationDestination(for: String.self) { string in
+      InitStringViewController(value: string)
+    }
+  }
+  required init?(coder: NSCoder) {
+    fatalError("init(coder:) has not been implemented")
+  }
+}
+
+private final class InitStringViewController: UIViewController, _ValueViewController {
+  let value: String
+  init(value: String) {
+    self.value = value
+    super.init(nibName: nil, bundle: nil)
+    navigationDestination(for: Bool.self) { bool in
+      BoolViewController(value: bool)
+    }
+  }
+  required init?(coder: NSCoder) {
+    fatalError("init(coder:) has not been implemented")
+  }
+}
+
 private final class UserViewController: UIViewController, _ValueViewController {
   let value: User
   init(value: User) {

Sources/UIKitNavigation/Navigation/NavigationStackController.swift

@@ -168,7 +168,9 @@
       guard
         let destinationType = navigationID.elementType,
         let destination = destinations[DestinationType(destinationType)],
-        let (viewController, element) = destination(navigationID)
+        let (viewController, element) = withUITransaction(\.stackController, self, {
+          destination(navigationID)
+        })
       else {
         return nil
       }
@@ -364,7 +366,10 @@
       for data: D.Type,
       destination: @escaping (D) -> UIViewController
     ) {
-      guard let navigationController = navigationController ?? self as? UINavigationController
+      guard
+        let navigationController = UITransaction.current.stackController
+          ?? navigationController
+          ?? self as? UINavigationController
       else {
         reportIssue(
           """
@@ -476,6 +481,17 @@
     }
   }
 
+  private extension UITransaction {
+    var stackController: NavigationStackController? {
+      get { self[NavigationStackControllerKey.self] }
+      set { self[NavigationStackControllerKey.self] = newValue }
+    }
+  }
+
+  private enum NavigationStackControllerKey: UITransactionKey {
+    static let defaultValue: NavigationStackController? = nil
+  }
+
   private func typeName(_ type: Any.Type) -> String {
     #if CustomDump
       return String(customDumping: type)