Add configuration options to App to choose reconciler

README.md

@@ -138,6 +138,31 @@ This way both [Semantic UI](https://semantic-ui.com/) styles and [moment.js](htt
 localized date formatting (or any arbitrary style/script/font added that way) are available in your
 app.
 
+### Fiber renderers
+
+A new reconciler modeled after React's [Fiber reconciler](https://reactjs.org/docs/faq-internals.html#what-is-react-fiber)
+is optionally available. It can provide faster updates and allow for larger View hierarchies.
+It also includes layout steps that can match SwiftUI layouts closer than CSS approximations.
+
+You can specify which reconciler to use in your `App`'s configuration:
+
+```swift
+struct CounterApp: App {
+  static let _configuration: _AppConfiguration = .init(
+    // Specify `useDynamicLayout` to enable the layout steps in place of CSS approximations.
+    reconciler: .fiber(useDynamicLayout: true)
+  )
+
+  var body: some Scene {
+    WindowGroup("Counter Demo") {
+      Counter(count: 5, limit: 15)
+    }
+  }
+}
+```
+
+> *Note*: Not all `View`s and `ViewModifier`s are supported by Fiber renderers yet.
+
 ## Requirements
 
 ### For app developers

Sources/TokamakCore/App/App.swift

@@ -28,22 +28,49 @@ public protocol App: _TitledApp {
   var body: Body { get }
 
   /// Implemented by the renderer to mount the `App`
-  static func _launch(_ app: Self, _ rootEnvironment: EnvironmentValues)
+  static func _launch(
+    _ app: Self,
+    with configuration: _AppConfiguration
+  )
 
   /// Implemented by the renderer to update the `App` on `ScenePhase` changes
   var _phasePublisher: AnyPublisher<ScenePhase, Never> { get }
 
   /// Implemented by the renderer to update the `App` on `ColorScheme` changes
   var _colorSchemePublisher: AnyPublisher<ColorScheme, Never> { get }
 
+  static var _configuration: _AppConfiguration { get }
+
   static func main()
 
   init()
 }
 
+public struct _AppConfiguration {
+  public let reconciler: Reconciler
+  public let rootEnvironment: EnvironmentValues
+
+  public init(
+    reconciler: Reconciler = .stack,
+    rootEnvironment: EnvironmentValues = .init()
+  ) {
+    self.reconciler = reconciler
+    self.rootEnvironment = rootEnvironment
+  }
+
+  public enum Reconciler {
+    /// Use the `StackReconciler`.
+    case stack
+    /// Use the `FiberReconciler` with layout steps optionally enabled.
+    case fiber(useDynamicLayout: Bool = false)
+  }
+}
+
 public extension App {
+  static var _configuration: _AppConfiguration { .init() }
+
   static func main() {
     let app = Self()
-    _launch(app, EnvironmentValues())
+    _launch(app, with: Self._configuration)
   }
 }

Sources/TokamakCore/App/Scenes/Scene.swift

@@ -21,8 +21,23 @@ public protocol Scene {
   // FIXME: If I put `@SceneBuilder` in front of this
   // it fails to build with no useful error message.
   var body: Self.Body { get }
+
+  /// Override the default implementation for `Scene`s with body types of `Never`
+  /// or in cases where the body would normally need to be type erased.
+  ///
+  /// You can `visit(_:)` either another `Scene` or a `View` with a `SceneVisitor`
+  func _visitChildren<V: SceneVisitor>(_ visitor: V)
+
+  /// Create `SceneOutputs`, including any modifications to the environment, preferences, or a custom
+  /// `LayoutComputer` from the `SceneInputs`.
+  ///
+  /// > At the moment, `SceneInputs`/`SceneOutputs` are identical to `ViewInputs`/`ViewOutputs`.
+  static func _makeScene(_ inputs: SceneInputs<Self>) -> SceneOutputs
 }
 
+public typealias SceneInputs<S: Scene> = ViewInputs<S>
+public typealias SceneOutputs = ViewOutputs
+
 protocol TitledScene {
   var title: Text? { get }
 }

Sources/TokamakCore/App/Scenes/SceneBuilder.swift

@@ -29,15 +29,30 @@ public extension SceneBuilder {
   static func buildBlock<C0, C1>(_ c0: C0, _ c1: C1) -> some Scene where C0: Scene,
     C1: Scene
   {
-    _TupleScene((c0, c1), children: [_AnyScene(c0), _AnyScene(c1)])
+    _TupleScene(
+      (c0, c1),
+      children: [_AnyScene(c0), _AnyScene(c1)],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+      }
+    )
   }
 }
 
 public extension SceneBuilder {
   static func buildBlock<C0, C1, C2>(_ c0: C0, _ c1: C1, _ c2: C2) -> some Scene
     where C0: Scene, C1: Scene, C2: Scene
   {
-    _TupleScene((c0, c1, c2), children: [_AnyScene(c0), _AnyScene(c1), _AnyScene(c2)])
+    _TupleScene(
+      (c0, c1, c2),
+      children: [_AnyScene(c0), _AnyScene(c1), _AnyScene(c2)],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+      }
+    )
   }
 }
 
@@ -50,7 +65,13 @@ public extension SceneBuilder {
   ) -> some Scene where C0: Scene, C1: Scene, C2: Scene, C3: Scene {
     _TupleScene(
       (c0, c1, c2, c3),
-      children: [_AnyScene(c0), _AnyScene(c1), _AnyScene(c2), _AnyScene(c3)]
+      children: [_AnyScene(c0), _AnyScene(c1), _AnyScene(c2), _AnyScene(c3)],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+      }
     )
   }
 }
@@ -65,7 +86,14 @@ public extension SceneBuilder {
   ) -> some Scene where C0: Scene, C1: Scene, C2: Scene, C3: Scene, C4: Scene {
     _TupleScene(
       (c0, c1, c2, c3, c4),
-      children: [_AnyScene(c0), _AnyScene(c1), _AnyScene(c2), _AnyScene(c3), _AnyScene(c4)]
+      children: [_AnyScene(c0), _AnyScene(c1), _AnyScene(c2), _AnyScene(c3), _AnyScene(c4)],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+        $0.visit(c4)
+      }
     )
   }
 }
@@ -90,7 +118,15 @@ public extension SceneBuilder {
         _AnyScene(c3),
         _AnyScene(c4),
         _AnyScene(c5),
-      ]
+      ],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+        $0.visit(c4)
+        $0.visit(c5)
+      }
     )
   }
 }
@@ -117,7 +153,16 @@ public extension SceneBuilder {
         _AnyScene(c4),
         _AnyScene(c5),
         _AnyScene(c6),
-      ]
+      ],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+        $0.visit(c4)
+        $0.visit(c5)
+        $0.visit(c6)
+      }
     )
   }
 }
@@ -146,7 +191,17 @@ public extension SceneBuilder {
         _AnyScene(c5),
         _AnyScene(c6),
         _AnyScene(c7),
-      ]
+      ],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+        $0.visit(c4)
+        $0.visit(c5)
+        $0.visit(c6)
+        $0.visit(c7)
+      }
     )
   }
 }
@@ -177,7 +232,18 @@ public extension SceneBuilder {
         _AnyScene(c6),
         _AnyScene(c7),
         _AnyScene(c8),
-      ]
+      ],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+        $0.visit(c4)
+        $0.visit(c5)
+        $0.visit(c6)
+        $0.visit(c7)
+        $0.visit(c8)
+      }
     )
   }
 }
@@ -210,7 +276,19 @@ public extension SceneBuilder {
         _AnyScene(c7),
         _AnyScene(c8),
         _AnyScene(c9),
-      ]
+      ],
+      visit: {
+        $0.visit(c0)
+        $0.visit(c1)
+        $0.visit(c2)
+        $0.visit(c3)
+        $0.visit(c4)
+        $0.visit(c5)
+        $0.visit(c6)
+        $0.visit(c7)
+        $0.visit(c8)
+        $0.visit(c9)
+      }
     )
   }
 }

Sources/TokamakCore/App/Scenes/WindowGroup.swift

@@ -75,4 +75,8 @@ public struct WindowGroup<Content>: Scene, TitledScene where Content: View {
 //  public init(_ titleKey: LocalizedStringKey,
 //              @ViewBuilder content: () -> Content) {
 //  }
+
+  public func _visitChildren<V>(_ visitor: V) where V: SceneVisitor {
+    visitor.visit(content)
+  }
 }

Sources/TokamakCore/App/_AnyApp.swift

@@ -42,7 +42,7 @@ public struct _AnyApp: App {
   }
 
   @_spi(TokamakCore)
-  public static func _launch(_ app: Self, _ rootEnvironment: EnvironmentValues) {
+  public static func _launch(_ app: Self, with configuration: _AppConfiguration) {
     fatalError("`_AnyApp` cannot be launched. Access underlying `app` value.")
   }
 
@@ -51,6 +51,10 @@ public struct _AnyApp: App {
     fatalError("`title` cannot be set for `AnyApp`. Access underlying `app` value.")
   }
 
+  public static var _configuration: _AppConfiguration {
+    fatalError("`configuration` cannot be set for `AnyApp`. Access underlying `app` value.")
+  }
+
   @_spi(TokamakCore)
   public var _phasePublisher: AnyPublisher<ScenePhase, Never> {
     fatalError("`_AnyApp` cannot monitor scenePhase. Access underlying `app` value.")

Sources/TokamakCore/App/_TupleScene.swift

@@ -17,11 +17,17 @@
 
 struct _TupleScene<T>: Scene, GroupScene {
   let value: T
-  var children: [_AnyScene]
+  let children: [_AnyScene]
+  let visit: (SceneVisitor) -> ()
 
-  init(_ value: T, children: [_AnyScene]) {
+  init(
+    _ value: T,
+    children: [_AnyScene],
+    visit: @escaping (SceneVisitor) -> ()
+  ) {
     self.value = value
     self.children = children
+    self.visit = visit
   }
 
   var body: Never {

Sources/TokamakCore/Fiber/App/AppVisitor.swift

@@ -0,0 +1,21 @@
+// Copyright 2022 Tokamak contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+//  Created by Carson Katri on 5/31/22.
+//
+
+/// A type that can visit an `App`.
+public protocol AppVisitor: ViewVisitor {
+  func visit<A: App>(_ app: A)
+}