Add Scene conformance to WithViewStore (#336)

* Add SceneWithViewStore for accessing stores in scenes

This would allow accessing `ViewStore` instances from a `body` definition of a type conforming to `Scene`. It could be useful for conditional rendering of scenes or sending actions from scene commands. Here's an example:

```swift
import ComposableArchitecture
import SwiftUI

@main
struct CommandsApp: App {
  private let store = Store(
    initialState: RootState(),
    reducer: rootReducer,
    environment: .live(rootEnvironment)
  )

  var body: some Scene {
    SceneWithViewStore(store) { viewStore in
      WindowGroup {
        WorkspaceView()
      }.commands {
        CommandGroup(after: CommandGroupPlacement.newItem) {
          Button("Open...") {
            viewStore.send(.open)
          }.keyboardShortcut("o", modifiers: [.command])
        }
      }
    }
  }
}
```

* Avoid building SceneWithViewStore with old Xcode

* Separate Catalina and Big Sur jobs

This allows testing APIs that are only available on Big Sur

* Unify `WithViewStore` and `SceneWithViewStore`

Author: MaxDesiatov

.github/workflows/ci.yml

@@ -10,13 +10,25 @@ on:
 
 jobs:
   tests:
-    runs-on: macOS-latest
+    runs-on: macos-10.15
     strategy:
       matrix:
         xcode:
           - 11.3
           - 11.7
-          - 12
+    steps:
+      - uses: actions/checkout@v2
+      - name: Select Xcode ${{ matrix.xcode }}
+        run: sudo xcode-select -s /Applications/Xcode_${{ matrix.xcode }}.app
+      - name: Run tests
+        run: make test
+
+  bigsur-tests:
+    runs-on: macos-11.0
+    strategy:
+      matrix:
+        xcode:
+          - 12.3
     steps:
       - uses: actions/checkout@v2
       - name: Select Xcode ${{ matrix.xcode }}

Sources/ComposableArchitecture/SwiftUI/WithViewStore.swift

@@ -17,11 +17,23 @@ import SwiftUI
 ///   inside a `WithViewStore` it will behave erratically. To work around you should use the
 ///   initializer that takes a binding (see
 ///   [here](https://gist.github.com/mbrandonw/dee2ceac2c316a1619cfdf1dc7945f66)).
-public struct WithViewStore<State, Action, Content>: View where Content: View {
+public struct WithViewStore<State, Action, Content> {
   private let content: (ViewStore<State, Action>) -> Content
   private var prefix: String?
   @ObservedObject private var viewStore: ViewStore<State, Action>
 
+  /// Prints debug information to the console whenever the view is computed.
+  ///
+  /// - Parameter prefix: A string with which to prefix all debug messages.
+  /// - Returns: A structure that prints debug messages for all computations.
+  public func debug(_ prefix: String = "") -> Self {
+    var view = self
+    view.prefix = prefix
+    return view
+  }
+}
+
+extension WithViewStore: View where Content: View {
   /// Initializes a structure that transforms a store into an observable view store in order to
   /// compute views from store state.
 
@@ -39,7 +51,7 @@ public struct WithViewStore<State, Action, Content>: View where Content: View {
     self.viewStore = ViewStore(store, removeDuplicates: isDuplicate)
   }
 
-  public var body: some View {
+  public var body: Content {
     #if DEBUG
       if let prefix = self.prefix {
         print(
@@ -52,19 +64,9 @@ public struct WithViewStore<State, Action, Content>: View where Content: View {
     #endif
     return self.content(self.viewStore)
   }
-
-  /// Prints debug information to the console whenever the view is computed.
-  ///
-  /// - Parameter prefix: A string with which to prefix all debug messages.
-  /// - Returns: A structure that prints debug messages for all computations.
-  public func debug(_ prefix: String = "") -> Self {
-    var view = self
-    view.prefix = prefix
-    return view
-  }
 }
 
-extension WithViewStore where State: Equatable {
+extension WithViewStore where Content: View, State: Equatable {
   /// Initializes a structure that transforms a store into an observable view store in order to
   /// compute views from equatable store state.
   ///
@@ -79,7 +81,7 @@ extension WithViewStore where State: Equatable {
   }
 }
 
-extension WithViewStore where State == Void {
+extension WithViewStore where Content: View, State == Void {
   /// Initializes a structure that transforms a store into an observable view store in order to
   /// compute views from equatable store state.
   ///
@@ -101,3 +103,79 @@ extension WithViewStore: DynamicViewContent where State: Collection, Content: Dy
     self.viewStore.state
   }
 }
+
+#if compiler(>=5.3)
+
+import SwiftUI
+
+/// A structure that transforms a store into an observable view store in order to compute scenes from
+/// store state.
+@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
+extension WithViewStore: Scene where Content: Scene {
+  public typealias Body = Content
+
+  /// Initializes a structure that transforms a store into an observable view store in order to
+  /// compute scenes from store state.
+
+  /// - Parameters:
+  ///   - store: A store.
+  ///   - isDuplicate: A function to determine when two `State` values are equal. When values are
+  ///     equal, repeat view computations are removed,
+  ///   - content: A function that can generate content from a view store.
+  public init(
+    _ store: Store<State, Action>,
+    removeDuplicates isDuplicate: @escaping (State, State) -> Bool,
+    @SceneBuilder content: @escaping (ViewStore<State, Action>) -> Content
+  ) {
+    self.content = content
+    self.viewStore = ViewStore(store, removeDuplicates: isDuplicate)
+  }
+
+  public var body: Content {
+    #if DEBUG
+      if let prefix = self.prefix {
+        print(
+          """
+          \(prefix.isEmpty ? "" : "\(prefix): ")\
+          Evaluating WithViewStore<\(State.self), \(Action.self), ...>.body
+          """
+        )
+      }
+    #endif
+    return self.content(self.viewStore)
+  }
+}
+
+@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
+extension WithViewStore where Content: Scene, State: Equatable {
+  /// Initializes a structure that transforms a store into an observable view store in order to
+  /// compute views from equatable store state.
+  ///
+  /// - Parameters:
+  ///   - store: A store of equatable state.
+  ///   - content: A function that can generate content from a view store.
+  public init(
+    _ store: Store<State, Action>,
+    @SceneBuilder content: @escaping (ViewStore<State, Action>) -> Content
+  ) {
+    self.init(store, removeDuplicates: ==, content: content)
+  }
+}
+
+@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
+extension WithViewStore where Content: Scene, State == Void {
+  /// Initializes a structure that transforms a store into an observable view store in order to
+  /// compute views from equatable store state.
+  ///
+  /// - Parameters:
+  ///   - store: A store of equatable state.
+  ///   - content: A function that can generate content from a view store.
+  public init(
+    _ store: Store<State, Action>,
+    @SceneBuilder content: @escaping (ViewStore<State, Action>) -> Content
+  ) {
+    self.init(store, removeDuplicates: ==, content: content)
+  }
+}
+
+#endif