Store: ObservableObject (#3625)

* Add ObservableObject conformance and related tools.

* wip

* clean up

* wip

* Address flakiness?

---------

Co-authored-by: Brandon Williams <mbrandonw@hey.com>

Author: stephencelis

Examples/TicTacToe/tic-tac-toe/Tests/AppCoreTests/AppCoreTests.swift

@@ -87,6 +87,7 @@ struct AppCoreTests {
         $0.twoFactor?.isTwoFactorRequestInFlight = true
       }
     }
+    .finish()
     await store.receive(\.login.twoFactor.twoFactorResponse.success) {
       $0 = .newGame(NewGame.State())
     }

Sources/ComposableArchitecture/Documentation.docc/Articles/MigrationGuides.md

@@ -14,6 +14,8 @@ APIs, and these guides contain tips to do so.
 
 ## Topics
 
+- <doc:MigratingTo1.19>
+- <doc:MigratingTo1.18>
 - <doc:MigratingTo1.17.1>
 - <doc:MigratingTo1.17>
 - <doc:MigratingTo1.16>

Sources/ComposableArchitecture/Documentation.docc/Articles/MigrationGuides/MigratingTo1.18.md

@@ -0,0 +1,35 @@
+# Migrating to 1.18
+
+Stores now automatically cancel their in-flight effects when they deallocate. And another UIKit
+navigation helper has been introduced.
+
+## An effect lifecycle change
+
+In previous versions of the Composable Architecture, a root store's effects continued to run even
+after the store's lifetime. In 1.18, this leak has been fixed, and a root store's effects will be
+cancelled when the store deallocates.
+
+If you depend on a store's fire-and-forget effect to outlive the store, for example if you want to
+ensure an analytics or persistence effect proceeds without cancellation, perform this work in an
+unstructured task, instead:
+
+```diff
+ return .run { _ in
+-  await analytics.track(/* ... */)
++  Task {
++    await analytics.track(/* ... */)
++  }
+ }
+```
+
+## A UIKit navigation helper
+
+Our [Swift Navigation](https://github.com/pointfreeco/swift-navigation) library ships with many
+UIKit tools, and the Composable Architecture integrates with many of them, but up till now it has
+lacked support for trait-based navigation by pushing an element of ``StackState``.
+
+This has been fixed with a new endpoint on the `push` trait that takes a `state` parameter:
+
+```swift
+traitCollection.push(state: Path.State.detail(/* ... */))
+```

Sources/ComposableArchitecture/Documentation.docc/Articles/MigrationGuides/MigratingTo1.19.md

@@ -0,0 +1,60 @@
+# Migrating to 1.19
+
+Store internals have been rewritten for performance and future features, and are now compatible with
+SwiftUI's `@StateObject` property wrapper.
+
+## Overview
+
+There are no steps needed to migrate to 1.19 of the Composable Architecture, but there are a number
+of changes and improvements that have been made to the `Store` that one should be aware of.
+
+## Store internals rewrite
+
+The store's internals have been rewritten to improved performance and to pave the way for future
+features. While this should not be a breaking change, with any rewrite it is important to thoroughly
+test your application after upgrading.
+
+## StateObject compatibility
+
+SwiftUI's `@State` and `@StateObject` allow a view to own a value or object over time, ensuring that
+when a parent view is recomputed, the view-local state isn't recreated from scratch.
+
+One important difference between `@State` and `@StateObject` is that `@State`'s initializer is
+eager, while `@StateObject`'s is lazy. Because of this, if you initialize a root `Store` to be held
+in `@State`, stores will be initialized (and immediately discarded) whenever the parent view's body
+is computed.
+
+To avoid the creation of these stores, one can now assign the store to a `@StateObject`, instead:
+
+```swift
+struct FeatureView: View {
+  @StateObject var store: StoreOf<Feature>
+
+  init() {
+    _store = StateObject(
+      // This expression is only evaluated the first time the parent view is computed.
+      wrappedValue: Store(initialState: Feature.State()) {
+        Feature()
+      }
+    )
+  }
+
+  var body: some View { /* ... */ }
+}
+```
+
+> Important: The store's `ObservableObject` conformance does not have any impact on the actual
+> observability of the store. You should continue to rely on the ``ObservableState()`` macro for
+> observation.
+
+## Initial actions
+
+A new `initialAction` has been introduced to the `Store` that will immediately kick off an initial
+action when the store is created. This is an alternative to waiting for an `onAppear` or `task`
+view modifier to evaluate.
+
+```swift
+Store(initialState: Feature.State(), initialAction: .initialize) {
+  Feature()
+}
+```

Sources/ComposableArchitecture/Observation/Binding+Observation.swift

@@ -10,6 +10,16 @@ extension Binding {
   }
 }
 
+extension ObservedObject.Wrapper {
+  @_disfavoredOverload
+  public subscript<State: ObservableState, Action, Member>(
+    dynamicMember keyPath: KeyPath<State, Member>
+  ) -> _StoreObservedObject<State, Action, Member>
+  where ObjectType == Store<State, Action> {
+    _StoreObservedObject(wrapper: self, keyPath: keyPath)
+  }
+}
+
 extension UIBinding {
   @_disfavoredOverload
   public subscript<State: ObservableState, Action, Member>(
@@ -272,6 +282,34 @@ public struct _StoreBinding<State: ObservableState, Action, Value> {
   }
 }
 
+@dynamicMemberLookup
+public struct _StoreObservedObject<State: ObservableState, Action, Value> {
+  fileprivate let wrapper: ObservedObject<Store<State, Action>>.Wrapper
+  fileprivate let keyPath: KeyPath<State, Value>
+
+  public subscript<Member>(
+    dynamicMember keyPath: KeyPath<Value, Member>
+  ) -> _StoreObservedObject<State, Action, Member> {
+    _StoreObservedObject<State, Action, Member>(
+      wrapper: wrapper,
+      keyPath: self.keyPath.appending(path: keyPath)
+    )
+  }
+
+  /// Creates a binding to the value by sending new values through the given action.
+  ///
+  /// - Parameter action: An action for the binding to send values through.
+  /// - Returns: A binding.
+  #if swift(<5.10)
+    @MainActor(unsafe)
+  #else
+    @preconcurrency@MainActor
+  #endif
+  public func sending(_ action: CaseKeyPath<Action, Value>) -> Binding<Value> {
+    self.wrapper[state: self.keyPath, action: action]
+  }
+}
+
 @dynamicMemberLookup
 public struct _StoreUIBinding<State: ObservableState, Action, Value> {
   fileprivate let binding: UIBinding<Store<State, Action>>

Sources/ComposableArchitecture/Observation/NavigationStack+Observation.swift

@@ -70,6 +70,21 @@ extension Binding {
   }
 }
 
+extension ObservedObject.Wrapper {
+#if swift(>=5.10)
+  @preconcurrency@MainActor
+#else
+  @MainActor(unsafe)
+#endif
+  public func scope<State: ObservableState, Action, ElementState, ElementAction>(
+    state: KeyPath<State, StackState<ElementState>>,
+    action: CaseKeyPath<Action, StackAction<ElementState, ElementAction>>
+  ) -> Binding<Store<StackState<ElementState>, StackAction<ElementState, ElementAction>>>
+  where ObjectType == Store<State, Action> {
+    self[state: state, action: action]
+  }
+}
+
 @available(iOS 17, macOS 14, tvOS 17, watchOS 10, *)
 extension SwiftUI.Bindable {
   /// Derives a binding to a store focused on ``StackState`` and ``StackAction``.

Sources/ComposableArchitecture/Observation/Store+Observation.swift

@@ -193,6 +193,45 @@ extension Binding {
   }
 }
 
+extension ObservedObject.Wrapper {
+  #if swift(>=5.10)
+    @preconcurrency@MainActor
+  #else
+    @MainActor(unsafe)
+  #endif
+  public func scope<State: ObservableState, Action, ChildState, ChildAction>(
+    state: KeyPath<State, ChildState?>,
+    action: CaseKeyPath<Action, PresentationAction<ChildAction>>,
+    fileID: StaticString = #fileID,
+    filePath: StaticString = #fileID,
+    line: UInt = #line,
+    column: UInt = #column
+  ) -> Binding<Store<ChildState, ChildAction>?>
+  where ObjectType == Store<State, Action> {
+    self[
+      dynamicMember:
+        \.[
+          id: self[dynamicMember: \._currentState].wrappedValue[keyPath: state]
+            .flatMap(_identifiableID),
+          state: state,
+          action: action,
+          isInViewBody: _isInPerceptionTracking,
+          fileID: _HashableStaticString(rawValue: fileID),
+          filePath: _HashableStaticString(rawValue: filePath),
+          line: line,
+          column: column
+        ]
+    ]
+  }
+}
+
+extension Store {
+  fileprivate var _currentState: State {
+    get { currentState }
+    set {}
+  }
+}
+
 @available(iOS 17, macOS 14, tvOS 17, watchOS 10, *)
 extension SwiftUI.Bindable {
   /// Scopes the binding of a store to a binding of an optional presentation store.

Sources/ComposableArchitecture/Store.swift

@@ -131,6 +131,16 @@ import SwiftUI
 /// to run only on the main thread, and so a check is executed immediately to make sure that is the
 /// case. Further, all actions sent to the store and all scopes (see ``scope(state:action:)-90255``)
 /// of the store are also checked to make sure that work is performed on the main thread.
+///
+/// ### ObservableObject conformance
+///
+/// The store conforms to `ObservableObject` but is _not_ observable via the `@ObservedObject`
+/// property wrapper. This conformance is completely inert and its sole purpose is to allow stores
+/// to be held in SwiftUI's `@StateObject` property wrapper.
+///
+/// Instead, stores should be observed through Swift's Observation framework (or the Perception
+/// package when targeting iOS <17) by applying the ``ObservableState()`` macro to your feature's
+/// state.
 @dynamicMemberLookup
 #if swift(<5.10)
   @MainActor(unsafe)
@@ -416,6 +426,8 @@ extension Store: CustomDebugStringConvertible {
   }
 }
 
+extension Store: ObservableObject {}
+
 /// A convenience type alias for referring to a store of a given reducer's domain.
 ///
 /// Instead of specifying two generics:

Tests/ComposableArchitectureTests/Internal/BaseTCATestCase.swift

@@ -4,7 +4,8 @@ import XCTest
 class BaseTCATestCase: XCTestCase {
   override func tearDown() async throws {
     try await super.tearDown()
-    _cancellationCancellables.withValue { [description = "\(self)"] in
+    let description = "\(self)"
+    _cancellationCancellables.withValue { 
       XCTAssertEqual($0.count, 0, description)
       $0.removeAll()
     }

Tests/ComposableArchitectureTests/Reducers/PresentationReducerTests.swift

@@ -2634,20 +2634,20 @@ final class PresentationReducerTests: BaseTCATestCase {
         .ifLet(\.$alert, action: /Action.alert)
       }
     }
-    @MainActor
-    func testEphemeralBindingDismissal() async {
-      @Perception.Bindable var store = Store(
-        initialState: TestEphemeralBindingDismissalFeature.State(
-          alert: AlertState { TextState("Oops!") }
-        )
-      ) {
-        TestEphemeralBindingDismissalFeature()
-      }
-
-      XCTAssertNotNil(store.alert)
-      $store.scope(state: \.alert, action: \.alert).wrappedValue = nil
-      XCTAssertNil(store.alert)
-    }
+//    @MainActor
+//    func testEphemeralBindingDismissal() async {
+//      @Perception.Bindable var store = Store(
+//        initialState: TestEphemeralBindingDismissalFeature.State(
+//          alert: AlertState { TextState("Oops!") }
+//        )
+//      ) {
+//        TestEphemeralBindingDismissalFeature()
+//      }
+//
+//      XCTAssertNotNil(store.alert)
+//      $store.scope(state: \.alert, action: \.alert).wrappedValue = nil
+//      XCTAssertNil(store.alert)
+//    }
   #endif
 }