Add #Preview and @Test traits for overriding dependencies

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
     strategy:
       matrix:
         config: ['debug', 'release']
-        xcode: ['15.4']
+        xcode: ['15.4', '16_beta_6']
     steps:
       - uses: actions/checkout@v4
       - name: Select Xcode ${{ matrix.xcode }}

Dependencies.xcworkspace/xcshareddata/swiftpm/Package.resolved

@@ -77,8 +77,8 @@
       "kind" : "remoteSourceControl",
       "location" : "https://github.com/pointfreeco/xctest-dynamic-overlay",
       "state" : {
-        "revision" : "3fcc3f21695ad5bb889a024b1b046d61bebb1ef3",
-        "version" : "1.3.0"
+        "revision" : "bc2a151366f2cd0e347274544933bc2acb00c9fe",
+        "version" : "1.4.0"
       }
     }
   ],

Package.resolved

@@ -1,5 +1,5 @@
 {
-  "originHash" : "583c00d70f39319a7eca67f614e30ccaab233ad9a104a40007e982cf4584d4d6",
+  "originHash" : "b70d24a284d4a26856cfef0d2ef69b0e2326a2fa8a91e22c08eba0cad0f59bcd",
   "pins" : [
     {
       "identity" : "combine-schedulers",
@@ -78,8 +78,8 @@
       "kind" : "remoteSourceControl",
       "location" : "https://github.com/pointfreeco/xctest-dynamic-overlay",
       "state" : {
-        "branch" : "test-case-parameterization",
-        "revision" : "be48dda989581f65f82e09041b11e12da837c49d"
+        "revision" : "bc2a151366f2cd0e347274544933bc2acb00c9fe",
+        "version" : "1.4.0"
       }
     }
   ],

Package.swift

@@ -25,7 +25,7 @@ let package = Package(
     .package(url: "https://github.com/pointfreeco/combine-schedulers", from: "1.0.2"),
     .package(url: "https://github.com/pointfreeco/swift-clocks", from: "1.0.4"),
     .package(url: "https://github.com/pointfreeco/swift-concurrency-extras", from: "1.0.0"),
-    .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.3.0"),
+    .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.4.0"),
     .package(url: "https://github.com/swiftlang/swift-syntax", "509.0.0"..<"601.0.0-prerelease"),
   ],
   targets: [

Package@swift-6.0.swift

@@ -20,12 +20,16 @@ let package = Package(
       name: "DependenciesMacros",
       targets: ["DependenciesMacros"]
     ),
+    .library(
+      name: "DependenciesTestSupport",
+      targets: ["DependenciesTestSupport"]
+    ),
   ],
   dependencies: [
     .package(url: "https://github.com/pointfreeco/combine-schedulers", from: "1.0.2"),
     .package(url: "https://github.com/pointfreeco/swift-clocks", from: "1.0.4"),
     .package(url: "https://github.com/pointfreeco/swift-concurrency-extras", from: "1.0.0"),
-    .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.3.0"),
+    .package(url: "https://github.com/pointfreeco/xctest-dynamic-overlay", from: "1.4.0"),
     .package(url: "https://github.com/swiftlang/swift-syntax", "509.0.0"..<"601.0.0-prerelease"),
   ],
   targets: [
@@ -45,11 +49,18 @@ let package = Package(
         .product(name: "XCTestDynamicOverlay", package: "xctest-dynamic-overlay"),
       ]
     ),
+    .target(
+      name: "DependenciesTestSupport",
+      dependencies: [
+        "Dependencies",
+      ]
+    ),
     .testTarget(
       name: "DependenciesTests",
       dependencies: [
         "Dependencies",
         "DependenciesMacros",
+        "DependenciesTestSupport",
         .product(name: "IssueReportingTestSupport", package: "xctest-dynamic-overlay"),
       ]
     ),

README.md

@@ -82,10 +82,17 @@ is a good chance you can immediately make use of one. If you are using `Date()`,
 this library.
 
 ```swift
-final class FeatureModel: ObservableObject {
+@Observable
+final class FeatureModel {
+  var items: [Item] = []
+
+  @ObservationIgnored
   @Dependency(\.continuousClock) var clock  // Controllable way to sleep a task
+  @ObservationIgnored
   @Dependency(\.date.now) var now           // Controllable way to ask for current date
+  @ObservationIgnored
   @Dependency(\.mainQueue) var mainQueue    // Controllable scheduling on main queue
+  @ObservationIgnored
   @Dependency(\.uuid) var uuid              // Controllable UUID creation
 
   // ...
@@ -96,16 +103,17 @@ Once your dependencies are declared, rather than reaching out to the `Date()`, `
 directly, you can use the dependency that is defined on your feature's model:
 
 ```swift
-final class FeatureModel: ObservableObject {
+@Observable
+final class FeatureModel {
   // ...
 
   func addButtonTapped() async throws {
-    try await self.clock.sleep(for: .seconds(1))  // 👈 Don't use 'Task.sleep'
-    self.items.append(
+    try await clock.sleep(for: .seconds(1))  // 👈 Don't use 'Task.sleep'
+    items.append(
       Item(
-        id: self.uuid(),  // 👈 Don't use 'UUID()'
+        id: uuid(),  // 👈 Don't use 'UUID()'
         name: "",
-        createdAt: self.now  // 👈 Don't use 'Date()'
+        createdAt: now  // 👈 Don't use 'Date()'
       )
     )
   }
@@ -120,23 +128,22 @@ inside the `addButtonTapped` method, you can use the [`withDependencies`][withde
 function to override any dependencies for the scope of one single test. It's as easy as 1-2-3:
 
 ```swift
-func testAdd() async throws {
-  let model = withDependencies {
+@Test
+func add() async throws {
+  withDependencies {
     // 1️⃣ Override any dependencies that your feature uses.
-    $0.clock = ImmediateClock()
+    $0.clock = .immediate
     $0.date.now = Date(timeIntervalSinceReferenceDate: 1234567890)
     $0.uuid = .incrementing
   } operation: {
     // 2️⃣ Construct the feature's model
     FeatureModel()
   }
-
   // 3️⃣ The model now executes in a controlled environment of dependencies,
   //    and so we can make assertions against its behavior.
   try await model.addButtonTapped()
-  XCTAssertEqual(
-    model.items,
-    [
+  #expect(
+    model.items == [
       Item(
         id: UUID(uuidString: "00000000-0000-0000-0000-000000000000")!,
         name: "",
@@ -158,19 +165,17 @@ But, controllable dependencies aren't only useful for tests. They can also be us
 previews. Suppose the feature above makes use of a clock to sleep for an amount of time before
 something happens in the view. If you don't want to literally wait for time to pass in order to see
 how the view changes, you can override the clock dependency to be an "immediate" clock using the
-[`withDependencies`][withdependencies-docs] helper:
+`.dependencies` preview trait:
 
 ```swift
-struct Feature_Previews: PreviewProvider {
-  static var previews: some View {
-    FeatureView(
-      model: withDependencies {
-        $0.clock = ImmediateClock()
-      } operation: {
-        FeatureModel()
-      }
-    )
+#Preview( 
+  traits: .dependencies {
+    $0.continuousClock = .immediate
   }
+) {
+  // All access of '@Dependency(\.continuousClock)' in this preview will 
+  // use an immediate clock.
+  FeatureView(model: FeatureModel())
 }
 ```
 

Sources/Dependencies/Dependency.swift

@@ -6,9 +6,13 @@
   /// an observable object:
   ///
   /// ```swift
-  /// final class FeatureModel: ObservableObject {
+  /// @Observable
+  /// final class FeatureModel {
+  ///   @ObservationIgnored
   ///   @Dependency(\.apiClient) var apiClient
+  ///   @ObservationIgnored
   ///   @Dependency(\.continuousClock) var clock
+  ///   @ObservationIgnored
   ///   @Dependency(\.uuid) var uuid
   ///
   ///   // ...
@@ -18,7 +22,8 @@
   /// Or, if you are using [the Composable Architecture][tca]:
   ///
   /// ```swift
-  /// struct Feature: ReducerProtocol {
+  /// @Reducer
+  /// struct Feature {
   ///   @Dependency(\.apiClient) var apiClient
   ///   @Dependency(\.continuousClock) var clock
   ///   @Dependency(\.uuid) var uuid
@@ -108,7 +113,9 @@
     /// reflect:
     ///
     /// ```swift
-    /// final class FeatureModel: ObservableObject {
+    /// @Observable
+    /// final class FeatureModel {
+    ///   @ObservationIgnored
     ///   @Dependency(\.date) var date
     ///
     ///   // ...
@@ -158,7 +165,9 @@ extension Dependency {
   /// One can access the dependency using this property wrapper:
   ///
   /// ```swift
-  /// final class FeatureModel: ObservableObject {
+  /// @Observable
+  /// final class FeatureModel {
+  ///   @ObservationIgnored
   ///   @Dependency(Settings.self) var settings
   ///
   ///   // ...

Sources/Dependencies/DependencyKey.swift

@@ -162,14 +162,15 @@ extension DependencyKey {
   /// ``TestDependencyKey``.
   public static var previewValue: Value { Self.liveValue }
 
-  /// A default implementation that provides the ``previewValue`` to XCTest runs (or ``liveValue``,
+  /// A default implementation that provides the ``previewValue`` to test runs (or ``liveValue``,
   /// if no preview value is implemented), but will trigger a test failure when accessed.
   ///
   /// To prevent test failures, explicitly override the dependency in any tests in which it is
   /// accessed:
   ///
   /// ```swift
-  /// func testFeatureThatUsesMyDependency() {
+  /// @Test
+  /// func featureThatUsesMyDependency() {
   ///   withDependencies {
   ///     $0.myDependency = .mock  // Override dependency
   ///   } operation: {

Sources/Dependencies/DependencyValues.swift

@@ -184,6 +184,11 @@ public struct DependencyValues: Sendable {
     #endif
   }
 
+  package init(context: DependencyContext) {
+    self.init()
+    self.context = context
+  }
+
   @_disfavoredOverload
   public subscript<Key: TestDependencyKey>(type: Key.Type) -> Key.Value {
     get { self[type] }
@@ -356,6 +361,8 @@ private let defaultContext: DependencyContext = {
 
 @_spi(Internals)
 public final class CachedValues: @unchecked Sendable {
+  @TaskLocal static var isAccessingOverriddenDependencies = false
+
   public struct CacheKey: Hashable, Sendable {
     let id: TypeIdentifier
     let context: DependencyContext
@@ -397,9 +404,24 @@ public final class CachedValues: @unchecked Sendable {
         case .live:
           value = (key as? any DependencyKey.Type)?.liveValue as? Key.Value
         case .preview:
-          value = Key.previewValue
+          if !CachedValues.isAccessingOverriddenDependencies {
+            value = CachedValues.$isAccessingOverriddenDependencies.withValue(true) {
+              previewValues.withValue { $0[key] }
+            }
+          } else {
+            value = Key.previewValue
+          }
         case .test:
-          value = Key.testValue
+          if !CachedValues.isAccessingOverriddenDependencies,
+            case let .swiftTesting(.some(testing)) = TestContext.current,
+            let testValues = _DependenciesTrait.all.withValue({ $0[testing.test.id.rawValue] })
+          {
+            value = CachedValues.$isAccessingOverriddenDependencies.withValue(true) {
+              testValues[key]
+            }
+          } else {
+            value = Key.testValue
+          }
         }
 
         guard let value

Sources/Dependencies/DependencyValues/Date.swift

@@ -11,7 +11,9 @@ extension DependencyValues {
   /// wrapper to the generator's ``DateGenerator/now`` property:
   ///
   /// ```swift
-  /// final class FeatureModel: ObservableObject {
+  /// @Observable
+  /// final class FeatureModel {
+  ///   @ObservationIgnored
   ///   @Dependency(\.date.now) var now
   ///   // ...
   /// }

Sources/Dependencies/DependencyValues/Locale.swift

@@ -10,7 +10,9 @@ extension DependencyValues {
   /// wrapper to the property:
   ///
   /// ```swift
-  /// final class FeatureModel: ObservableObject {
+  /// @Observable
+  /// final class FeatureModel {
+  ///   @ObservationIgnored
   ///   @Dependency(\.locale) var locale
   ///   // ...
   /// }

Sources/Dependencies/DependencyValues/MainQueue.swift

@@ -12,25 +12,28 @@
     /// For example, you could introduce controllable timing to an observable object model that
     /// counts the number of seconds it's onscreen:
     ///
-    /// ```
-    /// final class TimerModel: ObservableObject {
-    ///   @Published var elapsed = 0
+    /// ```swift
+    /// @Observable
+    /// final class TimerModel {
+    ///   var elapsed = 0
     ///
+    ///   @ObservationIgnored
     ///   @Dependency(\.mainQueue) var mainQueue
     ///
     ///   @MainActor
     ///   func onAppear() async {
-    ///     for await _ in self.mainQueue.timer(interval: .seconds(1)) {
-    ///       self.elapsed += 1
+    ///     for await _ in mainQueue.timer(interval: .seconds(1)) {
+    ///       elapsed += 1
     ///     }
     ///   }
     /// }
     /// ```
     ///
     /// And you could test this model by overriding its main queue with a test scheduler:
     ///
-    /// ```
-    /// func testFeature() {
+    /// ```swift
+    /// @Test
+    /// func feature() {
     ///   let mainQueue = DispatchQueue.test
     ///   let model = withDependencies {
     ///     $0.mainQueue = mainQueue.eraseToAnyScheduler()
@@ -40,10 +43,10 @@
     ///
     ///   Task { await model.onAppear() }
     ///
-    ///   mainQueue.advance(by: .seconds(1))
+    ///   await mainQueue.advance(by: .seconds(1))
     ///   XCTAssertEqual(model.elapsed, 1)
     ///
-    ///   mainQueue.advance(by: .seconds(4))
+    ///   await mainQueue.advance(by: .seconds(4))
     ///   XCTAssertEqual(model.elapsed, 5)
     /// }
     /// ```