Undeprecate preview traits? (#353)

* Undeprecate preview traits

* wip

* docs

Author: stephencelis

README.md

@@ -164,15 +164,11 @@ and `UUID()`, and we'd have to wait for real world time to pass, making the test
 But, controllable dependencies aren't only useful for tests. They can also be used in Xcode
 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
-`prepareDependencies`:
+how the view changes, you can override the clock dependency to be an "immediate" clock using the
+`.dependencies` preview trait:
 
 ```swift
-#Preview {
-  let _ = prepareDependencies {
-    $0.continuousClock = .immediate
-  }
-
+#Preview(trait: .dependencies { $0.continuousClock = ImmediateClock() }) {
   // All access of '@Dependency(\.continuousClock)' in this preview will 
   // use an immediate clock.
   FeatureView(model: FeatureModel())

Sources/Dependencies/DependencyValues.swift

@@ -579,11 +579,7 @@ public final class CachedValues: @unchecked Sendable {
           }
           if !CachedValues.isAccessingCachedDependencies {
             value = CachedValues.$isAccessingCachedDependencies.withValue(true) {
-              #if canImport(SwiftUI) && compiler(>=6)
-                return previewValues[key]
-              #else
-                return Key.previewValue
-              #endif
+              return Key.previewValue
             }
           } else {
             value = Key.previewValue

Sources/Dependencies/Documentation.docc/Articles/Lifetimes.md

@@ -218,10 +218,9 @@ feature behaves in very specific states. For example, if you wanted to see how y
 when the `fetchUser` endpoint throws an error, you can update the preview like so:
 
 ```swift
-#Preview {
-  let _ = prepareDependencies {
-    $0.apiClient.fetchUser = { _ in throw SomeError() }
-  }
+#Preview(traits: .dependencies {
+  $0.apiClient.fetchUser = { _ in throw SomeError() }
+}) {
   FeatureView(model: FeatureModel())
 }
 ```

Sources/Dependencies/Documentation.docc/Articles/LivePreviewTest.md

@@ -306,3 +306,8 @@ func testFeature() {
 [unimplemented-docs]: https://pointfreeco.github.io/xctest-dynamic-overlay/main/documentation/xctestdynamicoverlay/unimplemented(_:fileid:line:)-5098a
 [issue-reporting-gh]: http://github.com/pointfreeco/xctest-dynamic-overlay
 
+## Topics
+
+### Previews
+
+- ``DeveloperToolsSupport/PreviewTrait``

Sources/Dependencies/Documentation.docc/Articles/QuickStart.md

@@ -118,15 +118,11 @@ and `UUID()`, and we'd have to wait for real world time to pass, making the test
 But, controllable dependencies aren't only useful for tests. They can also be used in Xcode
 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
-``prepareDependencies(_:)``:
+how the view changes, you can override the clock dependency to be an "immediate" clock using the
+``DeveloperToolsSupport/PreviewTrait/dependencies(_:)`` preview trait:
 
 ```swift
-#Preview {
-  let _ = prepareDependencies {
-    $0.continuousClock = .immediate
-  }
-
+#Preview(trait: .dependencies { $0.continuousClock = ImmediateClock() }) {
   // All access of '@Dependency(\.continuousClock)' in this preview will
   // use an immediate clock.
   FeatureView(model: FeatureModel())

Sources/Dependencies/Documentation.docc/Articles/WhatAreDependencies.md

@@ -104,10 +104,7 @@ For previews, you can use the `.dependencies` preview trait to override the
 does not actually sleep for any amount of time:
 
 ```swift
-#Preview {
-  let _ = prepareDependencies {
-    $0.continuousClock = .immediate
-  }
+#Preview(traits: .dependencies { $0.continuousClock = ImmediateClock() }) {
   FeatureView(model: FeatureModel())
 }
 ```

Sources/Dependencies/Internal/Deprecations.swift

@@ -1,57 +1,3 @@
-// MARK: - Deprecated after 1.6.3
-
-#if canImport(SwiftUI) && compiler(>=6)
-  import SwiftUI
-
-  @available(iOS 18, macOS 15, tvOS 18, watchOS 11, visionOS 2, *)
-  extension PreviewTrait where T == Preview.ViewTraits {
-    @available(
-      *, deprecated,
-      message: """
-        Use 'withDependencies' or 'prepareDependencies' from the body of the preview, instead.
-        """
-    )
-    @_documentation(visibility: private)
-    public static func dependency<Value>(
-      _ keyPath: WritableKeyPath<DependencyValues, Value> & Sendable,
-      _ value: Value
-    ) -> PreviewTrait {
-      .dependencies { $0[keyPath: keyPath] = value }
-    }
-
-    @available(
-      *, deprecated,
-      message: """
-        Use 'withDependencies' or 'prepareDependencies' from the body of the preview, instead.
-        """
-    )
-    @_documentation(visibility: private)
-    public static func dependency<Value: TestDependencyKey>(
-      _ value: Value
-    ) -> PreviewTrait where Value == Value.Value {
-      .dependencies { $0[Value.self] = value }
-    }
-
-    @available(
-      *, deprecated,
-      message: """
-        Use 'withDependencies' or 'prepareDependencies' from the body of the preview, instead.
-        """
-    )
-    @_documentation(visibility: private)
-    public static func dependencies(
-      _ updateValuesForPreview: (inout DependencyValues) -> Void
-    ) -> PreviewTrait {
-      var copy = previewValues
-      defer { previewValues = copy }
-      updateValuesForPreview(&copy)
-      return PreviewTrait()
-    }
-  }
-
-  nonisolated(unsafe) var previewValues = DependencyValues(context: .preview)
-#endif
-
 // MARK: - Deprecated after 0.4.2
 
 extension AsyncStream {

Sources/Dependencies/Traits/PreviewTrait.swift

@@ -1 +1,34 @@
+#if canImport(SwiftUI) && compiler(>=6)
+  import SwiftUI
 
+  @available(iOS 18, macOS 15, tvOS 18, watchOS 11, visionOS 2, *)
+  extension PreviewTrait where T == Preview.ViewTraits {
+    public static func dependency<Value>(
+      _ keyPath: WritableKeyPath<DependencyValues, Value> & Sendable,
+      _ value: @autoclosure @escaping @Sendable () -> Value
+    ) -> PreviewTrait {
+      .dependencies { $0[keyPath: keyPath] = value() }
+    }
+
+    public static func dependency<Value: TestDependencyKey>(
+      _ value: Value
+    ) -> PreviewTrait where Value == Value.Value {
+      .dependencies { $0[Value.self] = value }
+    }
+
+    public static func dependencies(
+      _ updateValuesForPreview: @escaping @Sendable (inout DependencyValues) -> Void
+    ) -> PreviewTrait {
+      return .modifier(DependenciesPreviewModifier(updateValuesForPreview: updateValuesForPreview))
+    }
+  }
+
+  private struct DependenciesPreviewModifier: PreviewModifier {
+    let updateValuesForPreview: @Sendable (inout DependencyValues) -> Void
+
+    func body(content: Content, context: ()) -> some View {
+      prepareDependencies(updateValuesForPreview)
+      return content
+    }
+  }
+#endif