Add animation operator to Effect. (#1134)

* Add animation operator to Effect.

* Define it only on Effect.

Author: mbrandonw

Sources/ComposableArchitecture/Effects/Animation.swift

@@ -0,0 +1,39 @@
+#if canImport(SwiftUI)
+import ReactiveSwift
+import SwiftUI
+
+extension Effect {
+  /// Wraps the emission of each element with SwiftUI's `withAnimation`.
+  ///
+  /// This publisher is most useful when using with ``Effect/task(priority:operation:)-2czg0``
+  ///
+  /// ```swift
+  /// case .buttonTapped:
+  ///   return .task {
+  ///     .activityResponse(await environment.apiClient.fetchActivity())
+  ///   }
+  ///   .animation()
+  /// ```
+  ///
+  /// - Parameter animation: An animation.
+  /// - Returns: A publisher.
+  public func animation(_ animation: Animation? = .default) -> Self {
+    SignalProducer { observer, _ in
+      self.start { action in
+        switch action {
+        case let .value(value):
+          withAnimation(animation) {
+            observer.send(value: value)
+          }
+        case .completed:
+          observer.sendCompleted()
+        case let .failed(error):
+          observer.send(error: error)
+        case .interrupted:
+          observer.sendInterrupted()
+        }
+      }
+    }
+  }
+}
+#endif

Sources/ComposableArchitecture/TestSupport/TestStore.swift

@@ -175,8 +175,8 @@
 
     /// The current state.
     ///
-    /// When read from a trailing closure assertion in ``send`` or ``receive``, it will equal the
-    /// `inout` state passed to the closure.
+    /// When read from a trailing closure assertion in ``send(_:_:file:line:)`` or
+    /// ``receive(_:_:file:line:)``, it will equal the `inout` state passed to the closure.
     public private(set) var state: State
 
     private let file: StaticString