Fix Effect.throttle (#654)

* Fix Effect.throttle

Fixes #540.

* Simplify

* Publicize

Author: stephencelis

.swiftpm/xcode/xcshareddata/xcschemes/ComposableArchitecture.xcscheme

@@ -26,7 +26,8 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      shouldUseLaunchSchemeArgsEnv = "YES">
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      codeCoverageEnabled = "YES">
       <Testables>
          <TestableReference
             skipped = "NO">

Sources/ComposableArchitecture/Debugging/ReducerDebugging.swift

@@ -6,24 +6,24 @@ import Dispatch
 public enum ActionFormat {
   /// Prints the action in a single line by only specifying the labels of the associated values:
   ///
-  ///    ```swift
-  ///     Action.screenA(.row(index:, action: .textChanged(query:)))
-  ///    ```
+  /// ```swift
+  /// Action.screenA(.row(index:, action: .textChanged(query:)))
+  /// ```
   ///
   case labelsOnly
   /// Prints the action in a multiline, pretty-printed format, including all the labels of
   /// any associated values, as well as the data held in the associated values:
   ///
-  ///    ```swift
-  ///     Action.screenA(
-  ///       ScreenA.row(
-  ///         index: 1,
-  ///         action: RowAction.textChanged(
-  ///           query: "Hi"
-  ///         )
-  ///       )
+  /// ```swift
+  /// Action.screenA(
+  ///   ScreenA.row(
+  ///     index: 1,
+  ///     action: RowAction.textChanged(
+  ///       query: "Hi"
   ///     )
-  ///    ```
+  ///   )
+  /// )
+  /// ```
   ///
   case prettyPrint
 }

Sources/ComposableArchitecture/Internal/Throttling.swift renamed to Sources/ComposableArchitecture/Effects/Throttling.swift

@@ -2,7 +2,7 @@ import Combine
 import Dispatch
 
 extension Effect {
-  /// Turns an effect into one that can be throttled.
+  /// Throttles an effect so that it only publishes one output per given interval.
   ///
   /// - Parameters:
   ///   - id: The effect's identifier.
@@ -13,7 +13,7 @@ extension Effect {
   ///     `false`, the publisher emits the first element received during the interval.
   /// - Returns: An effect that emits either the most-recent or first element received during the
   ///   specified interval.
-  func throttle<S>(
+  public func throttle<S>(
     id: AnyHashable,
     for interval: S.SchedulerTimeType.Stride,
     scheduler: S,
@@ -26,19 +26,20 @@ extension Effect {
         return Just(value).setFailureType(to: Failure.self).eraseToAnyPublisher()
       }
 
+      let value = latest ? value : (throttleValues[id] as! Output? ?? value)
+      throttleValues[id] = value
+
       guard throttleTime.distance(to: scheduler.now) < interval else {
         throttleTimes[id] = scheduler.now
         throttleValues[id] = nil
         return Just(value).setFailureType(to: Failure.self).eraseToAnyPublisher()
       }
 
-      let value = latest ? value : (throttleValues[id] as! Output? ?? value)
-      throttleValues[id] = value
-
       return Just(value)
         .delay(
           for: scheduler.now.distance(to: throttleTime.advanced(by: interval)), scheduler: scheduler
         )
+        .handleEvents(receiveOutput: { _ in throttleTimes[id] = scheduler.now })
         .setFailureType(to: Failure.self)
         .eraseToAnyPublisher()
     }

Tests/ComposableArchitectureTests/Internal/EffectThrottleTests.swift renamed to Tests/ComposableArchitectureTests/EffectThrottleTests.swift

@@ -134,4 +134,40 @@ final class EffectThrottleTests: XCTestCase {
     // A second value is emitted right away.
     XCTAssertEqual(values, [1, 2])
   }
+
+  func testThrottleEmitsFirstValueOnce() {
+    var values: [Int] = []
+    var effectRuns = 0
+
+    func runThrottledEffect(value: Int) {
+      struct CancelToken: Hashable {}
+
+      Deferred { () -> Just<Int> in
+        effectRuns += 1
+        return Just(value)
+      }
+      .eraseToEffect()
+      .throttle(
+        id: CancelToken(), for: 1, scheduler: scheduler.eraseToAnyScheduler(), latest: false
+      )
+      .sink { values.append($0) }
+      .store(in: &self.cancellables)
+    }
+
+    runThrottledEffect(value: 1)
+
+    // A value emits right away.
+    XCTAssertEqual(values, [1])
+
+    scheduler.advance(by: 0.5)
+
+    runThrottledEffect(value: 2)
+
+    scheduler.advance(by: 0.5)
+
+    runThrottledEffect(value: 3)
+
+    // A second value is emitted right away.
+    XCTAssertEqual(values, [1, 2])
+  }
 }