Add Clock.sleep(for:).

Author: mbrandonw

stdlib/public/Concurrency/Clock.swift

@@ -76,6 +76,20 @@ extension Clock {
     return start.duration(to: end)
   }
 }
+extension Clock {
+  /// Suspends for the given duration.
+  ///
+  /// Prefer to use the `sleep(until:tolerance:)` method on `Clock` if you have access to an 
+  /// absolute instant. 
+  @available(SwiftStdlib 5.7, *)
+  @_alwaysEmitIntoClient
+  public func sleep(
+    for duration: Instant.Duration,
+    tolerance: Instant.Duration? = nil
+  ) async throws {
+    try await self.sleep(until: self.now.advanced(by: duration), tolerance: tolerance)
+  }
+}
 
 enum _ClockID: Int32 {
   case continuous = 1

stdlib/public/Concurrency/TaskSleepDuration.swift

@@ -139,7 +139,7 @@ extension Task where Success == Never, Failure == Never {
   public static func sleep<C: Clock>(
     until deadline: C.Instant,
     tolerance: C.Instant.Duration? = nil,
-    clock: C
+    clock: C = ContinuousClock()
   ) async throws {
     try await clock.sleep(until: deadline, tolerance: tolerance)
   }
@@ -156,8 +156,12 @@ extension Task where Success == Never, Failure == Never {
   /// - Parameter duration: The duration to wait.
   @available(SwiftStdlib 5.7, *)
   @_alwaysEmitIntoClient
-  public static func sleep(for duration: Duration) async throws {
-    try await sleep(until: .now + duration, clock: .continuous)
+  public static func sleep<C: Clock>(
+    for duration: C.Instant.Duration,
+    tolerance: C.Instant.Duration? = nil,
+    clock: C = ContinuousClock()
+  ) async throws {
+    try await sleep(until: clock.now.advanced(by: duration), tolerance: tolerance, clock: clock)
   }
 }
 #else
@@ -169,13 +173,17 @@ extension Task where Success == Never, Failure == Never {
   public static func sleep<C: Clock>(
     until deadline: C.Instant,
     tolerance: C.Instant.Duration? = nil,
-    clock: C
+    clock: C = ContinuousClock()
   ) async throws {
     fatalError("Unavailable in task-to-thread concurrency model")
   }
   @available(SwiftStdlib 5.7, *)
   @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
-  public static func sleep(for duration: Duration) async throws {
+  public static func sleep<C: Clock>(
+    for duration: C.Instant.Duration,
+    tolerance: C.Instant.Duration? = nil,
+    clock: C = ContinuousClock()
+  ) async throws {
     fatalError("Unavailable in task-to-thread concurrency model")
   }
 }