[SE-0392] Back-deploy assertIsolation/assumeIsolation

The assertIsolation/assumeIsolation operations on actors are
back-deployable back to the introduction of concurrency. Do so.

Resolves rdar://111880539

Author: DougGregor

stdlib/public/Concurrency/ExecutorAssertions.swift

@@ -18,7 +18,7 @@ import SwiftShims
 // ==== -----------------------------------------------------------------------
 // MARK: Precondition executors
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension SerialExecutor {
   /// Unconditionally if the current task is executing on the expected serial executor,
   /// and if not crash the program offering information about the executor mismatch.
@@ -35,7 +35,8 @@ extension SerialExecutor {
   /// * In `-Ounchecked` builds, the optimizer may assume that this function is
   ///   never called. Failure to satisfy that assumption is a serious
   ///   programming error.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   public func preconditionIsolated(
       _ message: @autoclosure () -> String = String(),
       file: StaticString = #fileID, line: UInt = #line
@@ -54,7 +55,7 @@ extension SerialExecutor {
   }
 }
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension Actor {
   /// Unconditionally if the current task is executing on the serial executor of the passed in `actor`,
   /// and if not crash the program offering information about the executor mismatch.
@@ -71,7 +72,8 @@ extension Actor {
   /// * In `-Ounchecked` builds, the optimizer may assume that this function is
   ///   never called. Failure to satisfy that assumption is a serious
   ///   programming error.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   public nonisolated func preconditionIsolated(
       _ message: @autoclosure () -> String = String(),
       file: StaticString = #fileID, line: UInt = #line
@@ -90,7 +92,7 @@ extension Actor {
   }
 }
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension GlobalActor {
   /// Unconditionally if the current task is executing on the serial executor of the passed in `actor`,
   /// and if not crash the program offering information about the executor mismatch.
@@ -107,7 +109,8 @@ extension GlobalActor {
   /// * In `-Ounchecked` builds, the optimizer may assume that this function is
   ///   never called. Failure to satisfy that assumption is a serious
   ///   programming error.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   public static func preconditionIsolated(
       _ message: @autoclosure () -> String = String(),
       file: StaticString = #fileID, line: UInt = #line
@@ -119,7 +122,7 @@ extension GlobalActor {
 // ==== -----------------------------------------------------------------------
 // MARK: Assert executors
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension SerialExecutor {
   /// Performs an executor check in debug builds.
   ///
@@ -133,7 +136,8 @@ extension SerialExecutor {
   /// * In `-Ounchecked` builds, `condition` is not evaluated, but the optimizer
   ///   may assume that it *always* evaluates to `true`. Failure to satisfy that
   ///   assumption is a serious programming error.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   public func assertIsolated(
       _ message: @autoclosure () -> String = String(),
       file: StaticString = #fileID, line: UInt = #line
@@ -152,7 +156,7 @@ extension SerialExecutor {
   }
 }
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension Actor {
   /// Performs an executor check in debug builds.
   ///
@@ -166,7 +170,8 @@ extension Actor {
   /// * In `-Ounchecked` builds, `condition` is not evaluated, but the optimizer
   ///   may assume that it *always* evaluates to `true`. Failure to satisfy that
   ///   assumption is a serious programming error.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   public nonisolated func assertIsolated(
       _ message: @autoclosure () -> String = String(),
       file: StaticString = #fileID, line: UInt = #line
@@ -186,7 +191,7 @@ extension Actor {
   }
 }
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension GlobalActor {
   /// Performs an executor check in debug builds.
   ///
@@ -200,7 +205,8 @@ extension GlobalActor {
   /// * In `-Ounchecked` builds, `condition` is not evaluated, but the optimizer
   ///   may assume that it *always* evaluates to `true`. Failure to satisfy that
   ///   assumption is a serious programming error.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   public static func assertIsolated(
       _ message: @autoclosure () -> String = String(),
       file: StaticString = #fileID, line: UInt = #line
@@ -212,7 +218,7 @@ extension GlobalActor {
 // ==== -----------------------------------------------------------------------
 // MARK: Assume Executor
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension Actor {
   /// A safe way to synchronously assume that the current execution context belongs to the passed in actor.
   ///
@@ -227,7 +233,8 @@ extension Actor {
   /// if another actor uses the same serial executor--by using that actor's ``Actor/unownedExecutor``
   /// as its own ``Actor/unownedExecutor``--this check will succeed, as from a concurrency safety
   /// perspective, the serial executor guarantees mutual exclusion of those two actors.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   @_unavailableFromAsync(message: "express the closure as an explicit function declared on the specified 'actor' instead")
   public nonisolated func assumeIsolated<T>(
       _ operation: (isolated Self) throws -> T,
@@ -253,4 +260,4 @@ extension Actor {
   }
 }
 
-#endif // not SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
+#endif // not SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY

stdlib/public/Concurrency/MainActor.swift

@@ -99,7 +99,7 @@ extension MainActor {
   }
 }
 
-@available(SwiftStdlib 5.9, *)
+@available(SwiftStdlib 5.1, *)
 extension MainActor {
   /// A safe way to synchronously assume that the current execution context belongs to the MainActor.
   ///
@@ -114,7 +114,8 @@ extension MainActor {
   /// if another actor uses the same serial executor--by using ``MainActor/sharedUnownedExecutor``
   /// as its own ``Actor/unownedExecutor``--this check will succeed, as from a concurrency safety
   /// perspective, the serial executor guarantees mutual exclusion of those two actors.
-  @available(SwiftStdlib 5.9, *)
+  @available(SwiftStdlib 5.1, *)
+  @backDeployed(before: SwiftStdlib 5.9)
   @_unavailableFromAsync(message: "await the call to the @MainActor closure directly")
   public static func assumeIsolated<T>(
       _ operation: @MainActor () throws -> T,

test/Concurrency/Runtime/actor_assume_executor.swift

@@ -100,7 +100,7 @@ final class MainActorEcho {
 
     let echo = MainActorEcho()
 
-    if #available(SwiftStdlib 5.9, *) {
+    if #available(SwiftStdlib 5.1, *) {
       // === MainActor --------------------------------------------------------
 
       tests.test("MainActor.assumeIsolated: assume the main executor, from 'main() async'") {