[Concurrency] Disable various things for task-to-thread model.

When in task-to-thread model concurrency mode, there is no `MainActor`
and we cannot use `ExecutorJob`, so disable various things.

rdar://141348916

stdlib/public/Concurrency/CooperativeExecutor.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
+
 import Swift
 
 // Store the Timestamp in the executor private data, if it will fit; otherwise,
@@ -255,3 +257,5 @@ extension CooperativeExecutor: TaskExecutor {}
 
 @available(SwiftStdlib 6.2, *)
 extension CooperativeExecutor: MainExecutor {}
+
+#endif // !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY

stdlib/public/Concurrency/DummyExecutor.swift

@@ -26,9 +26,15 @@ public final class DummyMainExecutor: MainExecutor, @unchecked Sendable {
     fatalError("There is no executor implementation active")
   }
 
+  #if SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
+  public func enqueue(_ job: UnownedJob) {
+    fatalError("There is no executor implementation active")
+  }
+  #else
   public func enqueue(_ job: consuming ExecutorJob) {
     fatalError("There is no executor implementation active")
   }
+  #endif
 
   public var isMainExecutor: Bool { true }
 
@@ -43,9 +49,15 @@ public final class DummyMainExecutor: MainExecutor, @unchecked Sendable {
 public final class DummyTaskExecutor: TaskExecutor, @unchecked Sendable {
   public init() {}
 
+  #if SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
+  public func enqueue(_ job: UnownedJob) {
+    fatalError("There is no executor implementation active")
+  }
+  #else
   public func enqueue(_ job: consuming ExecutorJob) {
     fatalError("There is no executor implementation active")
   }
+  #endif
 
   public var isMainExecutor: Bool { false }
 }

stdlib/public/Concurrency/Executor.swift

@@ -36,7 +36,7 @@ public protocol Executor: AnyObject, Sendable {
   func enqueue(_ job: consuming ExecutorJob)
   #endif // !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 
-  #if !$Embedded
+  #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
   // The functions below could have been added to a separate protocol,
   // but doing that would then mean doing an `as?` cast in e.g.
   // enqueueOnGlobalExecutor (in ExecutorBridge.swift), which is
@@ -51,7 +51,7 @@ public protocol Executor: AnyObject, Sendable {
 @available(SwiftStdlib 6.2, *)
 public protocol SchedulableExecutor: Executor {
 
-  #if !$Embedded
+  #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 
   /// Enqueue a job to run after a specified delay.
   ///
@@ -94,7 +94,7 @@ public protocol SchedulableExecutor: Executor {
                          tolerance: C.Duration?,
                          clock: C)
 
-  #endif // !$Embedded
+  #endif // !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 
 }
 
@@ -125,7 +125,7 @@ extension Executor where Self: Equatable {
 
 extension Executor {
 
-  #if !$Embedded
+  #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
   // This defaults to `false` so that existing third-party Executor
   // implementations will work as expected.
   @available(SwiftStdlib 6.2, *)
@@ -138,7 +138,7 @@ extension Executor {
 @available(SwiftStdlib 6.2, *)
 extension SchedulableExecutor {
 
-  #if !$Embedded
+  #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 
   @available(SwiftStdlib 6.2, *)
   public func enqueue<C: Clock>(_ job: consuming ExecutorJob,
@@ -162,7 +162,7 @@ extension SchedulableExecutor {
             tolerance: tolerance, clock: clock)
   }
 
-  #endif // !$Embedded
+  #endif // !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 }
 
 /// A service that executes jobs.
@@ -331,7 +331,7 @@ public protocol SerialExecutor: Executor {
 @available(SwiftStdlib 6.0, *)
 extension SerialExecutor {
 
-  #if !$Embedded
+  #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
   @available(SwiftStdlib 6.2, *)
   public var isMainExecutor: Bool { return MainActor.executor._isSameExecutor(self) }
   #endif
@@ -542,13 +542,13 @@ public protocol ExecutorFactory {
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_createExecutors")
 public func _createExecutors<F: ExecutorFactory>(factory: F.Type) {
-  #if !$Embedded
+  #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
   MainActor._executor = factory.mainExecutor
   #endif
   Task._defaultExecutor = factory.defaultExecutor
 }
 
-#if !$Embedded
+#if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 extension MainActor {
   @available(SwiftStdlib 6.2, *)
   static var _executor: (any MainExecutor)? = nil
@@ -566,7 +566,7 @@ extension MainActor {
     return _executor!
   }
 }
-#endif // !$Embedded
+#endif // !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 
 extension Task where Success == Never, Failure == Never {
   @available(SwiftStdlib 6.2, *)

stdlib/public/Concurrency/ExecutorBridge.swift

@@ -21,7 +21,7 @@ import Swift
 @_silgen_name("_swift_exit")
 internal func _exit(result: CInt)
 
-#if !$Embedded
+#if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("_swift_task_isMainExecutorSwift")
 internal func _isMainExecutor<E>(_ executor: E) -> Bool where E: SerialExecutor {
@@ -79,7 +79,7 @@ internal func _jobGetExecutorPrivateData(
   _ job: Builtin.Job
 ) -> UnsafeMutableRawPointer
 
-#if !$Embedded
+#if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_getMainExecutor")
 internal func _getMainExecutor() -> any MainExecutor {

stdlib/public/Concurrency/ExecutorImpl.swift

@@ -20,12 +20,14 @@
 
 import Swift
 
+#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_task_asyncMainDrainQueueImpl")
 internal func drainMainQueue() {
   try! MainActor.executor.run()
   _exit(result: 0)
 }
+#endif
 
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_task_donateThreadToGlobalExecutorUntilImpl")
@@ -40,6 +42,7 @@ internal func dontateToGlobalExecutor(
   }
 }
 
+#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_task_getMainExecutorImpl")
 internal func getMainExecutor() -> UnownedSerialExecutor {
@@ -51,14 +54,15 @@ internal func getMainExecutor() -> UnownedSerialExecutor {
 internal func enqueueOnMainExecutor(job unownedJob: UnownedJob) {
   MainActor.executor.enqueue(unownedJob)
 }
+#endif
 
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_task_enqueueGlobalImpl")
 internal func enqueueOnGlobalExecutor(job unownedJob: UnownedJob) {
   Task.defaultExecutor.enqueue(unownedJob)
 }
 
-#if !$Embedded
+#if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_task_enqueueGlobalWithDelayImpl")
 internal func enqueueOnGlobalExecutor(delay: CUnsignedLongLong,

stdlib/public/Concurrency/MainActor.swift

@@ -22,12 +22,12 @@ import Swift
 
   @inlinable
   public nonisolated var unownedExecutor: UnownedSerialExecutor {
-    return UnownedSerialExecutor(Builtin.buildMainActorExecutorRef())
+    return unsafe UnownedSerialExecutor(Builtin.buildMainActorExecutorRef())
   }
 
   @inlinable
   public static var sharedUnownedExecutor: UnownedSerialExecutor {
-    return UnownedSerialExecutor(Builtin.buildMainActorExecutorRef())
+    return unsafe UnownedSerialExecutor(Builtin.buildMainActorExecutorRef())
   }
 
   @inlinable

stdlib/public/Concurrency/PlatformExecutorDarwin.swift

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if !$Embedded && (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS))
+#if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY && (os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS))
 
 import Swift
 

stdlib/public/Concurrency/Task.swift

@@ -1254,7 +1254,7 @@ extension Task where Success == Never, Failure == Never {
           priority: Int(Task.currentPriority.rawValue),
           continuation: continuation)
 
-      #if !$Embedded
+      #if !$Embedded && !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
       if #available(SwiftStdlib 6.2, *) {
         let executor = Task.currentExecutor