[Freestanding] Disable unsafe continuations.

Author: nate-chandler

stdlib/public/Concurrency/PartialAsyncTask.swift

@@ -35,6 +35,7 @@ public struct UnownedJob: Sendable {
   }
 }
 
+#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 /// A mechanism to interface
 /// between synchronous and asynchronous code,
 /// without correctness checking.
@@ -213,6 +214,46 @@ extension UnsafeContinuation {
     self.resume(returning: ())
   }
 }
+#else
+@available(SwiftStdlib 5.1, *)
+@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+public struct UnsafeContinuation<T, E: Error>: Sendable {
+  @available(SwiftStdlib 5.1, *)
+  @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+  public func resume(returning value: __owned T) where E == Never {
+    fatalError("Unavailable in task-to-thread concurrency model")
+  }
+  @available(SwiftStdlib 5.1, *)
+  @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+  public func resume(returning value: __owned T) {
+    fatalError("Unavailable in task-to-thread concurrency model")
+  }
+  @available(SwiftStdlib 5.1, *)
+  @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+  public func resume(throwing error: __owned E) {
+    fatalError("Unavailable in task-to-thread concurrency model")
+  }
+}
+@available(SwiftStdlib 5.1, *)
+@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+extension UnsafeContinuation {
+  @available(SwiftStdlib 5.1, *)
+  @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+  public func resume<Er: Error>(with result: Result<T, Er>) where E == Error {
+    fatalError("Unavailable in task-to-thread concurrency model")
+  }
+  @available(SwiftStdlib 5.1, *)
+  @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+  public func resume(with result: Result<T, E>) {
+    fatalError("Unavailable in task-to-thread concurrency model")
+  }
+  @available(SwiftStdlib 5.1, *)
+  @available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+  public func resume() where T == Void {
+    fatalError("Unavailable in task-to-thread concurrency model")
+  }
+}
+#endif
 
 #if _runtime(_ObjC)
 
@@ -246,6 +287,8 @@ internal func _resumeUnsafeThrowingContinuationWithError<T>(
 
 #endif
 
+
+#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 /// Suspends the current task,
 /// then calls the given closure with an unsafe continuation for the current task.
 ///
@@ -291,3 +334,20 @@ public func withUnsafeThrowingContinuation<T>(
 public func _abiEnableAwaitContinuation() {
   fatalError("never use this function")
 }
+#else
+@available(SwiftStdlib 5.1, *)
+@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+public func withUnsafeContinuation<T>(
+  _ fn: (UnsafeContinuation<T, Never>) -> Void
+) async -> T {
+    fatalError("Unavailable in task-to-thread concurrency model")
+}
+
+@available(SwiftStdlib 5.1, *)
+@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+public func withUnsafeThrowingContinuation<T>(
+  _ fn: (UnsafeContinuation<T, Error>) -> Void
+) async throws -> T {
+    fatalError("Unavailable in task-to-thread concurrency model")
+}
+#endif

stdlib/public/Concurrency/SourceCompatibilityShims.swift

@@ -385,9 +385,15 @@ extension ThrowingTaskGroup {
   }
 }
 
+#if !SWIFT_STDLIB_TASK_TO_THREAD_MODEL_CONCURRENCY
 @available(SwiftStdlib 5.1, *)
 @available(*, deprecated, message: "please use UnsafeContinuation<..., Error>")
 public typealias UnsafeThrowingContinuation<T> = UnsafeContinuation<T, Error>
+#else
+@available(SwiftStdlib 5.1, *)
+@available(*, unavailable, message: "Unavailable in task-to-thread concurrency model")
+public typealias UnsafeThrowingContinuation<T> = UnsafeContinuation<T, Error>
+#endif
 
 @available(SwiftStdlib 5.1, *)
 @available(*, deprecated, renamed: "UnownedJob")

test/stdlib/freestanding_diags_stdlib.swift

@@ -11,7 +11,8 @@ func chowMein() async {
 @MainActor // expected-error{{not permitted within task-to-thread concurrency model}}
 class ChowMein {}
 
-func foo() async {
+@available(SwiftStdlib 5.1, *)
+func foo() async throws {
   Task<Void, Never> {} // expected-error{{Unavailable in task-to-thread concurrency model}}
   Task<Void, Error> {} // expected-error{{Unavailable in task-to-thread concurrency model}}
   Task<Void, Never>.detached {} // expected-error{{Unavailable in task-to-thread concurrency model}}
@@ -25,12 +26,11 @@ func foo() async {
   asyncDetached { () async throws -> () in } // expected-error{{Unavailable in task-to-thread concurrency model}}
   _ = MainActor.self // expected-error{{Unavailable in task-to-thread concurrency model}}
   let _: Int = await withCheckedContinuation { _ in } // expected-error{{Unavailable in task-to-thread concurrency model}}
-  do {
   let _: Int = try await withCheckedThrowingContinuation { _ in } // expected-error{{Unavailable in task-to-thread concurrency model}}
-  } catch let error {
-    _ = error
-  }
   _ = CheckedContinuation<Int, Never>.self // expected-error{{Unavailable in task-to-thread concurrency model}}
+  let _: Int = await withUnsafeContinuation { _ in } // expected-error{{Unavailable in task-to-thread concurrency model}}
+  let _: Int = try await withUnsafeThrowingContinuation { _ in } // expected-error{{Unavailable in task-to-thread concurrency model}}
+  _ = UnsafeContinuation<Int, Never>.self // expected-error{{Unavailable in task-to-thread concurrency model}}
 }
 
 func foo2(