[Concurrency] tasklocal withValue inside actor is safe

Author: ktoso

stdlib/public/BackDeployConcurrency/TaskLocal.swift

@@ -134,8 +134,9 @@ public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible
   ///
   /// If the value is a reference type, it will be retained for the duration of
   /// the operation closure.
+  @Sendable
   @discardableResult
-  public func withValue<R>(_ valueDuringOperation: Value, operation: () async throws -> R,
+  public func withValue<R>(_ valueDuringOperation: Value, operation: @Sendable () async throws -> R,
                            file: String = #file, line: UInt = #line) async rethrows -> R {
     // check if we're not trying to bind a value from an illegal context; this may crash
     _checkIllegalTaskLocalBindingWithinWithTaskGroup(file: file, line: line)

stdlib/public/Concurrency/TaskLocal.swift

@@ -135,7 +135,7 @@ public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible
   /// If the value is a reference type, it will be retained for the duration of
   /// the operation closure.
   @discardableResult
-  public func withValue<R>(_ valueDuringOperation: Value, operation: () async throws -> R,
+  public func withValue<R>(_ valueDuringOperation: Value, operation: @Sendable () async throws -> R,
                            file: String = #fileID, line: UInt = #line) async rethrows -> R {
     // check if we're not trying to bind a value from an illegal context; this may crash
     _checkIllegalTaskLocalBindingWithinWithTaskGroup(file: file, line: line)

test/Concurrency/Runtime/async_task_locals_basic.swift

@@ -199,6 +199,24 @@ func withLocal_body_mustNotEscape() async {
   _ = something // silence not used warning
 }
 
+@available(SwiftStdlib 5.1, *)
+actor Worker {
+  @TaskLocal
+  static var declaredInActor: String = "<default-value>"
+
+  func setAndRead() async {
+    print("setAndRead") // CHECK: setAndRead
+    await Worker.$declaredInActor.withValue("value-1") {
+      await printTaskLocalAsync(Worker.$declaredInActor) // CHECK-NEXT: TaskLocal<String>(defaultValue: <default-value>) (value-1)
+    }
+  }
+}
+
+@available(SwiftStdlib 5.1, *)
+func inside_actor() async {
+  await Worker().setAndRead()
+}
+
 @available(SwiftStdlib 5.1, *)
 @main struct Main {
   static func main() async {
@@ -210,5 +228,6 @@ func withLocal_body_mustNotEscape() async {
     await nested_3_onlyTopContributes()
     await nested_3_onlyTopContributesAsync()
     await nested_3_onlyTopContributesMixed()
+    await inside_actor()
   }
 }

test/Concurrency/async_task_locals_basic_warnings.swift

@@ -0,0 +1,23 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/OtherActors.swiftmodule -module-name OtherActors %S/Inputs/OtherActors.swift -disable-availability-checking
+// RUN: %target-typecheck-verify-swift -I %t  -disable-availability-checking -warn-concurrency -parse-as-library
+// REQUIRES: concurrency
+
+// REQUIRES: concurrency
+
+@available(SwiftStdlib 5.1, *)
+actor Test {
+
+  @TaskLocal static var local: Int?
+
+  func run() async {
+    // This should NOT produce any warnings, the closure withValue uses is @Sendable:
+    await Test.$local.withValue(42) {
+      await work()
+    }
+  }
+
+  func work() async {
+    print("Hello \(Test.local ?? 0)")
+  }
+}