Enable NonisolatedNonsendingByDefault

Package.swift

@@ -75,11 +75,13 @@ let package = Package(
 )
 
 for target in package.targets {
-    #if compiler(<6.2)
-    // Needed since Sendable checking with isolated methods is not working correctly before 6.2
     if target.swiftSettings == nil {
         target.swiftSettings = []
     }
+    #if compiler(<6.2)
+    // Needed since Sendable checking with isolated methods is not working correctly before 6.2
     target.swiftSettings?.append(.swiftLanguageMode(.v5))
+    #else
+    target.swiftSettings?.append(.enableUpcomingFeature("NonisolatedNonsendingByDefault"))
     #endif
 }

Sources/ConcurrencyHelpers/NonSendingIteratorNext.swift

@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftServiceLifecycle open source project
+//
+// Copyright (c) 2026 Apple Inc. and the SwiftServiceLifecycle project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftServiceLifecycle project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+@available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
+extension AsyncIteratorProtocol {
+    @usableFromInline
+    package mutating func nonSendingNext() async rethrows -> Element? {
+        guard #available(macOS 15.0, *) else {
+            // On older Apple platforms, we cannot pass through the isolation
+            // That means next() runs on task isolation
+            // That is not safe to the compiler, because the caller of this send function may have called
+            // it concurrently
+            // However, that shouldn't happen in practise since the iterator itself is not Sendable
+
+            nonisolated(unsafe) var this = self
+            defer {
+                self = this
+            }
+            return try await this.next()
+        }
+        return try await self.next(isolation: #isolation)
+    }
+}

Sources/ServiceLifecycle/AsyncCancelOnGracefulShutdownSequence.swift

@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 import AsyncAlgorithms
+import ConcurrencyHelpers
 
 @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
 extension AsyncSequence where Self: Sendable, Element: Sendable {
@@ -82,7 +83,7 @@ where Base.Element: Sendable {
                 return nil
             }
 
-            let value = try await self._iterator.next()
+            let value = try await self._iterator.nonSendingNext()
 
             switch value {
             case .base(let element):
@@ -157,7 +158,7 @@ struct AsyncMapNilSequence<Base: AsyncSequence & Sendable>: AsyncSequence, Senda
 
         @inlinable
         mutating func next() async rethrows -> Element? {
-            let value = try await self._iterator.next()
+            let value = try await self._iterator.nonSendingNext()
 
             if let value {
                 return .element(value)

Sources/ServiceLifecycle/Docs.docc/index.md

@@ -89,5 +89,5 @@ let package = Package(
 
 - ``cancelOnGracefulShutdown(_:)``
 - ``withGracefulShutdownHandler(operation:onGracefulShutdown:)``
-- ``withGracefulShutdownHandler(operation:onGracefulShutdown:)-1x21p``
-- ``withTaskCancellationOrGracefulShutdownHandler(operation:onCancelOrGracefulShutdown:)-81m01``
+- ``withGracefulShutdownHandler(isolation:operation:onGracefulShutdown:)``
+- ``withTaskCancellationOrGracefulShutdownHandler(isolation:operation:onCancelOrGracefulShutdown:)``

Sources/ServiceLifecycle/ServiceGroup.swift

@@ -885,7 +885,7 @@ public actor ServiceGroup: Sendable, Service {
         group.addTask {
             return await withTaskCancellationHandler {
                 var iterator = channel.makeAsyncIterator()
-                if let addedService = await iterator.next() {
+                if let addedService = await iterator.nonSendingNext() {
                     return .newServiceAdded(addedService)
                 }
 

Sources/UnixSignals/UnixSignalsSequence.swift

@@ -71,7 +71,7 @@ public struct UnixSignalsSequence: AsyncSequence, Sendable {
         }
 
         public mutating func next() async -> UnixSignal? {
-            return await self.iterator.next()
+            return await self.iterator.nonSendingNext()
         }
     }
 }

Tests/ServiceLifecycleTests/AsyncCancelOnGracefulShutdownSequenceTests.swift

@@ -36,11 +36,11 @@ final class AsyncCancelOnGracefulShutdownSequenceTests: XCTestCase {
 
                 var iterator = resultStream.makeAsyncIterator()
 
-                await XCTAsyncAssertEqual(await iterator.next(), 1)
+                await XCTAsyncAssertEqual(await iterator.nonSendingNext(), 1)
 
                 gracefulShutdownTrigger.triggerGracefulShutdown()
 
-                await XCTAsyncAssertEqual(await iterator.next(), nil)
+                await XCTAsyncAssertEqual(await iterator.nonSendingNext(), nil)
             }
         }
     }
@@ -61,11 +61,11 @@ final class AsyncCancelOnGracefulShutdownSequenceTests: XCTestCase {
                 var iterator = resultStream.makeAsyncIterator()
                 baseContinuation.yield(1)
 
-                await XCTAsyncAssertEqual(await iterator.next(), 1)
+                await XCTAsyncAssertEqual(await iterator.nonSendingNext(), 1)
 
                 baseContinuation.finish()
 
-                await XCTAsyncAssertEqual(await iterator.next(), nil)
+                await XCTAsyncAssertEqual(await iterator.nonSendingNext(), nil)
             }
         }
     }

Tests/ServiceLifecycleTests/GracefulShutdownTests.swift

@@ -57,8 +57,8 @@ final class GracefulShutdownTests: XCTestCase {
 
         var iterator = stream.makeAsyncIterator()
 
-        await XCTAsyncAssertEqual(await iterator.next(), "onGracefulShutdown")
-        await XCTAsyncAssertEqual(await iterator.next(), "operation")
+        await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "onGracefulShutdown")
+        await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "operation")
     }
 
     func testWithGracefulShutdownHandler_whenNested() async {
@@ -96,15 +96,15 @@ final class GracefulShutdownTests: XCTestCase {
 
                     var iterator = stream.makeAsyncIterator()
 
-                    await XCTAsyncAssertEqual(await iterator.next(), "outerOperation")
-                    await XCTAsyncAssertEqual(await iterator.next(), "innerOperation")
-                    await XCTAsyncAssertEqual(await iterator.next(), "innerOperation")
+                    await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "outerOperation")
+                    await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "innerOperation")
+                    await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "innerOperation")
 
                     gracefulShutdownTestTrigger.triggerGracefulShutdown()
 
-                    await XCTAsyncAssertEqual(await iterator.next(), "outerOnGracefulShutdown")
-                    await XCTAsyncAssertEqual(await iterator.next(), "innerOnGracefulShutdown")
-                    await XCTAsyncAssertEqual(await iterator.next(), "innerOnGracefulShutdown")
+                    await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "outerOnGracefulShutdown")
+                    await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "innerOnGracefulShutdown")
+                    await XCTAsyncAssertEqual(await iterator.nonSendingNext(), "innerOnGracefulShutdown")
                 }
             } onGracefulShutdown: {
                 continuation.yield("outerOnGracefulShutdown")