Propagate service error when gracefully shutting down (#152)

# Motivation

Propagate the service error when we shutdown the group after the service threw.

Author: FranzBusch

Sources/ServiceLifecycle/ServiceGroup.swift

@@ -309,25 +309,25 @@ public actor ServiceGroup: Sendable {
                         }
                     }
 
-                case .serviceThrew(let service, let index, let error):
+                case .serviceThrew(let service, let index, let serviceError):
                     switch service.failureTerminationBehavior.behavior {
                     case .cancelGroup:
                         self.logger.debug(
                             "Service threw error. Cancelling group.",
                             metadata: [
                                 self.loggingConfiguration.keys.serviceKey: "\(service.service)",
-                                self.loggingConfiguration.keys.errorKey: "\(error)",
+                                self.loggingConfiguration.keys.errorKey: "\(serviceError)",
                             ]
                         )
                         group.cancelAll()
-                        return .failure(error)
+                        return .failure(serviceError)
 
                     case .gracefullyShutdownGroup:
                         self.logger.debug(
                             "Service threw error. Shutting down group.",
                             metadata: [
                                 self.loggingConfiguration.keys.serviceKey: "\(service.service)",
-                                self.loggingConfiguration.keys.errorKey: "\(error)",
+                                self.loggingConfiguration.keys.errorKey: "\(serviceError)",
                             ]
                         )
                         services[index] = nil
@@ -338,16 +338,17 @@ public actor ServiceGroup: Sendable {
                                 group: &group,
                                 gracefulShutdownManagers: gracefulShutdownManagers
                             )
+                            return .failure(serviceError)
                         } catch {
-                            return .failure(error)
+                            return .failure(serviceError)
                         }
 
                     case .ignore:
                         self.logger.debug(
                             "Service threw error.",
                             metadata: [
                                 self.loggingConfiguration.keys.serviceKey: "\(service.service)",
-                                self.loggingConfiguration.keys.errorKey: "\(error)",
+                                self.loggingConfiguration.keys.errorKey: "\(serviceError)",
                             ]
                         )
                         services[index] = nil

Tests/ServiceLifecycleTests/ServiceGroupTests.swift

@@ -433,7 +433,7 @@ final class ServiceGroupTests: XCTestCase {
             ]
         )
 
-        await withThrowingTaskGroup(of: Void.self) { group in
+        try await withThrowingTaskGroup(of: Void.self) { group in
             group.addTask {
                 try await serviceGroup.run()
             }
@@ -474,6 +474,71 @@ final class ServiceGroupTests: XCTestCase {
 
             // Let's exit from the first service
             await service1.resumeRunContinuation(with: .success(()))
+
+            try await XCTAsyncAssertThrowsError(await group.next()) {
+                XCTAssertTrue($0 is ExampleError)
+            }
+        }
+    }
+
+    func testRun_whenServiceThrows_andShutdownGracefully_andOtherServiceThrows() async throws {
+        let service1 = MockService(description: "Service1")
+        let service2 = MockService(description: "Service2")
+        let service3 = MockService(description: "Service3")
+        let serviceGroup = self.makeServiceGroup(
+            services: [
+                .init(service: service1),
+                .init(service: service2, failureTerminationBehavior: .gracefullyShutdownGroup),
+                .init(service: service3),
+            ]
+        )
+
+        try await withThrowingTaskGroup(of: Void.self) { group in
+            group.addTask {
+                try await serviceGroup.run()
+            }
+
+            var eventIterator1 = service1.events.makeAsyncIterator()
+            await XCTAsyncAssertEqual(await eventIterator1.next(), .run)
+
+            var eventIterator2 = service2.events.makeAsyncIterator()
+            await XCTAsyncAssertEqual(await eventIterator2.next(), .run)
+
+            var eventIterator3 = service3.events.makeAsyncIterator()
+            await XCTAsyncAssertEqual(await eventIterator3.next(), .run)
+
+            await service2.resumeRunContinuation(with: .failure(ExampleError()))
+
+            // The last service should receive the shutdown signal first
+            await XCTAsyncAssertEqual(await eventIterator3.next(), .shutdownGracefully)
+
+            // Waiting to see that all two are still running
+            service1.sendPing()
+            service3.sendPing()
+            await XCTAsyncAssertEqual(await eventIterator1.next(), .runPing)
+            await XCTAsyncAssertEqual(await eventIterator3.next(), .runPing)
+
+            // Let's exit from the last service
+            await service3.resumeRunContinuation(with: .success(()))
+
+            // Waiting to see that the remaining is still running
+            service1.sendPing()
+            await XCTAsyncAssertEqual(await eventIterator1.next(), .runPing)
+
+            // The first service should now receive the signal
+            await XCTAsyncAssertEqual(await eventIterator1.next(), .shutdownGracefully)
+
+            // Waiting to see that the one remaining are still running
+            service1.sendPing()
+            await XCTAsyncAssertEqual(await eventIterator1.next(), .runPing)
+
+            // Let's throw from this service as well
+            struct OtherError: Error {}
+            await service1.resumeRunContinuation(with: .failure(OtherError()))
+
+            try await XCTAsyncAssertThrowsError(await group.next()) {
+                XCTAssertTrue($0 is ExampleError)
+            }
         }
     }