[Swift 6] Add Swift 6 testing for Sessions (#14599)

Co-authored-by: Morgan Chen <morganchen12@gmail.com>

Author: ncooke3

.github/workflows/sessions.yml

@@ -39,10 +39,17 @@ jobs:
           - os: macos-14
             xcode: Xcode_16.2
             tests:
+            swift_version: 5.9
           # Flaky tests on CI
           - os: macos-15
             xcode: Xcode_16.3
             tests: --skip-tests
+            swift_version: 5.9
+          # Flaky tests on CI
+          - os: macos-15
+            xcode: Xcode_16.2
+            tests: --skip-tests
+            swift_version: 6.0
     runs-on: ${{ matrix.build-env.os }}
     steps:
     - uses: actions/checkout@v4
@@ -51,6 +58,8 @@ jobs:
       run: scripts/setup_bundler.sh
     - name: Xcode
       run: sudo xcode-select -s /Applications/${{ matrix.build-env.xcode }}.app/Contents/Developer
+    - name: Set Swift swift_version
+      run: sed -i "" "s/s.swift_version[[:space:]]*=[[:space:]]*'5.9'/s.swift_version = '${{ matrix.build-env.swift_version }}'/" FirebaseSessions.podspec
     - uses: nick-fields/retry@ce71cc2ab81d554ebbe88c79ab5975992d79ba08 # v3
       with:
         timeout_minutes: 120

FirebaseInstallations/Source/Library/Public/FirebaseInstallations/FIRInstallations.h

@@ -57,8 +57,7 @@ typedef void (^FIRInstallationsTokenHandler)(
  * as the ability to delete it. A Firebase Installation is unique by `FirebaseApp.name` and
  * `FirebaseApp.options.googleAppID` .
  */
-NS_SWIFT_NAME(Installations)
-@interface FIRInstallations : NSObject
+NS_SWIFT_NAME(Installations) NS_SWIFT_SENDABLE @interface FIRInstallations : NSObject
 
 - (instancetype)init NS_UNAVAILABLE;
 

FirebaseSessions/Sources/ApplicationInfo.swift

@@ -34,7 +34,7 @@ enum DevEnvironment: String {
   case autopush // Autopush environment
 }
 
-protocol ApplicationInfoProtocol {
+protocol ApplicationInfoProtocol: Sendable {
   /// Google App ID / GMP App ID
   var appID: String { get }
 
@@ -62,12 +62,15 @@ protocol ApplicationInfoProtocol {
   var osDisplayVersion: String { get }
 }
 
-class ApplicationInfo: ApplicationInfoProtocol {
+final class ApplicationInfo: ApplicationInfoProtocol {
   let appID: String
 
   private let networkInformation: NetworkInfoProtocol
   private let envParams: [String: String]
-  private let infoDict: [String: Any]?
+
+  // Used to hold bundle info, so the `Any` params should also
+  // be Sendable.
+  private nonisolated(unsafe) let infoDict: [String: Any]?
 
   init(appID: String, networkInfo: NetworkInfoProtocol = NetworkInfo(),
        envParams: [String: String] = ProcessInfo.processInfo.environment,

FirebaseSessions/Sources/Development/DevEventConsoleLogger.swift

@@ -19,7 +19,7 @@ import Foundation
   import FirebaseSessionsObjC
 #endif // SWIFT_PACKAGE
 
-class DevEventConsoleLogger: EventGDTLoggerProtocol {
+final class DevEventConsoleLogger: EventGDTLoggerProtocol {
   private let commandLineArgument = "-FIRSessionsDebugEvents"
 
   func logEvent(event: SessionStartEvent, completion: @escaping (Result<Void, Error>) -> Void) {

FirebaseSessions/Sources/EventGDTLogger.swift

@@ -17,7 +17,7 @@ import Foundation
 
 internal import GoogleDataTransport
 
-protocol EventGDTLoggerProtocol {
+protocol EventGDTLoggerProtocol: Sendable {
   func logEvent(event: SessionStartEvent, completion: @escaping (Result<Void, Error>) -> Void)
 }
 
@@ -26,7 +26,7 @@ protocol EventGDTLoggerProtocol {
 ///   1) Creating GDT Events and logging them to the GoogleDataTransport SDK
 ///   2) Handling debugging situations (eg. running in Simulator or printing the event to console)
 ///
-class EventGDTLogger: EventGDTLoggerProtocol {
+final class EventGDTLogger: EventGDTLoggerProtocol {
   let googleDataTransport: GoogleDataTransportProtocol
   let devEventConsoleLogger: EventGDTLoggerProtocol
 

FirebaseSessions/Sources/FirebaseSessions.swift

@@ -62,13 +62,13 @@ private enum GoogleDataTransportConfig {
 
   // Initializes the SDK and top-level classes
   required convenience init(appID: String, installations: InstallationsProtocol) {
-    let googleDataTransport = GDTCORTransport(
+    let googleDataTransport = GoogleDataTransporter(
       mappingID: GoogleDataTransportConfig.sessionsLogSource,
       transformers: nil,
       target: GoogleDataTransportConfig.sessionsTarget
     )
 
-    let fireLogger = EventGDTLogger(googleDataTransport: googleDataTransport!)
+    let fireLogger = EventGDTLogger(googleDataTransport: googleDataTransport)
 
     let appInfo = ApplicationInfo(appID: appID)
     let settings = SessionsSettings(
@@ -135,10 +135,10 @@ private enum GoogleDataTransportConfig {
   }
 
   // Initializes the SDK and begins the process of listening for lifecycle events and logging
-  // events
+  // events. `logEventCallback` is invoked on a global background queue.
   init(appID: String, sessionGenerator: SessionGenerator, coordinator: SessionCoordinatorProtocol,
        initiator: SessionInitiator, appInfo: ApplicationInfoProtocol, settings: SettingsProtocol,
-       loggedEventCallback: @escaping (Result<Void, FirebaseSessionsError>) -> Void) {
+       loggedEventCallback: @escaping @Sendable (Result<Void, FirebaseSessionsError>) -> Void) {
     self.appID = appID
 
     self.sessionGenerator = sessionGenerator
@@ -247,18 +247,40 @@ private enum GoogleDataTransportConfig {
     return SessionDetails(sessionId: sessionGenerator.currentSession?.sessionId)
   }
 
+  // This type is not actually sendable, but works around an issue below.
+  // It's safe only if executed on the main actor.
+  private struct MainActorNotificationCallback: @unchecked Sendable {
+    private let callback: (Notification) -> Void
+
+    init(_ callback: @escaping (Notification) -> Void) {
+      self.callback = callback
+    }
+
+    func invoke(notification: Notification) {
+      dispatchPrecondition(condition: .onQueue(.main))
+      callback(notification)
+    }
+  }
+
   func register(subscriber: SessionsSubscriber) {
     Logger
       .logDebug(
         "Registering Sessions SDK subscriber with name: \(subscriber.sessionsSubscriberName), data collection enabled: \(subscriber.isDataCollectionEnabled)"
       )
 
+    // TODO(Firebase 12): After bumping to iOS 13, this hack should be replaced
+    // with `Task { @MainActor in }`.
+    let callback = MainActorNotificationCallback { notification in
+      subscriber.onSessionChanged(self.currentSessionDetails)
+    }
+
+    // Guaranteed to execute its callback on the main queue because of the queue parameter.
     notificationCenter.addObserver(
       forName: Sessions.SessionIDChangedNotificationName,
       object: nil,
-      queue: nil
+      queue: OperationQueue.main
     ) { notification in
-      subscriber.onSessionChanged(self.currentSessionDetails)
+      callback.invoke(notification: notification)
     }
     // Immediately call the callback because the Sessions SDK starts
     // before subscribers, so subscribers will miss the first Notification

FirebaseSessions/Sources/FirebaseSessionsError.swift

@@ -15,7 +15,7 @@
 import Foundation
 
 /// Contains the list of errors that are localized for Firebase Sessions Library
-enum FirebaseSessionsError: Error {
+enum FirebaseSessionsError: Error, Sendable {
   /// Event sampling related error
   case SessionSamplingError
   /// Firebase Installation ID related error

FirebaseSessions/Sources/GoogleDataTransport+GoogleDataTransportProtocol.swift

@@ -15,20 +15,31 @@
 
 import Foundation
 
-internal import GoogleDataTransport
+@preconcurrency internal import GoogleDataTransport
 
 enum GoogleDataTransportProtocolErrors: Error {
   case writeFailure
 }
 
-protocol GoogleDataTransportProtocol {
+protocol GoogleDataTransportProtocol: Sendable {
   func logGDTEvent(event: GDTCOREvent, completion: @escaping (Result<Void, Error>) -> Void)
   func eventForTransport() -> GDTCOREvent
 }
 
-extension GDTCORTransport: GoogleDataTransportProtocol {
-  func logGDTEvent(event: GDTCOREvent, completion: @escaping (Result<Void, Error>) -> Void) {
-    sendDataEvent(event) { wasWritten, error in
+/// Workaround in combo with preconcurrency import of GDT. When GDT's
+/// `GDTCORTransport`type conforms to Sendable within the GDT module,
+/// this can be removed.
+final class GoogleDataTransporter: GoogleDataTransportProtocol {
+  private let transporter: GDTCORTransport
+
+  init(mappingID: String,
+       transformers: [any GDTCOREventTransformer]?,
+       target: GDTCORTarget) {
+    transporter = GDTCORTransport(mappingID: mappingID, transformers: transformers, target: target)!
+  }
+
+  func logGDTEvent(event: GDTCOREvent, completion: @escaping (Result<Void, any Error>) -> Void) {
+    transporter.sendDataEvent(event) { wasWritten, error in
       if let error {
         completion(.failure(error))
       } else if !wasWritten {
@@ -38,4 +49,8 @@ extension GDTCORTransport: GoogleDataTransportProtocol {
       }
     }
   }
+
+  func eventForTransport() -> GDTCOREvent {
+    transporter.eventForTransport()
+  }
 }

FirebaseSessions/Sources/Installations+InstallationsProtocol.swift

@@ -17,7 +17,7 @@ import Foundation
 
 internal import FirebaseInstallations
 
-protocol InstallationsProtocol {
+protocol InstallationsProtocol: Sendable {
   var installationsWaitTimeInSecond: Int { get }
 
   /// Override Installation function for testing

FirebaseSessions/Sources/NetworkInfo.swift

@@ -25,13 +25,13 @@ import Foundation
   internal import GoogleUtilities
 #endif // SWIFT_PACKAGE
 
-protocol NetworkInfoProtocol {
+protocol NetworkInfoProtocol: Sendable {
   var networkType: GULNetworkType { get }
 
   var mobileSubtype: String { get }
 }
 
-class NetworkInfo: NetworkInfoProtocol {
+final class NetworkInfo: NetworkInfoProtocol {
   var networkType: GULNetworkType {
     return GULNetworkInfo.getNetworkType()
   }

FirebaseSessions/Sources/Public/SessionsSubscriber.swift

@@ -18,7 +18,7 @@ import Foundation
 /// Sessions Subscriber is an interface that dependent SDKs
 /// must implement.
 @objc(FIRSessionsSubscriber)
-public protocol SessionsSubscriber {
+public protocol SessionsSubscriber: Sendable {
   func onSessionChanged(_ session: SessionDetails)
   var isDataCollectionEnabled: Bool { get }
   var sessionsSubscriberName: SessionsSubscriberName { get }
@@ -38,7 +38,7 @@ public class SessionDetails: NSObject {
 
 /// Session Subscriber Names are used for identifying subscribers
 @objc(FIRSessionsSubscriberName)
-public enum SessionsSubscriberName: Int, CustomStringConvertible {
+public enum SessionsSubscriberName: Int, CustomStringConvertible, Sendable {
   case Unknown
   case Crashlytics
   case Performance

FirebaseSessions/Sources/SessionCoordinator.swift

@@ -14,7 +14,7 @@
 
 import Foundation
 
-protocol SessionCoordinatorProtocol {
+protocol SessionCoordinatorProtocol: Sendable {
   func attemptLoggingSessionStart(event: SessionStartEvent,
                                   callback: @escaping (Result<Void, FirebaseSessionsError>) -> Void)
 }
@@ -23,8 +23,9 @@ protocol SessionCoordinatorProtocol {
 /// SessionCoordinator is responsible for coordinating the systems in this SDK
 /// involved with sending a Session Start event.
 ///
-class SessionCoordinator: SessionCoordinatorProtocol {
+final class SessionCoordinator: SessionCoordinatorProtocol {
   let installations: InstallationsProtocol
+
   let fireLogger: EventGDTLoggerProtocol
 
   init(installations: InstallationsProtocol,

FirebaseSessions/Sources/SessionInitiator.swift

@@ -41,9 +41,9 @@ import Foundation
 ///
 class SessionInitiator {
   let currentTime: () -> Date
-  var settings: SettingsProtocol
-  var backgroundTime = Date.distantFuture
-  var initiateSessionStart: () -> Void = {}
+  let settings: SettingsProtocol
+  private var backgroundTime = Date.distantFuture
+  private var initiateSessionStart: () -> Void = {}
 
   init(settings: SettingsProtocol, currentTimeProvider: @escaping () -> Date = Date.init) {
     currentTime = currentTimeProvider