fix sessions build

Author: morganchen12

FirebaseSessions/Sources/Settings/RemoteSettings.swift

@@ -31,7 +31,7 @@ final class RemoteSettings: SettingsProvider, Sendable {
   private static let flagSessionsCache = "app_quality"
   private let appInfo: ApplicationInfoProtocol
   private let downloader: SettingsDownloadClient
-  private let cache: AtomicBox<SettingsCacheClient>
+  private let cache: FIRAllocatedUnfairLock<SettingsCacheClient>
 
   private var cacheDurationSeconds: TimeInterval {
     cache.withLock { cache in
@@ -52,7 +52,7 @@ final class RemoteSettings: SettingsProvider, Sendable {
        downloader: SettingsDownloadClient,
        cache: SettingsCacheClient = SettingsCache()) {
     self.appInfo = appInfo
-    self.cache = AtomicBox<SettingsCacheClient>(cache)
+    self.cache = FIRAllocatedUnfairLock(initialState: cache)
     self.downloader = downloader
   }
 

FirebaseSessions/Sources/Settings/SettingsCacheClient.swift

@@ -15,10 +15,11 @@
 
 import Foundation
 
+// TODO: sendable (remove preconcurrency)
 #if SWIFT_PACKAGE
-  @_implementationOnly import GoogleUtilities_UserDefaults
+  @_implementationOnly @preconcurrency import GoogleUtilities_UserDefaults
 #else
-  @_implementationOnly import GoogleUtilities
+  @_implementationOnly @preconcurrency import GoogleUtilities
 #endif // SWIFT_PACKAGE
 
 /// CacheKey is like a "key" to a "safe". It provides necessary metadata about the current cache to
@@ -30,7 +31,7 @@ struct CacheKey: Codable {
 }
 
 /// SettingsCacheClient is responsible for accessing the cache that Settings are stored in.
-protocol SettingsCacheClient {
+protocol SettingsCacheClient: Sendable {
   /// Returns in-memory cache content in O(1) time. Returns empty dictionary if it does not exist in
   /// cache.
   var cacheContent: [String: Any] { get set }
@@ -45,7 +46,7 @@ protocol SettingsCacheClient {
 /// when accessing Settings values during run-time. This is because UserDefaults encapsulates both
 /// in-memory and persisted-on-disk storage, allowing fast synchronous access in-app while hiding
 /// away the complexity of managing persistence asynchronously.
-class SettingsCache: SettingsCacheClient {
+final class SettingsCache: SettingsCacheClient {
   private static let settingsVersion: Int = 1
   private enum UserDefaultsKeys {
     static let forContent = "firebase-sessions-settings"