Save to file storage when app is about to be terminated (#2992)

* Save file storage on termination too.

* wip

Author: mbrandonw

Sources/ComposableArchitecture/Internal/NotificationName.swift

@@ -26,7 +26,7 @@ public var willResignNotificationName: Notification.Name? {
 }
 
 @_spi(Internals)
-public var willEnterForegroundNotificationName: Notification.Name? {
+public let willEnterForegroundNotificationName: Notification.Name? = {
   #if os(iOS) || os(tvOS) || os(visionOS)
     return UIApplication.willEnterForegroundNotification
   #elseif os(macOS)
@@ -38,7 +38,18 @@ public var willEnterForegroundNotificationName: Notification.Name? {
       return nil
     }
   #endif
-}
+}()
+
+@_spi(Internals)
+public let willTerminateNotificationName: Notification.Name? = {
+  #if os(iOS) || os(tvOS) || os(visionOS)
+    return UIApplication.willTerminateNotification
+  #elseif os(macOS)
+    return NSApplication.willTerminateNotification
+  #else
+    return nil
+  #endif
+}()
 
 var canListenForResignActive: Bool {
   willResignNotificationName != nil

Sources/ComposableArchitecture/SharedState/PersistenceKey/AppStorageKey.swift

@@ -300,16 +300,23 @@ extension AppStorageKey: PersistenceKey {
       else { return }
       didSet(self.store.value(forKey: self.key) as? Value ?? initialValue)
     }
-    let willEnterForeground = NotificationCenter.default.addObserver(
-      forName: willEnterForegroundNotificationName,
-      object: nil,
-      queue: nil
-    ) { _ in
-      didSet(self.store.value(forKey: self.key) as? Value ?? initialValue)
+    let willEnterForeground: (any NSObjectProtocol)?
+    if let willEnterForegroundNotificationName {
+      willEnterForeground = NotificationCenter.default.addObserver(
+        forName: willEnterForegroundNotificationName,
+        object: nil,
+        queue: nil
+      ) { _ in
+        didSet(self.store.value(forKey: self.key) as? Value ?? initialValue)
+      }
+    } else {
+      willEnterForeground = nil
     }
     return Shared.Subscription {
       NotificationCenter.default.removeObserver(userDefaultsDidChange)
-      NotificationCenter.default.removeObserver(willEnterForeground)
+      if let willEnterForeground {
+        NotificationCenter.default.removeObserver(willEnterForeground)
+      }
     }
   }
 }

Sources/ComposableArchitecture/SharedState/PersistenceKey/FileStorageKey.swift

@@ -81,30 +81,56 @@ public final class FileStorageKey<Value: Codable & Sendable>: PersistenceKey, @u
         didSet(self.load(initialValue: initialValue))
       }
     }
-    #if canImport(AppKit) || canImport(UIKit) || canImport(WatchKit)
-      let willResign = NotificationCenter.default.addObserver(
+    let willResign: (any NSObjectProtocol)?
+    if let willResignNotificationName {
+      willResign = NotificationCenter.default.addObserver(
         forName: willResignNotificationName,
         object: nil,
         queue: nil
       ) { [weak self] _ in
-        guard
-          let self,
-          let workItem = self.workItem
+        guard let self
         else { return }
-        self.storage.async(execute: workItem)
-        self.storage.async(
-          execute: DispatchWorkItem {
-            self.workItem?.cancel()
-            self.workItem = nil
-          }
-        )
+        performImmediately()
+      }
+    } else {
+      willResign = nil
+    }
+    let willTerminate: (any NSObjectProtocol)?
+    if let willTerminateNotificationName {
+      willTerminate = NotificationCenter.default.addObserver(
+        forName: willTerminateNotificationName,
+        object: nil,
+        queue: nil
+      ) { [weak self] _ in
+        guard let self
+        else { return }
+        performImmediately()
       }
-    #endif
+    } else {
+      willTerminate = nil
+    }
     return Shared.Subscription {
       cancellable.cancel()
-      NotificationCenter.default.removeObserver(willResign)
+      if let willResign {
+        NotificationCenter.default.removeObserver(willResign)
+      }
+      if let willTerminate {
+        NotificationCenter.default.removeObserver(willTerminate)
+      }
     }
   }
+
+  private func performImmediately() {
+    guard let workItem = self.workItem
+    else { return }
+    self.storage.async(execute: workItem)
+    self.storage.async(
+      execute: DispatchWorkItem {
+        self.workItem?.cancel()
+        self.workItem = nil
+      }
+    )
+  }
 }
 
 extension FileStorageKey: Hashable {

Tests/ComposableArchitectureTests/FileStorageTests.swift

@@ -77,6 +77,7 @@ final class FileStorageTests: XCTestCase {
 
   func testWillResign() throws {
     guard let willResignNotificationName else { return }
+
     let testScheduler = DispatchQueue.test
     let fileStorage = InMemoryFileStorage(scheduler: testScheduler.eraseToAnyScheduler())
     try withDependencies {
@@ -94,6 +95,26 @@ final class FileStorageTests: XCTestCase {
     }
   }
 
+  func testWillTerminate() throws {
+    guard let willTerminateNotificationName else { return }
+    
+    let testScheduler = DispatchQueue.test
+    let fileStorage = InMemoryFileStorage(scheduler: testScheduler.eraseToAnyScheduler())
+    try withDependencies {
+      $0.defaultFileStorage = fileStorage
+    } operation: {
+      @Shared(.fileStorage(.fileURL)) var users = [User]()
+      XCTAssertNoDifference(fileStorage.fileSystem.value, [.fileURL: Data()])
+
+      users.append(.blob)
+      XCTAssertNoDifference(fileStorage.fileSystem.value, [.fileURL: Data()])
+
+      NotificationCenter.default.post(name: willTerminateNotificationName, object: nil)
+      testScheduler.advance()
+      try XCTAssertNoDifference(fileStorage.fileSystem.value.users(for: .fileURL), [.blob])
+    }
+  }
+
   func testWillResignAndDebounce() async throws {
     guard let willResignNotificationName else { return }
     let testScheduler = DispatchQueue.test