Add AsyncSequence support for Firestore

This change introduces support for `AsyncSequence` to `DocumentReference` and `Query`, allowing developers to use `for await in` to receive real-time updates from Firestore.

The implementation wraps the existing snapshot listener APIs in an `AsyncThrowingStream`, providing a modern, Swift-native way to work with real-time data.

This change also includes unit tests for the new functionality.

Author: peterfriese

Firestore/Swift/Source/AsyncAwait/DocumentReference+AsyncSequence.swift

@@ -36,13 +36,14 @@ public extension DocumentReference {
   /// - Returns: An `AsyncThrowingStream` of `DocumentSnapshot` events.
   func snapshots(includeMetadataChanges: Bool) -> AsyncThrowingStream<DocumentSnapshot, Error> {
     return AsyncThrowingStream { continuation in
-      let listener = self.addSnapshotListener(includeMetadataChanges: includeMetadataChanges) { snapshot, error in
-        if let error = error {
-          continuation.finish(throwing: error)
-        } else if let snapshot = snapshot {
-          continuation.yield(snapshot)
+      let listener = self
+        .addSnapshotListener(includeMetadataChanges: includeMetadataChanges) { snapshot, error in
+          if let error = error {
+            continuation.finish(throwing: error)
+          } else if let snapshot = snapshot {
+            continuation.yield(snapshot)
+          }
         }
-      }
       continuation.onTermination = { @Sendable _ in
         listener.remove()
       }

Firestore/Swift/Source/AsyncAwait/Query+AsyncSequence.swift

@@ -36,13 +36,14 @@ public extension Query {
   /// - Returns: An `AsyncThrowingStream` of `QuerySnapshot` events.
   func snapshots(includeMetadataChanges: Bool) -> AsyncThrowingStream<QuerySnapshot, Error> {
     return AsyncThrowingStream { continuation in
-      let listener = self.addSnapshotListener(includeMetadataChanges: includeMetadataChanges) { snapshot, error in
-        if let error = error {
-          continuation.finish(throwing: error)
-        } else if let snapshot = snapshot {
-          continuation.yield(snapshot)
+      let listener = self
+        .addSnapshotListener(includeMetadataChanges: includeMetadataChanges) { snapshot, error in
+          if let error = error {
+            continuation.finish(throwing: error)
+          } else if let snapshot = snapshot {
+            continuation.yield(snapshot)
+          }
         }
-      }
       continuation.onTermination = { @Sendable _ in
         listener.remove()
       }

Firestore/Swift/Tests/Unit/AsyncAwait/AsyncSequenceTests.swift

@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
-import XCTest
 @testable import FirebaseFirestore
+import XCTest
 
 // MARK: - Mock Objects for Testing
 
@@ -33,17 +33,14 @@ private class MockQuery: Query {
   var capturedListener: SnapshotListener?
   let mockListenerRegistration = MockListenerRegistration()
 
-  override func addSnapshotListener(
-    _ listener: @escaping SnapshotListener
-  ) -> ListenerRegistration {
+  override func addSnapshotListener(_ listener: @escaping SnapshotListener)
+    -> ListenerRegistration {
     capturedListener = listener
     return mockListenerRegistration
   }
 
-  override func addSnapshotListener(
-    includeMetadataChanges: Bool,
-    listener: @escaping SnapshotListener
-  ) -> ListenerRegistration {
+  override func addSnapshotListener(includeMetadataChanges: Bool,
+                                    listener: @escaping SnapshotListener) -> ListenerRegistration {
     capturedListener = listener
     return mockListenerRegistration
   }
@@ -53,17 +50,15 @@ private class MockDocumentReference: DocumentReference {
   var capturedListener: DocumentSnapshotListener?
   let mockListenerRegistration = MockListenerRegistration()
 
-  override func addSnapshotListener(
-    _ listener: @escaping DocumentSnapshotListener
-  ) -> ListenerRegistration {
+  override func addSnapshotListener(_ listener: @escaping DocumentSnapshotListener)
+    -> ListenerRegistration {
     capturedListener = listener
     return mockListenerRegistration
   }
 
-  override func addSnapshotListener(
-    includeMetadataChanges: Bool,
-    listener: @escaping DocumentSnapshotListener
-  ) -> ListenerRegistration {
+  override func addSnapshotListener(includeMetadataChanges: Bool,
+                                    listener: @escaping DocumentSnapshotListener)
+    -> ListenerRegistration {
     capturedListener = listener
     return mockListenerRegistration
   }
@@ -180,4 +175,4 @@ class AsyncSequenceTests: XCTestCase {
 
     XCTAssertTrue(mockDocRef.mockListenerRegistration.isRemoved)
   }
-}
+}