feat(firestore): count() feature for counting documents without retrieving documents.

.swiftformat

@@ -2,4 +2,5 @@
 --maxwidth 100
 --wrapparameters afterfirst
 --disable sortedImports,unusedArguments,wrapMultilineStatementBraces
---exclude Pods,**/MainFlutterWindow.swift,**/AppDelegate.swift,**/.symlinks/**
+--exclude Pods,**/MainFlutterWindow.swift,**/AppDelegate.swift,**/.symlinks/**
+--swiftversion 5.7

packages/cloud_firestore/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/firestore/FlutterFirebaseFirestorePlugin.java

@@ -10,6 +10,9 @@
 import com.google.android.gms.tasks.TaskCompletionSource;
 import com.google.android.gms.tasks.Tasks;
 import com.google.firebase.FirebaseApp;
+import com.google.firebase.firestore.AggregateQuery;
+import com.google.firebase.firestore.AggregateQuerySnapshot;
+import com.google.firebase.firestore.AggregateSource;
 import com.google.firebase.firestore.DocumentReference;
 import com.google.firebase.firestore.DocumentSnapshot;
 import com.google.firebase.firestore.FieldPath;
@@ -482,6 +485,32 @@ private Task<Void> waitForPendingWrites(Map<String, Object> arguments) {
     return taskCompletionSource.getTask();
   }
 
+  private Task<Map<String, Object>> aggregateQuery(Map<String, Object> arguments) {
+    TaskCompletionSource<Map<String, Object>> taskCompletionSource = new TaskCompletionSource<>();
+
+    cachedThreadPool.execute(
+        () -> {
+          try {
+            Query query = (Query) Objects.requireNonNull(arguments.get("query"));
+            // NOTE: There is only "server" as the source at the moment. So this
+            // is unused for the time being. Using "AggregateSource.SERVER".
+            // String source = (String) Objects.requireNonNull(arguments.get("source"));
+
+            AggregateQuery aggregateQuery = query.count();
+            AggregateQuerySnapshot aggregateQuerySnapshot =
+                Tasks.await(aggregateQuery.get(AggregateSource.SERVER));
+            Map<String, Object> result = new HashMap<>();
+            result.put("count", aggregateQuerySnapshot.getCount());
+            taskCompletionSource.setResult(result);
+
+          } catch (Exception e) {
+            taskCompletionSource.setException(e);
+          }
+        });
+
+    return taskCompletionSource.getTask();
+  }
+
   @Override
   public void onMethodCall(MethodCall call, @NonNull final MethodChannel.Result result) {
     Task<?> methodCallTask;
@@ -560,6 +589,9 @@ public void onMethodCall(MethodCall call, @NonNull final MethodChannel.Result re
       case "Firestore#waitForPendingWrites":
         methodCallTask = waitForPendingWrites(call.arguments());
         break;
+      case "AggregateQuery#count":
+        methodCallTask = aggregateQuery(call.arguments());
+        break;
       default:
         result.notImplemented();
         return;

packages/cloud_firestore/cloud_firestore/example/ios/Podfile

@@ -56,6 +56,9 @@ end
 
 post_install do |installer|
   installer.pods_project.targets.each do |target|
+    target.build_configurations.each do |config|
+      config.build_settings.delete 'IPHONEOS_DEPLOYMENT_TARGET'
+    end
     flutter_additional_ios_build_settings(target)
   end
 end

packages/cloud_firestore/cloud_firestore/example/test_driver/query_e2e.dart

@@ -1807,6 +1807,27 @@ void runQueryTests() {
         },
         timeout: const Timeout.factor(3),
       );
+
+      test(
+        'count()',
+        () async {
+          final collection = await initializeTest('count');
+
+          await Future.wait([
+            collection.add({'foo': 'bar'}),
+            collection.add({'bar': 'baz'})
+          ]);
+
+          AggregateQuery query = collection.count();
+
+          AggregateQuerySnapshot snapshot = await query.get();
+
+          expect(
+            snapshot.count,
+            2,
+          );
+        },
+      );
     });
   });
 }

packages/cloud_firestore/cloud_firestore/ios/Classes/FLTFirebaseFirestorePlugin.m

@@ -225,6 +225,8 @@ - (void)handleMethodCall:(FlutterMethodCall *)call result:(FlutterResult)flutter
                              withMethodCallResult:methodCallResult];
   } else if ([@"LoadBundle#snapshots" isEqualToString:call.method]) {
     [self setupLoadBundleListener:call.arguments withMethodCallResult:methodCallResult];
+  } else if ([@"AggregateQuery#count" isEqualToString:call.method]) {
+    [self aggregateQuery:call.arguments withMethodCallResult:methodCallResult];
   } else {
     methodCallResult.success(FlutterMethodNotImplemented);
   }
@@ -535,6 +537,29 @@ - (void)batchCommit:(id)arguments withMethodCallResult:(FLTFirebaseMethodCallRes
   }];
 }
 
+- (void)aggregateQuery:(id)arguments withMethodCallResult:(FLTFirebaseMethodCallResult *)result {
+  FIRQuery *query = arguments[@"query"];
+
+  // NOTE: There is only "server" as the source at the moment. So this
+  // is unused for the time being. Using "FIRAggregateSourceServer".
+  // NSString *source = arguments[@"source"];
+
+  FIRAggregateQuery *aggregateQuery = [query count];
+
+  [aggregateQuery aggregationWithSource:FIRAggregateSourceServer
+                             completion:^(FIRAggregateQuerySnapshot *_Nullable snapshot,
+                                          NSError *_Nullable error) {
+                               if (error != nil) {
+                                 result.error(nil, nil, nil, error);
+                               } else {
+                                 NSMutableDictionary *response = [NSMutableDictionary dictionary];
+                                 response[@"count"] = snapshot.count;
+
+                                 result.success(response);
+                               }
+                             }];
+}
+
 - (NSString *)registerEventChannelWithPrefix:(NSString *)prefix
                                streamHandler:(NSObject<FlutterStreamHandler> *)handler {
   return [self registerEventChannelWithPrefix:prefix

packages/cloud_firestore/cloud_firestore/lib/cloud_firestore.dart

@@ -17,6 +17,7 @@ import 'package:meta/meta.dart';
 
 export 'package:cloud_firestore_platform_interface/cloud_firestore_platform_interface.dart'
     show
+        AggregateSource,
         ListEquality,
         FieldPath,
         Blob,
@@ -46,3 +47,5 @@ part 'src/snapshot_metadata.dart';
 part 'src/transaction.dart';
 part 'src/utils/codec_utility.dart';
 part 'src/write_batch.dart';
+part 'src/aggregate_query.dart';
+part 'src/aggregate_query_snapshot.dart';

packages/cloud_firestore/cloud_firestore/lib/src/aggregate_query.dart

@@ -0,0 +1,26 @@
+// Copyright 2022, the Chromium project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of cloud_firestore;
+
+/// [AggregateQuery] represents the data at a particular location for retrieving metadata
+/// without retrieving the actual documents.
+class AggregateQuery {
+  AggregateQuery._(this._delegate, this.query) {
+    AggregateQueryPlatform.verifyExtends(_delegate);
+  }
+
+  /// [Query] represents the query over the data at a particular location used by the [AggregateQuery] to
+  /// retrieve the metadata.
+  final Query query;
+
+  final AggregateQueryPlatform _delegate;
+
+  /// Returns an [AggregateQuerySnapshot] with the count of the documents that match the query.
+  Future<AggregateQuerySnapshot> get({
+    AggregateSource source = AggregateSource.server,
+  }) async {
+    return AggregateQuerySnapshot._(await _delegate.get(source: source), query);
+  }
+}

packages/cloud_firestore/cloud_firestore/lib/src/aggregate_query_snapshot.dart

@@ -0,0 +1,20 @@
+// Copyright 2022, the Chromium project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of cloud_firestore;
+
+/// [AggregateQuerySnapshot] represents a response to an [AggregateQuery] request.
+class AggregateQuerySnapshot {
+  AggregateQuerySnapshot._(this._delegate, this.query) {
+    AggregateQuerySnapshotPlatform.verifyExtends(_delegate);
+  }
+  final AggregateQuerySnapshotPlatform _delegate;
+
+  /// [Query] represents the query over the data at a particular location used by the [AggregateQuery] to
+  /// retrieve the metadata.
+  final Query query;
+
+  /// Returns the count of the documents that match the query.
+  int get count => _delegate.count;
+}

packages/cloud_firestore/cloud_firestore/lib/src/query.dart

@@ -186,6 +186,8 @@ abstract class Query<T extends Object?> {
     required FromFirestore<R> fromFirestore,
     required ToFirestore<R> toFirestore,
   });
+
+  AggregateQuery count();
 }
 
 /// Represents a [Query] over the data at a particular location.
@@ -808,6 +810,13 @@ class _JsonQuery implements Query<Map<String, dynamic>> {
 
   @override
   int get hashCode => Object.hash(runtimeType, firestore, _delegate);
+
+  /// Represents an [AggregateQuery] over the data at a particular location for retrieving metadata
+  /// without retrieving the actual documents.
+  @override
+  AggregateQuery count() {
+    return AggregateQuery._(_delegate.count(), this);
+  }
 }
 
 class _WithConverterQuery<T extends Object?> implements Query<T> {
@@ -970,4 +979,11 @@ class _WithConverterQuery<T extends Object?> implements Query<T> {
   @override
   int get hashCode =>
       Object.hash(runtimeType, _fromFirestore, _toFirestore, _originalQuery);
+
+  /// Represents an [AggregateQuery] over the data at a particular location for retrieving metadata
+  /// without retrieving the actual documents.
+  @override
+  AggregateQuery count() {
+    return _originalQuery.count();
+  }
 }

packages/cloud_firestore/cloud_firestore/test/aggregate_query_test.dart

@@ -0,0 +1,87 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:cloud_firestore_platform_interface/src/method_channel/method_channel_firestore.dart';
+import 'package:cloud_firestore_platform_interface/src/method_channel/method_channel_query.dart';
+import 'package:cloud_firestore_platform_interface/src/method_channel/utils/firestore_message_codec.dart';
+import 'package:firebase_core/firebase_core.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/services.dart';
+
+import './mock.dart';
+
+int kCount = 4;
+
+void main() {
+  setupCloudFirestoreMocks();
+  MethodChannelFirebaseFirestore.channel = const MethodChannel(
+    'plugins.flutter.io/firebase_firestore',
+    StandardMethodCodec(AggregateQueryMessageCodec()),
+  );
+
+  MethodChannelFirebaseFirestore.channel.setMockMethodCallHandler((call) async {
+    if (call.method == 'AggregateQuery#count') {
+      return {
+        'count': kCount,
+      };
+    }
+
+    return null;
+  });
+
+  FirebaseFirestore? firestore;
+
+  group('$AggregateQuery', () {
+    setUpAll(() async {
+      await Firebase.initializeApp();
+      firestore = FirebaseFirestore.instance;
+    });
+
+    test('returns the correct `AggregateQuerySnapshot` with correct `count`',
+        () async {
+      Query query = firestore!.collection('flutter-tests');
+      AggregateQuery aggregateQuery = query.count();
+
+      expect(query, aggregateQuery.query);
+      AggregateQuerySnapshot snapshot = await aggregateQuery.get();
+
+      expect(snapshot.count, equals(kCount));
+    });
+  });
+}
+
+class AggregateQueryMessageCodec extends FirestoreMessageCodec {
+  /// Constructor.
+  const AggregateQueryMessageCodec();
+  static const int _kFirestoreInstance = 144;
+  static const int _kFirestoreQuery = 145;
+  static const int _kFirestoreSettings = 146;
+
+  @override
+  Object? readValueOfType(int type, ReadBuffer buffer) {
+    switch (type) {
+      // The following cases are only used by unit tests, and not by actual application
+      // code paths.
+      case _kFirestoreInstance:
+        String appName = readValue(buffer)! as String;
+        readValue(buffer);
+        final FirebaseApp app = Firebase.app(appName);
+        return MethodChannelFirebaseFirestore(app: app);
+      case _kFirestoreQuery:
+        Map<dynamic, dynamic> values =
+            readValue(buffer)! as Map<dynamic, dynamic>;
+        final FirebaseApp app = Firebase.app();
+        return MethodChannelQuery(
+          MethodChannelFirebaseFirestore(app: app),
+          values['path'],
+        );
+      case _kFirestoreSettings:
+        readValue(buffer);
+        return const Settings();
+      default:
+        return super.readValueOfType(type, buffer);
+    }
+  }
+}

packages/cloud_firestore/cloud_firestore_platform_interface/lib/cloud_firestore_platform_interface.dart

@@ -24,6 +24,9 @@ export 'src/platform_interface/platform_interface_transaction.dart';
 export 'src/platform_interface/platform_interface_write_batch.dart';
 export 'src/platform_interface/platform_interface_load_bundle_task.dart';
 export 'src/platform_interface/platform_interface_load_bundle_task_snapshot.dart';
+export 'src/platform_interface/platform_interface_aggregate_query.dart';
+export 'src/platform_interface/platform_interface_aggregate_query_snapshot.dart';
+export 'src/aggregate_source.dart';
 export 'src/snapshot_metadata.dart';
 export 'src/source.dart';
 export 'src/load_bundle_task_state.dart';

packages/cloud_firestore/cloud_firestore_platform_interface/lib/src/aggregate_source.dart

@@ -0,0 +1,9 @@
+// Copyright 2022, the Chromium project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// [AggregateSource] represents the source of data for an [AggregateQuery].
+enum AggregateSource {
+  /// Indicates that the data should be retrieved from the server.
+  server,
+}

packages/cloud_firestore/cloud_firestore_platform_interface/lib/src/method_channel/method_channel_aggregate_query.dart

@@ -0,0 +1,33 @@
+// Copyright 2022, the Chromium project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:cloud_firestore_platform_interface/src/method_channel/utils/source.dart';
+
+import 'method_channel_firestore.dart';
+import '../../cloud_firestore_platform_interface.dart';
+
+/// An implementation of [AggregateQueryPlatform] for the [MethodChannel]
+class MethodChannelAggregateQuery extends AggregateQueryPlatform {
+  MethodChannelAggregateQuery(QueryPlatform query) : super(query);
+
+  @override
+  Future<AggregateQuerySnapshotPlatform> get({
+    required AggregateSource source,
+  }) async {
+    final Map<String, dynamic>? data = await MethodChannelFirebaseFirestore
+        .channel
+        .invokeMapMethod<String, dynamic>(
+      'AggregateQuery#count',
+      <String, dynamic>{
+        'query': query,
+        'firestore': query.firestore,
+        'source': getAggregateSourceString(source),
+      },
+    );
+
+    return AggregateQuerySnapshotPlatform(
+      count: data!['count'] as int,
+    );
+  }
+}

packages/cloud_firestore/cloud_firestore_platform_interface/lib/src/method_channel/method_channel_query.dart

@@ -11,6 +11,7 @@ import 'package:cloud_firestore_platform_interface/src/internal/pointer.dart';
 import 'package:collection/collection.dart';
 import 'package:flutter/services.dart';
 
+import 'method_channel_aggregate_query.dart';
 import 'method_channel_firestore.dart';
 import 'method_channel_query_snapshot.dart';
 import 'utils/source.dart';
@@ -212,6 +213,13 @@ class MethodChannelQuery extends QueryPlatform {
     });
   }
 
+  @override
+  AggregateQueryPlatform count() {
+    return MethodChannelAggregateQuery(
+      this,
+    );
+  }
+
   @override
   bool operator ==(Object other) {
     return runtimeType == other.runtimeType &&