Add discarded_futures lint

add_to_app/android_view/flutter_module_using_plugin/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
@@ -44,7 +46,7 @@ void showCell() {
 class CounterModel extends ChangeNotifier {
   CounterModel() {
     _channel.setMethodCallHandler(_handleMessage);
-    _channel.invokeMethod<void>('requestCounter');
+    unawaited(_channel.invokeMethod<void>('requestCounter'));
   }
 
   final _channel = const MethodChannel('dev.flutter.example/counter');
@@ -54,7 +56,7 @@ class CounterModel extends ChangeNotifier {
   int get count => _count;
 
   void increment() {
-    _channel.invokeMethod<void>('incrementCounter');
+    unawaited(_channel.invokeMethod<void>('incrementCounter'));
   }
 
   Future<dynamic> _handleMessage(MethodCall call) async {
@@ -175,7 +177,7 @@ class Contents extends StatelessWidget {
                 if (showExit) ...[
                   const SizedBox(height: 16),
                   ElevatedButton(
-                    onPressed: () => SystemNavigator.pop(),
+                    onPressed: () async => SystemNavigator.pop(),
                     child: const Text('Exit this screen'),
                   ),
                 ],

add_to_app/books/flutter_module_books/lib/main.dart

@@ -115,8 +115,8 @@ class _BookDetailState extends State<BookDetail> {
           icon: const Icon(Icons.clear),
           // Pressing clear cancels the edit and leaves the activity without
           // modification.
-          onPressed: () {
-            hostApi.cancel();
+          onPressed: () async {
+            await hostApi.cancel();
             clear();
           },
         ),
@@ -125,8 +125,8 @@ class _BookDetailState extends State<BookDetail> {
             icon: const Icon(Icons.check),
             // Pressing save sends the updated book to the platform.
             onPressed: book != null
-                ? () {
-                    hostApi.finishEditingBook(book!);
+                ? () async {
+                    await hostApi.finishEditingBook(book!);
                     clear();
                   }
                 : null,

add_to_app/fullscreen/flutter_module/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
@@ -32,7 +34,7 @@ void main() {
 class CounterModel extends ChangeNotifier {
   CounterModel() {
     _channel.setMethodCallHandler(_handleMessage);
-    _channel.invokeMethod<void>('requestCounter');
+    unawaited(_channel.invokeMethod<void>('requestCounter'));
   }
 
   final _channel = const MethodChannel('dev.flutter.example/counter');
@@ -42,7 +44,7 @@ class CounterModel extends ChangeNotifier {
   int get count => _count;
 
   void increment() {
-    _channel.invokeMethod<void>('incrementCounter');
+    unawaited(_channel.invokeMethod<void>('incrementCounter'));
   }
 
   Future<dynamic> _handleMessage(MethodCall call) async {
@@ -151,7 +153,7 @@ class Contents extends StatelessWidget {
                 if (showExit) ...[
                   const SizedBox(height: 16),
                   ElevatedButton(
-                    onPressed: () => SystemNavigator.pop(animated: true),
+                    onPressed: () async => SystemNavigator.pop(animated: true),
                     child: const Text('Exit this screen'),
                   ),
                 ],

add_to_app/multiple_flutters/multiple_flutters_module/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:url_launcher/url_launcher.dart' as launcher;
@@ -61,7 +63,7 @@ class _MyHomePageState extends State<MyHomePage> {
 
   void _incrementCounter() {
     // Mutations to the data model are forwarded to the host platform.
-    _channel.invokeMethod<void>("incrementCount", _counter);
+    unawaited(_channel.invokeMethod<void>("incrementCount", _counter));
   }
 
   @override
@@ -87,7 +89,7 @@ class _MyHomePageState extends State<MyHomePage> {
             ),
             TextButton(
               onPressed: () {
-                _channel.invokeMethod<void>("next", _counter);
+                unawaited(_channel.invokeMethod<void>("next", _counter));
               },
               child: const Text('Next'),
             ),

add_to_app/plugin/flutter_module_using_plugin/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
@@ -43,7 +45,7 @@ void showCell() {
 class CounterModel extends ChangeNotifier {
   CounterModel() {
     _channel.setMethodCallHandler(_handleMessage);
-    _channel.invokeMethod<void>('requestCounter');
+    unawaited(_channel.invokeMethod<void>('requestCounter'));
   }
 
   final _channel = const MethodChannel('dev.flutter.example/counter');
@@ -53,7 +55,7 @@ class CounterModel extends ChangeNotifier {
   int get count => _count;
 
   void increment() {
-    _channel.invokeMethod<void>('incrementCounter');
+    unawaited(_channel.invokeMethod<void>('incrementCounter'));
   }
 
   Future<dynamic> _handleMessage(MethodCall call) async {
@@ -174,7 +176,7 @@ class Contents extends StatelessWidget {
                 if (showExit) ...[
                   const SizedBox(height: 16),
                   ElevatedButton(
-                    onPressed: () => SystemNavigator.pop(),
+                    onPressed: () async => SystemNavigator.pop(),
                     child: const Text('Exit this screen'),
                   ),
                 ],

add_to_app/prebuilt_module/flutter_module/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
@@ -32,7 +34,7 @@ void main() {
 class CounterModel extends ChangeNotifier {
   CounterModel() {
     _channel.setMethodCallHandler(_handleMessage);
-    _channel.invokeMethod<void>('requestCounter');
+    unawaited(_channel.invokeMethod<void>('requestCounter'));
   }
 
   final _channel = const MethodChannel('dev.flutter.example/counter');
@@ -42,7 +44,7 @@ class CounterModel extends ChangeNotifier {
   int get count => _count;
 
   void increment() {
-    _channel.invokeMethod<void>('incrementCounter');
+    unawaited(_channel.invokeMethod<void>('incrementCounter'));
   }
 
   Future<dynamic> _handleMessage(MethodCall call) async {
@@ -151,7 +153,7 @@ class Contents extends StatelessWidget {
                 if (showExit) ...[
                   const SizedBox(height: 16),
                   ElevatedButton(
-                    onPressed: () => SystemNavigator.pop(animated: true),
+                    onPressed: () async => SystemNavigator.pop(animated: true),
                     child: const Text('Exit this screen'),
                   ),
                 ],

analysis_options.yaml

@@ -12,6 +12,7 @@ linter:
     cancel_subscriptions: true
     close_sinks: true
     directives_ordering: true
+    discarded_futures: true
     package_api_docs: true
     package_prefixed_library_names: true
     test_types_in_equals: true

animations/lib/main.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:flutter/foundation.dart';
@@ -45,13 +46,13 @@ void setupWindow() {
     setWindowTitle('Animation Samples');
     setWindowMinSize(const Size(windowWidth, windowHeight));
     setWindowMaxSize(const Size(windowWidth, windowHeight));
-    getCurrentScreen().then((screen) {
+    unawaited(getCurrentScreen().then((screen) {
       setWindowFrame(Rect.fromCenter(
         center: screen!.frame.center,
         width: windowWidth,
         height: windowHeight,
       ));
-    });
+    }));
   }
 }
 

animations/lib/src/basics/02_page_route_builder.dart

@@ -17,9 +17,8 @@ class PageRouteBuilderDemo extends StatelessWidget {
       body: Center(
         child: ElevatedButton(
           child: const Text('Go!'),
-          onPressed: () {
-            Navigator.of(context).push<void>(_createRoute());
-          },
+          onPressed: () async =>
+              Navigator.of(context).push<void>(_createRoute()),
         ),
       ),
     );

animations/lib/src/basics/06_custom_tween.dart

@@ -52,13 +52,13 @@ class _CustomTweenDemoState extends State<CustomTweenDemo>
         actions: [
           MaterialButton(
             textColor: Colors.white,
-            onPressed: () {
+            onPressed: () async {
               if (controller.status == AnimationStatus.completed) {
-                controller.reverse().whenComplete(() {
+                await controller.reverse().whenComplete(() {
                   setState(() {});
                 });
               } else {
-                controller.forward().whenComplete(() {
+                await controller.forward().whenComplete(() {
                   setState(() {});
                 });
               }

animations/lib/src/basics/08_fade_transition.dart

@@ -64,10 +64,10 @@ class _FadeTransitionDemoState extends State<FadeTransitionDemo>
             ),
             ElevatedButton(
               child: const Text('animate'),
-              onPressed: () => setState(() {
-                _controller.animateTo(1.0).then<TickerFuture>(
-                    (value) => _controller.animateBack(0.0));
-              }),
+              onPressed: () async {
+                await _controller.animateTo(1.0);
+                await _controller.animateBack(0.0);
+              },
             ),
           ],
         ),

animations/lib/src/misc/card_swipe.dart

@@ -167,15 +167,15 @@ class _SwipeableCardState extends State<SwipeableCard>
 
   /// Runs the fling / spring animation using the final velocity of the drag
   /// gesture.
-  void _dragEnd(DragEndDetails details) {
+  Future<void> _dragEnd(DragEndDetails details) async {
     final size = context.size;
 
     if (size == null) {
       return;
     }
 
     var velocity = (details.velocity.pixelsPerSecond.dx / size.width).abs();
-    _animate(velocity: velocity);
+    await _animate(velocity: velocity);
   }
 
   void _updateAnimation(double dragPosition) {
@@ -185,12 +185,12 @@ class _SwipeableCardState extends State<SwipeableCard>
     ));
   }
 
-  void _animate({double velocity = 0}) {
+  Future<void> _animate({double velocity = 0}) async {
     var description =
         const SpringDescription(mass: 50, stiffness: 1, damping: 1);
     var simulation =
         SpringSimulation(description, _controller.value, 1, velocity);
-    _controller.animateWith(simulation).then<void>((_) {
+    await _controller.animateWith(simulation).then<void>((_) {
       widget.onSwiped();
     });
   }

animations/lib/src/misc/focus_image.dart

@@ -80,9 +80,9 @@ class SmallCard extends StatelessWidget {
     return Card(
       child: Material(
         child: InkWell(
-          onTap: () {
+          onTap: () async {
             var nav = Navigator.of(context);
-            nav.push<void>(_createRoute(context, imageAssetName));
+            await nav.push<void>(_createRoute(context, imageAssetName));
           },
           child: Image.asset(
             imageAssetName,

animations/lib/src/misc/hero_animation.dart

@@ -22,7 +22,7 @@ class HeroAnimationDemo extends StatelessWidget {
             color: Colors.grey.shade300,
           ),
         ),
-        onTap: () => Navigator.of(context).push<void>(
+        onTap: () async => Navigator.of(context).push<void>(
             MaterialPageRoute(builder: (context) => const HeroPage())),
       ),
     );