prefer_is_empty and prefer_is_not_empty (#8474)

dev/devicelab/lib/framework/adb.dart

@@ -299,7 +299,7 @@ class IosDeviceDiscovery implements DeviceDiscovery {
       .map((String id) => new IosDevice(deviceId: id))
       .toList();
 
-    if (allDevices.length == 0)
+    if (allDevices.isEmpty)
       throw 'No iOS devices detected';
 
     // TODO(yjbanov): filter out and warn about those with low battery level

examples/flutter_gallery/lib/demo/calculator/home.dart

@@ -29,7 +29,7 @@ class _CalculatorState extends State<Calculator> {
 
   /// Pop the top expression off of the stack and make it the current expression.
   void popCalcExpression() {
-    if (_expressionStack.length > 0) {
+    if (_expressionStack.isNotEmpty) {
       _expression = _expressionStack.removeLast();
     } else {
       _expression = new CalcExpression.Empty();

examples/flutter_gallery/lib/demo/calculator/logic.dart

@@ -287,7 +287,7 @@ class CalcExpression {
     // where a "term" is defined to be a sequence of numbers separated by
     // multiplcation or division symbols.
     num currentTermValue = removeNextTerm(list);
-    while (list.length > 0) {
+    while (list.isNotEmpty) {
       OperationToken opToken = list.removeAt(0);
       num nextTermValue = removeNextTerm(list);
       switch (opToken.operation) {
@@ -312,10 +312,10 @@ class CalcExpression {
   /// A "term" is a sequence of number tokens separated by multiplication
   /// and division symbols.
   static num removeNextTerm(List<ExpressionToken> list) {
-    assert(list != null && list.length >= 1);
+    assert(list != null && list.isNotEmpty);
     final NumberToken firstNumToken = list.removeAt(0);
     num currentValue = firstNumToken.number;
-    while (list.length > 0) {
+    while (list.isNotEmpty) {
       bool isDivision = false;
       OperationToken nextOpToken = list.first;
       switch (nextOpToken.operation) {

examples/flutter_gallery/lib/demo/shrine/shrine_order.dart

@@ -118,7 +118,7 @@ class OrderItem extends StatelessWidget {
 class OrderPage extends StatefulWidget {
   OrderPage({ Key key, this.order, this.products, this.shoppingCart }) : super(key: key) {
     assert(order != null);
-    assert(products != null && products.length > 0);
+    assert(products != null && products.isNotEmpty);
     assert(shoppingCart != null);
   }
 

examples/flutter_gallery/lib/demo/shrine/shrine_types.dart

@@ -54,7 +54,7 @@ class Product {
       description != null &&
       imageAsset != null &&
       categories != null &&
-      categories.length > 0 &&
+      categories.isNotEmpty &&
       price != null &&
       vendor.isValid();
   }

examples/flutter_gallery/lib/gallery/syntax_highlighter.dart

@@ -309,7 +309,7 @@ class DartSyntaxHighlighter extends SyntaxHighlighter {
   }
 
   bool _firstLetterIsUpperCase(String str) {
-    if (str.length > 0) {
+    if (str.isNotEmpty) {
       String first = str.substring(0, 1);
       return first == first.toUpperCase();
     }

packages/flutter/lib/src/widgets/routes.dart

@@ -775,7 +775,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// * [removeScopedWillPopCallback], which removes a callback.
   @protected
   bool get hasScopedWillPopCallback {
-    return _scopeKey.currentState == null || _scopeKey.currentState._willPopCallbacks.length > 0;
+    return _scopeKey.currentState == null || _scopeKey.currentState._willPopCallbacks.isNotEmpty;
   }
 
   @override

packages/flutter_driver/lib/src/driver.dart

@@ -408,7 +408,7 @@ class FlutterDriver {
 
   /// Starts recording performance traces.
   Future<Null> startTracing({List<TimelineStream> streams: _defaultStreams}) async {
-    assert(streams != null && streams.length > 0);
+    assert(streams != null && streams.isNotEmpty);
     try {
       await _peer.sendRequest(_kSetVMTimelineFlagsMethod, <String, String>{
         'recordedStreams': _timelineStreamsToString(streams)

packages/flutter_markdown/lib/src/markdown_raw.dart

@@ -264,7 +264,7 @@ class _Renderer implements md.NodeVisitor {
       _listIndents.removeLast();
 
     if (_isBlockTag(element.tag)) {
-      if (_currentBlock.stack.length > 0) {
+      if (_currentBlock.stack.isNotEmpty) {
         _MarkdownNodeList stackList = _currentBlock.stack.first;
         _currentBlock.stack = stackList.list;
         _currentBlock.open = false;
@@ -358,7 +358,7 @@ class _Block {
   bool get open => _open;
   set open(bool open) {
     _open = open;
-    if (!open && subBlocks.length > 0)
+    if (!open && subBlocks.isNotEmpty)
       subBlocks.last.isLast = true;
   }
 
@@ -376,7 +376,7 @@ class _Block {
 
     Widget contents;
 
-    if (subBlocks.length > 0) {
+    if (subBlocks.isNotEmpty) {
       List<Widget> subWidgets = <Widget>[];
       for (_Block subBlock in subBlocks) {
         subWidgets.add(subBlock.build(context));
@@ -390,7 +390,7 @@ class _Block {
       TextSpan span = _stackToTextSpan(new _MarkdownNodeList(stack));
       contents = new RichText(text: span);
 
-      if (listIndents.length > 0) {
+      if (listIndents.isNotEmpty) {
         Widget bullet;
         if (listIndents.last == 'ul') {
           bullet = new Text(
@@ -479,7 +479,7 @@ class _Block {
 
   Widget _buildImage(BuildContext context, String src) {
     List<String> parts = src.split('#');
-    if (parts.length == 0) return new Container();
+    if (parts.isEmpty) return new Container();
 
     String path = parts.first;
     double width;

packages/flutter_tools/lib/src/devfs.dart

@@ -247,7 +247,7 @@ class _DevFSHttpWriter {
 
   void _scheduleWrites(DevFSProgressReporter progressReporter) {
     while (_inFlight < kMaxInFlight) {
-      if (_outstanding.length == 0) {
+      if (_outstanding.isEmpty) {
         // Finished.
         break;
       }
@@ -289,7 +289,7 @@ class _DevFSHttpWriter {
       progressReporter(_done, _max);
     }
     _inFlight--;
-    if ((_outstanding.length == 0) && (_inFlight == 0)) {
+    if ((_outstanding.isEmpty) && (_inFlight == 0)) {
       _completer.complete(null);
     } else {
       _scheduleWrites(progressReporter);
@@ -411,7 +411,7 @@ class DevFS {
           assetPathsToEvict.add(archivePath);
       }
     });
-    if (dirtyEntries.length > 0) {
+    if (dirtyEntries.isNotEmpty) {
       printTrace('Updating files');
       if (_httpWriter != null) {
         try {

packages/flutter_tools/lib/src/ios/devices.dart

@@ -251,7 +251,7 @@ class IOSDevice extends Device {
       '--justlaunch',
     ];
 
-    if (launchArguments.length > 0) {
+    if (launchArguments.isNotEmpty) {
       launchCommand.add('--args');
       launchCommand.add('${launchArguments.join(" ")}');
     }

packages/flutter_tools/test/devfs_test.dart

@@ -329,7 +329,7 @@ Directory _newTempDir() {
 }
 
 void _cleanupTempDirs() {
-  while (_tempDirs.length > 0) {
+  while (_tempDirs.isNotEmpty) {
     _tempDirs.removeLast().deleteSync(recursive: true);
   }
 }