add @required when there's an assert not null (#9124)

* add @required when there's an assert not null

* address review comments

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

@@ -31,8 +31,8 @@ const double _kAppBarMidHeight = 256.0;
 // TODO(hansmuller): it would be worth adding something like this to the framework.
 class _RenderStatusBarPaddingSliver extends RenderSliver {
   _RenderStatusBarPaddingSliver({
-    double maxHeight,
-    double scrollFactor,
+    @required double maxHeight,
+    @required double scrollFactor,
   }) : _maxHeight = maxHeight, _scrollFactor = scrollFactor {
     assert(maxHeight != null && maxHeight >= 0.0);
     assert(scrollFactor != null && scrollFactor >= 1.0);
@@ -264,8 +264,8 @@ class _AllSectionsView extends AnimatedWidget {
   _AllSectionsView({
     Key key,
     this.sectionIndex,
-    this.sections,
-    this.selectedIndex,
+    @required this.sections,
+    @required this.selectedIndex,
     this.minHeight,
     this.midHeight,
     this.maxHeight,

examples/flutter_gallery/lib/demo/animation/widgets.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import 'sections.dart';
@@ -10,7 +11,7 @@ const double kSectionIndicatorWidth = 32.0;
 
 // The card for a single section. Displays the section's gradient and background image.
 class SectionCard extends StatelessWidget {
-  SectionCard({ Key key, this.section }) : super(key: key) {
+  SectionCard({ Key key, @required this.section }) : super(key: key) {
     assert(section != null);
   }
 
@@ -60,7 +61,12 @@ class SectionTitle extends StatelessWidget {
     color: const Color(0x19000000),
   );
 
-  SectionTitle({ Key key, this.section, this.scale, this.opacity }) : super(key: key) {
+  SectionTitle({
+    Key key,
+    @required this.section,
+    @required this.scale,
+    @required this.opacity,
+  }) : super(key: key) {
     assert(section != null);
     assert(scale != null);
     assert(opacity != null && opacity >= 0.0 && opacity <= 1.0);
@@ -115,7 +121,7 @@ class SectionIndicator extends StatelessWidget {
 
 // Display a single SectionDetail.
 class SectionDetailView extends StatelessWidget {
-  SectionDetailView({ Key key, this.detail }) : super(key: key) {
+  SectionDetailView({ Key key, @required this.detail }) : super(key: key) {
     assert(detail != null && detail.imageAsset != null);
     assert((detail.imageAsset ?? detail.title) != null);
   }

examples/flutter_gallery/lib/demo/colors_demo.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 const double kColorItemHeight = 48.0;
@@ -41,7 +42,12 @@ final List<Palette> allPalettes = <Palette>[
 
 
 class ColorItem extends StatelessWidget {
-  ColorItem({ Key key, this.index, this.color, this.prefix: '' }) : super(key: key) {
+  ColorItem({
+    Key key,
+    @required this.index,
+    @required this.color,
+    this.prefix: '',
+  }) : super(key: key) {
     assert(index != null);
     assert(color != null);
     assert(prefix != null);

examples/flutter_gallery/lib/demo/material/cards_demo.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 class TravelDestination {
@@ -36,7 +37,7 @@ final List<TravelDestination> destinations = <TravelDestination>[
 ];
 
 class TravelDestinationItem extends StatelessWidget {
-  TravelDestinationItem({ Key key, this.destination }) : super(key: key) {
+  TravelDestinationItem({ Key key, @required this.destination }) : super(key: key) {
     assert(destination != null && destination.isValid);
   }
 

examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart

@@ -2,8 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:intl/intl.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
+import 'package:intl/intl.dart';
 
 // This demo is based on
 // https://material.google.com/components/dialogs.html#dialogs-full-screen-dialogs
@@ -15,7 +16,7 @@ enum DismissDialogAction {
 }
 
 class DateTimeItem extends StatelessWidget {
-  DateTimeItem({ Key key, DateTime dateTime, this.onChanged })
+  DateTimeItem({ Key key, DateTime dateTime, @required this.onChanged })
     : date = new DateTime(dateTime.year, dateTime.month, dateTime.day),
       time = new TimeOfDay(hour: dateTime.hour, minute: dateTime.minute),
       super(key: key) {

examples/flutter_gallery/lib/demo/material/grid_list_demo.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 enum GridDemoTileStyle {
@@ -143,9 +144,9 @@ class _GridPhotoViewerState extends State<GridPhotoViewer> with SingleTickerProv
 class GridDemoPhotoItem extends StatelessWidget {
   GridDemoPhotoItem({
     Key key,
-    this.photo,
-    this.tileStyle,
-    this.onBannerTap
+    @required this.photo,
+    @required this.tileStyle,
+    @required this.onBannerTap
   }) : super(key: key) {
     assert(photo != null && photo.isValid);
     assert(tileStyle != null);

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

@@ -116,7 +116,7 @@ class _ShrineGridDelegate extends SliverGridDelegate {
 
 // Displays the Vendor's name and avatar.
 class _VendorItem extends StatelessWidget {
-  _VendorItem({ Key key, this.vendor }) : super(key: key) {
+  _VendorItem({ Key key, @required this.vendor }) : super(key: key) {
     assert(vendor != null);
   }
 
@@ -148,7 +148,7 @@ class _VendorItem extends StatelessWidget {
 // Displays the product's price. If the product is in the shopping cart then the
 // background is highlighted.
 abstract class _PriceItem extends StatelessWidget {
-  _PriceItem({ Key key, this.product }) : super(key: key) {
+  _PriceItem({ Key key, @required this.product }) : super(key: key) {
     assert(product != null);
   }
 
@@ -240,7 +240,8 @@ class _HeadingLayout extends MultiChildLayoutDelegate {
 
 // A card that highlights the "featured" catalog item.
 class _Heading extends StatelessWidget {
-  _Heading({ Key key, this.product }) : super(key: key) {
+  _Heading({ Key key, @required this.product }) : super(key: key) {
+    assert(product != null);
     assert(product.featureTitle != null);
     assert(product.featureDescription != null);
   }
@@ -293,7 +294,7 @@ class _Heading extends StatelessWidget {
 // A card that displays a product's image, price, and vendor. The _ProductItem
 // cards appear in a grid below the heading.
 class _ProductItem extends StatelessWidget {
-  _ProductItem({ Key key, this.product, this.onPressed }) : super(key: key) {
+  _ProductItem({ Key key, @required this.product, this.onPressed }) : super(key: key) {
     assert(product != null);
   }
 

examples/flutter_gallery/lib/demo/shrine/shrine_order.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import '../shrine_demo.dart' show ShrinePageRoute;
@@ -11,7 +12,12 @@ import 'shrine_types.dart';
 
 // Displays the product title's, description, and order quantity dropdown.
 class _ProductItem extends StatelessWidget {
-  _ProductItem({ Key key, this.product, this.quantity, this.onChanged }) : super(key: key) {
+  _ProductItem({
+    Key key,
+    @required this.product,
+    @required this.quantity,
+    @required this.onChanged,
+  }) : super(key: key) {
     assert(product != null);
     assert(quantity != null);
     assert(onChanged != null);
@@ -64,7 +70,7 @@ class _ProductItem extends StatelessWidget {
 
 // Vendor name and description
 class _VendorItem extends StatelessWidget {
-  _VendorItem({ Key key, this.vendor }) : super(key: key) {
+  _VendorItem({ Key key, @required this.vendor }) : super(key: key) {
     assert(vendor != null);
   }
 
@@ -135,7 +141,12 @@ class _HeadingLayout extends MultiChildLayoutDelegate {
 // Describes a product and vendor in detail, supports specifying
 // a order quantity (0-5). Appears at the top of the OrderPage.
 class _Heading extends StatelessWidget {
-  _Heading({ Key key, this.product, this.quantity, this.quantityChanged }) : super(key: key) {
+  _Heading({
+    Key key,
+    @required this.product,
+    @required this.quantity,
+    this.quantityChanged,
+  }) : super(key: key) {
     assert(product != null);
     assert(quantity != null && quantity >= 0 && quantity <= 5);
   }
@@ -197,7 +208,12 @@ class _Heading extends StatelessWidget {
 }
 
 class OrderPage extends StatefulWidget {
-  OrderPage({ Key key, this.order, this.products, this.shoppingCart }) : super(key: key) {
+  OrderPage({
+    Key key,
+    @required this.order,
+    @required this.products,
+    @required this.shoppingCart,
+  }) : super(key: key) {
     assert(order != null);
     assert(products != null && products.isNotEmpty);
     assert(shoppingCart != null);

examples/flutter_gallery/lib/demo/shrine/shrine_page.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import 'shrine_theme.dart';
@@ -16,8 +17,8 @@ enum ShrineAction {
 class ShrinePage extends StatefulWidget {
   ShrinePage({
     Key key,
-    this.scaffoldKey,
-    this.body,
+    @required this.scaffoldKey,
+    @required this.body,
     this.floatingActionButton,
     this.products,
     this.shoppingCart

examples/flutter_gallery/lib/demo/shrine/shrine_theme.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 class ShrineStyle extends TextStyle {
@@ -26,7 +27,7 @@ TextStyle abrilFatfaceRegular34(Color color) => new ShrineStyle.abrilFatface(34.
 /// InheritedWidget is shared by all of the routes and widgets created for
 /// the Shrine app.
 class ShrineTheme extends InheritedWidget {
-  ShrineTheme({ Key key, Widget child }) : super(key: key, child: child) {
+  ShrineTheme({ Key key, @required Widget child }) : super(key: key, child: child) {
     assert(child != null);
   }
 

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

@@ -4,6 +4,8 @@
 
 import 'dart:ui' show hashValues;
 
+import 'package:flutter/foundation.dart';
+
 class Vendor {
   const Vendor({
     this.name,
@@ -64,7 +66,7 @@ class Product {
 }
 
 class Order {
-  Order({ this.product, this.quantity: 1, this.inCart: false }) {
+  Order({ @required this.product, this.quantity: 1, this.inCart: false }) {
     assert(product != null);
     assert(quantity != null && quantity >= 0);
     assert(inCart != null);

examples/flutter_gallery/lib/demo/typography_demo.dart

@@ -2,10 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 class TextStyleItem extends StatelessWidget {
-  TextStyleItem({ Key key, this.name, this.style, this.text }) : super(key: key) {
+  TextStyleItem({
+    Key key,
+    @required this.name,
+    @required this.style,
+    @required this.text,
+  }) : super(key: key) {
     assert(name != null);
     assert(style != null);
     assert(text != null);

examples/flutter_gallery/lib/gallery/drawer.dart

@@ -4,7 +4,7 @@
 
 import 'dart:math' as math;
 
-import 'package:flutter/foundation.dart' show defaultTargetPlatform;
+import 'package:flutter/foundation.dart' show defaultTargetPlatform, required;
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -90,9 +90,9 @@ class GalleryDrawer extends StatelessWidget {
   GalleryDrawer({
     Key key,
     this.useLightTheme,
-    this.onThemeChanged,
+    @required this.onThemeChanged,
     this.timeDilation,
-    this.onTimeDilationChanged,
+    @required this.onTimeDilationChanged,
     this.showPerformanceOverlay,
     this.onShowPerformanceOverlayChanged,
     this.checkerboardRasterCacheImages,

examples/flutter_gallery/lib/gallery/home.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 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import 'drawer.dart';
@@ -68,9 +69,9 @@ class GalleryHome extends StatefulWidget {
   GalleryHome({
     Key key,
     this.useLightTheme,
-    this.onThemeChanged,
+    @required this.onThemeChanged,
     this.timeDilation,
-    this.onTimeDilationChanged,
+    @required this.onTimeDilationChanged,
     this.showPerformanceOverlay,
     this.onShowPerformanceOverlayChanged,
     this.checkerboardRasterCacheImages,

examples/flutter_gallery/lib/gallery/item.dart

@@ -4,6 +4,7 @@
 
 import 'dart:developer';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import '../demo/all.dart';
@@ -11,7 +12,13 @@ import '../demo/all.dart';
 typedef Widget GalleryDemoBuilder();
 
 class GalleryItem extends StatelessWidget {
-  GalleryItem({ this.title, this.subtitle, this.category, this.routeName, this.buildRoute }) {
+  GalleryItem({
+    @required this.title,
+    this.subtitle,
+    @required this.category,
+    @required this.routeName,
+    @required this.buildRoute,
+  }) {
     assert(title != null);
     assert(category != null);
     assert(routeName != null);

examples/flutter_gallery/lib/gallery/updates.dart

@@ -4,13 +4,14 @@
 
 import 'dart:async';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
 typedef Future<String> UpdateUrlFetcher();
 
 class Updater extends StatefulWidget {
-  Updater({ this.updateUrlFetcher, this.child, Key key }) : super(key: key) {
+  Updater({ @required this.updateUrlFetcher, this.child, Key key }) : super(key: key) {
     assert(updateUrlFetcher != null);
   }
 

examples/layers/services/isolate.dart

@@ -5,6 +5,7 @@
 import 'dart:convert';
 import 'dart:isolate';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
@@ -16,7 +17,7 @@ typedef void OnResultListener(String result);
 // The choice of JSON parsing here is meant as an example that might surface
 // in real-world applications.
 class Calculator {
-  Calculator({ this.onProgressListener, this.onResultListener, String data })
+  Calculator({ @required this.onProgressListener, @required this.onResultListener, String data })
   // In order to keep the example files smaller, we "cheat" a little and
   // replicate our small json string into a 10,000-element array.
   : _data = _replicateJson(data, 10000) {
@@ -85,7 +86,7 @@ class CalculationMessage {
 // This class manages these ports and maintains state related to the
 // progress of the background computation.
 class CalculationManager {
-  CalculationManager({ this.onProgressListener, this.onResultListener })
+  CalculationManager({ @required this.onProgressListener, @required this.onResultListener })
   : _receivePort = new ReceivePort() {
     assert(onProgressListener != null);
     assert(onResultListener != null);

examples/stocks/lib/stock_types.dart

@@ -2,21 +2,23 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
+
 enum StockMode { optimistic, pessimistic }
 enum BackupMode { enabled, disabled }
 
 class StockConfiguration {
   StockConfiguration({
-    this.stockMode,
-    this.backupMode,
-    this.debugShowGrid,
-    this.debugShowSizes,
-    this.debugShowBaselines,
-    this.debugShowLayers,
-    this.debugShowPointers,
-    this.debugShowRainbow,
-    this.showPerformanceOverlay,
-    this.showSemanticsDebugger
+    @required this.stockMode,
+    @required this.backupMode,
+    @required this.debugShowGrid,
+    @required this.debugShowSizes,
+    @required this.debugShowBaselines,
+    @required this.debugShowLayers,
+    @required this.debugShowPointers,
+    @required this.debugShowRainbow,
+    @required this.showPerformanceOverlay,
+    @required this.showSemanticsDebugger
   }) {
     assert(stockMode != null);
     assert(backupMode != null);

packages/flutter/lib/src/animation/animations.dart

@@ -324,8 +324,8 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
   ///
   /// The parent and curve arguments must not be null.
   CurvedAnimation({
-    this.parent,
-    this.curve,
+    @required this.parent,
+    @required this.curve,
     this.reverseCurve
   }) {
     assert(parent != null);
@@ -546,8 +546,8 @@ abstract class CompoundAnimation<T> extends Animation<T>
   /// Creates a CompoundAnimation. Both arguments must be non-null. Either can
   /// be a CompoundAnimation itself to combine multiple animations.
   CompoundAnimation({
-    this.first,
-    this.next,
+    @required this.first,
+    @required this.next,
   }) {
     assert(first != null);
     assert(next != null);

packages/flutter/lib/src/animation/tween.dart

@@ -4,6 +4,8 @@
 
 import 'dart:ui' show Color, Size, Rect;
 
+import 'package:flutter/foundation.dart';
+
 import 'animation.dart';
 import 'animations.dart';
 import 'curves.dart';
@@ -231,7 +233,7 @@ class CurveTween extends Animatable<double> {
   /// Creates a curve tween.
   ///
   /// The [curve] argument must not be null.
-  CurveTween({ this.curve }) {
+  CurveTween({ @required this.curve }) {
     assert(curve != null);
   }
 

packages/flutter/lib/src/cupertino/slider.dart

@@ -189,7 +189,7 @@ const double _kAdjustmentUnit = 0.1; // Matches iOS implementation of material s
 
 class _RenderCupertinoSlider extends RenderConstrainedBox implements SemanticsActionHandler {
   _RenderCupertinoSlider({
-    double value,
+    @required double value,
     int divisions,
     Color activeColor,
     this.onChanged,

packages/flutter/lib/src/cupertino/switch.dart

@@ -135,8 +135,8 @@ const Duration _kToggleDuration = const Duration(milliseconds: 200);
 
 class _RenderCupertinoSwitch extends RenderConstrainedBox implements SemanticsActionHandler {
   _RenderCupertinoSwitch({
-    bool value,
-    Color activeColor,
+    @required bool value,
+    @required Color activeColor,
     ValueChanged<bool> onChanged,
     @required TickerProvider vsync,
   }) : _value = value,

packages/flutter/lib/src/foundation/binding.dart

@@ -199,7 +199,7 @@ abstract class BindingBase {
   /// service extension method is called with a new value.
   @protected
   void registerBoolServiceExtension({
-    String name,
+    @required String name,
     @required AsyncValueGetter<bool> getter,
     @required AsyncValueSetter<bool> setter
   }) {

packages/flutter/lib/src/material/bottom_navigation_bar.dart

@@ -487,9 +487,9 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
 
 class _Circle {
   _Circle({
-    this.state,
-    this.index,
-    this.color,
+    @required this.state,
+    @required this.index,
+    @required this.color,
     @required TickerProvider vsync,
   }) {
     assert(state != null);

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
@@ -49,8 +50,8 @@ class BottomSheet extends StatefulWidget {
   BottomSheet({
     Key key,
     this.animationController,
-    this.onClosing,
-    this.builder
+    @required this.onClosing,
+    @required this.builder
   }) : super(key: key) {
     assert(onClosing != null);
     assert(builder != null);
@@ -256,7 +257,7 @@ class _ModalBottomSheetRoute<T> extends PopupRoute<T> {
 ///  * [BottomSheet]
 ///  * [Scaffold.showBottomSheet]
 ///  * <https://material.google.com/components/bottom-sheets.html#bottom-sheets-modal-bottom-sheets>
-Future<T> showModalBottomSheet<T>({ BuildContext context, WidgetBuilder builder }) {
+Future<T> showModalBottomSheet<T>({ @required BuildContext context, @required WidgetBuilder builder }) {
   assert(context != null);
   assert(builder != null);
   return Navigator.push(context, new _ModalBottomSheetRoute<T>(

packages/flutter/lib/src/material/data_table.dart

@@ -253,11 +253,11 @@ class DataTable extends StatelessWidget {
   /// otherwise it should be false.
   DataTable({
     Key key,
-    this.columns,
+    @required this.columns,
     this.sortColumnIndex,
     this.sortAscending: true,
     this.onSelectAll,
-    this.rows
+    @required this.rows
   }) : _onlyTextColumn = _initOnlyTextColumn(columns), super(key: key) {
     assert(columns != null);
     assert(columns.isNotEmpty);

packages/flutter/lib/src/material/drawer.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 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
@@ -117,7 +118,7 @@ class DrawerController extends StatefulWidget {
   /// The [child] argument must not be null and is typically a [Drawer].
   DrawerController({
     GlobalKey key,
-    this.child
+    @required this.child
   }) : super(key: key) {
     assert(child != null);
   }

packages/flutter/lib/src/material/dropdown.dart

@@ -286,7 +286,7 @@ class _DropdownRoute<T> extends PopupRoute<_DropdownRouteResult<T>> {
     this.selectedIndex,
     this.elevation: 8,
     this.theme,
-    this.style,
+    @required this.style,
   }) {
     assert(style != null);
   }
@@ -336,7 +336,7 @@ class DropdownMenuItem<T> extends StatelessWidget {
   DropdownMenuItem({
     Key key,
     this.value,
-    this.child,
+    @required this.child,
   }) : super(key: key) {
     assert(child != null);
   }
@@ -372,7 +372,7 @@ class DropdownButtonHideUnderline extends InheritedWidget {
   /// be given.
   DropdownButtonHideUnderline({
     Key key,
-    Widget child,
+    @required Widget child,
   }) : super(key: key, child: child) {
     assert(child != null);
   }

packages/flutter/lib/src/material/flat_button.dart

@@ -58,7 +58,7 @@ class FlatButton extends StatelessWidget {
     this.disabledColor,
     this.textTheme,
     this.colorBrightness,
-    this.child
+    @required this.child
   }) : super(key: key) {
     assert(child != null);
   }

packages/flutter/lib/src/material/input.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 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 
@@ -691,7 +692,7 @@ class _AnimatedLabel extends ImplicitlyAnimatedWidget {
   _AnimatedLabel({
     Key key,
     this.text,
-    this.style,
+    @required this.style,
     Curve curve: Curves.linear,
     Duration duration,
   }) : super(key: key, curve: curve, duration: duration) {

packages/flutter/lib/src/material/page.dart

@@ -195,7 +195,7 @@ class _CupertinoBackGestureController extends NavigationGestureController {
 class MaterialPageRoute<T> extends PageRoute<T> {
   /// Creates a page route for use in a material design app.
   MaterialPageRoute({
-    this.builder,
+    @required this.builder,
     RouteSettings settings: const RouteSettings(),
     this.maintainState: true,
   }) : super(settings: settings) {

packages/flutter/lib/src/material/paginated_data_table.dart

@@ -66,7 +66,7 @@ class PaginatedDataTable extends StatefulWidget {
     Key key,
     @required this.header,
     this.actions,
-    this.columns,
+    @required this.columns,
     this.sortColumnIndex,
     this.sortAscending: true,
     this.onSelectAll,

packages/flutter/lib/src/material/popup_menu.dart

@@ -438,9 +438,9 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
 /// 12, 16, 24. The elevation defaults to 8, the appropriate elevation for popup
 /// menus.
 Future<T> showMenu<T>({
-  BuildContext context,
+  @required BuildContext context,
   RelativeRect position,
-  List<PopupMenuEntry<T>> items,
+  @required List<PopupMenuEntry<T>> items,
   T initialValue,
   int elevation: 8
 }) {

packages/flutter/lib/src/material/refresh_indicator.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'progress_indicator.dart';
@@ -81,9 +82,9 @@ class RefreshIndicator extends StatefulWidget {
   /// [displacement] is 40.0 logical pixels.
   RefreshIndicator({
     Key key,
-    this.child,
+    @required this.child,
     this.displacement: 40.0,
-    this.onRefresh,
+    @required this.onRefresh,
     this.color,
     this.backgroundColor
   }) : super(key: key) {

packages/flutter/lib/src/material/slider.dart

@@ -261,7 +261,7 @@ BoxConstraints _getAdditionalConstraints(String label) {
 
 class _RenderSlider extends RenderConstrainedBox implements SemanticsActionHandler {
   _RenderSlider({
-    double value,
+    @required double value,
     int divisions,
     String label,
     Color activeColor,

packages/flutter/lib/src/material/snack_bar.dart

@@ -81,7 +81,7 @@ class SnackBarAction extends StatefulWidget {
   /// The [label] and [onPressed] arguments must be non-null.
   SnackBarAction({
     Key key,
-    this.label,
+    @required this.label,
     @required this.onPressed
   }) : super(key: key) {
     assert(label != null);

packages/flutter/lib/src/material/stepper.dart

@@ -131,7 +131,7 @@ class Stepper extends StatefulWidget {
   /// The [steps], [type], and [currentStep] arguments must not be null.
   Stepper({
     Key key,
-    this.steps,
+    @required this.steps,
     this.type: StepperType.vertical,
     this.currentStep: 0,
     this.onStepTapped,

packages/flutter/lib/src/material/tabs.dart

@@ -158,7 +158,7 @@ class _TabLabelBarRenderer extends RenderFlex {
     MainAxisAlignment mainAxisAlignment,
     CrossAxisAlignment crossAxisAlignment,
     TextBaseline textBaseline,
-    this.onPerformLayout,
+    @required this.onPerformLayout,
   }) : super(
     children: children,
     direction: direction,

packages/flutter/lib/src/material/theme.dart

@@ -35,7 +35,7 @@ class Theme extends InheritedWidget {
     Key key,
     @required this.data,
     this.isMaterialAppTheme: false,
-    Widget child
+    @required Widget child
   }) : super(key: key, child: child) {
     assert(child != null);
     assert(data != null);

packages/flutter/lib/src/material/theme_data.dart

@@ -184,36 +184,36 @@ class ThemeData {
   /// create intermediate themes based on two themes created with the
   /// [new ThemeData] constructor.
   ThemeData.raw({
-    this.brightness,
-    this.primaryColor,
-    this.primaryColorBrightness,
-    this.accentColor,
-    this.accentColorBrightness,
-    this.canvasColor,
-    this.scaffoldBackgroundColor,
-    this.cardColor,
-    this.dividerColor,
-    this.highlightColor,
-    this.splashColor,
-    this.selectedRowColor,
-    this.unselectedWidgetColor,
-    this.disabledColor,
-    this.buttonColor,
-    this.secondaryHeaderColor,
-    this.textSelectionColor,
-    this.textSelectionHandleColor,
-    this.backgroundColor,
-    this.dialogBackgroundColor,
-    this.indicatorColor,
-    this.hintColor,
-    this.errorColor,
-    this.textTheme,
-    this.primaryTextTheme,
-    this.accentTextTheme,
-    this.iconTheme,
-    this.primaryIconTheme,
-    this.accentIconTheme,
-    this.platform
+    @required this.brightness,
+    @required this.primaryColor,
+    @required this.primaryColorBrightness,
+    @required this.accentColor,
+    @required this.accentColorBrightness,
+    @required this.canvasColor,
+    @required this.scaffoldBackgroundColor,
+    @required this.cardColor,
+    @required this.dividerColor,
+    @required this.highlightColor,
+    @required this.splashColor,
+    @required this.selectedRowColor,
+    @required this.unselectedWidgetColor,
+    @required this.disabledColor,
+    @required this.buttonColor,
+    @required this.secondaryHeaderColor,
+    @required this.textSelectionColor,
+    @required this.textSelectionHandleColor,
+    @required this.backgroundColor,
+    @required this.dialogBackgroundColor,
+    @required this.indicatorColor,
+    @required this.hintColor,
+    @required this.errorColor,
+    @required this.textTheme,
+    @required this.primaryTextTheme,
+    @required this.accentTextTheme,
+    @required this.iconTheme,
+    @required this.primaryIconTheme,
+    @required this.accentIconTheme,
+    @required this.platform
   }) {
     assert(brightness != null);
     assert(primaryColor != null);
@@ -222,7 +222,6 @@ class ThemeData {
     assert(accentColorBrightness != null);
     assert(canvasColor != null);
     assert(scaffoldBackgroundColor != null);
-    assert(dialogBackgroundColor != null);
     assert(cardColor != null);
     assert(dividerColor != null);
     assert(highlightColor != null);
@@ -234,7 +233,8 @@ class ThemeData {
     assert(secondaryHeaderColor != null);
     assert(textSelectionColor != null);
     assert(textSelectionHandleColor != null);
-    assert(disabledColor != null);
+    assert(backgroundColor != null);
+    assert(dialogBackgroundColor != null);
     assert(indicatorColor != null);
     assert(hintColor != null);
     assert(errorColor != null);

packages/flutter/lib/src/material/time_picker.dart

@@ -625,7 +625,7 @@ class _DialState extends State<_Dial> with SingleTickerProviderStateMixin {
 class _TimePickerDialog extends StatefulWidget {
   _TimePickerDialog({
     Key key,
-    this.initialTime
+    @required this.initialTime
   }) : super(key: key) {
     assert(initialTime != null);
   }
@@ -793,9 +793,10 @@ class _TimePickerDialogState extends State<_TimePickerDialog> {
 ///  * [showDatePicker]
 ///  * <https://material.google.com/components/pickers.html#pickers-time-pickers>
 Future<TimeOfDay> showTimePicker({
-  BuildContext context,
-  TimeOfDay initialTime
+  @required BuildContext context,
+  @required TimeOfDay initialTime
 }) async {
+  assert(context != null);
   assert(initialTime != null);
   return await showDialog(
     context: context,

packages/flutter/lib/src/material/toggleable.dart

@@ -24,10 +24,10 @@ abstract class RenderToggleable extends RenderConstrainedBox implements Semantic
   /// The [value], [activeColor], and [inactiveColor] arguments must not be
   /// null.
   RenderToggleable({
-    bool value,
+    @required bool value,
     Size size,
-    Color activeColor,
-    Color inactiveColor,
+    @required Color activeColor,
+    @required Color inactiveColor,
     ValueChanged<bool> onChanged,
     @required TickerProvider vsync,
   }) : _value = value,

packages/flutter/lib/src/material/tooltip.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/widgets.dart';
 
@@ -42,12 +43,12 @@ class Tooltip extends StatefulWidget {
   /// The [message] argument cannot be null.
   Tooltip({
     Key key,
-    this.message,
+    @required this.message,
     this.height: 32.0,
     this.padding: const EdgeInsets.symmetric(horizontal: 16.0),
     this.verticalOffset: 24.0,
     this.preferBelow: true,
-    this.child,
+    @required this.child,
   }) : super(key: key) {
     assert(message != null);
     assert(height != null);

packages/flutter/lib/src/painting/box_painter.dart

@@ -1259,7 +1259,7 @@ class BoxDecoration extends Decoration {
 
 /// An object that paints a [BoxDecoration] into a canvas.
 class _BoxDecorationPainter extends BoxPainter {
-  _BoxDecorationPainter(this._decoration, VoidCallback onChange) : super(onChange) {
+  _BoxDecorationPainter(@required this._decoration, VoidCallback onChange) : super(onChange) {
     assert(_decoration != null);
   }
 

packages/flutter/lib/src/rendering/custom_layout.dart

@@ -267,7 +267,7 @@ class RenderCustomMultiChildLayoutBox extends RenderBox
   /// The [delegate] argument must not be null.
   RenderCustomMultiChildLayoutBox({
     List<RenderBox> children,
-    MultiChildLayoutDelegate delegate
+    @required MultiChildLayoutDelegate delegate
   }) : _delegate = delegate {
     assert(delegate != null);
     addAll(children);

packages/flutter/lib/src/rendering/flow.dart

@@ -180,7 +180,7 @@ class RenderFlow extends RenderBox
   /// [isRepaintBounday].
   RenderFlow({
     List<RenderBox> children,
-    FlowDelegate delegate
+    @required FlowDelegate delegate
   }) : _delegate = delegate {
     assert(delegate != null);
     addAll(children);

packages/flutter/lib/src/rendering/object.dart

@@ -613,9 +613,14 @@ class _SemanticsGeometry {
       parent.applyPaintTransform(child, transform);
     }
   }
-  void updateSemanticsNode({ RenderObject rendering, SemanticsNode semantics, SemanticsNode parentSemantics }) {
+  void updateSemanticsNode({
+    @required RenderObject rendering,
+    @required SemanticsNode semantics,
+    @required SemanticsNode parentSemantics,
+  }) {
     assert(rendering != null);
     assert(semantics != null);
+    assert(parentSemantics != null);
     assert(parentSemantics.wasAffectedByClip != null);
     semantics.transform = transform;
     if (clipRect != null) {
@@ -630,7 +635,7 @@ class _SemanticsGeometry {
 
 abstract class _SemanticsFragment {
   _SemanticsFragment({
-    RenderObject renderObjectOwner,
+    @required RenderObject renderObjectOwner,
     this.annotator,
     List<_SemanticsFragment> children
   }) {
@@ -670,8 +675,9 @@ abstract class _SemanticsFragment {
 /// that comes from the (dirty) ancestors.)
 class _CleanSemanticsFragment extends _SemanticsFragment {
   _CleanSemanticsFragment({
-    RenderObject renderObjectOwner
+    @required RenderObject renderObjectOwner
   }) : super(renderObjectOwner: renderObjectOwner) {
+    assert(renderObjectOwner != null);
     assert(renderObjectOwner._semantics != null);
   }
 
@@ -829,14 +835,18 @@ class _ImplicitSemanticsFragment extends _InterestingSemanticsFragment {
 class _ForkingSemanticsFragment extends _SemanticsFragment {
   _ForkingSemanticsFragment({
     RenderObject renderObjectOwner,
-    Iterable<_SemanticsFragment> children
+    @required Iterable<_SemanticsFragment> children
   }) : super(renderObjectOwner: renderObjectOwner, children: children) {
     assert(children != null);
     assert(children.length > 1);
   }
 
   @override
-  Iterable<SemanticsNode> compile({ _SemanticsGeometry geometry, SemanticsNode currentSemantics, SemanticsNode parentSemantics }) sync* {
+  Iterable<SemanticsNode> compile({
+    @required _SemanticsGeometry geometry,
+    SemanticsNode currentSemantics,
+    SemanticsNode parentSemantics
+  }) sync* {
     assert(!_debugCompiled);
     assert(() { _debugCompiled = true; return true; });
     assert(geometry != null);

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -835,7 +835,7 @@ class RenderBackdropFilter extends RenderProxyBox {
   /// Creates a backdrop filter.
   ///
   /// The [filter] argument must not be null.
-  RenderBackdropFilter({ RenderBox child, ui.ImageFilter filter })
+  RenderBackdropFilter({ RenderBox child, @required ui.ImageFilter filter })
     : _filter = filter, super(child) {
     assert(filter != null);
   }
@@ -1426,7 +1426,7 @@ class RenderTransform extends RenderProxyBox {
   ///
   /// The [transform] argument must not be null.
   RenderTransform({
-    Matrix4 transform,
+    @required Matrix4 transform,
     Offset origin,
     FractionalOffset alignment,
     this.transformHitTests: true,

packages/flutter/lib/src/rendering/rotated_box.dart

@@ -4,6 +4,7 @@
 
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/painting.dart';
 import 'package:vector_math/vector_math_64.dart';
@@ -23,7 +24,7 @@ class RenderRotatedBox extends RenderBox with RenderObjectWithChildMixin<RenderB
   ///
   /// The [quarterTurns] argument must not be null.
   RenderRotatedBox({
-    int quarterTurns,
+    @required int quarterTurns,
     RenderBox child
   }) : _quarterTurns = quarterTurns {
     assert(quarterTurns != null);

packages/flutter/lib/src/rendering/shifted_box.dart

@@ -93,7 +93,7 @@ class RenderPadding extends RenderShiftedBox {
   ///
   /// The [padding] argument must not be null and must have non-negative insets.
   RenderPadding({
-    EdgeInsets padding,
+    @required EdgeInsets padding,
     RenderBox child
   }) : _padding = padding, super(child) {
     assert(padding != null);
@@ -499,7 +499,7 @@ class RenderSizedOverflowBox extends RenderAligningShiftedBox {
   /// The [requestedSize] argument must not be null.
   RenderSizedOverflowBox({
     RenderBox child,
-    Size requestedSize,
+    @required Size requestedSize,
     FractionalOffset alignment: FractionalOffset.center
   }) : _requestedSize = requestedSize,
        super(child: child, alignment: alignment) {
@@ -792,7 +792,7 @@ class RenderCustomSingleChildLayoutBox extends RenderShiftedBox {
   /// The [delegate] argument must not be null.
   RenderCustomSingleChildLayoutBox({
     RenderBox child,
-    SingleChildLayoutDelegate delegate
+    @required SingleChildLayoutDelegate delegate
   }) : _delegate = delegate, super(child) {
     assert(delegate != null);
   }
@@ -901,8 +901,8 @@ class RenderBaseline extends RenderShiftedBox {
   /// The [baseline] and [baselineType] arguments must not be null.
   RenderBaseline({
     RenderBox child,
-    double baseline,
-    TextBaseline baselineType
+    @required double baseline,
+    @required TextBaseline baselineType
   }) : _baseline = baseline,
        _baselineType = baselineType,
        super(child) {

packages/flutter/lib/src/rendering/sliver_padding.dart

@@ -29,7 +29,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
   ///
   /// The [padding] argument must not be null and must have non-negative insets.
   RenderSliverPadding({
-    EdgeInsets padding,
+    @required EdgeInsets padding,
     RenderSliver child,
   }) : _padding = padding {
     assert(padding != null);

packages/flutter/lib/src/rendering/stack.dart

@@ -489,7 +489,7 @@ class RenderIndexedStack extends RenderStack {
   }
 
   @override
-  bool hitTestChildren(HitTestResult result, { Point position }) {
+  bool hitTestChildren(HitTestResult result, { @required Point position }) {
     if (firstChild == null || index == null)
       return false;
     assert(position != null);

packages/flutter/lib/src/services/image_stream.dart

@@ -15,7 +15,7 @@ class ImageInfo {
   /// Creates an [ImageInfo] object for the given image and scale.
   ///
   /// Both the image and the scale must not be null.
-  ImageInfo({ this.image, this.scale: 1.0 }) {
+  ImageInfo({ @required this.image, this.scale: 1.0 }) {
     assert(image != null);
     assert(scale != null);
   }

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

@@ -2314,7 +2314,7 @@ class Flow extends MultiChildRenderObjectWidget {
   /// The [delegate] argument must not be null.
   Flow.unwrapped({
     Key key,
-    this.delegate,
+    @required this.delegate,
     List<Widget> children: const <Widget>[],
   }) : super(key: key, children: children) {
     assert(delegate != null);

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

@@ -128,8 +128,8 @@ class Dismissible extends StatefulWidget {
 
 class _DismissibleClipper extends CustomClipper<Rect> {
   _DismissibleClipper({
-    this.axis,
-    this.moveAnimation
+    @required this.axis,
+    @required this.moveAnimation
   }) : super(reclip: moveAnimation) {
     assert(axis != null);
     assert(moveAnimation != null);

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

@@ -437,7 +437,7 @@ typedef void _OnDragEnd(Velocity velocity, Offset offset, bool wasAccepted);
 // eeding this object pointer events even after it has been disposed.
 class _DragAvatar<T> extends Drag {
   _DragAvatar({
-    this.overlayState,
+    @required this.overlayState,
     this.data,
     Point initialPosition,
     this.dragStartPoint: Point.origin,

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

@@ -21,7 +21,7 @@ class _FocusScope extends InheritedWidget {
   _FocusScope({
     Key key,
     this.focusState,
-    this.scopeFocused,
+    @required this.scopeFocused,
     this.focusedScope,
     this.focusedWidget,
     @required Widget child,

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

@@ -516,7 +516,7 @@ class AnimatedOpacity extends ImplicitlyAnimatedWidget {
   AnimatedOpacity({
     Key key,
     this.child,
-    this.opacity,
+    @required this.opacity,
     Curve curve: Curves.linear,
     @required Duration duration,
   }) : super(key: key, curve: curve, duration: duration) {

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

@@ -825,7 +825,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
   ///
   /// This can be useful in combination with [removeRouteBelow] when building a
   /// non-linear user experience.
-  void replace({ Route<dynamic> oldRoute, Route<dynamic> newRoute }) {
+  void replace({ @required Route<dynamic> oldRoute, @required Route<dynamic> newRoute }) {
     assert(!_debugLocked);
     assert(oldRoute != null);
     assert(newRoute != null);
@@ -919,7 +919,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
   /// route must not be the first route in the history.
   ///
   /// In every other way, this acts the same as [replace].
-  void replaceRouteBelow({ Route<dynamic> anchorRoute, Route<dynamic> newRoute }) {
+  void replaceRouteBelow({ @required Route<dynamic> anchorRoute, Route<dynamic> newRoute }) {
     assert(anchorRoute != null);
     assert(anchorRoute._navigator == this);
     assert(_history.indexOf(anchorRoute) > 0);

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

@@ -386,7 +386,7 @@ class OverlayState extends State<Overlay> with TickerProviderStateMixin {
 class _Theatre extends RenderObjectWidget {
   _Theatre({
     this.onstage,
-    this.offstage,
+    @required this.offstage,
   }) {
     assert(offstage != null);
     assert(!offstage.any((Widget child) => child == null));

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

@@ -222,7 +222,7 @@ enum _GlowState { idle, absorb, pull, recede }
 
 class _GlowController extends ChangeNotifier {
   _GlowController({
-    TickerProvider vsync,
+    @required TickerProvider vsync,
     @required Color color,
     @required Axis axis,
   }) : _color = color,

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

 // Copyright 2015 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:flutter/foundation.dart';
 
 import 'basic.dart';
 import 'framework.dart';
@@ -68,7 +69,7 @@ class PageRouteBuilder<T> extends PageRoute<T> {
   /// and [maintainState] arguments must not be null.
   PageRouteBuilder({
     RouteSettings settings: const RouteSettings(),
-    this.pageBuilder,
+    @required this.pageBuilder,
     this.transitionsBuilder: _defaultTransitionsBuilder,
     this.transitionDuration: const Duration(milliseconds: 300),
     this.opaque: true,

packages/flutter/lib/src/widgets/size_changed_layout_notifier.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 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
@@ -56,7 +57,7 @@ class SizeChangedLayoutNotifier extends SingleChildRenderObjectWidget {
 class _RenderSizeChangedWithCallback extends RenderProxyBox {
   _RenderSizeChangedWithCallback({
     RenderBox child,
-    this.onLayoutChangedCallback
+    @required this.onLayoutChangedCallback
   }) : super(child) {
     assert(onLayoutChangedCallback != null);
   }

packages/flutter/test/widgets/layout_builder_mutations_test.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 'package:flutter/foundation.dart';
 import 'package:flutter/src/widgets/basic.dart';
 import 'package:flutter/src/widgets/framework.dart';
 import 'package:flutter/src/widgets/layout_builder.dart';
@@ -10,7 +11,7 @@ import 'package:flutter_test/flutter_test.dart' hide TypeMatcher;
 class Wrapper extends StatelessWidget {
   Wrapper({
     Key key,
-    this.child
+    @required this.child
   }) : super(key: key) {
     assert(child != null);
   }

packages/flutter_test/lib/src/test_pointer.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 
 import 'test_async_utils.dart';
@@ -135,8 +136,8 @@ class TestGesture {
   /// via the `dispatcher` argument.
   static Future<TestGesture> down(Point downLocation, {
     int pointer: 1,
-    HitTester hitTester,
-    EventDispatcher dispatcher
+    @required HitTester hitTester,
+    @required EventDispatcher dispatcher,
   }) async {
     assert(hitTester != null);
     assert(dispatcher != null);

packages/flutter_tools/lib/src/application_package.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 'package:meta/meta.dart' show required;
 import 'package:xml/xml.dart' as xml;
 
 import 'android/android_sdk.dart';
@@ -18,7 +19,7 @@ abstract class ApplicationPackage {
   /// Package ID from the Android Manifest or equivalent.
   final String id;
 
-  ApplicationPackage({ this.id }) {
+  ApplicationPackage({ @required this.id }) {
     assert(id != null);
   }
 
@@ -41,8 +42,8 @@ class AndroidApk extends ApplicationPackage {
 
   AndroidApk({
     String id,
-    this.apkPath,
-    this.launchActivity
+    @required this.apkPath,
+    @required this.launchActivity
   }) : super(id: id) {
     assert(apkPath != null);
     assert(launchActivity != null);

packages/flutter_tools/lib/src/commands/build_apk.dart

@@ -4,6 +4,8 @@
 
 import 'dart:async';
 
+import 'package:meta/meta.dart' show required;
+
 import '../android/android_sdk.dart';
 import '../android/gradle.dart';
 import '../base/common.dart';
@@ -14,7 +16,7 @@ import 'build.dart';
 export '../android/android_device.dart' show AndroidDevice;
 
 class ApkKeystoreInfo {
-  ApkKeystoreInfo({ this.keystore, this.password, this.keyAlias, this.keyPassword }) {
+  ApkKeystoreInfo({ this.keystore, this.password, this.keyAlias, @required this.keyPassword }) {
     assert(keystore != null);
   }
 

packages/flutter_tools/lib/src/flx.dart

@@ -4,6 +4,8 @@
 
 import 'dart:async';
 
+import 'package:meta/meta.dart' show required;
+
 import 'artifacts.dart';
 import 'asset.dart';
 import 'base/common.dart';
@@ -27,10 +29,10 @@ const String _kKernelKey = 'kernel_blob.bin';
 const String _kSnapshotKey = 'snapshot_blob.bin';
 
 Future<int> createSnapshot({
-  String mainPath,
-  String snapshotPath,
+  @required String mainPath,
+  @required String snapshotPath,
   String depfilePath,
-  String packages
+  @required String packages
 }) {
   assert(mainPath != null);
   assert(snapshotPath != null);

packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -72,7 +72,7 @@ typedef Future<Null> _Finalizer();
 
 class _FlutterPlatform extends PlatformPlugin {
   _FlutterPlatform({
-    this.shellPath,
+    @required this.shellPath,
     this.collector,
     this.debuggerMode,
     this.explicitObservatoryPort,

packages/flutter_tools/lib/src/vmservice.dart

@@ -8,6 +8,7 @@ import 'dart:convert' show BASE64;
 import 'package:file/file.dart';
 import 'package:json_rpc_2/error_code.dart' as rpc_error_code;
 import 'package:json_rpc_2/json_rpc_2.dart' as rpc;
+import 'package:meta/meta.dart' show required;
 import 'package:stream_channel/stream_channel.dart';
 import 'package:web_socket_channel/io.dart';
 import 'package:web_socket_channel/web_socket_channel.dart';
@@ -680,8 +681,8 @@ class VM extends ServiceObjectOwner {
 
   // Write one file into a file system.
   Future<Map<String, dynamic>> writeDevFSFile(String fsName, {
-    String path,
-    List<int> fileContents
+    @required String path,
+    @required List<int> fileContents
   }) {
     assert(path != null);
     assert(fileContents != null);