Add const non-null asserts where required (#9945)

Also includes minor doc fixes.

dev/benchmarks/complex_layout/lib/main.dart

@@ -349,10 +349,10 @@ class UserHeader extends StatelessWidget {
       child: new Row(
         crossAxisAlignment: CrossAxisAlignment.start,
         children: <Widget>[
-          new Padding(
+          const Padding(
             padding: const EdgeInsets.only(right: 8.0),
-            child: new Image(
-              image: new AssetImage('packages/flutter_gallery_assets/ali_connors_sml.png'),
+            child: const Image(
+              image: const AssetImage('packages/flutter_gallery_assets/ali_connors_sml.png'),
               width: 32.0,
               height: 32.0
             )
@@ -407,10 +407,10 @@ class ItemImageBox extends StatelessWidget {
           children: <Widget>[
             new Stack(
               children: <Widget>[
-                new SizedBox(
+                const SizedBox(
                   height: 230.0,
-                  child: new Image(
-                    image: new AssetImage('packages/flutter_gallery_assets/top_10_australian_beaches.png')
+                  child: const Image(
+                    image: const AssetImage('packages/flutter_gallery_assets/top_10_australian_beaches.png')
                   )
                 ),
                 new Theme(

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

@@ -93,10 +93,10 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
             new UserAccountsDrawerHeader(
               accountName: const Text('Zach Widget'),
               accountEmail: const Text('zach.widget@example.com'),
-              currentAccountPicture: new CircleAvatar(backgroundImage: new AssetImage(_kAsset0)),
-              otherAccountsPictures: <Widget>[
-                new CircleAvatar(backgroundImage: new AssetImage(_kAsset1)),
-                new CircleAvatar(backgroundImage: new AssetImage(_kAsset2)),
+              currentAccountPicture: const CircleAvatar(backgroundImage: const AssetImage(_kAsset0)),
+              otherAccountsPictures: const <Widget>[
+                const CircleAvatar(backgroundImage: const AssetImage(_kAsset1)),
+                const CircleAvatar(backgroundImage: const AssetImage(_kAsset2)),
               ],
               onDetailsPressed: () {
                 _showDrawerContents = !_showDrawerContents;
@@ -164,10 +164,10 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
               new Container(
                 width: 100.0,
                 height: 100.0,
-                decoration: new BoxDecoration(
+                decoration: const BoxDecoration(
                   shape: BoxShape.circle,
-                  image: new DecorationImage(
-                    image: new AssetImage(_kAsset0),
+                  image: const DecorationImage(
+                    image: const AssetImage(_kAsset0),
                   ),
                 ),
               ),

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

@@ -33,7 +33,7 @@ class FlutterErrorDetails {
     this.stackFilter,
     this.informationCollector,
     this.silent: false
-  }) : assert(exception != null);
+  });
 
   /// The exception. Often this will be an [AssertionError], maybe specifically
   /// a [FlutterError]. However, this could be any value at all.

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

@@ -504,7 +504,9 @@ class BoxHitTestEntry extends HitTestEntry {
   /// Creates a box hit test entry.
   ///
   /// The [localPosition] argument must not be null.
-  const BoxHitTestEntry(RenderBox target, this.localPosition) : super(target);
+  const BoxHitTestEntry(RenderBox target, this.localPosition)
+      : assert(localPosition != null),
+        super(target);
 
   @override
   RenderBox get target => super.target;

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

@@ -229,6 +229,7 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
   TextBaseline get textBaseline => _textBaseline;
   TextBaseline _textBaseline;
   set textBaseline(TextBaseline value) {
+    assert(_crossAxisAlignment != CrossAxisAlignment.baseline || value != null);
     if (_textBaseline != value) {
       _textBaseline = value;
       markNeedsLayout();

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

@@ -2627,7 +2627,8 @@ class RenderSemanticsGestureHandler extends RenderProxyBox implements SemanticsA
     GestureDragUpdateCallback onHorizontalDragUpdate,
     GestureDragUpdateCallback onVerticalDragUpdate,
     this.scrollFactor: 0.8
-  }) : _onTap = onTap,
+  }) : assert(scrollFactor != null),
+       _onTap = onTap,
        _onLongPress = onLongPress,
        _onHorizontalDragUpdate = onHorizontalDragUpdate,
        _onVerticalDragUpdate = onVerticalDragUpdate,

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

@@ -189,7 +189,14 @@ class SliverConstraints extends Constraints {
     @required this.remainingPaintExtent,
     @required this.crossAxisExtent,
     @required this.viewportMainAxisExtent,
-  });
+  }) : assert(axisDirection != null),
+       assert(growthDirection != null),
+       assert(userScrollDirection != null),
+       assert(scrollOffset != null),
+       assert(overlap != null),
+       assert(remainingPaintExtent != null),
+       assert(crossAxisExtent != null),
+       assert(viewportMainAxisExtent != null);
 
   /// Creates a copy of this object but with the given fields replaced with the
   /// new values.
@@ -469,7 +476,13 @@ class SliverGeometry {
     bool visible,
     this.hasVisualOverflow: false,
     this.scrollOffsetCorrection: 0.0
-  }) : layoutExtent = layoutExtent ?? paintExtent,
+  }) : assert(scrollExtent != null),
+       assert(paintExtent != null),
+       assert(paintOrigin != null),
+       assert(maxPaintExtent != null),
+       assert(hasVisualOverflow != null),
+       assert(scrollOffsetCorrection != null),
+       layoutExtent = layoutExtent ?? paintExtent,
        hitTestExtent = hitTestExtent ?? paintExtent,
        visible = visible ?? paintExtent > 0.0;
 
@@ -635,7 +648,9 @@ class SliverHitTestEntry extends HitTestEntry {
   const SliverHitTestEntry(RenderSliver target, {
     @required this.mainAxisPosition,
     @required this.crossAxisPosition,
-  }) : super(target);
+  }) : assert(mainAxisPosition != null),
+       assert(crossAxisPosition != null),
+       super(target);
 
   @override
   RenderSliver get target => super.target;

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

@@ -151,7 +151,11 @@ class SliverGridRegularTileLayout extends SliverGridLayout {
     @required this.crossAxisStride,
     @required this.childMainAxisExtent,
     @required this.childCrossAxisExtent,
-  });
+  }) : assert(crossAxisCount != null && crossAxisCount > 0),
+       assert(mainAxisStride != null && mainAxisStride >= 0),
+       assert(crossAxisStride != null && crossAxisStride >= 0),
+       assert(childMainAxisExtent != null && childMainAxisExtent >= 0),
+       assert(childCrossAxisExtent != null && childCrossAxisExtent >= 0);
 
   /// The number of children in the cross axis.
   final int crossAxisCount;
@@ -272,7 +276,10 @@ class SliverGridDelegateWithFixedCrossAxisCount extends SliverGridDelegate {
     this.mainAxisSpacing: 0.0,
     this.crossAxisSpacing: 0.0,
     this.childAspectRatio: 1.0,
-  });
+  }) : assert(crossAxisCount != null && crossAxisCount > 0),
+       assert(mainAxisSpacing != null && mainAxisSpacing >= 0),
+       assert(crossAxisSpacing != null && crossAxisSpacing >= 0),
+       assert(childAspectRatio != null && childAspectRatio > 0);
 
   /// The number of children in the cross axis.
   final int crossAxisCount;
@@ -347,15 +354,18 @@ class SliverGridDelegateWithMaxCrossAxisExtent extends SliverGridDelegate {
   /// Creates a delegate that makes grid layouts with tiles that have a maximum
   /// cross-axis extent.
   ///
-  /// All of the arguments must not be null. The `maxCrossAxisExtent` and
-  /// `crossAxisSpacing` arguments must not be negative. The `crossAxisCount`
-  /// and `childAspectRatio` arguments must be greater than zero.
+  /// All of the arguments must not be null. The [maxCrossAxisExtent] and
+  /// [mainAxisSpacing], and [crossAxisSpacing] arguments must not be negative.
+  /// The [childAspectRatio] argument must be greater than zero.
   const SliverGridDelegateWithMaxCrossAxisExtent({
     @required this.maxCrossAxisExtent,
     this.mainAxisSpacing: 0.0,
     this.crossAxisSpacing: 0.0,
     this.childAspectRatio: 1.0,
-  });
+  }) : assert(maxCrossAxisExtent != null && maxCrossAxisExtent >= 0),
+       assert(mainAxisSpacing != null && mainAxisSpacing >= 0),
+       assert(crossAxisSpacing != null && crossAxisSpacing >= 0),
+       assert(childAspectRatio != null && childAspectRatio > 0);
 
   /// The maximum extent of tiles in the cross axis.
   ///

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

@@ -121,7 +121,7 @@ class FixedColumnWidth extends TableColumnWidth {
   /// Creates a column width based on a fixed number of logical pixels.
   ///
   /// The [value] argument must not be null.
-  const FixedColumnWidth(this.value);
+  const FixedColumnWidth(this.value) : assert(value != null);
 
   /// The width the column should occupy in logical pixels.
   final double value;
@@ -148,7 +148,7 @@ class FractionColumnWidth extends TableColumnWidth {
   /// maxWidth.
   ///
   /// The [value] argument must not be null.
-  const FractionColumnWidth(this.value);
+  const FractionColumnWidth(this.value) : assert(value != null);
 
   /// The fraction of the table's constraints' maxWidth that this column should
   /// occupy.
@@ -184,7 +184,7 @@ class FlexColumnWidth extends TableColumnWidth {
   /// the other columns have been laid out.
   ///
   /// The [value] argument must not be null.
-  const FlexColumnWidth([this.value = 1.0]);
+  const FlexColumnWidth([this.value = 1.0]) : assert(value != null);
 
   /// The reaction of the of the remaining space once all the other columns have
   /// been laid out that this column should occupy.

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

@@ -223,7 +223,9 @@ class AssetBundleImageKey {
     @required this.bundle,
     @required this.name,
     @required this.scale
-  });
+  }) : assert(bundle != null),
+       assert(name != null),
+       assert(scale != null);
 
   /// The bundle from which the image will be obtained.
   ///
@@ -312,7 +314,9 @@ class NetworkImage extends ImageProvider<NetworkImage> {
   /// Creates an object that fetches the image at the given URL.
   ///
   /// The arguments must not be null.
-  const NetworkImage(this.url, { this.scale: 1.0 }) : assert(url != null);
+  const NetworkImage(this.url, { this.scale: 1.0 })
+      : assert(url != null),
+        assert(scale != null);
 
   /// The URL from which the image will be fetched.
   final String url;
@@ -382,7 +386,9 @@ class FileImage extends ImageProvider<FileImage> {
   /// Creates an object that decodes a [File] as an image.
   ///
   /// The arguments must not be null.
-  const FileImage(this.file, { this.scale: 1.0 });
+  const FileImage(this.file, { this.scale: 1.0 })
+      : assert(file != null),
+        assert(scale != null);
 
   /// The file to decode into an image.
   final File file;
@@ -444,7 +450,9 @@ class MemoryImage extends ImageProvider<MemoryImage> {
   /// Creates an object that decodes a [Uint8List] buffer as an image.
   ///
   /// The arguments must not be null.
-  const MemoryImage(this.bytes, { this.scale: 1.0 });
+  const MemoryImage(this.bytes, { this.scale: 1.0 })
+      : assert(bytes != null),
+        assert(scale != null);
 
   /// The bytes to decode into an image.
   final Uint8List bytes;
@@ -504,13 +512,11 @@ class ExactAssetImage extends AssetBundleImageProvider {
   /// defaults to 1.0. The [bundle] argument may be null, in which case the
   /// bundle provided in the [ImageConfiguration] passed to the [resolve] call
   /// will be used instead.
-  ExactAssetImage(this.name, {
+  const ExactAssetImage(this.name, {
     this.scale: 1.0,
     this.bundle
-  }) {
-    assert(name != null);
-    assert(scale != null);
-  }
+  }) : assert(name != null),
+       assert(scale != null);
 
   /// The key to use to obtain the resource from the [bundle]. This is the
   /// argument passed to [AssetBundle.load].

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

@@ -60,11 +60,7 @@ class AssetImage extends AssetBundleImageProvider {
   ///
   /// The [name] argument must not be null. It should name the main asset from
   /// the set of images to chose from.
-  AssetImage(this.name, {
-    this.bundle
-  }) {
-    assert(name != null);
-  }
+  const AssetImage(this.name, { this.bundle }) : assert(name != null);
 
   /// The name of the main asset from the set of images to chose from. See the
   /// documentation for the [AssetImage] class itself for details.

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

@@ -16,10 +16,9 @@ class ImageInfo {
   /// Creates an [ImageInfo] object for the given image and scale.
   ///
   /// Both the image and the scale must not be null.
-  ImageInfo({ @required this.image, this.scale: 1.0 }) {
-    assert(image != null);
-    assert(scale != null);
-  }
+  const ImageInfo({ @required this.image, this.scale: 1.0 })
+      : assert(image != null),
+        assert(scale != null);
 
   /// The raw image pixels.
   ///

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

@@ -42,7 +42,11 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
     this.keyCode: 0,
     this.scanCode: 0,
     this.metaState: 0,
-  });
+  }) : assert(flags != null),
+       assert(codePoint != null),
+       assert(keyCode != null),
+       assert(scanCode != null),
+       assert(metaState != null);
 
   /// See <https://developer.android.com/reference/android/view/KeyEvent.html#getFlags()>
   final int flags;
@@ -67,12 +71,14 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
 class RawKeyEventDataFuchsia extends RawKeyEventData {
   /// Creates a key event data structure specific for Android.
   ///
-  /// The [hidUsage] and [codePoint] arguments must not be null.
+  /// The [hidUsage], [codePoint], and [modifiers] arguments must not be null.
   const RawKeyEventDataFuchsia({
     this.hidUsage: 0,
     this.codePoint: 0,
     this.modifiers: 0,
-  });
+  }) : assert(hidUsage != null),
+       assert(codePoint != null),
+       assert(modifiers != null);
 
   /// The USB HID usage.
   ///
@@ -84,7 +90,7 @@ class RawKeyEventDataFuchsia extends RawKeyEventData {
   /// If there is no Unicode code point, this value is zero.
   final int codePoint;
 
-  /// The modifiers that we present when the key event occured.
+  /// The modifiers that we present when the key event occurred.
   ///
   /// See <https://fuchsia.googlesource.com/mozart/+/master/services/input/input_event_constants.fidl>
   /// for the numerical values of the modifiers.

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

@@ -21,11 +21,15 @@ class TextRange {
   const TextRange({
     @required this.start,
     @required this.end
-  });
+  }) : assert(start != null && start >= -1),
+       assert(end != null && end >= -1);
 
   /// A text range that starts and ends at offset.
+  ///
+  /// The [offset] argument must be non-null and greater than or equal to -1.
   const TextRange.collapsed(int offset)
-    : start = offset,
+    : assert(offset != null && offset >= -1),
+      start = offset,
       end = offset;
 
   /// A text range that contains nothing and is not in the text.