* Reland "Nnbd widgets (#64672)"

This reverts commit 127e6790.

* remove non-nullable enforcement on AsyncSnapshot

* make data param non-nullable for AsyncSnapshot.withData

* make some Text params non-nullable

This reverts commit e682ec71.

* migrate widget to nullsafety

* remove double blank line after license

* address review comments in actions.dart

* nullable ObjectKey.value

* use local variable oldElement

* make State.build non-nullable

* make State.context non-nullable

* newline at eof

* make ProxyWidget.child non-nullable

* make _InactiveElements.debugContains non-nullable

* make Element.depth non-nullable

* make ProxyElement.build non-nullable

* make StatefulElement.state non-nullable

* remove 'Notice that'

* avoid cast of list in RenderObjectElement.updateChildren

* make IndexedSlot.value non-nullable

* avoid cast of list in MultiChildRenderObjectElement.mount

* make some WidgetsApp parameters non-nullable

* hitTest take non-nullable position

* make ScrollableState.position non-nullable

* use _pixels instead of pixels

* make ViewportOffset.pixels non-nullable

* make param and return type of IndexedWidgetBuilder non-nullable

* unused_import

* make context param non-nullable for Builder in animated_list.dart

* make ScrollMetrics.viewportDimension non-nullable

* make ScrollMetrics.{min,max}ScrollExtent non-nullable

* make _Location.file non-nullable

* _WidgetForTypeTests.createElement throw UnimplementedError

* update _NullWidget.build error message

* make _ShortcutsState.manager non-nullable

* Fix childCount issues for NNBD

* fix childCount computation on web

* increase max value on js side to compute childCount

* make aspect parameter of dependOnInheritedWidgetOfExactType nullable

* merge has{min,max}ScrollExtent into hasScrollExtents

* update focus_manager.dart

* address review comments in icon.dart

* address review comments in image.dart

* address review comments in routes.dart

* address review comments in scroll_activity.dart

* update doc comments

* make UserScrollNotification.direction non-nullable and required

* rename hasScrollExtents to hasContentDimensions

* unnecessary late
Co-authored-by: Ian Hickson <ian@hixie.ch>

A frequent request from the last Flutter developer survey was for an easier method of testing light/dark mode changes. Currently, a user needs to manually change the theme settings or adjust phone settings to see the difference. Instead we should add a toggle from the CLI, and eventually devtools/Intellij/Vscode that allows developers to override the current setting.

Fixes #59495

Adds flutter.ext.brightnessOverride service protocol which either queries the current platform brightness, or overrides it to a new value. This accepts either Brightness.light or Brightness.dark as a value.

Adds a CLI toggle b which allows the setting to be toggled manually.

Requires an update to the MediaQuery, to conditionally use a debug override when not in release mode

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

This updates the Action API in accordance with the design doc for the changes: flutter.dev/go/actions-and-shortcuts-design-revision

Fixes #53276

This PR adds the linux and windows target platform enum values, along with automatically setting the defaultTargetPlatform to the appropriate value on those platforms.

Fixes #31366

* Fix doc typo

This PR is a follow up of https://github.com/flutter/flutter/pull/42640
Some changes of that PR includes redundant changes using FlutterError.fromParts constructor even though it's not necessary.

Some minor changes are:

- Remove one unnecessary todo
- Fix indent consistencies

This re-lands #49235 with the addition of includeSemantics flag on the Focus widget so that the FocusTraversalGroup can create a Focus widget without affecting the semantics tree.

The FocusTraversalGroup uses the Focus widget to create a grouping of descendants for traversal, but doesn't actually participate in focus (canRequestFocus is always false), so we don't want it to add a Semantics widget in that case, since that can cause semantics changes. The canRequestFocus attribute can also be used when a widget is disabled, so we do sometimes want to include Semantics even if that is false, but not in the case where it is always false, as for FocusTraversalGroup.

- Added a test to make sure that FocusTraversalGroup doesn't add any semantics information.

This reverts commit 8ef5e2f0 because it breaks some semantics tests.

This change adds a way to provide explicit focus order for a part of the widget tree.

It adds FocusTraversalPolicyGroup, which in many ways is similar to DefaultFocusTraversal, except that it groups a widget subtree together so that those nodes are traversed as a group. DefaultFocusTraversal doesn't work as one would expect: If there is more than one DefaultFocusTraversal inside of a focus scope, the policy can change depending on which node was asked to move "next", which can cause unexpected behavior. The new grouping mechanism doesn't have that problem. I deprecate DefaultFocusTraversal in this PR.

It also adds OrderedFocusTraversalPolicy, which is a policy that can be supplied to FocusTraversalPolicyGroup to set the policy for a sub-tree. It looks for FocusTraversalOrder inherited widgets, which use a FocusOrder to do the sorting. FocusOrder has two subclasses: NumericalFocusOrder (which sorts based on a double), and LexicalFocusOrder, which sorts based on a String.

As part of doing this, I refactored the way FocusTraversalPolicy is implemented so that it has more default implementation methods, and exposes a new protected member: sortDescendants, which makes it easier for developers to make their own policy subclasses: they only need to implement sortDescendants to get a new ordering behavior, but can also still override any of the default implementation behaviors if they need different behavior.

I was able to do this without breaking the API (AFAICT).

Navigator 2.0: Refactor the imperative api to continue working in the new navigation system (#44930)

This simplifies the diagnostic output for the Shortcuts widget so that if a debugLabel is supplied, then that is printed instead of the full list of shortcut keys in the map. Also, the output of the shortcut map is simplified to have the list of keys presented in more readable text.

This normalizes all of the "See also" blocks in comments so that they conform in style.

They all look like this now:

  /// See also:
  ///
  ///  * [MyFavoriteWidget], because it's cool.
  class Foo {}

I removed some useless "See also" blocks, and added commentary to ones that were just "bare" references.

This is my penance for adding so many bullets that are "-" instead of "*". :-)

This adds actions and shortcuts arguments to WidgetsApp (and MaterialApp and CupertinoApp) to allow developers to override the default mappings on an application, and to allow for a more complex definition of the default mappings.

I've stopped using SelectAction here, in favor of using ActivateAction for all activations, but haven't removed it, to avoid a breaking change, and to allow a common base class for these types of actions. This is because some platforms use the same mapping (web) for both kinds of activations (both select and activate).

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

This adds the ability to scroll and page up/down in a Scrollable using the keyboard. Currently, the macOS bindings use Platform.isMacOS as a check, but we'll switch that to be defaultTargetPlatform == TargetPlatform.macOS once that exists.

This re-lands the change that adds focus nodes, hover, and shortcuts to switches, checkboxes, and radio buttons. (#43213), with fixes for the web tests that weren't enabled in the master that it was synced to when I first landed it.

Revert "Re-Land: Add focus nodes, hover, and shortcuts to switches, checkboxes, and radio buttons. (#43384)" (#43647)

This reverts commit 8017f63b, since it breaks web tests.

* Add structured errors in Animations, TabView, ChangeNotifier

* Add structured error on MaterialPageRoute, BoxBorder, DecorationImagePainter, TextSpan

* Add structured errors in Debug

* Fix test errors

* Add structured errors in Scaffold and Stepper

* Add structured errors in part of Rendering Layer

* Fix failing test due to FloatingPoint precision

* Fix failing tests due to precision error and not using final

* Fix failing test due to floating precision error with RegEx instead

* Add structured error in CustomLayout and increase test coverage

* Add structured error & its test in ListBody

* Add structured error in ProxyBox and increase test coverage

* Add structured error message in Viewport

* Fix styles and add more assertions on ErrorHint and DiagnosticProperty

* Add structured error in scheduler/binding and scheduler/ticker
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in AssetBundle and TextInput
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured errors in several widgets #1
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove unused import
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add assertions on hint messages
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix catch spacing
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in several widgets part 2 and increase code coverage
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in flutter_test/widget_tester

* Fix floating precision accuracy by using RegExp
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove todo to add tests in Scaffold showBottomSheet
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix reviews by indenting lines and fixing the assertion orders
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix failing tests due to renaming class
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Try skipping the NetworkBundleTest
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove leading space in material/debug error hint
Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

This re-lands the change that adds focus nodes, hover, and shortcuts to switches, checkboxes, and radio buttons. (#43213)

No changes from original, except for finding the right RenderBox in dev/integration_tests/android_semantics_testing/test_driver/main_test.dart.

Revert "Add focus nodes, hover, and shortcuts to switches, checkboxes, and radio buttons. (#43213)" (#43367)

This reverts commit 90006720.