## What's new?
This pull request makes it so that multi window applications can be
tested via `testWidgets`. This PR implements the following:
- A `_TestWindowingOwner` that is used by the
`TestWidgetsFlutterBinding`
- A `_TestRegularWindowController` implementation
- A `_TestDialogWindowController` implementation
- A `_TestFlutterView` and `_TestDisplay` for use by the controllers
- Proper `isActivated` status across controllers
- Proper minimization, maximization, and fullscreen status
- Proper sizing (based on constraints)
- Using the new testing abilities in the multiple windows example app
I have purposefully not implemented tooltip windows yet, as they are
still awaiting an implementation in Win32 to be useful.
## Pre-launch Checklist
- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.
Fixes#169119
## Details
The error caused by drag is due to the reference to
`ServicesBinding.instance.restorationManager` in the
`ScrollableState.saveOffset` method.
018897e3f1/packages/flutter/lib/src/widgets/scrollable.dart (L648-L656)
The TestWidgetsFlutterBinding now only cleans up the
`restorationManager` when `reset` is called. Therefore, we need to find
an appropriate place to clean up the `restorationManager`.
018897e3f1/packages/flutter_test/lib/src/binding.dart (L239-L263)018897e3f1/packages/flutter_test/lib/src/widget_tester.dart (L188-L193)
## Pre-launch Checklist
- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.
---------
Co-authored-by: Victor Sanni <victorsanniay@gmail.com>
Current implementation runs timers and microtask callbacks in the root
zone. That assumes that the top-level `scheduleMicrotask` or `Timer`
constructors have been used, which have so far wrapped the callback with
`runCallbackGuarded` before calling the zone implementation.
That means that doing `zone.scheduleMicrotask` directly would not ensure
that the microtask was run in the correct zone. If a `run` handler
throws, it wouldn't be caught.
This change makes the `realAsyncZone` do whatever the root zone would do
if its `ZoneDelegate` got called with the intended zone and arguments.
That should be consistent with the current behavior, and be compatible
with incoming bug-fixes to the platform `Zone` behavior.
Prepares Flutter for landing
https://dart-review.googlesource.com/c/sdk/+/406961
which is currently blocked (so this indirectly fixes
https://github.com/dart-lang/sdk/issues/59913).
There are no new tests, the goal is that all existing tests keep
running, and that they keep doing so when the Dart CL lands. Currently
that CL only breaks one test, the
`dev/automated_tests/test_smoke_test/fail_test_on_exception_after_test.dart`
test which threw the error-after-test in the root zone instead of the
test zone. This change fixes that.
This auto-formats all *.dart files in the repository outside of the
`engine` subdirectory and enforces that these files stay formatted with
a presubmit check.
**Reviewers:** Please carefully review all the commits except for the
one titled "formatted". The "formatted" commit was auto-generated by
running `dev/tools/format.sh -a -f`. The other commits were hand-crafted
to prepare the repo for the formatting change. I recommend reviewing the
commits one-by-one via the "Commits" tab and avoiding Github's "Files
changed" tab as it will likely slow down your browser because of the
size of this PR.
---------
Co-authored-by: Kate Lovett <katelovett@google.com>
Co-authored-by: LongCatIsLooong <31859944+LongCatIsLooong@users.noreply.github.com>
This pull request aims to improve code readability, based on feedback gathered in a recent design doc.
<br>
There are two factors that hugely impact how easy it is to understand a piece of code: **verbosity** and **complexity**.
Reducing **verbosity** is important, because boilerplate makes a project more difficult to navigate. It also has a tendency to make one's eyes gloss over, and subtle typos/bugs become more likely to slip through.
Reducing **complexity** makes the code more accessible to more people. This is especially important for open-source projects like Flutter, where the code is read by those who make contributions, as well as others who read through source code as they debug their own projects.
<hr>
<br>
The following examples show how pattern-matching might affect these two factors:
<details> <summary><h3>Example 1 (GOOD)</h3> [click to expand]</summary>
```dart
if (ancestor case InheritedElement(:final InheritedTheme widget)) {
themes.add(widget);
}
```
Without using patterns, this might expand to
```dart
if (ancestor is InheritedElement) {
final InheritedWidget widget = ancestor.widget;
if (widget is InheritedTheme) {
themes.add(widget);
}
}
```
Had `ancestor` been a non-local variable, it would need to be "converted" as well:
```dart
final Element ancestor = this.ancestor;
if (ancestor is InheritedElement) {
final InheritedWidget inheritedWidget = ancestor.widget;
if (widget is InheritedTheme) {
themes.add(theme);
}
}
```
</details>
<details> <summary><h3>Example 2 (BAD) </h3> [click to expand]</summary>
```dart
if (widget case PreferredSizeWidget(preferredSize: Size(:final double height))) {
return height;
}
```
Assuming `widget` is a non-local variable, this would expand to:
```dart
final Widget widget = this.widget;
if (widget is PreferredSizeWidget) {
return widget.preferredSize.height;
}
```
<br>
</details>
In both of the examples above, an `if-case` statement simultaneously verifies that an object meets the specified criteria and performs a variable assignment accordingly.
But there are some differences: Example 2 uses a more deeply-nested pattern than Example 1 but makes fewer useful checks.
**Example 1:**
- checks that `ancestor` is an `InheritedElement`
- checks that the inherited element's `widget` is an `InheritedTheme`
**Example 2:**
- checks that `widget` is a `PreferredSizeWidget`
(every `PreferredSizeWidget` has a `size` field, and every `Size` has a `height` field)
<br>
<hr>
I feel hesitant to try presenting a set of cut-and-dry rules as to which scenarios should/shouldn't use pattern-matching, since there are an abundance of different types of patterns, and an abundance of different places where they might be used.
But hopefully the conversations we've had recently will help us converge toward a common intuition of how pattern-matching can best be utilized for improved readability.
<br><br>
- resolves https://github.com/flutter/flutter/issues/152313
- Design Doc: [flutter.dev/go/dart-patterns](https://flutter.dev/go/dart-patterns)
Recently the microbenchmarks were flakey, but from an older bug. Turns out, `LiveTestWidgetsFlutterBindingFramePolicy` is defaulted to `fadePointers` with this fun note:
> This can result in additional frames being pumped beyond those that
the test itself requests, which can cause differences in behavior
Both `text_intrinsic_bench` and `build_bench` use a similar pattern:
* Load stocks app
* Open the menu
* Switch to `benchmark` frame policy
What happens, rarely, is that
`LiveTestWidgetsFlutterBinding.pumpBenchmark()` will call (async) `handleBeginFrame` and `handleDrawFrame`. `handleDrawFrame` juggles a tri-state boolean (null, false, true). This boolean is only reset to `null` when handleDrawFrame is called back to back, say, from an extra frame that was scheduled.
1. Switch tri-state boolean to an enum, its easier to read
2. remove asserts that compile away in benchmarks (`--profile`)
3. use `Error.throwWithStackTrace` to keep stack traces.
I've been running this test on device lab hardware for hundreds of runs and have not hit a failure yet.
Fixes#150542Fixes#150543 - throw stack!
This change fixes an issue where SelectionArea would clear its selection when the application window lost focus by first checking if the application is running. This is needed because `FocusManager` is aware of the application lifecycle as of https://github.com/flutter/flutter/pull/142930 , and triggers a focus lost if the application is not active.
Also fixes an issue where the `FocusManager` was not being reset on tests at the right time, causing it always to build with `TargetPlatform.android` as its context.
* Adds support for `flutter test --wasm`.
* The test compilation flow is a bit different now, so that it supports compilers other than DDC. Specifically, when we run a set of unit tests, we generate a "switchboard" main function that imports each unit test and runs the main function for a specific one based off of a value set by the JS bootstrapping code. This way, there is one compile step and the same compile output is invoked for each unit test file.
* Also, removes all references to `dart:html` from flutter/flutter.
* Adds CI steps for running the framework unit tests with dart2wasm+skwasm
* These steps are marked as `bringup: true`, so we don't know what kind of failures they will result in. Any failures they have will not block the tree at all yet while we're still in `bringup: true`. Once this PR is merged, I plan on looking at any failures and either fixing them or disabling them so we can get these CI steps running on presubmit.
This fixes https://github.com/flutter/flutter/issues/126692
Reverts: flutter/flutter#144706
Initiated by: gspencergoog
Reason for reverting: This has broken the tree because some tests are still failing post completion. This particular one looks like it might have to do with a gold image not existing.
Original PR Author: goderbauer
Reviewed By: {Piinks}
This change reverts the following previous change:
A test was failing silently because of this (see https://github.com/flutter/flutter/issues/144353 and fixed in https://github.com/flutter/flutter/pull/144709). The failure went undetected for months. Ideally, this should have been a regular non-silent failure. This change makes that so. `package:test` can properly handle reported exceptions outside of test cases. With this change, the test fails as follows:
```
00:03 +82: Smoke test material/color_scheme/dynamic_content_color.0.dart
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown running a test (but after the test had completed):
setState() called after dispose(): _DynamicColorExampleState#1cd37(lifecycle state: defunct, not
mounted)
This error happens if you call setState() on a State object for a widget that no longer appears in
the widget tree (e.g., whose parent widget no longer includes the widget in its build). This error
can occur when code calls setState() from a timer or an animation callback.
The preferred solution is to cancel the timer or stop listening to the animation in the dispose()
callback. Another solution is to check the "mounted" property of this object before calling
setState() to ensure the object is still in the tree.
This error might indicate a memory leak if setState() is being called because another object is
retaining a reference to this State object after it has been removed from the tree. To avoid memory
leaks, consider breaking the reference to this object during dispose().
When the exception was thrown, this was the stack:
#0 State.setState.<anonymous closure> (package:flutter/src/widgets/framework.dart:1167:9)
#1 State.setState (package:flutter/src/widgets/framework.dart:1202:6)
#2 _DynamicColorExampleState._updateImage (package:flutter_api_samples/material/color_scheme/dynamic_content_color.0.dart:191:5)
<asynchronous suspension>
════════════════════════════════════════════════════════════════════════════════════════════════════
00:03 +81 -1: Smoke test material/context_menu/context_menu_controller.0.dart
00:03 +81 -1: Smoke test material/color_scheme/dynamic_content_color.0.dart [E]
Test failed. See exception logs above.
The test description was: Smoke test material/color_scheme/dynamic_content_color.0.dart
This test failed after it had already completed.
Make sure to use a matching library which informs the test runner
of pending async work.
```
A test was failing silently because of this (see
https://github.com/flutter/flutter/issues/144353 and fixed in
https://github.com/flutter/flutter/pull/144709). The failure went
undetected for months. Ideally, this should have been a regular
non-silent failure. This change makes that so. `package:test` can
properly handle reported exceptions outside of test cases. With this
change, the test fails as follows:
```
00:03 +82: Smoke test material/color_scheme/dynamic_content_color.0.dart
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown running a test (but after the test had completed):
setState() called after dispose(): _DynamicColorExampleState#1cd37(lifecycle state: defunct, not
mounted)
This error happens if you call setState() on a State object for a widget that no longer appears in
the widget tree (e.g., whose parent widget no longer includes the widget in its build). This error
can occur when code calls setState() from a timer or an animation callback.
The preferred solution is to cancel the timer or stop listening to the animation in the dispose()
callback. Another solution is to check the "mounted" property of this object before calling
setState() to ensure the object is still in the tree.
This error might indicate a memory leak if setState() is being called because another object is
retaining a reference to this State object after it has been removed from the tree. To avoid memory
leaks, consider breaking the reference to this object during dispose().
When the exception was thrown, this was the stack:
#0 State.setState.<anonymous closure> (package:flutter/src/widgets/framework.dart:1167:9)
#1 State.setState (package:flutter/src/widgets/framework.dart:1202:6)
#2 _DynamicColorExampleState._updateImage (package:flutter_api_samples/material/color_scheme/dynamic_content_color.0.dart:191:5)
<asynchronous suspension>
════════════════════════════════════════════════════════════════════════════════════════════════════
00:03 +81 -1: Smoke test material/context_menu/context_menu_controller.0.dart
00:03 +81 -1: Smoke test material/color_scheme/dynamic_content_color.0.dart [E]
Test failed. See exception logs above.
The test description was: Smoke test material/color_scheme/dynamic_content_color.0.dart
This test failed after it had already completed.
Make sure to use a matching library which informs the test runner
of pending async work.
```
This pull request fixes#143803 by taking advantage of Dart's null-aware operators.
And unlike `switch` expressions ([9 PRs](https://github.com/flutter/flutter/pull/143634) and counting), the Flutter codebase is already fantastic when it comes to null-aware coding. After refactoring the entire repo, all the changes involving `?.` and `??` can fit into a single pull request.
This PR implements the functionality described above and hides it behind
the `--experimental-faster-testing` flag of `flutter test`.
### The following are some performance measurements from test runs
conducted on GitHub Actions
run 1 logs:
https://github.com/derekxu16/flutter_test_ci/actions/runs/8008029772/attempts/1
run 2 logs:
https://github.com/derekxu16/flutter_test_ci/actions/runs/8008029772/attempts/2
run 3 logs:
https://github.com/derekxu16/flutter_test_ci/actions/runs/8008029772/attempts/3
**length of `flutter test --reporter=expanded test/animation
test/foundation` step**
run 1: 54s
run 2: 52s
run 3: 56s
average: 54s
**length of `flutter test --experimental-faster-testing
--reporter=expanded test/animation test/foundation` step**
run 1: 27s
run 2: 27s
run 3: 29s
average: 27.67s (~48.77% shorter than 54s)
**length of `flutter test --reporter=expanded test/animation
test/foundation test/gestures test/painting test/physics test/rendering
test/scheduler test/semantics test/services` step**
run 1: 260s
run 2: 270s
run 3: 305s
average: 278.33s
**length of `flutter test --experimental-faster-testing
--reporter=expanded test/animation test/foundation test/gestures
test/painting test/physics test/rendering test/scheduler test/semantics
test/services` step**
from a clean build (right after deleting the build folder):
run 1: 215s
run 2: 227s
run 3: 245s
average: 229s (~17.72% shorter than 278.33s)
Note that in reality, `test/material` was not passed to `flutter test`
in the trials below. All of the test files under `test/material` except
for `test/material/icons_test.dart` were listed out individually
**length of `flutter test --reporter=expanded test/material` step**
run 1: 408s
run 2: 421s
run 3: 451s
average: 426.67s
**length of `flutter test --experimental-faster-testing
--reporter=expanded test/material` step**
run 1: 382s
run 2: 373s
run 3: 400s
average: 385s (~9.77% shorter than 426.67s)
---------
Co-authored-by: Dan Field <dnfield@google.com>
The old doc says that, AutomatedTestWidgetsFlutterBinding for `flutter test` and LiveTestWidgetsFlutterBinding for `flutter run`. However, suppose we `flutter test integration_test/simple_test.dart` with the following code:
```
void main() {
testWidgets('hi', (WidgetTester tester) async {
print('hi ${TestWidgetsFlutterBinding.instance} ${Platform.operatingSystem}');
});
}
```
We will see: `hi <IntegrationTestWidgetsFlutterBinding> ios`. Therefore, we see `IntegrationTestWidgetsFlutterBinding` is used in a `flutter test` command, which is contrary to the documentation.
This reverts commit
d24c01bd0c.
The original change was reverted because it caused some apps to get
stuck on the splash screen on some phones.
An investigation determined that this was due to a rounding error.
Example: The device reports a physical size of 1008.0 x 2198.0 with a
dpr of 1.912500023841858. Flutter would translate that to a logical size
of 527.0588169589221 x 1149.2810314243163 and use that as the input for
its layout algorithm. Since the constraints here are tight, the layout
algorithm would determine that the resulting logical size of the root
render object must be 527.0588169589221 x 1149.2810314243163.
Translating this back to physical pixels by applying the dpr resulted in
a physical size of 1007.9999999999999 x 2198.0 for the frame. Android
now rejected that frame because it didn't match the expected size of
1008.0 x 2198.0 and since no frame had been rendered would never take
down the splash screen.
Prior to dynamically sized views, this wasn't an issue because we would
hard-code the frame size to whatever the requested size was.
Changes in this PR over the original PR:
* The issue has been fixed now by constraining the calculated physical
size to the input physical constraints which makes sure that we always
end up with a size that is acceptable to the operating system.
* The `ViewConfiguration` was refactored to use the slightly more
convenient `BoxConstraints` over the `ViewConstraints` to represent
constraints. Both essentially represent the same thing, but
`BoxConstraints` are more powerful and we avoid a couple of translations
between the two by translating the` ViewConstraints` from the
`FlutterView` to `BoxConstraints` directly when the `ViewConfiguration`
is created.
All changes over the original PR are contained in the second commit of
this PR.
Fixes b/316813075
Part of https://github.com/flutter/flutter/issues/134501.
Towards https://github.com/flutter/flutter/issues/134501.
This change is based on https://github.com/flutter/engine/pull/48090. It changes the `RenderView` to be dynamically sized based on its content if the `FlutterView` it is configured with allows it (i.e. the `FlutterView` has loose `FlutterView.physicalConstraints`). For that, it uses those `physicalConstraints` as input to the layout algorithm by passing them on to its child (after translating them to logical constraints via the device pixel ratio). The resulting `Size` that the `RenderView` would like to be is then communicated back to the engine by passing it to the `FlutterView.render` call.
Tests will fail until https://github.com/flutter/engine/pull/48090 has rolled into the framework.
This updates the implementation to use the stopwatch from the Clock object and pipes it through to the TestWidgetsFlutterBinding so it will be kept in sync with FakeAsync.
Relands https://github.com/flutter/flutter/pull/138843 attempted to reland https://github.com/flutter/flutter/pull/137381 which attempted to reland #132291
Fixes https://github.com/flutter/flutter/issues/97761
1. The original change was reverted due to flakiness it introduced in tests that use fling gestures.
* Using a mocked clock through the test binding fixes this now
2. It was reverted a second time because a change at tip of tree broke it, exposing memory leaks, but it was not rebased before landing.
* These leaks are now fixed
3. It was reverted a third time, because we were so excellently quick to revert those other times, that we did not notice the broken benchmark that only runs in postsubmit.
* The benchmark is now fixed
Reverts flutter/flutter#137381
Initiated by: Piinks
This change reverts the following previous change:
Original Description:
This updates the implementation to use the stopwatch from the Clock object and piping it through to the TestWidgetsFlutterBinding so it will be kept in sync with FakeAsync.
Relands #132291
Fixes https://github.com/flutter/flutter/issues/97761
The change was reverted due to flakiness it introduced in tests that use fling gestures.
* https://github.com/flutter/flutter/issues/135728
Fixes https://github.com/flutter/flutter/issues/137696
This will get the tree green again.
The problem is that `CustomSemanticsAction` has static state in it, and todays test seed order makes things unhappy.
## Description
This removes all of the comments that are of the form "so-and-so must not be null" or "so-and-so must be non-null" from the cases where those values are defines as non-nullable values.
This PR removes them from the library in the repo that don't have anything to do with the framework.
This was done by hand, since it really didn't lend itself to scripting, so it needs to be more than just spot-checked, I think. I was careful to leave any comment that referred to parameters that were nullable, but I may have missed some.
In addition to being no longer relevant after null safety has been made the default, these comments were largely fragile, in that it was easy for them to get out of date, and not be accurate anymore anyhow.
This did create a number of constructor comments which basically say "Creates a [Foo].", but I don't really know how to avoid that in a large scale change, since there's not much you can really say in a lot of cases. I think we might consider some leniency for constructors to the "Comment must be meaningful" style guidance (which we de facto have already, since there are a bunch of these).
## Related PRs
- https://github.com/flutter/flutter/pull/134984
- https://github.com/flutter/flutter/pull/134991
- https://github.com/flutter/flutter/pull/134992
- https://github.com/flutter/flutter/pull/134993
## Tests
- Documentation only change.
Part of https://github.com/flutter/flutter/issues/133171.
Removes from `TestWindow`:
* `localeTestValue`
* `clearLocaleTestValue`
* `localesTestValue`
* `clearLocalesTestValue`
* `initialLifecycleStateTestValue`
* `alwaysUse24HourFormatTestValue`
* `clearAlwaysUse24HourTestValue`
* `brieflyShowPasswordTestValue`
* `defaultRouteNameTestValue`
* `clearDefaultRouteNameTestValue`
* `semanticsEnabledTestValue`
* `clearSemanticsEnabledTestValue`
* `accessibilityFeaturesTestValue`
* `clearAccessibilityFeaturesTestValue`
These properties have reached the end of their deprecation period.
* Updated `AutomatedTestWidgetsFlutterBinding.pump` to use microseconds instead of milliseconds
* Added a test to prevent regression of the microsecond precision
* Fixed a test that incorrectly assumed millisecond precision
Closes#112610
This change enables Flutter to generate multiple Scenes to be rendered into separate FlutterViews from a single widget tree. Each Scene is described by a separate render tree, which are all associated with the single widget tree.
This PR implements the framework-side mechanisms to describe the content to be rendered into multiple views. Separate engine-side changes are necessary to provide these views to the framework and to draw the framework-generated Scene into them.
## Summary of changes
The details of this change are described in [flutter.dev/go/multiple-views](https://flutter.dev/go/multiple-views). Below is a high-level summary organized by layers.
### Rendering layer changes
* The `RendererBinding` no longer owns a single `renderView`. In fact, it doesn't OWN any `RenderView`s at all anymore. Instead, it offers an API (`addRenderView`/`removeRenderView`) to add and remove `RenderView`s that then will be MANAGED by the binding. The `RenderView` itself is now owned by a higher-level abstraction (e.g. the `RawView` Element of the widgets layer, see below), who is also in charge of adding it to the binding. When added, the binding will interact with the `RenderView` to produce a frame (e.g. by calling `compositeFrame` on it) and to perform hit tests for incoming pointer events. Multiple `RenderView`s can be added to the binding (typically one per `FlutterView`) to produce multiple Scenes.
* Instead of owning a single `pipelineOwner`, the `RendererBinding` now owns the root of the `PipelineOwner` tree (exposed as `rootPipelineOwner` on the binding). Each `PipelineOwner` in that tree (except for the root) typically manages its own render tree typically rooted in one of the `RenderView`s mentioned in the previous bullet. During frame production, the binding will instruct each `PipelineOwner` of that tree to flush layout, paint, semantics etc. A higher-level abstraction (e.g. the widgets layer, see below) is in charge of adding `PipelineOwner`s to this tree.
* Backwards compatibility: The old `renderView` and `pipelineOwner` properties of the `RendererBinding` are retained, but marked as deprecated. Care has been taken to keep their original behavior for the deprecation period, i.e. if you just call `runApp`, the render tree bootstrapped by this call is rooted in the deprecated `RendererBinding.renderView` and managed by the deprecated `RendererBinding.pipelineOwner`.
### Widgets layer changes
* The `WidgetsBinding` no longer attaches the widget tree to an existing render tree. Instead, it bootstraps a stand-alone widget tree that is not backed by a render tree. For this, `RenderObjectToWidgetAdapter` has been replaced by `RootWidget`.
* Multiple render trees can be bootstrapped and attached to the widget tree with the help of the `View` widget, which internally is backed by a `RawView` widget. Configured with a `FlutterView` to render into, the `RawView` creates a new `PipelineOwner` and a new `RenderView` for the new render tree. It adds the new `RenderView` to the `RendererBinding` and its `PipelineOwner` to the pipeline owner tree.
* The `View` widget can only appear in certain well-defined locations in the widget tree since it bootstraps a new render tree and does not insert a `RenderObject` into an ancestor. However, almost all Elements expect that their children insert `RenderObject`s, otherwise they will not function properly. To produce a good error message when the `View` widget is used in an illegal location, the `debugMustInsertRenderObjectIntoSlot` method has been added to Element, where a child can ask whether a given slot must insert a RenderObject into its ancestor or not. In practice, the `View` widget can be used as a child of the `RootWidget`, inside the `view` slot of the `ViewAnchor` (see below) and inside a `ViewCollection` (see below). In those locations, the `View` widget may be wrapped in other non-RenderObjectWidgets (e.g. InheritedWidgets).
* The new `ViewAnchor` can be used to create a side-view inside a parent `View`. The `child` of the `ViewAnchor` widget renders into the parent `View` as usual, but the `view` slot can take on another `View` widget, which has access to all inherited widgets above the `ViewAnchor`. Metaphorically speaking, the view is anchored to the location of the `ViewAnchor` in the widget tree.
* The new `ViewCollection` widget allows for multiple sibling views as it takes a list of `View`s as children. It can be used in all the places that accept a `View` widget.
## Google3
As of July 5, 2023 this change passed a TAP global presubmit (TGP) in google3: tap/OCL:544707016:BASE:545809771:1688597935864:e43dd651
## Note to reviewers
This change is big (sorry). I suggest focusing the initial review on the changes inside of `packages/flutter` first. The majority of the changes describe above are implemented in (listed in suggested review order):
* `rendering/binding.dart`
* `widgets/binding.dart`
* `widgets/view.dart`
* `widgets/framework.dart`
All other changes included in the PR are basically the fallout of what's implemented in those files. Also note that a lot of the lines added in this PR are documentation and tests.
I am also very happy to walk reviewers through the code in person or via video call, if that is helpful.
I appreciate any feedback.
## Feedback to address before submitting ("TODO")
In the multi view world, `RenderViews` are created by the `View` widget and no longer owned by the binding. Prior to this change, the `LiveTestWidgetsFlutterBinding` owned and managed a special subclass of `RenderView`, the `_LiveTestRenderView`. In the new world, where `RenderView`s can be created anywhere in the widget tree where a `View` widget is used, this setup is no longer feasible. This change removes this special `_LiveTestRenderView` and instead adds debug hocks to `RenderView` to allow the `LiveTestWidgetsFlutterBinding` to draw a debug overlay on top of the content of any `RenderView`.
## Description
This fixes the parsing of `AppLifecycleState` in the services binding so that it knows what it is.
## Related Issues
- Fixes https://github.com/flutter/flutter/issues/127974
## Tests
- Added a test that causes parsing of all the different app lifecycle states.
Move imports of API available in `hooks.dart` or `scaffolding.dart` to use those more narrow libraries.
Move imports of APIs from `package:matcher` to import directly. The next major version of `test_api` will remove the exports of `matcher` APIs.
