Use tristate checkbox engine changes (#111032)

* Introduce tests for tristate checkboxes

* Initial

* Use tristate changes in engine

* Flutter_test matchers test update

* Comments, tests

* Update packages/flutter/lib/src/semantics/semantics.dart

Co-authored-by: Chris Bracken <chris@bracken.jp>

* Assert mutual exclusivity

* Assert valid state before updating state

* Update packages/flutter/lib/src/semantics/semantics.dart

Typo fix in comment

Co-authored-by: Loïc Sharma <737941+loic-sharma@users.noreply.github.com>

Co-authored-by: Chris Bracken <chris@bracken.jp>
Co-authored-by: Loïc Sharma <737941+loic-sharma@users.noreply.github.com>

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

@@ -474,6 +474,7 @@ class _CheckboxState extends State<Checkbox> with TickerProviderStateMixin, Togg
 
     return Semantics(
       checked: widget.value ?? false,
+      mixed: widget.tristate ? widget.value == null : null,
       child: buildToggleable(
         mouseCursor: effectiveMouseCursor,
         focusNode: widget.focusNode,

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

@@ -872,6 +872,9 @@ class RenderCustomPaint extends RenderProxyBox {
     if (properties.checked != null) {
       config.isChecked = properties.checked;
     }
+    if (properties.mixed != null) {
+      config.isCheckStateMixed = properties.mixed;
+    }
     if (properties.selected != null) {
       config.isSelected = properties.selected!;
     }

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

@@ -4355,6 +4355,9 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     if (_properties.checked != null) {
       config.isChecked = _properties.checked;
     }
+    if (_properties.mixed != null) {
+      config.isCheckStateMixed = _properties.mixed;
+    }
     if (_properties.toggled != null) {
       config.isToggled = _properties.toggled;
     }

packages/flutter/lib/src/semantics/semantics.dart

@@ -776,6 +776,7 @@ class SemanticsProperties extends DiagnosticableTree {
   const SemanticsProperties({
     this.enabled,
     this.checked,
+    this.mixed,
     this.selected,
     this.toggled,
     this.button,
@@ -851,14 +852,30 @@ class SemanticsProperties extends DiagnosticableTree {
   /// or similar widget with a "checked" state, and what its current
   /// state is.
   ///
-  /// This is mutually exclusive with [toggled].
+  /// When the [Checkbox.value] of a tristate Checkbox is null,
+  /// indicating a mixed-state, this value shall be false, in which
+  /// case, [mixed] will be true.
+  ///
+  /// This is mutually exclusive with [toggled] and [mixed].
   final bool? checked;
 
+  /// If non-null, indicates that this subtree represents a checkbox
+  /// or similar widget with a "half-checked" state or similar, and
+  /// whether it is currently in this half-checked state.
+  ///
+  /// This must be null when [Checkbox.tristate] is false, or
+  /// when the widget is not a checkbox. When a tristate
+  /// checkbox is fully unchecked/checked, this value shall
+  /// be false.
+  ///
+  /// This is mutually exclusive with [checked] and [toggled].
+  final bool? mixed;
+
   /// If non-null, indicates that this subtree represents a toggle switch
   /// or similar widget with an "on" state, and what its current
   /// state is.
   ///
-  /// This is mutually exclusive with [checked].
+  /// This is mutually exclusive with [checked] and [mixed].
   final bool? toggled;
 
   /// If non-null indicates that this subtree represents something that can be
@@ -1490,6 +1507,7 @@ class SemanticsProperties extends DiagnosticableTree {
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     properties.add(DiagnosticsProperty<bool>('checked', checked, defaultValue: null));
+    properties.add(DiagnosticsProperty<bool>('mixed', mixed, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('selected', selected, defaultValue: null));
     properties.add(StringProperty('label', label, defaultValue: null));
     properties.add(AttributedStringProperty('attributedLabel', attributedLabel, defaultValue: null));
@@ -4189,10 +4207,26 @@ class SemanticsConfiguration {
   /// checked/unchecked state.
   bool? get isChecked => _hasFlag(SemanticsFlag.hasCheckedState) ? _hasFlag(SemanticsFlag.isChecked) : null;
   set isChecked(bool? value) {
+    assert(value != true || isCheckStateMixed != true);
     _setFlag(SemanticsFlag.hasCheckedState, true);
     _setFlag(SemanticsFlag.isChecked, value!);
   }
 
+  /// If this node has tristate that can be controlled by the user, whether
+  /// that state is in its mixed state.
+  ///
+  /// Do not call the setter for this field if the owning [RenderObject] doesn't
+  /// have checked/unchecked state that can be controlled by the user.
+  ///
+  /// The getter returns null if the owning [RenderObject] does not have
+  /// mixed checked state.
+  bool? get isCheckStateMixed => _hasFlag(SemanticsFlag.hasCheckedState) ? _hasFlag(SemanticsFlag.isCheckStateMixed) : null;
+  set isCheckStateMixed(bool? value) {
+    assert(value != true || isChecked != true);
+    _setFlag(SemanticsFlag.hasCheckedState, true);
+    _setFlag(SemanticsFlag.isCheckStateMixed, value!);
+  }
+
   /// If this node has Boolean state that can be controlled by the user, whether
   /// that state is on or off, corresponding to true and false, respectively.
   ///

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

@@ -6878,6 +6878,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     bool excludeSemantics = false,
     bool? enabled,
     bool? checked,
+    bool? mixed,
     bool? selected,
     bool? toggled,
     bool? button,
@@ -6943,6 +6944,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     properties: SemanticsProperties(
       enabled: enabled,
       checked: checked,
+      mixed: mixed,
       toggled: toggled,
       selected: selected,
       button: button,

packages/flutter/test/material/checkbox_test.dart

@@ -139,6 +139,57 @@ void main() {
       hasEnabledState: true,
       isChecked: true,
     ));
+
+    await tester.pumpWidget(Theme(
+      data: theme,
+      child: const Material(
+        child: Checkbox(
+          value: null,
+          tristate: true,
+          onChanged: null,
+        ),
+      ),
+    ));
+
+    expect(tester.getSemantics(find.byType(Checkbox)), matchesSemantics(
+      hasCheckedState: true,
+      hasEnabledState: true,
+      isCheckStateMixed: true,
+    ));
+
+    await tester.pumpWidget(Theme(
+      data: theme,
+      child: const Material(
+        child: Checkbox(
+          value: true,
+          tristate: true,
+          onChanged: null,
+        ),
+      ),
+    ));
+
+    expect(tester.getSemantics(find.byType(Checkbox)), matchesSemantics(
+      hasCheckedState: true,
+      hasEnabledState: true,
+      isChecked: true,
+    ));
+
+    await tester.pumpWidget(Theme(
+      data: theme,
+      child: const Material(
+        child: Checkbox(
+          value: false,
+          tristate: true,
+          onChanged: null,
+        ),
+      ),
+    ));
+
+    expect(tester.getSemantics(find.byType(Checkbox)), matchesSemantics(
+      hasCheckedState: true,
+      hasEnabledState: true,
+    ));
+
     handle.dispose();
   });
 
@@ -239,6 +290,7 @@ void main() {
         SemanticsFlag.hasEnabledState,
         SemanticsFlag.isEnabled,
         SemanticsFlag.isFocusable,
+        SemanticsFlag.isCheckStateMixed,
       ],
       actions: <SemanticsAction>[SemanticsAction.tap],
     ), hasLength(1));

packages/flutter/test/widgets/custom_painter_test.dart

@@ -451,7 +451,9 @@ void _defineTests() {
     List<SemanticsFlag> flags = SemanticsFlag.values.values.toList();
     // [SemanticsFlag.hasImplicitScrolling] isn't part of [SemanticsProperties]
     // therefore it has to be removed.
-    flags.remove(SemanticsFlag.hasImplicitScrolling);
+    flags
+      ..remove(SemanticsFlag.hasImplicitScrolling)
+      ..remove(SemanticsFlag.isCheckStateMixed);
     TestSemantics expectedSemantics = TestSemantics.root(
       children: <TestSemantics>[
         TestSemantics.rootChild(
@@ -475,7 +477,8 @@ void _defineTests() {
           rect: Rect.fromLTRB(1.0, 2.0, 3.0, 4.0),
           properties: SemanticsProperties(
             enabled: true,
-            checked: true,
+            checked: false,
+            mixed: true,
             toggled: true,
             selected: true,
             hidden: true,
@@ -502,7 +505,9 @@ void _defineTests() {
     flags = SemanticsFlag.values.values.toList();
     // [SemanticsFlag.hasImplicitScrolling] isn't part of [SemanticsProperties]
     // therefore it has to be removed.
-    flags.remove(SemanticsFlag.hasImplicitScrolling);
+    flags
+      ..remove(SemanticsFlag.hasImplicitScrolling)
+      ..remove(SemanticsFlag.isChecked);
     expectedSemantics = TestSemantics.root(
       children: <TestSemantics>[
         TestSemantics.rootChild(
@@ -519,7 +524,7 @@ void _defineTests() {
     );
     expect(semantics, hasSemantics(expectedSemantics, ignoreRect: true, ignoreTransform: true));
     semantics.dispose();
-  }, skip: true); // [intended] https://github.com/flutter/flutter/issues/110107
+  });
 
   group('diffing', () {
     testWidgets('complains about duplicate keys', (WidgetTester tester) async {

packages/flutter/test/widgets/semantics_test.dart

@@ -584,7 +584,8 @@ void main() {
     flags
       ..remove(SemanticsFlag.hasToggledState)
       ..remove(SemanticsFlag.isToggled)
-      ..remove(SemanticsFlag.hasImplicitScrolling);
+      ..remove(SemanticsFlag.hasImplicitScrolling)
+      ..remove(SemanticsFlag.isCheckStateMixed);
 
     TestSemantics expectedSemantics = TestSemantics.root(
       children: <TestSemantics>[
@@ -631,8 +632,50 @@ void main() {
     );
 
     expect(semantics, hasSemantics(expectedSemantics, ignoreId: true));
+
+    await tester.pumpWidget(
+        Semantics(
+          key: const Key('a'),
+          container: true,
+          explicitChildNodes: true,
+          // flags
+          enabled: true,
+          hidden: true,
+          checked: false,
+          mixed: true,
+          selected: true,
+          button: true,
+          slider: true,
+          keyboardKey: true,
+          link: true,
+          textField: true,
+          readOnly: true,
+          focused: true,
+          focusable: true,
+          inMutuallyExclusiveGroup: true,
+          header: true,
+          obscured: true,
+          multiline: true,
+          scopesRoute: true,
+          namesRoute: true,
+          image: true,
+          liveRegion: true,
+        ),
+    );
+    flags
+      ..remove(SemanticsFlag.isChecked)
+      ..add(SemanticsFlag.isCheckStateMixed);
     semantics.dispose();
-  }, skip: true); // [intended] https://github.com/flutter/flutter/issues/110107
+    expectedSemantics = TestSemantics.root(
+      children: <TestSemantics>[
+        TestSemantics.rootChild(
+          rect: TestSemantics.fullScreen,
+          flags: flags,
+        ),
+      ],
+    );
+    expect(semantics, hasSemantics(expectedSemantics, ignoreId: true));
+  });
 
   testWidgets('Actions can be replaced without triggering semantics update', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);

packages/flutter_test/lib/src/matchers.dart

@@ -542,6 +542,7 @@ Matcher matchesSemantics({
   // Flags //
   bool hasCheckedState = false,
   bool isChecked = false,
+  bool isCheckStateMixed = false,
   bool isSelected = false,
   bool isButton = false,
   bool isSlider = false,
@@ -617,6 +618,7 @@ Matcher matchesSemantics({
     // Flags
     hasCheckedState: hasCheckedState,
     isChecked: isChecked,
+    isCheckStateMixed: isCheckStateMixed,
     isSelected: isSelected,
     isButton: isButton,
     isSlider: isSlider,
@@ -713,6 +715,7 @@ Matcher containsSemantics({
   // Flags
   bool? hasCheckedState,
   bool? isChecked,
+  bool? isCheckStateMixed,
   bool? isSelected,
   bool? isButton,
   bool? isSlider,
@@ -788,6 +791,7 @@ Matcher containsSemantics({
     // Flags
     hasCheckedState: hasCheckedState,
     isChecked: isChecked,
+    isCheckStateMixed: isCheckStateMixed,
     isSelected: isSelected,
     isButton: isButton,
     isSlider: isSlider,
@@ -2085,6 +2089,7 @@ class _MatchesSemanticsData extends Matcher {
     // Flags
     required bool? hasCheckedState,
     required bool? isChecked,
+    required bool? isCheckStateMixed,
     required bool? isSelected,
     required bool? isButton,
     required bool? isSlider,
@@ -2138,6 +2143,7 @@ class _MatchesSemanticsData extends Matcher {
   })  : flags = <SemanticsFlag, bool>{
           if (hasCheckedState != null) SemanticsFlag.hasCheckedState: hasCheckedState,
           if (isChecked != null) SemanticsFlag.isChecked: isChecked,
+          if (isCheckStateMixed != null) SemanticsFlag.isCheckStateMixed: isCheckStateMixed,
           if (isSelected != null) SemanticsFlag.isSelected: isSelected,
           if (isButton != null) SemanticsFlag.isButton: isButton,
           if (isSlider != null) SemanticsFlag.isSlider: isSlider,

packages/flutter_test/test/matchers_test.dart

@@ -656,6 +656,7 @@ void main() {
          /* Flags */
          hasCheckedState: true,
          isChecked: true,
+         isCheckStateMixed: true,
          isSelected: true,
          isButton: true,
          isSlider: true,