Adds API in semanticsconfiguration to decide how to merge child semanticsConfigurations (#110730)

* Adds semantics merger API and fix input decorator

* addressing comments

* abstractnode to object

* feature complete

* addressing comments

* fix comments

* conditionally add sort order

* fix bool

* fix test

* more fix

* fix tests

Author: chunhtai

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

@@ -1326,6 +1326,35 @@ class _RenderDecoration extends RenderBox with SlottedContainerRenderObjectMixin
     return Size.zero;
   }
 
+  ChildSemanticsConfigurationsResult _childSemanticsConfigurationDelegate(List<SemanticsConfiguration> childConfigs) {
+    final ChildSemanticsConfigurationsResultBuilder builder = ChildSemanticsConfigurationsResultBuilder();
+    List<SemanticsConfiguration>? prefixMergeGroup;
+    List<SemanticsConfiguration>? suffixMergeGroup;
+    for (final SemanticsConfiguration childConfig in childConfigs) {
+      if (childConfig.tagsChildrenWith(_InputDecoratorState._kPrefixSemanticsTag)) {
+        prefixMergeGroup ??= <SemanticsConfiguration>[];
+        prefixMergeGroup.add(childConfig);
+      } else if (childConfig.tagsChildrenWith(_InputDecoratorState._kSuffixSemanticsTag)) {
+        suffixMergeGroup ??= <SemanticsConfiguration>[];
+        suffixMergeGroup.add(childConfig);
+      } else {
+        builder.markAsMergeUp(childConfig);
+      }
+    }
+    if (prefixMergeGroup != null) {
+      builder.markAsSiblingMergeGroup(prefixMergeGroup);
+    }
+    if (suffixMergeGroup != null) {
+      builder.markAsSiblingMergeGroup(suffixMergeGroup);
+    }
+    return builder.build();
+  }
+
+  @override
+  void describeSemanticsConfiguration(SemanticsConfiguration config) {
+    config.childConfigurationsDelegate = _childSemanticsConfigurationDelegate;
+  }
+
   @override
   void performLayout() {
     final BoxConstraints constraints = this.constraints;
@@ -1713,12 +1742,16 @@ class _AffixText extends StatelessWidget {
     this.text,
     this.style,
     this.child,
+    this.semanticsSortKey,
+    required this.semanticsTag,
   });
 
   final bool labelIsFloating;
   final String? text;
   final TextStyle? style;
   final Widget? child;
+  final SemanticsSortKey? semanticsSortKey;
+  final SemanticsTag semanticsTag;
 
   @override
   Widget build(BuildContext context) {
@@ -1728,7 +1761,11 @@ class _AffixText extends StatelessWidget {
         duration: _kTransitionDuration,
         curve: _kTransitionCurve,
         opacity: labelIsFloating ? 1.0 : 0.0,
-        child: child ?? (text == null ? null : Text(text!, style: style)),
+        child: Semantics(
+          sortKey: semanticsSortKey,
+          tagForChildren: semanticsTag,
+          child: child ?? (text == null ? null : Text(text!, style: style)),
+        ),
       ),
     );
   }
@@ -1899,6 +1936,11 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
   late AnimationController _floatingLabelController;
   late AnimationController _shakingLabelController;
   final _InputBorderGap _borderGap = _InputBorderGap();
+  static const OrdinalSortKey _kPrefixSemanticsSortOrder = OrdinalSortKey(0);
+  static const OrdinalSortKey _kInputSemanticsSortOrder = OrdinalSortKey(1);
+  static const OrdinalSortKey _kSuffixSemanticsSortOrder = OrdinalSortKey(2);
+  static const SemanticsTag _kPrefixSemanticsTag = SemanticsTag('_InputDecoratorState.prefix');
+  static const SemanticsTag _kSuffixSemanticsTag = SemanticsTag('_InputDecoratorState.suffix');
 
   @override
   void initState() {
@@ -2218,22 +2260,42 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
       ),
     );
 
-    final Widget? prefix = decoration.prefix == null && decoration.prefixText == null ? null :
-      _AffixText(
-        labelIsFloating: widget._labelShouldWithdraw,
-        text: decoration.prefixText,
-        style: MaterialStateProperty.resolveAs(decoration.prefixStyle, materialState) ?? hintStyle,
-        child: decoration.prefix,
-      );
-
-    final Widget? suffix = decoration.suffix == null && decoration.suffixText == null ? null :
-      _AffixText(
-        labelIsFloating: widget._labelShouldWithdraw,
-        text: decoration.suffixText,
-        style: MaterialStateProperty.resolveAs(decoration.suffixStyle, materialState) ?? hintStyle,
-        child: decoration.suffix,
+    final bool hasPrefix = decoration.prefix != null || decoration.prefixText != null;
+    final bool hasSuffix = decoration.suffix != null || decoration.suffixText != null;
+
+    Widget? input = widget.child;
+    // If at least two out of the three are visible, it needs semantics sort
+    // order.
+    final bool needsSemanticsSortOrder = widget._labelShouldWithdraw && (input != null ? (hasPrefix || hasSuffix) : (hasPrefix && hasSuffix));
+
+    final Widget? prefix = hasPrefix
+      ? _AffixText(
+          labelIsFloating: widget._labelShouldWithdraw,
+          text: decoration.prefixText,
+          style: MaterialStateProperty.resolveAs(decoration.prefixStyle, materialState) ?? hintStyle,
+          semanticsSortKey: needsSemanticsSortOrder ? _kPrefixSemanticsSortOrder : null,
+          semanticsTag: _kPrefixSemanticsTag,
+          child: decoration.prefix,
+        )
+      : null;
+
+    final Widget? suffix = hasSuffix
+      ? _AffixText(
+          labelIsFloating: widget._labelShouldWithdraw,
+          text: decoration.suffixText,
+          style: MaterialStateProperty.resolveAs(decoration.suffixStyle, materialState) ?? hintStyle,
+          semanticsSortKey: needsSemanticsSortOrder ? _kSuffixSemanticsSortOrder : null,
+          semanticsTag: _kSuffixSemanticsTag,
+          child: decoration.suffix,
+        )
+      : null;
+
+    if (input != null && needsSemanticsSortOrder) {
+      input = Semantics(
+        sortKey: _kInputSemanticsSortOrder,
+        child: input,
       );
-
+    }
 
     final bool decorationIsDense = decoration.isDense ?? false;
     final double iconSize = decorationIsDense ? 18.0 : 24.0;
@@ -2272,7 +2334,9 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
                 color: _getPrefixIconColor(themeData, defaults),
                 size: iconSize,
               ),
-              child: decoration.prefixIcon!,
+              child: Semantics(
+                child: decoration.prefixIcon,
+              ),
             ),
           ),
         ),
@@ -2297,7 +2361,9 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
                 color: _getSuffixIconColor(themeData, defaults),
                 size: iconSize,
               ),
-              child: decoration.suffixIcon!,
+              child: Semantics(
+                child: decoration.suffixIcon,
+              ),
             ),
           ),
         ),
@@ -2374,7 +2440,7 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
         isDense: decoration.isDense,
         visualDensity: themeData.visualDensity,
         icon: icon,
-        input: widget.child,
+        input: input,
         label: label,
         hint: hint,
         prefix: prefix,