Expose 'enable' property to allow the user to disable the SearchBar (#137388)

This exposes the `enabled` property of the `TextField` widget to the `Searchbar` widget.

## Related Issues

https://github.com/flutter/flutter/issues/136943

Still missing tests

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

@@ -35,6 +35,7 @@ const Curve _kViewFadeOnInterval = Interval(0.0, 1/2);
 const Curve _kViewIconsFadeOnInterval = Interval(1/6, 2/6);
 const Curve _kViewDividerFadeOnInterval = Interval(0.0, 1/6);
 const Curve _kViewListFadeOnInterval = Interval(133 / _kOpenViewMilliseconds, 233 / _kOpenViewMilliseconds);
+const double _kDisableSearchBarOpacity = 0.38;
 
 /// Signature for a function that creates a [Widget] which is used to open a search view.
 ///
@@ -1115,6 +1116,7 @@ class SearchBar extends StatefulWidget {
     this.textStyle,
     this.hintStyle,
     this.textCapitalization,
+    this.enabled = true,
     this.autoFocus = false,
     this.textInputAction,
     this.keyboardType,
@@ -1239,6 +1241,9 @@ class SearchBar extends StatefulWidget {
   /// {@macro flutter.widgets.editableText.textCapitalization}
   final TextCapitalization? textCapitalization;
 
+  /// If false the text field is "disabled" so the SearchBar will ignore taps.
+  final bool enabled;
+
   /// {@macro flutter.widgets.editableText.autofocus}
   final bool autoFocus;
 
@@ -1340,12 +1345,16 @@ class _SearchBarState extends State<SearchBar> {
 
     return ConstrainedBox(
       constraints: widget.constraints ?? searchBarTheme.constraints ?? defaults.constraints!,
+      child: Opacity(
+        opacity: widget.enabled ? 1 : _kDisableSearchBarOpacity,
         child: Material(
           elevation: effectiveElevation!,
           shadowColor: effectiveShadowColor,
           color: effectiveBackgroundColor,
           surfaceTintColor: effectiveSurfaceTintColor,
           shape: effectiveShape?.copyWith(side: effectiveSide),
+          child: IgnorePointer(
+            ignoring: !widget.enabled,
             child: InkWell(
               onTap: () {
                 widget.onTap?.call();
@@ -1374,6 +1383,7 @@ class _SearchBarState extends State<SearchBar> {
                           onSubmitted: widget.onSubmitted,
                           controller: widget.controller,
                           style: effectiveTextStyle,
+                          enabled: widget.enabled,
                           decoration: InputDecoration(
                             hintText: widget.hintText,
                           ).applyDefaults(InputDecorationTheme(
@@ -1400,6 +1410,8 @@ class _SearchBarState extends State<SearchBar> {
               ),
             ),
           ),
+        ),
+      ),
     );
   }
 }

packages/flutter/test/material/search_anchor_test.dart

@@ -10,6 +10,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../widgets/semantics_tester.dart';
+
 void main() {
   // Returns the RenderEditable at the given index, or the first if not given.
   RenderEditable findRenderEditable(WidgetTester tester, {int index = 0}) {
@@ -2945,6 +2947,72 @@ void main() {
     final TextField textField = tester.widget(find.byType(TextField));
     expect(textField.textInputAction, TextInputAction.previous);
   });
+
+  testWidgets('Block entering text on disabled widget', (WidgetTester tester) async {
+    const String initValue = 'init';
+    final TextEditingController controller = TextEditingController(text: initValue);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: Center(
+            child: SearchBar(
+              controller: controller,
+              enabled: false,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    const String testValue = 'abcdefghi';
+    await tester.enterText(find.byType(SearchBar), testValue);
+    expect(controller.value.text, initValue);
+  });
+
+  testWidgets('Disabled SearchBar semantics node still contains value', (WidgetTester tester) async {
+    final SemanticsTester semantics = SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: Center(
+            child: SearchBar(
+              controller: TextEditingController(text: 'text'),
+              enabled: false,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(semantics, includesNodeWith(actions: <SemanticsAction>[], value: 'text'));
+    semantics.dispose();
+  });
+
+  testWidgets('Check SearchBar opacity when disabled', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Material(
+          child: Center(
+            child: SearchBar(
+              enabled: false,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final Finder searchBarFinder = find.byType(SearchBar);
+    expect(searchBarFinder, findsOneWidget);
+    final Finder opacityFinder = find.descendant(
+      of: searchBarFinder,
+      matching: find.byType(Opacity),
+    );
+    expect(opacityFinder, findsOneWidget);
+    final Opacity opacityWidget = tester.widget<Opacity>(opacityFinder);
+    expect(opacityWidget.opacity, 0.38);
+  });
 }
 
 Future<void> checkSearchBarDefaults(WidgetTester tester, ColorScheme colorScheme, Material material) async {