Horizontally expand text selection toolbar buttons in overflow menu (#144391)

## Description

This PR expands the items displayed in the overflow menu of a `TextSelectionToolbar` making buttons clickable in the blank area.

| Before | After |
|--------|--------|
| Each item has its own width | All items expand horizontally |
|  ![Capture d’écran 2024-02-29 à 14 43 57](https://github.com/flutter/flutter/assets/840911/f7379eef-9185-4cc4-bf14-e4c916c432b1) | ![Capture d’écran 2024-02-29 à 14 40 47](https://github.com/flutter/flutter/assets/840911/bff272cd-9fe2-4f07-adaf-61edef03d26e) | 

## Related Issue

Fixes https://github.com/flutter/flutter/issues/144089.

## Tests

Adds 1 tests.

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

@@ -262,6 +262,7 @@ class AdaptiveTextSelectionToolbar extends StatelessWidget {
           buttons.add(TextSelectionToolbarTextButton(
             padding: TextSelectionToolbarTextButton.getPadding(i, buttonItems.length),
             onPressed: buttonItem.onPressed,
+            alignment: AlignmentDirectional.centerStart,
             child: Text(getButtonLabel(context, buttonItem)),
           ));
         }

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

@@ -267,6 +267,7 @@ class _TextSelectionControlsToolbarState extends State<_TextSelectionControlsToo
       children: itemDatas.asMap().entries.map((MapEntry<int, _TextSelectionToolbarItemData> entry) {
         return TextSelectionToolbarTextButton(
           padding: TextSelectionToolbarTextButton.getPadding(entry.key, itemDatas.length),
+          alignment: AlignmentDirectional.centerStart,
           onPressed: entry.value.onPressed,
           child: Text(entry.value.label),
         );

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

@@ -569,6 +569,40 @@ class _RenderTextSelectionToolbarItemsLayout extends RenderBox with ContainerRen
     size = nextSize;
   }
 
+  // Horizontally expand the children when the menu overflows so they can react to
+  // pointer events into their whole area.
+  void _resizeChildrenWhenOverflow() {
+    if (!overflowOpen) {
+      return;
+    }
+
+    final RenderBox navButton = firstChild!;
+    int i = -1;
+
+    visitChildren((RenderObject renderObjectChild) {
+      final RenderBox child = renderObjectChild as RenderBox;
+      final ToolbarItemsParentData childParentData = child.parentData! as ToolbarItemsParentData;
+
+      i++;
+
+      // Ignore the navigation button.
+      if (renderObjectChild == navButton) {
+        return;
+      }
+
+      // There is no need to update children that won't be painted.
+      if (!_shouldPaintChild(renderObjectChild, i)) {
+        childParentData.shouldPaint = false;
+        return;
+      }
+
+      child.layout(
+        BoxConstraints.tightFor(width: size.width),
+        parentUsesSize: true,
+      );
+    });
+  }
+
   @override
   void performLayout() {
     _lastIndexThatFits = -1;
@@ -579,6 +613,7 @@ class _RenderTextSelectionToolbarItemsLayout extends RenderBox with ContainerRen
 
     _layoutChildren();
     _placeChildren();
+    _resizeChildrenWhenOverflow();
   }
 
   @override

packages/flutter/test/material/text_selection_toolbar_test.dart

@@ -291,4 +291,64 @@ void main() {
       );
     });
   }
+
+  testWidgets('Overflowed menu expands children horizontally', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/144089.
+    late StateSetter setState;
+    final List<Widget> children = List<Widget>.generate(7, (int i) => const TestBox());
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: StatefulBuilder(
+            builder: (BuildContext context, StateSetter setter) {
+              setState = setter;
+              return TextSelectionToolbar(
+                anchorAbove: const Offset(50.0, 100.0),
+                anchorBelow: const Offset(50.0, 200.0),
+                children: children,
+              );
+            },
+          ),
+        ),
+      ),
+    );
+
+    // All children fit on the screen, so they are all rendered.
+    expect(find.byType(TestBox), findsNWidgets(children.length));
+    expect(findOverflowButton(), findsNothing);
+
+    const String short = 'Short';
+    const String medium = 'Medium length';
+    const String long = 'Long label in the overflow menu';
+
+    // Adding several children makes the menu overflow.
+    setState(() {
+      children.addAll(const <Text>[
+        Text(short),
+        Text(medium),
+        Text(long),
+      ]);
+    });
+    await tester.pumpAndSettle();
+    expect(findOverflowButton(), findsOneWidget);
+
+    // Tap the overflow button to show the overflow menu.
+    await tester.tap(findOverflowButton());
+    await tester.pumpAndSettle();
+    expect(find.byType(TestBox), findsNothing);
+    expect(find.byType(Text), findsNWidgets(3));
+    expect(findOverflowButton(), findsOneWidget);
+
+    Finder findToolbarContainer() {
+      return find.byWidgetPredicate((Widget w) => '${w.runtimeType}' == '_TextSelectionToolbarContainer');
+    }
+    expect(findToolbarContainer(), findsAtLeastNWidgets(1));
+
+    // Buttons have their width set to the container width.
+    final double overflowMenuWidth = tester.getRect(findToolbarContainer()).width;
+    expect(tester.getRect(find.text(long)).width, overflowMenuWidth);
+    expect(tester.getRect(find.text(medium)).width, overflowMenuWidth);
+    expect(tester.getRect(find.text(short)).width, overflowMenuWidth);
+  });
 }