handleSelectWord in MultiSelectableSelectionContainerDelegate should handle...

handleSelectWord in MultiSelectableSelectionContainerDelegate should handle rects inside of rects (#127478)

Fixes #127076

Sometimes a `Selectable`s rect may contain another `Selectable`s rect within it. In the case of `handleSelectWord` when choosing which `Selectable` to dispatch the `SelectionEvent` to, the event would be dispatched to the wrong `Selectable` causing an assertion error to be thrown. 

<img width="577" alt="Screenshot 2023-05-24 at 2 46 13 AM" src="https://github.com/flutter/flutter/assets/948037/bb246966-acad-4d81-bd87-758c3ea6ea39">

In the picture above the red outline shows the rect of a two-line piece of text. And the blue rect shows the rect of a piece of text that is on the second line of the two-line piece of text, but has been separated into its own rect for some case, for example when `TextSpan`s are separated by a `WidgetSpan`.

We should check if the text layout of the selectable that has been dispatched the SelectionEvent contains the word, if not then return `SelectionResult.next`, and continue to look through the list of selectables.

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

@@ -1476,6 +1476,11 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     }
     final TextRange word = paragraph.getWordBoundary(position);
     assert(word.isNormalized);
+    if (word.start < range.start && word.end < range.start) {
+      return SelectionResult.previous;
+    } else if (word.start > range.end && word.end > range.end) {
+      return SelectionResult.next;
+    }
     // Fragments are separated by placeholder span, the word boundary shouldn't
     // expand across fragments.
     assert(word.start >= range.start && word.end <= range.end);

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

@@ -1669,12 +1669,21 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
   ///
   /// Returns positive if a is lower, negative if a is higher.
   static int _compareHorizontally(Rect a, Rect b) {
+    // a encloses b.
     if (a.left - b.left < precisionErrorTolerance && a.right - b.right > - precisionErrorTolerance) {
-      // a encloses b.
+      // b ends before a.
+      if (a.right - b.right > precisionErrorTolerance) {
+        return 1;
+      }
       return -1;
     }
+
+    // b encloses a.
     if (b.left - a.left < precisionErrorTolerance && b.right - a.right > - precisionErrorTolerance) {
-      // b encloses a.
+      // a ends before b.
+      if (b.right - a.right > precisionErrorTolerance) {
+        return -1;
+      }
       return 1;
     }
     if ((a.left - b.left).abs() > precisionErrorTolerance) {
@@ -1888,13 +1897,23 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
   /// [SelectWordSelectionEvent.globalPosition].
   @protected
   SelectionResult handleSelectWord(SelectWordSelectionEvent event) {
+    SelectionResult? lastSelectionResult;
     for (int index = 0; index < selectables.length; index += 1) {
       final Rect localRect = Rect.fromLTWH(0, 0, selectables[index].size.width, selectables[index].size.height);
       final Matrix4 transform = selectables[index].getTransformTo(null);
       final Rect globalRect = MatrixUtils.transformRect(transform, localRect);
       if (globalRect.contains(event.globalPosition)) {
         final SelectionGeometry existingGeometry = selectables[index].value;
-        dispatchSelectionEventToChild(selectables[index], event);
+        lastSelectionResult = dispatchSelectionEventToChild(selectables[index], event);
+        if (lastSelectionResult == SelectionResult.next) {
+          continue;
+        }
+        if (index == 0 && lastSelectionResult == SelectionResult.previous) {
+          return SelectionResult.previous;
+        }
+        if (index == selectables.length - 1 && lastSelectionResult == SelectionResult.next) {
+          return SelectionResult.next;
+        }
         if (selectables[index].value != existingGeometry) {
           // Geometry has changed as a result of select word, need to clear the
           // selection of other selectables to keep selection in sync.
@@ -1904,9 +1923,15 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
           currentSelectionStartIndex = currentSelectionEndIndex = index;
         }
         return SelectionResult.end;
+      } else {
+        if (lastSelectionResult == SelectionResult.next) {
+          currentSelectionStartIndex = currentSelectionEndIndex = index - 1;
+          return SelectionResult.end;
+        }
       }
     }
-    return SelectionResult.none;
+    assert(lastSelectionResult == null);
+    return SelectionResult.end;
   }
 
   /// Removes the selection of all selectables this delegate manages.

packages/flutter/test/widgets/selectable_region_test.dart

@@ -769,6 +769,48 @@ void main() {
       skip: isBrowser, // https://github.com/flutter/flutter/issues/61020
     );
 
+    testWidgets(
+      'can select word when a selectables rect is completely inside of another selectables rect', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/127076.
+      final UniqueKey outerText = UniqueKey();
+      await tester.pumpWidget(
+        MaterialApp(
+          home: SelectableRegion(
+            focusNode: FocusNode(),
+            selectionControls: materialTextSelectionControls,
+            child: Scaffold(
+              body: Center(
+                child: Text.rich(
+                  const TextSpan(
+                      children: <InlineSpan>[
+                        TextSpan(
+                          text:
+                              'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.',
+                        ),
+                        WidgetSpan(child: Text('Some text in a WidgetSpan. ')),
+                        TextSpan(text: 'Hello, world.'),
+                      ],
+                  ),
+                  key: outerText,
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+      final RenderParagraph paragraph = tester.renderObject<RenderParagraph>(find.descendant(of: find.byKey(outerText), matching: find.byType(RichText)).first);
+      // Right click to select word at position.
+      final TestGesture gesture = await tester.startGesture(textOffsetToPosition(paragraph, 125), kind: PointerDeviceKind.mouse, buttons: kSecondaryMouseButton);
+      addTearDown(gesture.removePointer);
+      await tester.pump();
+      await gesture.up();
+      await tester.pump();
+      // Should select "Hello".
+      expect(paragraph.selections[0], const TextSelection(baseOffset: 124, extentOffset: 129));
+    },
+      skip: isBrowser, // https://github.com/flutter/flutter/issues/61020
+    );
+
     testWidgets(
       'widget span is ignored if it does not contain text - non Apple',
       (WidgetTester tester) async {