Fix SelectionArea select-word edge cases (flutter#136920)

This change fixes issues with screen order comparison logic when rects are encompassed within each other. This was causing issues when trying to select text that includes inline `WidgetSpan`s inside of a `SelectionArea`.

* Adds `boundingBoxes` to `Selectable` for a more precise hit testing region.

Fixes flutter#132821
Fixes updating selection edge by word boundary when widget spans are involved.
Fixes crash when sending select word selection event to an unselectable element.

Author: Renzo-Olivares

examples/api/lib/material/selectable_region/selectable_region.0.dart

@@ -115,6 +115,9 @@ class _RenderSelectableAdapter extends RenderProxyBox with Selectable, Selection
 
   // Selectable APIs.
 
+  @override
+  List<Rect> get boundingBoxes => <Rect>[paintBounds];
+
   // Adjust this value to enlarge or shrink the selection highlight.
   static const double _padding = 10.0;
   Rect _getSelectionHighlightRect() {

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

@@ -409,7 +409,13 @@ class RenderParagraph extends RenderBox with ContainerRenderObjectMixin<RenderBo
         if (end == -1) {
           end = plainText.length;
         }
-        result.add(_SelectableFragment(paragraph: this, range: TextRange(start: start, end: end), fullText: plainText));
+        result.add(
+          _SelectableFragment(
+            paragraph: this,
+            range: TextRange(start: start, end: end),
+            fullText: plainText,
+          ),
+        );
         start = end;
       }
       start += 1;
@@ -1314,7 +1320,7 @@ class RenderParagraph extends RenderBox with ContainerRenderObjectMixin<RenderBo
 /// [PlaceholderSpan]. The [RenderParagraph] splits itself on [PlaceholderSpan]
 /// to create multiple `_SelectableFragment`s so that they can be selected
 /// separately.
-class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutMetrics {
+class _SelectableFragment with Selectable, Diagnosticable, ChangeNotifier implements TextLayoutMetrics {
   _SelectableFragment({
     required this.paragraph,
     required this.fullText,
@@ -1366,7 +1372,6 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
       ? startOffsetInParagraphCoordinates
       : paragraph._getOffsetForPosition(TextPosition(offset: selectionEnd));
     final bool flipHandles = isReversed != (TextDirection.rtl == paragraph.textDirection);
-    final Matrix4 paragraphToFragmentTransform = getTransformToParagraph()..invert();
     final TextSelection selection = TextSelection(
       baseOffset: selectionStart,
       extentOffset: selectionEnd,
@@ -1377,12 +1382,12 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     }
     return SelectionGeometry(
       startSelectionPoint: SelectionPoint(
-        localPosition: MatrixUtils.transformPoint(paragraphToFragmentTransform, startOffsetInParagraphCoordinates),
+        localPosition: startOffsetInParagraphCoordinates,
         lineHeight: paragraph._textPainter.preferredLineHeight,
         handleType: flipHandles ? TextSelectionHandleType.right : TextSelectionHandleType.left
       ),
       endSelectionPoint: SelectionPoint(
-        localPosition: MatrixUtils.transformPoint(paragraphToFragmentTransform, endOffsetInParagraphCoordinates),
+        localPosition: endOffsetInParagraphCoordinates,
         lineHeight: paragraph._textPainter.preferredLineHeight,
         handleType: flipHandles ? TextSelectionHandleType.left : TextSelectionHandleType.right,
       ),
@@ -1665,7 +1670,16 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     // we do not need to look up the word boundary for that position. This is to
     // maintain a selectables selection collapsed at 0 when the local position is
     // not located inside its rect.
-    final _WordBoundaryRecord? wordBoundary = !_rect.contains(localPosition) ? null : _getWordBoundaryAtPosition(position);
+    _WordBoundaryRecord? wordBoundary = _rect.contains(localPosition) ? _getWordBoundaryAtPosition(position) : null;
+    if (wordBoundary != null
+        && (wordBoundary.wordStart.offset < range.start && wordBoundary.wordEnd.offset <= range.start
+        || wordBoundary.wordStart.offset >= range.end && wordBoundary.wordEnd.offset > range.end)) {
+      // When the position is located at a placeholder inside of the text, then we may compute
+      // a word boundary that does not belong to the current selectable fragment. In this case
+      // we should invalidate the word boundary so that it is not taken into account when
+      // computing the target position.
+      wordBoundary = null;
+    }
     final TextPosition targetPosition = _clampTextPosition(isEnd ? _updateSelectionEndEdgeByWord(wordBoundary, position, existingSelectionStart, existingSelectionEnd) : _updateSelectionStartEdgeByWord(wordBoundary, position, existingSelectionStart, existingSelectionEnd));
 
     _setSelectionPosition(targetPosition, isEnd: isEnd);
@@ -1717,23 +1731,26 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
   }
 
   SelectionResult _handleSelectWord(Offset globalPosition) {
-    _selectableContainsOriginWord = true;
-
     final TextPosition position = paragraph.getPositionForOffset(paragraph.globalToLocal(globalPosition));
     if (_positionIsWithinCurrentSelection(position) && _textSelectionStart != _textSelectionEnd) {
       return SelectionResult.end;
     }
     final _WordBoundaryRecord wordBoundary = _getWordBoundaryAtPosition(position);
-    if (wordBoundary.wordStart.offset < range.start && wordBoundary.wordEnd.offset < range.start) {
+    // This fragment may not contain the word, decide what direction the target
+    // fragment is located in. Because fragments are separated by placeholder
+    // spans, we also check if the beginning or end of the word is touching
+    // either edge of this fragment.
+    if (wordBoundary.wordStart.offset < range.start && wordBoundary.wordEnd.offset <= range.start) {
       return SelectionResult.previous;
-    } else if (wordBoundary.wordStart.offset > range.end && wordBoundary.wordEnd.offset > range.end) {
+    } else if (wordBoundary.wordStart.offset >= range.end && wordBoundary.wordEnd.offset > range.end) {
       return SelectionResult.next;
     }
     // Fragments are separated by placeholder span, the word boundary shouldn't
     // expand across fragments.
     assert(wordBoundary.wordStart.offset >= range.start && wordBoundary.wordEnd.offset <= range.end);
     _textSelectionStart = wordBoundary.wordStart;
     _textSelectionEnd = wordBoundary.wordEnd;
+    _selectableContainsOriginWord = true;
     return SelectionResult.end;
   }
 
@@ -1957,13 +1974,9 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     }
   }
 
-  Matrix4 getTransformToParagraph() {
-    return Matrix4.translationValues(_rect.left, _rect.top, 0.0);
-  }
-
   @override
   Matrix4 getTransformTo(RenderObject? ancestor) {
-    return getTransformToParagraph()..multiply(paragraph.getTransformTo(ancestor));
+    return paragraph.getTransformTo(ancestor);
   }
 
   @override
@@ -1982,6 +1995,28 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     }
   }
 
+  List<Rect>? _cachedBoundingBoxes;
+  @override
+  List<Rect> get boundingBoxes {
+    if (_cachedBoundingBoxes == null) {
+      final List<TextBox> boxes = paragraph.getBoxesForSelection(
+        TextSelection(baseOffset: range.start, extentOffset: range.end),
+      );
+      if (boxes.isNotEmpty) {
+        _cachedBoundingBoxes = <Rect>[];
+        for (final TextBox textBox in boxes) {
+          _cachedBoundingBoxes!.add(textBox.toRect());
+        }
+      } else {
+        final Offset offset = paragraph._getOffsetForPosition(TextPosition(offset: range.start));
+        final Rect rect = Rect.fromPoints(offset, offset.translate(0, - paragraph._textPainter.preferredLineHeight));
+        _cachedBoundingBoxes = <Rect>[rect];
+      }
+    }
+    return _cachedBoundingBoxes!;
+  }
+
+  Rect? _cachedRect;
   Rect get _rect {
     if (_cachedRect == null) {
       final List<TextBox> boxes = paragraph.getBoxesForSelection(
@@ -2000,7 +2035,6 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
     }
     return _cachedRect!;
   }
-  Rect? _cachedRect;
 
   void didChangeParagraphLayout() {
     _cachedRect = null;
@@ -2028,12 +2062,11 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
             textBox.toRect().shift(offset), selectionPaint);
       }
     }
-    final Matrix4 transform = getTransformToParagraph();
     if (_startHandleLayerLink != null && value.startSelectionPoint != null) {
       context.pushLayer(
         LeaderLayer(
           link: _startHandleLayerLink!,
-          offset: offset + MatrixUtils.transformPoint(transform, value.startSelectionPoint!.localPosition),
+          offset: offset + value.startSelectionPoint!.localPosition,
         ),
         (PaintingContext context, Offset offset) { },
         Offset.zero,
@@ -2043,7 +2076,7 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
       context.pushLayer(
         LeaderLayer(
           link: _endHandleLayerLink!,
-          offset: offset + MatrixUtils.transformPoint(transform, value.endSelectionPoint!.localPosition),
+          offset: offset + value.endSelectionPoint!.localPosition,
         ),
         (PaintingContext context, Offset offset) { },
         Offset.zero,
@@ -2071,4 +2104,12 @@ class _SelectableFragment with Selectable, ChangeNotifier implements TextLayoutM
 
   @override
   TextRange getWordBoundary(TextPosition position) => paragraph.getWordBoundary(position);
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(DiagnosticsProperty<String>('textInsideRange', range.textInside(fullText)));
+    properties.add(DiagnosticsProperty<TextRange>('range', range));
+    properties.add(DiagnosticsProperty<String>('fullText', fullText));
+  }
 }

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

@@ -142,6 +142,10 @@ mixin Selectable implements SelectionHandler {
   /// The size of this [Selectable].
   Size get size;
 
+  /// A list of [Rect]s that represent the bounding box of this [Selectable]
+  /// in local coordinates.
+  List<Rect> get boundingBoxes;
+
   /// Disposes resources held by the mixer.
   void dispose();
 }

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

@@ -1817,6 +1817,14 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
     _updateHandleLayersAndOwners();
   }
 
+  Rect _getBoundingBox(Selectable selectable) {
+    Rect result = selectable.boundingBoxes.first;
+    for (int index = 1; index < selectable.boundingBoxes.length; index += 1) {
+      result = result.expandToInclude(selectable.boundingBoxes[index]);
+    }
+    return result;
+  }
+
   /// The compare function this delegate used for determining the selection
   /// order of the selectables.
   ///
@@ -1827,11 +1835,11 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
   int _compareScreenOrder(Selectable a, Selectable b) {
     final Rect rectA = MatrixUtils.transformRect(
       a.getTransformTo(null),
-      Rect.fromLTWH(0, 0, a.size.width, a.size.height),
+      _getBoundingBox(a),
     );
     final Rect rectB = MatrixUtils.transformRect(
       b.getTransformTo(null),
-      Rect.fromLTWH(0, 0, b.size.width, b.size.height),
+      _getBoundingBox(b),
     );
     final int result = _compareVertically(rectA, rectB);
     if (result != 0) {
@@ -1846,6 +1854,7 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
   /// Returns positive if a is lower, negative if a is higher, 0 if their
   /// order can't be determine solely by their vertical position.
   static int _compareVertically(Rect a, Rect b) {
+    // The rectangles overlap so defer to horizontal comparison.
     if ((a.top - b.top < _kSelectableVerticalComparingThreshold && a.bottom - b.bottom > - _kSelectableVerticalComparingThreshold) ||
         (b.top - a.top < _kSelectableVerticalComparingThreshold && b.bottom - a.bottom > - _kSelectableVerticalComparingThreshold)) {
       return 0;
@@ -1863,19 +1872,10 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
   static int _compareHorizontally(Rect a, Rect b) {
     // a encloses b.
     if (a.left - b.left < precisionErrorTolerance && a.right - b.right > - precisionErrorTolerance) {
-      // 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) {
-      // a ends before b.
-      if (b.right - a.right > precisionErrorTolerance) {
-        return -1;
-      }
       return 1;
     }
     if ((a.left - b.left).abs() > precisionErrorTolerance) {
@@ -2140,10 +2140,17 @@ abstract class MultiSelectableSelectionContainerDelegate extends SelectionContai
   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)) {
+      bool globalRectsContainsPosition = false;
+      if (selectables[index].boundingBoxes.isNotEmpty) {
+        for (final Rect rect in selectables[index].boundingBoxes) {
+          final Rect globalRect = MatrixUtils.transformRect(selectables[index].getTransformTo(null), rect);
+          if (globalRect.contains(event.globalPosition)) {
+            globalRectsContainsPosition = true;
+            break;
+          }
+        }
+      }
+      if (globalRectsContainsPosition) {
         final SelectionGeometry existingGeometry = selectables[index].value;
         lastSelectionResult = dispatchSelectionEventToChild(selectables[index], event);
         if (index == selectables.length - 1 && lastSelectionResult == SelectionResult.next) {

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

@@ -200,6 +200,9 @@ class _SelectionContainerState extends State<SelectionContainer> with Selectable
   @override
   Size get size => (context.findRenderObject()! as RenderBox).size;
 
+  @override
+  List<Rect> get boundingBoxes => <Rect>[(context.findRenderObject()! as RenderBox).paintBounds];
+
   @override
   void dispose() {
     if (!widget._disabled) {

packages/flutter/test/material/selection_area_test.dart

@@ -90,7 +90,7 @@ void main() {
         ),
       );
 
-      final TestGesture longpress = await tester.startGesture(const Offset(10, 10));
+      final TestGesture longpress = await tester.startGesture(tester.getCenter(find.byType(Text)));
       addTearDown(longpress.removePointer);
       await tester.pump(const Duration(milliseconds: 500));
       await longpress.up();

packages/flutter/test/widgets/selectable_region_context_menu_test.dart

@@ -138,9 +138,14 @@ class RenderSelectionSpy extends RenderProxyBox
   Size get size => _size;
   Size _size = Size.zero;
 
+  @override
+  List<Rect> get boundingBoxes => _boundingBoxes;
+  final List<Rect> _boundingBoxes = <Rect>[];
+
   @override
   Size computeDryLayout(BoxConstraints constraints) {
     _size = Size(constraints.maxWidth, constraints.maxHeight);
+    _boundingBoxes.add(Rect.fromLTWH(0.0, 0.0, constraints.maxWidth, constraints.maxHeight));
     return _size;
   }