Triple tap selection should not move beyond text boundary at the tapped location (#132357)

This PR makes sure we do not select beyond the text boundary at the tapped position unless, we tap at the end of the text which in that case we should select the previous text boundary.

```dart
    // if x is a boundary defined by `textBoundary`, most textBoundaries (except
    // LineBreaker) guarantees `x == textBoundary.getLeadingTextBoundaryAt(x)`.
    // Use x - 1 here to make sure we don't get stuck at the fixed point x.
    final int start = textBoundary.getLeadingTextBoundaryAt(extent.offset - 1) ?? 0;
```

This was originally carried over from https://github.com/flutter/flutter/blob/f468f3366c26a5092eb964a230ce7892fda8f2f8/packages/flutter/lib/src/widgets/editable_text.dart#L4167-L4179 which used this `x - 1` to be able to move to the previous word boundary when navigating with a keyboard. When selecting by tapping/clicking we do not want to move past the text boundary at the tapped position so this adjustment is not needed.

Fixes #132126

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

@@ -2567,14 +2567,13 @@ class TextSelectionGestureDetectorBuilder {
     _selectTextBoundariesInRange(boundary: lineBoundary, from: from, to: to, cause: cause);
   }
 
-  // Returns the closest boundary location to `extent` but not including `extent`
-  // itself.
-  TextRange _moveBeyondTextBoundary(TextPosition extent, TextBoundary textBoundary) {
+  // Returns the location of a text boundary at `extent`. When `extent` is at
+  // the end of the text, returns the previous text boundary's location.
+  TextRange _moveToTextBoundary(TextPosition extent, TextBoundary textBoundary) {
     assert(extent.offset >= 0);
-    // if x is a boundary defined by `textBoundary`, most textBoundaries (except
-    // LineBreaker) guarantees `x == textBoundary.getLeadingTextBoundaryAt(x)`.
-    // Use x - 1 here to make sure we don't get stuck at the fixed point x.
-    final int start = textBoundary.getLeadingTextBoundaryAt(extent.offset - 1) ?? 0;
+    // Use extent.offset - 1 when `extent` is at the end of the text to retrieve
+    // the previous text boundary's location.
+    final int start = textBoundary.getLeadingTextBoundaryAt(extent.offset == editableText.textEditingValue.text.length ? extent.offset - 1 : extent.offset) ?? 0;
     final int end = textBoundary.getTrailingTextBoundaryAt(extent.offset) ?? editableText.textEditingValue.text.length;
     return TextRange(start: start, end: end);
   }
@@ -2589,13 +2588,13 @@ class TextSelectionGestureDetectorBuilder {
   // beginning and end of a text boundary respectively.
   void _selectTextBoundariesInRange({required TextBoundary boundary, required Offset from, Offset? to, SelectionChangedCause? cause}) {
     final TextPosition fromPosition = renderEditable.getPositionForPoint(from);
-    final TextRange fromRange = _moveBeyondTextBoundary(fromPosition, boundary);
+    final TextRange fromRange = _moveToTextBoundary(fromPosition, boundary);
     final TextPosition toPosition = to == null
         ? fromPosition
         : renderEditable.getPositionForPoint(to);
     final TextRange toRange = toPosition == fromPosition
         ? fromRange
-        : _moveBeyondTextBoundary(toPosition, boundary);
+        : _moveToTextBoundary(toPosition, boundary);
     final bool isFromBoundaryBeforeToBoundary = fromRange.start < toRange.end;
 
     final TextSelection newSelection = isFromBoundaryBeforeToBoundary

packages/flutter/test/cupertino/text_field_test.dart

@@ -3804,6 +3804,121 @@ void main() {
       variant: TargetPlatformVariant.mobile(),
     );
 
+    testWidgets(
+      'Triple click at the beginning of a line should not select the previous paragraph',
+      (WidgetTester tester) async {
+        // Regression test for https://github.com/flutter/flutter/issues/132126
+        final TextEditingController controller = TextEditingController();
+
+        await tester.pumpWidget(
+          CupertinoApp(
+            home: Center(
+              child: CupertinoTextField(
+                dragStartBehavior: DragStartBehavior.down,
+                controller: controller,
+                maxLines: null,
+              ),
+            ),
+          ),
+        );
+
+        await tester.enterText(find.byType(CupertinoTextField), testValueB);
+        // Skip past scrolling animation.
+        await tester.pump();
+        await tester.pump(const Duration(milliseconds: 200));
+        expect(controller.value.text, testValueB);
+
+        final Offset thirdLinePos = textOffsetToPosition(tester, 38);
+
+        // Click on text field to gain focus, and move the selection.
+        final TestGesture gesture = await tester.startGesture(thirdLinePos, kind: PointerDeviceKind.mouse);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+
+        expect(controller.selection.isCollapsed, true);
+        expect(controller.selection.baseOffset, 38);
+
+        // Here we click on same position again, to register a double click. This will select
+        // the word at the clicked position.
+        await gesture.down(thirdLinePos);
+        await gesture.up();
+
+        expect(controller.selection.baseOffset, 38);
+        expect(controller.selection.extentOffset, 40);
+
+        // Here we click on same position again, to register a triple click. This will select
+        // the paragraph at the clicked position.
+        await gesture.down(thirdLinePos);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+        await tester.pumpAndSettle();
+
+        expect(controller.selection.baseOffset, 38);
+        expect(controller.selection.extentOffset, 57);
+      },
+      variant: TargetPlatformVariant.all(excluding: <TargetPlatform>{ TargetPlatform.linux }),
+    );
+
+    testWidgets(
+      'Triple click at the end of text should select the previous paragraph',
+      (WidgetTester tester) async {
+        // Regression test for https://github.com/flutter/flutter/issues/132126.
+        final TextEditingController controller = TextEditingController();
+
+        await tester.pumpWidget(
+          CupertinoApp(
+            home: Center(
+              child: CupertinoTextField(
+                dragStartBehavior: DragStartBehavior.down,
+                controller: controller,
+                maxLines: null,
+              ),
+            ),
+          ),
+        );
+
+        await tester.enterText(find.byType(CupertinoTextField), testValueB);
+        // Skip past scrolling animation.
+        await tester.pump();
+        await tester.pump(const Duration(milliseconds: 200));
+        expect(controller.value.text, testValueB);
+
+        final Offset endOfTextPos = textOffsetToPosition(tester, 74);
+
+        // Click on text field to gain focus, and move the selection.
+        final TestGesture gesture = await tester.startGesture(endOfTextPos, kind: PointerDeviceKind.mouse);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+
+        expect(controller.selection.isCollapsed, true);
+        expect(controller.selection.baseOffset, 74);
+
+        // Here we click on same position again, to register a double click.
+        await gesture.down(endOfTextPos);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+
+        expect(controller.selection.baseOffset, 74);
+        expect(controller.selection.extentOffset, 74);
+
+        // Here we click on same position again, to register a triple click. This will select
+        // the paragraph at the clicked position.
+        await gesture.down(endOfTextPos);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+        await tester.pumpAndSettle();
+
+        expect(controller.selection.baseOffset, 57);
+        expect(controller.selection.extentOffset, 74);
+      },
+      variant: TargetPlatformVariant.all(excluding: <TargetPlatform>{ TargetPlatform.linux }),
+    );
+
     testWidgets(
       'triple tap chains work on Non-Apple mobile platforms',
       (WidgetTester tester) async {

packages/flutter/test/material/text_field_test.dart

@@ -9771,6 +9771,117 @@ void main() {
       variant: TargetPlatformVariant.mobile(),
     );
 
+    testWidgets(
+      'Triple click at the beginning of a line should not select the previous paragraph',
+      (WidgetTester tester) async {
+        // Regression test for https://github.com/flutter/flutter/issues/132126
+        final TextEditingController controller = TextEditingController();
+
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Material(
+              child: TextField(
+                dragStartBehavior: DragStartBehavior.down,
+                controller: controller,
+                maxLines: null,
+              ),
+            ),
+          ),
+        );
+
+        await tester.enterText(find.byType(TextField), testValueB);
+        await skipPastScrollingAnimation(tester);
+        expect(controller.value.text, testValueB);
+
+        final Offset thirdLinePos = textOffsetToPosition(tester, 38);
+
+        // Click on text field to gain focus, and move the selection.
+        final TestGesture gesture = await tester.startGesture(thirdLinePos, kind: PointerDeviceKind.mouse);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+
+        expect(controller.selection.isCollapsed, true);
+        expect(controller.selection.baseOffset, 38);
+
+        // Here we click on same position again, to register a double click. This will select
+        // the word at the clicked position.
+        await gesture.down(thirdLinePos);
+        await gesture.up();
+
+        expect(controller.selection.baseOffset, 38);
+        expect(controller.selection.extentOffset, 40);
+
+        // Here we click on same position again, to register a triple click. This will select
+        // the paragraph at the clicked position.
+        await gesture.down(thirdLinePos);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+        await tester.pumpAndSettle();
+
+        expect(controller.selection.baseOffset, 38);
+        expect(controller.selection.extentOffset, 57);
+      },
+      variant: TargetPlatformVariant.all(excluding: <TargetPlatform>{ TargetPlatform.linux }),
+    );
+
+    testWidgets(
+      'Triple click at the end of text should select the previous paragraph',
+      (WidgetTester tester) async {
+        // Regression test for https://github.com/flutter/flutter/issues/132126.
+        final TextEditingController controller = TextEditingController();
+
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Material(
+              child: TextField(
+                dragStartBehavior: DragStartBehavior.down,
+                controller: controller,
+                maxLines: null,
+              ),
+            ),
+          ),
+        );
+
+        await tester.enterText(find.byType(TextField), testValueB);
+        await skipPastScrollingAnimation(tester);
+        expect(controller.value.text, testValueB);
+
+        final Offset endOfTextPos = textOffsetToPosition(tester, 74);
+
+        // Click on text field to gain focus, and move the selection.
+        final TestGesture gesture = await tester.startGesture(endOfTextPos, kind: PointerDeviceKind.mouse);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+
+        expect(controller.selection.isCollapsed, true);
+        expect(controller.selection.baseOffset, 74);
+
+        // Here we click on same position again, to register a double click.
+        await gesture.down(endOfTextPos);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+
+        expect(controller.selection.baseOffset, 74);
+        expect(controller.selection.extentOffset, 74);
+
+        // Here we click on same position again, to register a triple click. This will select
+        // the paragraph at the clicked position.
+        await gesture.down(endOfTextPos);
+        await tester.pump();
+        await gesture.up();
+        await tester.pump();
+        await tester.pumpAndSettle();
+
+        expect(controller.selection.baseOffset, 57);
+        expect(controller.selection.extentOffset, 74);
+      },
+      variant: TargetPlatformVariant.all(excluding: <TargetPlatform>{ TargetPlatform.linux }),
+    );
+
     testWidgets(
       'triple tap chains work on Non-Apple mobile platforms',
       (WidgetTester tester) async {