From 7db26b09bb5fdb020b1347dd5545d41bd4f5db90 Mon Sep 17 00:00:00 2001
From: LongCatIsLooong <31859944+LongCatIsLooong@users.noreply.github.com>
Date: Sat, 13 Apr 2024 04:58:02 +0800
Subject: [PATCH] Fix `getOffsetForCaret` crash (#146669)

Fixes a crash in Google tests (b/333560406) related to a decomposed complex character.
---
 .../flutter/lib/src/painting/text_painter.dart     |  9 +++++++--
 .../flutter/test/painting/text_painter_test.dart   | 14 ++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/packages/flutter/lib/src/painting/text_painter.dart b/packages/flutter/lib/src/painting/text_painter.dart
index 097379f19ea..18a8b6110f8 100644
--- a/packages/flutter/lib/src/painting/text_painter.dart
+++ b/packages/flutter/lib/src/painting/text_painter.dart
@@ -1468,10 +1468,15 @@ class TextPainter {
     final _LineCaretMetrics metrics;
     final List<TextBox> boxes = cachedLayout.paragraph
       .getBoxesForRange(graphemeRange.start, graphemeRange.end, boxHeightStyle: ui.BoxHeightStyle.strut);
+
     if (boxes.isNotEmpty) {
-      final TextBox box = boxes.single;
+      final bool ahchorToLeft = switch (glyphInfo.writingDirection) {
+        TextDirection.ltr => anchorToLeadingEdge,
+        TextDirection.rtl => !anchorToLeadingEdge,
+      };
+      final TextBox box = ahchorToLeft ? boxes.first : boxes.last;
       metrics = _LineCaretMetrics(
-        offset: Offset(anchorToLeadingEdge ? box.start : box.end, box.top),
+        offset: Offset(ahchorToLeft ? box.left : box.right, box.top),
         writingDirection: box.direction,
       );
     } else {
diff --git a/packages/flutter/test/painting/text_painter_test.dart b/packages/flutter/test/painting/text_painter_test.dart
index f8feb2afd8b..47f4f18f870 100644
--- a/packages/flutter/test/painting/text_painter_test.dart
+++ b/packages/flutter/test/painting/text_painter_test.dart
@@ -1682,6 +1682,20 @@ void main() {
     });
   }, skip: kIsWeb && !isSkiaWeb); // [intended] strut spport for HTML renderer https://github.com/flutter/flutter/issues/32243.
 
+  test('getOffsetForCaret does not crash on decomposed characters', () {
+    final TextPainter painter = TextPainter(
+      textDirection: TextDirection.ltr,
+      text: const TextSpan(
+        text: '각',
+        style: TextStyle(fontSize: 10),
+      ),
+    )..layout(maxWidth: 1); // Force the jamo characters to soft wrap.
+    expect(
+      () => painter.getOffsetForCaret(const TextPosition(offset: 0), Rect.zero),
+      returnsNormally,
+    );
+  });
+
   test('TextPainter dispatches memory events', () async {
     await expectLater(
       await memoryEvents(() => TextPainter().dispose(), TextPainter),