RTL caret position (#60009)

packages/flutter/lib/src/painting/text_painter.dart

@@ -563,6 +563,9 @@ class TextPainter {
     }
     _lastMinWidth = minWidth;
     _lastMaxWidth = maxWidth;
+    // A change in layout invalidates the cached caret metrics as well.
+    _previousCaretPosition = null;
+    _previousCaretPrototype = null;
     _paragraph.layout(ui.ParagraphConstraints(width: maxWidth));
     if (minWidth != maxWidth) {
       final double newWidth = maxIntrinsicWidth.clamp(minWidth, maxWidth) as double;

packages/flutter/test/material/text_field_test.dart

@@ -143,6 +143,8 @@ void main() {
   const String kMoreThanFourLines =
     kThreeLines +
     "\nFourth line won't display and ends at";
+  // Gap between caret and edge of input, defined in editable.dart.
+  const int kCaretGap = 1;
 
   setUp(() async {
     debugResetSemanticsIdCounter();
@@ -754,10 +756,7 @@ void main() {
       const TextPosition(offset: testValueSpaces.length),
     ).bottomRight;
 
-    // Gap between caret and edge of input, defined in editable.dart.
-    const int _kCaretGap = 1;
-
-    expect(cursorOffsetSpaces.dx, inputWidth - _kCaretGap);
+    expect(cursorOffsetSpaces.dx, inputWidth - kCaretGap);
   });
 
   testWidgets('mobile obscureText control test', (WidgetTester tester) async {
@@ -8011,4 +8010,63 @@ void main() {
     expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
     await gesture.moveTo(center);
   });
+
+  testWidgets('Caret rtl with changing width', (WidgetTester tester) async {
+    StateSetter setState;
+    bool isWide = false;
+    const double wideWidth = 300.0;
+    const double narrowWidth = 200.0;
+    final TextEditingController controller = TextEditingController();
+    await tester.pumpWidget(
+      boilerplate(
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setter) {
+            setState = setter;
+            return Container(
+              width: isWide ? wideWidth : narrowWidth,
+              child: TextField(
+                key: textFieldKey,
+                controller: controller,
+                textDirection: TextDirection.rtl,
+              ),
+            );
+          }
+        ),
+      ),
+    );
+
+    // The cursor is on the right of the input because it's RTL.
+    RenderEditable editable = findRenderEditable(tester);
+    double cursorRight = editable.getLocalRectForCaret(
+      TextPosition(offset: controller.value.text.length),
+    ).topRight.dx;
+    double inputWidth = editable.size.width;
+    expect(inputWidth, narrowWidth);
+    expect(cursorRight, inputWidth - kCaretGap);
+
+    // After entering some text, the cursor remains on the right of the input.
+    await tester.enterText(find.byType(TextField), '12345');
+    await tester.pump();
+    editable = findRenderEditable(tester);
+    cursorRight = editable.getLocalRectForCaret(
+      TextPosition(offset: controller.value.text.length),
+    ).topRight.dx;
+    inputWidth = editable.size.width;
+    expect(cursorRight, inputWidth - kCaretGap);
+
+    // Since increasing the width of the input moves its right edge further to
+    // the right, the cursor has followed this change and still appears on the
+    // right of the input.
+    setState(() {
+      isWide = true;
+    });
+    await tester.pump();
+    editable = findRenderEditable(tester);
+    cursorRight = editable.getLocalRectForCaret(
+      TextPosition(offset: controller.value.text.length),
+    ).topRight.dx;
+    inputWidth = editable.size.width;
+    expect(inputWidth, wideWidth);
+    expect(cursorRight, inputWidth - kCaretGap);
+  });
 }