import 'dart:ui';

import 'package:flutter/widgets.dart';

void main() {
  runApp(BugReport());
}

class BugReport extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ColoredBox(
      color: const Color(0xffffffff),
      child: Padding(
        padding: EdgeInsets.all(20),
        child: CustomPaint(
          painter: TitledBorderPainter(),
        ),
      ),
    );
  }
}

class TitledBorderPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final Rect titleRect = Rect.fromLTWH(20, 0, 50, 20);
    final Paint paint = Paint()
      ..style = PaintingStyle.stroke
      ..color = const Color(0xff000000)
      ..strokeWidth = 1;

    canvas.save();
    try {
      final Rect borderRect = Rect.fromLTRB(0, 10, size.width, size.height);
      canvas.clipRect(titleRect, clipOp: ClipOp.difference);
      canvas.drawRect(borderRect, paint);
    } finally {
      canvas.restore();
    }

    canvas..drawRect(titleRect, paint);
  }

  @override
  bool shouldRepaint(TitledBorderPainter oldDelegate) => false;
}