ConstraintsTransformBox makes widget invisible, even when the constraints are not changed #146840
Description
Steps to reproduce
I am not sure what is the minimal reproduction for this, as I got it in a very edgy case. The minimal case I managed to reproduced is presented in the sample code below, and can be reproduced both on master and stable. It can be reproduced on DartPad.
It does not have to be unmodified for the bug to happen. Actually, the first time I produced it I was trying to halve the constraints, so I though I messed something in the constraints, but the unmodified makes it clear that it is something with the widget.
I can make it work by either removing ConstraintsTransformBox or by passing a non-zero width to the widget.
Expected results
As the ConstraintsTransformBox does not changes the constraints, the rendered widget should be exactly the same as if there was no ConstraintsTransformBox.
Actual results
The child becomes invisible, while removing the ConstraintsTransformBox makes it visible again.
Code sample
Code sample
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Center(
child: ConstrainedBox(
constraints: BoxConstraints(maxHeight: 24.0),
child: ConstraintsTransformBox( // Remove this widget to get it working
constraintsTransform: ConstraintsTransformBox.unmodified,
child: const VerticalLine(),
),
),
),
),
);
}
}
final class VerticalLine extends StatelessWidget {
const VerticalLine({super.key});
@override
Widget build(BuildContext context) {
return CustomPaint(
painter: _VerticalLinePainter(),
size: Size.fromWidth(0.0),
);
}
}
final class _VerticalLinePainter extends CustomPainter {
const _VerticalLinePainter();
@override
void paint(Canvas canvas, Size size) {
final path = Path();
path.moveTo(size.width / 2.0, 0.0);
path.lineTo(size.width / 2.0, size.height);
final paint = Paint()
..color = const Color(0xFFFF0000)
..strokeWidth = 1.0
..style = PaintingStyle.stroke;
canvas.drawPath(path, paint);
}
@override
bool shouldRepaint(_VerticalLinePainter oldDelegate) => false;
}
Screenshots or Video
Screenshots / Video demonstration
Without ContraintsTransformBox:
With ContraintsTransformBox:
Logs
No response
Flutter Doctor output
[✓] Flutter (Channel stable, 3.19.5, on macOS 14.4.1 23E224 darwin-x64, locale
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[✓] Connected device (3 available)
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