Expanded widget not working as expected inside Columns and Rows

Question

Note. this is just an example to simplify what I want to achieve.

I want to fill this space with a yellow container:

So I made a container and wrap it with Expanded widget to fill the whole space and this is what I got:

the code:

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
  decoration:
      BoxDecoration(border: Border.all(width: 5, color: Colors.black)),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.start,
        mainAxisSize: MainAxisSize.min,
        children: [
          Container(
            width: 300,
            height: 300,
            color: Colors.blue,
            alignment: Alignment.center,
            child: Text('300x300')),
          Column(mainAxisSize: MainAxisSize.min, children: [
            Container(
              width: 100,
              height: 100,
              color: Colors.green,
              alignment: Alignment.center,
              child: Text('100x100')),
            Expanded(
              child: Container(width: 100, color: Colors.amber),
            )
            ],
          )
        ],
      ),
    );
  }

what I want to achieve is something like this:

the code of this shape:

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
      decoration:
      BoxDecoration(border: Border.all(width: 5, color: Colors.black)),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.start,
        mainAxisSize: MainAxisSize.min,
        children: [
          Container(
            width: 300,
            height: 300,
            color: Colors.blue,
            alignment: Alignment.center,
            child: Text('300x300')),
          Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Container(
                width: 100,
                height: 100,
                color: Colors.green,
                alignment: Alignment.center,
                child: Text('100x100')),
              Container(
                width: 100,
                height: 200,
                color: Colors.amber,
                alignment: Alignment.center,
                child: Text('100x200')),
            ],
          )
        ],
      ),
    );
  }

If I know the heights and widths so yes I can design this shape. but, what If I don't know the height of the blue Container?

I think it's a problem with Expanded that should be fixed.

Expanded widget should expand its child to the limit boundary of its parent, not expanding its parent too!!

Edited.

I will explain my actual problem to anyone who didn't understand my problem:

I have this list of comments and what I want is that green line beside the comment fills the height to the end of the comment widget.

so I can't set a fixed size to the comment because I may have a comment with a long string so the line won't fill to the end of the comment text would exceed its limits.

Answer 1

Finally, I could solve it by using the IntrinsicHeight widget.

I just wrap my Container with it and then the Expanded widget works as expected.

the final UI:

Here is the code:

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: IntrinsicHeight(
        child: Container(
          decoration:
              BoxDecoration(border: Border.all(width: 5, color: Colors.black)),
          child: Row(
            crossAxisAlignment: CrossAxisAlignment.start,
            mainAxisSize: MainAxisSize.min,
            children: [
              Container(
                  width: 300,
                  height: 300,
                  color: Colors.blue,
                  alignment: Alignment.center,
                  child: Text('300x300')),
              Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  Container(
                      width: 100,
                      height: 100,
                      color: Colors.green,
                      alignment: Alignment.center,
                      child: Text('100x100')),
                  Expanded(
                    child: Container(width: 100, color: Colors.amber),
                  ),
                ],
              )
            ],
          ),
        ),
      ),
    );
  }