Const propagation is thinking model content is const when it shouldn't about slint

[tronical]

Wow, this is unexpected. Good that you found a workaround - this seems like a bug to me.

[ogoffart]

Thanks for filling a bug.

Here is a smaller testcase:

export component Btn {
  in-out property <[int]> model;
  width: 30px;
  height: 30px;
  Rectangle {
    background: red;
  }
  TouchArea {
    clicked => {
      model[0] += 1;
    }
  }
}

export component MainWindow inherits Window {
    preferred-height: 500px;
    preferred-width: 500px;
    //in-out     //changing the property to in-out fixes it in the viewer
    property <[int]> model: [42];

    // adding a change in the same component fixes the problem
    // TouchArea {  enabled: false; clicked => { model[0] += 10; }  }

    Btn{ model: model; }
    Text { text: model[0]; }
}

In that testcase, clicking on the red rectangle doesn't increment the text value.
That's because the const propagation phase thinks this is a const model as it doesn't "see" the change.
Changing the property to be in fixes it on the viewer but not on the LSP or slintpad because they add an extra layer so the property is still considered constant.
Adding a setter somewhere does workaround the problem though, as then the compiler sees it changes.

The problem is that the const propagation think that the model is const because nothing gets assigned to it. But this analysis is incorrect for model that are assigned to other property and then get modified trough it.