Interpreter panics if animation properties depends on model about slint

[danutsu]

As a note: building/running the above code locally, in Rust, works fine, so it seems to be a slintpad issue.

[ogoffart]

Thanks for filling a bug.
This can be reproduced with the Slint viewer.

thread 'main' panicked at internal/interpreter/eval.rs:1541:49:
called `Result::unwrap()` on an `Err` value: ()
...
   4: slint_interpreter::eval::new_struct_with_bindings
             at ./internal/interpreter/eval.rs:1541:13
   5: slint_interpreter::dynamic_item_tree::animation_for_property
             at ./internal/interpreter/dynamic_item_tree.rs:1236:44
   6: slint_interpreter::dynamic_item_tree::instantiate::{{closure}}
             at ./internal/interpreter/dynamic_item_tree.rs:1473:39
   7: i_slint_compiler::generator::handle_property_bindings_init::handle_property_inner
             at ./internal/compiler/generator.rs:433:9

[ogoffart]

Even more reduced testcase:

export component Demo {
    for d in [8s]: TouchArea {
        property <float> progress: 0.0;
        function set() {
            progress = 1
        }
        animate progress { duration: d; }
    }
}

[ogoffart]

I investigated the issue. The problem is that the bindings for animated property are read when the itemtree is instentiated. (Because of issue #348)
And in this case, we are reading the model data before it's been set in the update call, so it still has a value of Value::Void and we panic as that's not the correct type for a duration.