Handling 0.0 Flex params

[arthmis]

The docs don't warn against or protect against using 0.0 as a Flex parameter or mixing negative and positive flex parameters.

• Using 0.0 as a Flex parameter causes the BoxConstraints passed into the flex children to be infinite.
• If there are multiple flex children then their params all have to be negative or all positive.
• If different children have a mix of positive and negative flex params then the sizes are incorrect.

Using 0.0:

    let button = Label::new("Hello").center();
    let container = Container::new(button);
    let child = SizedBox::new(container)
        .width(300.)
        .height(300.)
        .expand()
        .center();
    Flex::column().with_flex_child(child, 0.0)

These are the warnings for using 0.0

Mar 25 11:08:28.826  WARN layout: druid::box_constraints: Infinite minimum height constraint passed to Container:
Mar 25 11:08:28.827  WARN layout: druid::box_constraints: Infinite minimum height constraint passed to Align:
Mar 25 11:08:28.828  WARN layout: druid::core: Widget `druid::widget::align::Align<()>` has an infinite height.
Mar 25 11:08:28.829  WARN layout: druid::widget::sized_box: SizedBox is returning an infinite height.
Mar 25 11:08:28.829  WARN layout: druid::core: Widget `druid::widget::sized_box::SizedBox<()>` has an infinite height.
Mar 25 11:08:28.829  WARN layout: druid::widget::align: Align widget's child has an infinite height.
Mar 25 11:08:28.830  WARN layout: druid::core: Widget `druid::widget::align::Align<()>` has an infinite height.
Mar 25 11:08:28.830  WARN layout: druid::widget::flex: A non-Flex child has an infinite height.

Mixing negative and positive params like this will give incorrect sizes:

    let button = Label::new("Hello").center();
    let container = Container::new(button);
    let child = SizedBox::new(container)
        .width(300.)
        .height(300.)
        .expand()
        .center();
     let second_child = SizedBox::empty()
         .width(500.)
         .height(400.)
         .background(Color::WHITE);
    Flex::column().with_flex_child(child, 1.0)
     .with_flex_child(second_child, -2.0)

This is the warning output:

Mar 25 11:07:55.656  WARN layout: druid::box_constraints: Bad BoxConstraints passed to Align:
Mar 25 11:07:55.656  WARN layout: druid::box_constraints: BoxConstraints { min: 0.0W×0.0H, max: 584.0W×-561.0H }
Mar 25 11:07:55.657  WARN layout: druid::box_constraints: Bad BoxConstraints passed to SizedBox:
Mar 25 11:07:55.657  WARN layout: druid::box_constraints: BoxConstraints { min: 0.0W×0.0H, max: 584.0W×-561.0H }
Mar 25 11:07:55.657  WARN layout: druid::box_constraints: Bad BoxConstraints passed to Container:
Mar 25 11:07:55.658  WARN layout: druid::box_constraints: BoxConstraints { min: 584.0W×-561.0H, max: 584.0W×-561.0H }
[druid\src\widget\flex.rs:678] child_bc = BoxConstraints {
    min: 0.0W×0.0H,
    max: 584.0W×-561.0H,
}
[druid\src\widget\flex.rs:674] desired_major = 1122.0
[druid\src\widget\flex.rs:674] actual_major = 1122.0
[druid\src\widget\flex.rs:678] child_bc = BoxConstraints {
    min: 0.0W×0.0H,
    max: 584.0W×1122.0H,
}
[druid\src\widget\flex.rs:678] child_size = 500.0W×400.0H

I think flex values should be forced to be greater than 0.0.

[cmyr]

Agreed, I think either an assert or a warning + replacing with 1.0 would both be reasonable here. Since these params tend to be static and not computed I think an assert (or at least a debug assert) is reasonable? I would be happy for a PR for this.

[arthmis]

Would it be ok to do debug assert, so that it crashes in debug mode, but when it's release it will warn and replace with 1.0?

[cmyr]

@arthmis sure, that works for me.

[arthmis]

closed with #1691