Access to a state in `on_enter`, and maybe `on_exit`

[soanvig]

This is actually self-descriptive.

I need to perform some behavior (insert a component) that depends on the state I'm inserting. If I have no access to the state, then I cannot effectively perform any logic inside on_enter.

I can help on PR.

[Seldom-SE]

This seems reasonable API-wise, but I may significantly change some of the APIs in Bevy 0.14 (because of observers). So I'll get back to this.

For now, you can use the Added filter in a system, or an odd workaround like this:

commands.spawn((
    SomeInitialState,
    StateMachine::default()
        .on_enter::<MyState>(|entity_cmds| entity_cmds.add(|entity: Entity, world: &mut World| {
            if world.get::<MyState>(entity).unwrap().should_also_be_fancy {
                world.entity_mut(entity).insert(Fancy);
            }
        })),
));

[soanvig]

I actually did use .command_on_enter as I have only one entity with a given state at the moment, so I can just query it. But thanks for the idea.

Looking forward 0.14 and observers

[Seldom-SE]

Ok, I don't plan to make large API changes, so this issue is unblocked. I'd accept a PR for this.