State can't be used in two stages at once (even with get_driver)

[concave-sphere]

Bevy version

0.5

Operating system & version

Debian GNU/Linux "buster"

What you did

1. Invoke app.add_state(MyState::StateOne)
2. Create a stage MyStage
3. Invoke app.add_system_set(State::<MyState>::get_driver())
4. Add some systems to MyStage via SystemSet::on_update(MyState::StateOne), etc.
5. Add a system that switches between states.

What you expected to happen

Systems that trigger on state enter and exit should run when the state changes, regardless of stage.

What actually happened

Only state change systems in the Update stage are executed.

I know that the program hasn't completely locked because if I put state change systems into Update, they work fine. It does lock if I don't add State::<MyState>::get_driver(), so that's having an effect.

This text in the Bevy Rustdoc made me think this is supposed to work:

If you need to use your state in a different stage, consider using Self::add_state_to_stage or manually adding State::get_driver to additional stages you need it in.

Additional information

Sample code:
test.tar.gz

[alice-i-cecile]

Currently, States are owned by Stages, like all other run_criteria :( This should be fixed as part of the grand effort in #1375.

[Ixentus]

Instead of app.add_system_set(State::<MyState>::get_driver()) you need add_state_to_stage(MyStage, MyState::StateOne). Internally it does get_driver(), but adds it to the stage.

[concave-sphere]

Instead of app.add_system_set(State::<MyState>::get_driver()) you need add_state_to_stage(MyStage, MyState::StateOne). Internally it does get_driver(), but adds it to the stage.

I tried replacing

.add_system_set_to_stage(MyStage, State::<MyState>::get_driver())

with

.add_state_to_stage(MyStage, MyState::StateOne)

The behavior I see is exactly the same: only the systems in the Update stage are executed on state transitions.

As a workaround, I've modified the actual code I was working on to just pull in the State resource and check for state transitions by hand (by storing the last-seen state).

[nicopap]

This is a major issue for me. I'd be happy to contribute a fix.

[cart]

Pulling in @TheRawMeatball (author of the current state system). I recommend discussing alternative designs with them.

[alice-i-cecile]

More discussion is roughly centralized in #2801. The existing run-criteria based states are deeply limited and a full redesign is needed.

[alice-i-cecile]

Fixed by #7267.