App::update crashes with default plugins due to pipelined rendering

[alice-i-cecile]

Bevy version

9d52aae

What you did

Run

fn main() {
    App::new().add_plugins(DefaultPlugins).update();
}

What went wrong

Two different errors, depending on the run:

1. thread 'main' panicked at 'resource does not exist: bevy_render::ExtractStage', /home/alice/Documents/Code/bevy/crates/bevy_ecs/src/world/mod.rs:1311:32 note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

2. thread 'main' panicked at 'called Option::unwrap()on aNonevalue', crates/bevy_render/src/pipelined_rendering.rs:143:84 note: run withRUST_BACKTRACE=1environment variable to display a backtrace thread 'main' panicked at 'calledOption::unwrap()on aNone value', /home/alice/Documents/Code/bevy/crates/bevy_tasks/src/task_pool.rs:354:49

Additional context

This failure does not occur with App::run instead.

[hymm]

This is because only App.run calls the setup functions that are used by pipelined rendering. Is this just necessary for testing?

If it is we could add a setup/build function that you can call explicitly to run that step.

[alice-i-cecile]

I can replicate this on #7267.

Yes, I primarily want this for testing and teaching purposes. Walking one-frame-at-a-time through the app is very useful for catching bugs.

Right, that explanation makes sense. I think ultimately we should go back to AppBuilder, for this and other reasons.
I'm unsure if that's the right fix for this immediately though: it's fairly controversial and invasive.

[hymm]

I think ultimately we should go back to AppBuilder

I agree here. There's a bunch of stuff for improving plugins that can only really be done with a finalizing build step.

I'm unsure if that's the right fix for this immediately though: it's fairly controversial and invasive.

Also agree here. I'm not sure I want to try to get something like this in before 0.10.

I think adding a method you can call explicitly for testing isn't ideal, but it should work as a temporary workaround for 0.10.