add_system(foo.in_schedule(CoreSchedule::Startup)) is a lot to type.

Note that we have 6 different ways to add systems to the startup schedule! Adding systems to schedules should be ergonomic and extensible

add_systems((foo, bar).on_startup()): add multiple systems to the startup schedule.

add_system(foo.on_startup()): add one systems to the startup schedule.

add_startup_systems((foo, bar)): add multiple systems to the startup schedule.

add_startup_system(foo): add a system to the startup schedule.

add_systems((foo, bar).in_schedule(CoreSchedule::Startup)): add multiple systems to a specified schedule.add_system(foo.in_schedule(CoreSchedule::Startup)): add one system to a specified schedule.add_systems((foo, bar)): add multiple systems to the default schedule.add_system(foo): add a single system to the default schedule.We have way too many ways to add systems to schedules: It is completely unreasonable to expect Bevy users to be aware of all present and future 'built in' and 3rd party engine systems. Engine features like events, assets, transforms, animation, etc would silently fail for users. Without a solution to this problem, add_system(foo) would be unconstrained in the schedule.

We can't just remove 'base sets', as they enable normal 'update' systems to work 'as expected' automatically. This produced roughly equivalent behavior to the old 'default update stage' in Bevy 0.9 and below. They were largely added to enable 'default base sets', which enabled add_system(foo) to be automatically added to CoreSet::Update, ensuring that foo can interact with 'engine features' without ordering itself relative to all present (and future) 'engine features'.It was easy to accidentally create invalid orderings: add_system(foo.after(TransformPropagate)) would fail because foo is implicitly in CoreSet::Update by default, but transform propagation happens in CoreSet::PostUpdate.It is a new concept that users need to contend with.The 'base set' concept introduced in Bevy 0.10 is more confusing than we would like: Please read this entire description before sharing your thoughts. While these changes are relatively straightforward, this is a very complicated and controversial topic.

Plugins for mainstage 3