Remove OnUpdate system set (#8260)

# Objective

- Fixes https://github.com/bevyengine/bevy/issues/8239.

## Solution

- Replace `OnUpdate` with `run_if(in_state(xxx))`.

---

## Migration Guide

- Replace `OnUpdate` with `run_if(in_state(xxx))`.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

crates/bevy_app/src/app.rs

@@ -312,10 +312,6 @@ impl App {
     /// [`run_once`](`run_once_condition`) condition to run the on enter schedule of the
     /// initial state.
     ///
-    /// This also adds an [`OnUpdate`] system set for each state variant,
-    /// which runs during [`Update`] after the transitions are applied.
-    /// These system sets only run if the [`State<S>`] resource matches the respective state variant.
-    ///
     /// If you would like to control how other systems run based on the current state,
     /// you can emulate this behavior using the [`in_state`] [`Condition`](bevy_ecs::schedule::Condition).
     ///
@@ -333,10 +329,6 @@ impl App {
                     .chain(),
             );
 
-        for variant in S::variants() {
-            self.configure_set(Update, OnUpdate(variant.clone()).run_if(in_state(variant)));
-        }
-
         // The OnEnter, OnExit, and OnTransition schedules are lazily initialized
         // (i.e. when the first system is added to them), and World::try_run_schedule is used to fail
         // gracefully if they aren't present.

crates/bevy_ecs/src/lib.rs

@@ -40,7 +40,7 @@ pub mod prelude {
         schedule::{
             apply_state_transition, apply_system_buffers, common_conditions::*, Condition,
             IntoSystemConfigs, IntoSystemSet, IntoSystemSetConfig, IntoSystemSetConfigs, NextState,
-            OnEnter, OnExit, OnTransition, OnUpdate, Schedule, Schedules, State, States, SystemSet,
+            OnEnter, OnExit, OnTransition, Schedule, Schedules, State, States, SystemSet,
         },
         system::{
             adapter as system_adapter,

crates/bevy_ecs/src/schedule/state.rs

@@ -4,7 +4,7 @@ use std::mem;
 
 use crate as bevy_ecs;
 use crate::change_detection::DetectChangesMut;
-use crate::schedule::{ScheduleLabel, SystemSet};
+use crate::schedule::ScheduleLabel;
 use crate::system::Resource;
 use crate::world::World;
 
@@ -20,8 +20,6 @@ pub use bevy_ecs_macros::States;
 ///
 /// State transitions typically occur in the [`OnEnter<T::Variant>`] and [`OnExit<T:Variant>`] schedules,
 /// which can be run via the [`apply_state_transition::<T>`] system.
-/// Systems that run each frame in various states are typically stored in the main schedule,
-/// and are conventionally part of the [`OnUpdate(T::Variant)`] system set.
 ///
 /// # Example
 ///
@@ -66,14 +64,6 @@ pub struct OnTransition<S: States> {
     pub to: S,
 }
 
-/// A [`SystemSet`] that will run within `CoreSet::Update` when this state is active.
-///
-/// This set, when created via `App::add_state`, is configured with a run condition.
-/// If all you want is the run condition, use the [`in_state`](crate::schedule::common_conditions::in_state)
-/// [condition](super::Condition) directly.
-#[derive(SystemSet, Clone, Debug, PartialEq, Eq, Hash)]
-pub struct OnUpdate<S: States>(pub S);
-
 /// A finite-state machine whose transitions have associated schedules
 /// ([`OnEnter(state)`] and [`OnExit(state)`]).
 ///

examples/2d/texture_atlas.rs

@@ -9,7 +9,7 @@ fn main() {
         .add_plugins(DefaultPlugins.set(ImagePlugin::default_nearest())) // prevents blurry sprites
         .add_state::<AppState>()
         .add_systems(OnEnter(AppState::Setup), load_textures)
-        .add_systems(Update, check_textures.in_set(OnUpdate(AppState::Setup)))
+        .add_systems(Update, check_textures.run_if(in_state(AppState::Setup)))
         .add_systems(OnEnter(AppState::Finished), setup)
         .run();
 }

examples/ecs/generic_system.rs

@@ -39,7 +39,7 @@ fn main() {
             Update,
             (
                 print_text_system,
-                transition_to_in_game_system.in_set(OnUpdate(AppState::MainMenu)),
+                transition_to_in_game_system.run_if(in_state(AppState::MainMenu)),
             ),
         )
         // Cleanup systems.

examples/ecs/state.rs

@@ -18,12 +18,12 @@ fn main() {
         .add_systems(OnEnter(AppState::Menu), setup_menu)
         // By contrast, update systems are stored in the `Update` schedule. They simply
         // check the value of the `State<T>` resource to see if they should run each frame.
-        .add_systems(Update, menu.in_set(OnUpdate(AppState::Menu)))
+        .add_systems(Update, menu.run_if(in_state(AppState::Menu)))
         .add_systems(OnExit(AppState::Menu), cleanup_menu)
         .add_systems(OnEnter(AppState::InGame), setup_game)
         .add_systems(
             Update,
-            (movement, change_color).in_set(OnUpdate(AppState::InGame)),
+            (movement, change_color).run_if(in_state(AppState::InGame)),
         )
         .run();
 }

examples/games/alien_cake_addict.rs

@@ -35,14 +35,14 @@ fn main() {
                 scoreboard_system,
                 spawn_bonus,
             )
-                .in_set(OnUpdate(GameState::Playing)),
+                .run_if(in_state(GameState::Playing)),
         )
         .add_systems(OnExit(GameState::Playing), teardown)
         .add_systems(OnEnter(GameState::GameOver), display_score)
         .add_systems(
             Update,
             (
-                gameover_keyboard.in_set(OnUpdate(GameState::GameOver)),
+                gameover_keyboard.run_if(in_state(GameState::GameOver)),
                 bevy::window::close_on_esc,
             ),
         )

examples/games/game_menu.rs

@@ -62,7 +62,7 @@ mod splash {
                 // When entering the state, spawn everything needed for this screen
                 .add_systems(OnEnter(GameState::Splash), splash_setup)
                 // While in this state, run the `countdown` system
-                .add_systems(Update, countdown.in_set(OnUpdate(GameState::Splash)))
+                .add_systems(Update, countdown.run_if(in_state(GameState::Splash)))
                 // When exiting the state, despawn everything that was spawned for this screen
                 .add_systems(OnExit(GameState::Splash), despawn_screen::<OnSplashScreen>);
         }
@@ -131,7 +131,7 @@ mod game {
     impl Plugin for GamePlugin {
         fn build(&self, app: &mut App) {
             app.add_systems(OnEnter(GameState::Game), game_setup)
-                .add_systems(Update, game.in_set(OnUpdate(GameState::Game)))
+                .add_systems(Update, game.run_if(in_state(GameState::Game)))
                 .add_systems(OnExit(GameState::Game), despawn_screen::<OnGameScreen>);
         }
     }
@@ -284,7 +284,7 @@ mod menu {
                     Update,
                     (
                         setting_button::<DisplayQuality>
-                            .in_set(OnUpdate(MenuState::SettingsDisplay)),
+                            .run_if(in_state(MenuState::SettingsDisplay)),
                     ),
                 )
                 .add_systems(
@@ -295,7 +295,7 @@ mod menu {
                 .add_systems(OnEnter(MenuState::SettingsSound), sound_settings_menu_setup)
                 .add_systems(
                     Update,
-                    setting_button::<Volume>.in_set(OnUpdate(MenuState::SettingsSound)),
+                    setting_button::<Volume>.run_if(in_state(MenuState::SettingsSound)),
                 )
                 .add_systems(
                     OnExit(MenuState::SettingsSound),
@@ -304,7 +304,7 @@ mod menu {
                 // Common systems to all screens that handles buttons behaviour
                 .add_systems(
                     Update,
-                    (menu_action, button_system).in_set(OnUpdate(GameState::Menu)),
+                    (menu_action, button_system).run_if(in_state(GameState::Menu)),
                 );
         }
     }