new behavior only applies if TimePlugin is installed

Author: maniwani

crates/bevy_app/src/app.rs

@@ -1,7 +1,6 @@
 use crate::{First, FixedUpdate, Main, MainSchedulePlugin, Plugin, Plugins, StateTransition};
 pub use bevy_derive::AppLabel;
 use bevy_ecs::{
-    event::EventUpdateSignal,
     prelude::*,
     schedule::{
         apply_state_transition, common_conditions::run_once as run_once_condition,
@@ -184,6 +183,8 @@ impl Default for App {
         app.init_resource::<AppTypeRegistry>();
 
         app.add_plugins(MainSchedulePlugin);
+        app.add_systems(FixedUpdate, bevy_ecs::event::event_queue_update_system);
+
         app.add_event::<AppExit>();
 
         #[cfg(feature = "bevy_ci_testing")]
@@ -448,18 +449,11 @@ impl App {
         T: Event,
     {
         if !self.world.contains_resource::<Events<T>>() {
-            self.init_resource::<Events<T>>()
-                .init_resource::<EventUpdateSignal<T>>()
-                .add_systems(
-                    First,
-                    bevy_ecs::event::event_update_system::<T>
-                        .run_if(bevy_ecs::event::event_update_condition::<T>),
-                )
-                .add_systems(
-                    FixedUpdate,
-                    bevy_ecs::event::event_queue_update_system::<T>
-                        .run_if(bevy_ecs::event::event_update_condition::<T>),
-                );
+            self.init_resource::<Events<T>>().add_systems(
+                First,
+                bevy_ecs::event::event_update_system::<T>
+                    .run_if(bevy_ecs::event::event_update_condition::<T>),
+            );
         }
         self
     }

crates/bevy_ecs/src/event.rs

@@ -750,25 +750,19 @@ impl<'a, E: Event> ExactSizeIterator for EventIteratorWithId<'a, E> {
 }
 
 #[doc(hidden)]
-#[derive(Resource)]
-pub struct EventUpdateSignal<T>(bool, PhantomData<T>);
-
-impl<T> Default for EventUpdateSignal<T> {
-    fn default() -> Self {
-        Self(false, PhantomData)
-    }
-}
+#[derive(Resource, Default)]
+pub struct EventUpdateSignal(bool);
 
 /// A system that queues a call to [`Events::update`].
-pub fn event_queue_update_system<T: Event>(signal: Option<ResMut<EventUpdateSignal<T>>>) {
+pub fn event_queue_update_system(signal: Option<ResMut<EventUpdateSignal>>) {
     if let Some(mut s) = signal {
         s.0 = true;
     }
 }
 
 /// A system that calls [`Events::update`].
 pub fn event_update_system<T: Event>(
-    signal: Option<ResMut<EventUpdateSignal<T>>>,
+    signal: Option<ResMut<EventUpdateSignal>>,
     mut events: ResMut<Events<T>>,
 ) {
     if let Some(mut s) = signal {

crates/bevy_time/src/lib.rs

@@ -15,7 +15,10 @@ pub use stopwatch::*;
 pub use time::*;
 pub use timer::*;
 
-use bevy_ecs::system::{Res, ResMut};
+use bevy_ecs::{
+    event::EventUpdateSignal,
+    system::{Res, ResMut},
+};
 use bevy_utils::{tracing::warn, Duration, Instant};
 pub use crossbeam_channel::TrySendError;
 use crossbeam_channel::{Receiver, Sender};
@@ -48,6 +51,7 @@ impl Plugin for TimePlugin {
             .register_type::<Time>()
             .register_type::<Stopwatch>()
             .init_resource::<FixedTime>()
+            .init_resource::<EventUpdateSignal>()
             .add_systems(First, time_system.in_set(TimeSystem))
             .add_systems(RunFixedUpdateLoop, run_fixed_update_schedule);