[Merged by Bors] - Add TimeUpdateStrategy resource for manual Time updating

crates/bevy_time/src/lib.rs

@@ -44,6 +44,12 @@ impl Plugin for TimePlugin {
     }
 }
 
+/// Resource for updating time with a desired value.
+///
+/// See [`update_with_interval`](self::TimeUpdater::update_with_instant) for more details.
+#[derive(Resource)]
+pub struct DesiredTime(pub Instant);
+
 /// Channel resource used to receive time from render world
 #[derive(Resource)]
 pub struct TimeReceiver(pub Receiver<Instant>);
@@ -64,6 +70,7 @@ pub fn create_time_channels() -> (TimeSender, TimeReceiver) {
 /// there to this system through channels. Otherwise the time is updated in this system.
 fn time_system(
     mut time: ResMut<Time>,
+    wanted_time: Option<Res<DesiredTime>>,
     time_recv: Option<Res<TimeReceiver>>,
     mut has_received_time: Local<bool>,
 ) {
@@ -75,6 +82,8 @@ fn time_system(
         } else if *has_received_time {
             warn!("time_system did not receive the time from the render world! Calculations depending on the time may be incorrect.");
         }
+    } else if let Some(wanted_time) = wanted_time {
+        time.update_with_instant(wanted_time.0);
     } else {
         time.update();
     }

crates/bevy_time/src/time.rs

@@ -2,8 +2,14 @@ use bevy_ecs::{reflect::ReflectResource, system::Resource};
 use bevy_reflect::{FromReflect, Reflect};
 use bevy_utils::{Duration, Instant};
 
+use crate::DesiredTime;
+
 const SECONDS_PER_HOUR: u64 = 60 * 60;
 
+pub trait TimeUpdater {
+    fn update_with_instant(&mut self, instant: Instant);
+}
+
 /// Tracks elapsed time since the last update and since the App has started
 #[derive(Resource, Reflect, FromReflect, Debug, Clone)]
 #[reflect(Resource)]
@@ -170,6 +176,18 @@ impl Time {
     }
 }
 
+impl TimeUpdater for bevy_app::App {
+    /// Runs the app's schedule once, manually setting the [`Time`] resource to the provided value.
+    ///
+    /// This is ordinarily done automatically, but setting this time value directly can be useful when writing tests,
+    /// dealing with networking code, or similar.
+    fn update_with_instant(&mut self, instant: Instant) {
+        self.world.insert_resource(DesiredTime(instant));
+        self.update();
+        self.world.remove_resource::<DesiredTime>();
+    }
+}
+
 #[cfg(test)]
 #[allow(clippy::float_cmp)]
 mod tests {