Merge ScheduleRunnerSettings into ScheduleRunnerPlugin (#8585)

# Objective

`ScheduleRunnerPlugin` was still configured via a resource, meaning
users would be able to change the settings while the app is running, but
the changes wouldn't have an effect.

## Solution

Configure plugin directly

---

## Changelog

- Changed: merged `ScheduleRunnerSettings` into `ScheduleRunnerPlugin` 

## Migration Guide

- instead of inserting the `ScheduleRunnerSettings` resource, configure
the `ScheduleRunnerPlugin`

crates/bevy_app/src/schedule_runner.rs

@@ -3,7 +3,6 @@ use crate::{
     plugin::Plugin,
 };
 use bevy_ecs::event::{Events, ManualEventReader};
-use bevy_ecs::prelude::Resource;
 use bevy_utils::{Duration, Instant};
 
 #[cfg(target_arch = "wasm32")]
@@ -13,7 +12,7 @@ use wasm_bindgen::{prelude::*, JsCast};
 
 /// Determines the method used to run an [`App`]'s [`Schedule`](bevy_ecs::schedule::Schedule).
 ///
-/// It is used in the [`ScheduleRunnerSettings`].
+/// It is used in the [`ScheduleRunnerPlugin`].
 #[derive(Copy, Clone, Debug)]
 pub enum RunMode {
     /// Indicates that the [`App`]'s schedule should run repeatedly.
@@ -32,33 +31,6 @@ impl Default for RunMode {
     }
 }
 
-/// The configuration information for the [`ScheduleRunnerPlugin`].
-///
-/// It gets added as a [`Resource`](bevy_ecs::system::Resource) inside of the [`ScheduleRunnerPlugin`].
-#[derive(Copy, Clone, Default, Resource)]
-pub struct ScheduleRunnerSettings {
-    /// Determines whether the [`Schedule`](bevy_ecs::schedule::Schedule) is run once or repeatedly.
-    pub run_mode: RunMode,
-}
-
-impl ScheduleRunnerSettings {
-    /// See [`RunMode::Once`].
-    pub fn run_once() -> Self {
-        ScheduleRunnerSettings {
-            run_mode: RunMode::Once,
-        }
-    }
-
-    /// See [`RunMode::Loop`].
-    pub fn run_loop(wait_duration: Duration) -> Self {
-        ScheduleRunnerSettings {
-            run_mode: RunMode::Loop {
-                wait: Some(wait_duration),
-            },
-        }
-    }
-}
-
 /// Configures an [`App`] to run its [`Schedule`](bevy_ecs::schedule::Schedule) according to a given
 /// [`RunMode`].
 ///
@@ -72,17 +44,35 @@ impl ScheduleRunnerSettings {
 /// (see [`WinitPlugin`](https://docs.rs/bevy/latest/bevy/winit/struct.WinitPlugin.html))
 /// executes the schedule making [`ScheduleRunnerPlugin`] unnecessary.
 #[derive(Default)]
-pub struct ScheduleRunnerPlugin;
+pub struct ScheduleRunnerPlugin {
+    /// Determines whether the [`Schedule`](bevy_ecs::schedule::Schedule) is run once or repeatedly.
+    pub run_mode: RunMode,
+}
+
+impl ScheduleRunnerPlugin {
+    /// See [`RunMode::Once`].
+    pub fn run_once() -> Self {
+        ScheduleRunnerPlugin {
+            run_mode: RunMode::Once,
+        }
+    }
+
+    /// See [`RunMode::Loop`].
+    pub fn run_loop(wait_duration: Duration) -> Self {
+        ScheduleRunnerPlugin {
+            run_mode: RunMode::Loop {
+                wait: Some(wait_duration),
+            },
+        }
+    }
+}
 
 impl Plugin for ScheduleRunnerPlugin {
     fn build(&self, app: &mut App) {
-        let settings = app
+        let run_mode = self.run_mode;
-            .world
-            .get_resource_or_insert_with(ScheduleRunnerSettings::default)
-            .to_owned();
         app.set_runner(move |mut app: App| {
             let mut app_exit_event_reader = ManualEventReader::<AppExit>::default();
-            match settings.run_mode {
+            match run_mode {
                 RunMode::Once => {
                     app.update();
                 }

examples/app/headless.rs

@@ -6,22 +6,22 @@
 //! bevy = { version = "*", default-features = false }
 //! # replace "*" with the most recent version of bevy
 
-use bevy::{app::ScheduleRunnerSettings, prelude::*, utils::Duration};
+use bevy::{app::ScheduleRunnerPlugin, prelude::*, utils::Duration};
 
 fn main() {
-    // this app runs once
+    // This app runs once
     App::new()
-        .insert_resource(ScheduleRunnerSettings::run_once())
+        .add_plugins(MinimalPlugins.set(ScheduleRunnerPlugin::run_once()))
-        .add_plugins(MinimalPlugins)
         .add_systems(Update, hello_world_system)
         .run();
 
-    // this app loops forever at 60 fps
+    // This app loops forever at 60 fps
     App::new()
-        .insert_resource(ScheduleRunnerSettings::run_loop(Duration::from_secs_f64(
+        .add_plugins(
+            MinimalPlugins.set(ScheduleRunnerPlugin::run_loop(Duration::from_secs_f64(
                 1.0 / 60.0,
-        )))
+            ))),
-        .add_plugins(MinimalPlugins)
+        )
         .add_systems(Update, counter)
         .run();
 }

examples/ecs/ecs_guide.rs

@@ -25,7 +25,7 @@
 //! We will now make a simple "game" to illustrate what Bevy's ECS looks like in practice.
 
 use bevy::{
-    app::{AppExit, ScheduleRunnerPlugin, ScheduleRunnerSettings},
+    app::{AppExit, ScheduleRunnerPlugin},
     prelude::*,
     utils::Duration,
 };
@@ -253,13 +253,10 @@ fn main() {
     App::new()
         // Resources that implement the Default or FromWorld trait can be added like this:
         .init_resource::<GameState>()
-        // Some systems are configured by adding their settings as a resource.
-        .insert_resource(ScheduleRunnerSettings::run_loop(Duration::from_secs(5)))
         // Plugins are just a grouped set of app builder calls (just like we're doing here).
         // We could easily turn our game into a plugin, but you can check out the plugin example for
-        // that :) The plugin below runs our app's "system schedule" once every 5 seconds
+        // that :) The plugin below runs our app's "system schedule" once every 5 seconds.
-        // (configured above).
+        .add_plugin(ScheduleRunnerPlugin::run_loop(Duration::from_secs(5)))
-        .add_plugin(ScheduleRunnerPlugin::default())
         // `Startup` systems run exactly once BEFORE all other systems. These are generally used for
         // app initialization code (ex: adding entities and resources)
         .add_systems(Startup, startup_system)