Cleanup some things which shouldn't be components (#2982)

# Objective

- Using `Stopwatch` and `Timer` as raw components is a footgun.

## Solution

- Stop them from being components

crates/bevy_core/src/time/stopwatch.rs

@@ -1,4 +1,3 @@
-use bevy_ecs::{component::Component, reflect::ReflectComponent};
 use bevy_reflect::Reflect;
 use bevy_utils::Duration;
 
@@ -23,8 +22,7 @@ use bevy_utils::Duration;
 /// assert!(stopwatch.paused());
 /// assert_eq!(stopwatch.elapsed_secs(), 0.0);
 /// ```
-#[derive(Component, Clone, Debug, Default, Reflect)]
-#[reflect(Component)]
+#[derive(Clone, Debug, Default, Reflect)]
 pub struct Stopwatch {
     elapsed: Duration,
     paused: bool,

crates/bevy_core/src/time/timer.rs

@@ -1,5 +1,4 @@
 use crate::Stopwatch;
-use bevy_ecs::{component::Component, reflect::ReflectComponent};
 use bevy_reflect::Reflect;
 use bevy_utils::Duration;
 
@@ -10,8 +9,7 @@ use bevy_utils::Duration;
 /// exceeded, and can still be reset at any given point.
 ///
 /// Paused timers will not have elapsed time increased.
-#[derive(Component, Clone, Debug, Default, Reflect)]
-#[reflect(Component)]
+#[derive(Clone, Debug, Default, Reflect)]
 pub struct Timer {
     stopwatch: Stopwatch,
     duration: Duration,

examples/2d/contributors.rs

@@ -15,6 +15,7 @@ fn main() {
         .add_system(move_system)
         .add_system(collision_system)
         .add_system(select_system)
+        .insert_resource(SelectTimer(Timer::from_seconds(SHOWCASE_TIMER_SECS, true)))
         .run();
 }
 
@@ -26,8 +27,7 @@ struct ContributorSelection {
     idx: usize,
 }
 
-#[derive(Component)]
-struct SelectTimer;
+struct SelectTimer(Timer);
 
 #[derive(Component)]
 struct ContributorDisplay;
@@ -120,8 +120,6 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
     commands.spawn_bundle(OrthographicCameraBundle::new_2d());
     commands.spawn_bundle(UiCameraBundle::default());
 
-    commands.spawn_bundle((SelectTimer, Timer::from_seconds(SHOWCASE_TIMER_SECS, true)));
-
     commands
         .spawn()
         .insert(ContributorDisplay)
@@ -157,22 +155,13 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
 
 /// Finds the next contributor to display and selects the entity
 fn select_system(
+    mut timer: ResMut<SelectTimer>,
     mut contributor_selection: ResMut<ContributorSelection>,
     mut text_query: Query<&mut Text, With<ContributorDisplay>>,
-    mut timer_query: Query<&mut Timer, With<SelectTimer>>,
     mut query: Query<(&Contributor, &mut Sprite, &mut Transform)>,
     time: Res<Time>,
 ) {
-    let mut timer_fired = false;
-    for mut timer in timer_query.iter_mut() {
-        if !timer.tick(time.delta()).just_finished() {
-            continue;
-        }
-        timer.reset();
-        timer_fired = true;
-    }
-
-    if !timer_fired {
+    if !timer.0.tick(time.delta()).just_finished() {
         return;
     }
 

examples/2d/many_sprites.rs

@@ -17,8 +17,8 @@ fn main() {
         .add_plugin(FrameTimeDiagnosticsPlugin::default())
         .add_plugins(DefaultPlugins)
         .add_startup_system(setup)
-        .add_system(tick_system.label("Tick"))
-        .add_system(move_camera_system.after("Tick"))
+        .add_system(print_sprite_count.label("Tick"))
+        .add_system(move_camera.after("Tick"))
         .run()
 }
 
@@ -37,7 +37,6 @@ fn setup(mut commands: Commands, assets: Res<AssetServer>) {
     commands
         .spawn()
         .insert_bundle(OrthographicCameraBundle::new_2d())
-        .insert(Timer::from_seconds(1.0, true))
         .insert(Transform::from_xyz(0.0, 0.0, 1000.0));
 
     // Builds and spawns the sprites
@@ -68,19 +67,26 @@ fn setup(mut commands: Commands, assets: Res<AssetServer>) {
 }
 
 // System for rotating and translating the camera
-fn move_camera_system(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
+fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
     let mut camera_transform = camera_query.single_mut();
     camera_transform.rotate(Quat::from_rotation_z(time.delta_seconds() * 0.5));
     *camera_transform = *camera_transform
         * Transform::from_translation(Vec3::X * CAMERA_SPEED * time.delta_seconds());
 }
 
-// System for printing the number of sprites on every tick of the timer
-fn tick_system(time: Res<Time>, sprites_query: Query<&Sprite>, mut timer_query: Query<&mut Timer>) {
-    let mut timer = timer_query.single_mut();
-    timer.tick(time.delta());
+struct PrintingTimer(Timer);
 
-    if timer.just_finished() {
-        info!("Sprites: {}", sprites_query.iter().count(),);
+impl Default for PrintingTimer {
+    fn default() -> Self {
+        Self(Timer::from_seconds(1.0, true))
+    }
+}
+
+// System for printing the number of sprites on every tick of the timer
+fn print_sprite_count(time: Res<Time>, mut timer: Local<PrintingTimer>, sprites: Query<&Sprite>) {
+    timer.0.tick(time.delta());
+
+    if timer.0.just_finished() {
+        info!("Sprites: {}", sprites.iter().count(),);
     }
 }

examples/2d/sprite_sheet.rs

@@ -4,18 +4,25 @@ fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
         .add_startup_system(setup)
-        .add_system(animate_sprite_system)
+        .add_system(animate_sprite)
         .run();
 }
 
-fn animate_sprite_system(
+#[derive(Component)]
+struct AnimationTimer(Timer);
+
+fn animate_sprite(
     time: Res<Time>,
     texture_atlases: Res<Assets<TextureAtlas>>,
-    mut query: Query<(&mut Timer, &mut TextureAtlasSprite, &Handle<TextureAtlas>)>,
+    mut query: Query<(
+        &mut AnimationTimer,
+        &mut TextureAtlasSprite,
+        &Handle<TextureAtlas>,
+    )>,
 ) {
     for (mut timer, mut sprite, texture_atlas_handle) in query.iter_mut() {
-        timer.tick(time.delta());
-        if timer.finished() {
+        timer.0.tick(time.delta());
+        if timer.0.just_finished() {
             let texture_atlas = texture_atlases.get(texture_atlas_handle).unwrap();
             sprite.index = (sprite.index + 1) % texture_atlas.textures.len();
         }
@@ -37,5 +44,5 @@ fn setup(
             transform: Transform::from_scale(Vec3::splat(6.0)),
             ..Default::default()
         })
-        .insert(Timer::from_seconds(0.1, true));
+        .insert(AnimationTimer(Timer::from_seconds(0.1, true)));
 }

examples/ecs/timers.rs

@@ -4,12 +4,15 @@ fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
         .init_resource::<Countdown>()
-        .add_startup_system(setup_system)
-        .add_system(countdown_system)
-        .add_system(timer_system)
+        .add_startup_system(setup)
+        .add_system(countdown)
+        .add_system(print_when_completed)
         .run();
 }
 
+#[derive(Component)]
+pub struct PrintOnCompletionTimer(Timer);
+
 pub struct Countdown {
     pub percent_trigger: Timer,
     pub main_timer: Timer,
@@ -30,16 +33,18 @@ impl Default for Countdown {
     }
 }
 
-fn setup_system(mut commands: Commands) {
+fn setup(mut commands: Commands) {
     // Add an entity to the world with a timer
-    commands.spawn().insert(Timer::from_seconds(5.0, false));
+    commands
+        .spawn()
+        .insert(PrintOnCompletionTimer(Timer::from_seconds(5.0, false)));
 }
 
 /// This system ticks all the `Timer` components on entities within the scene
 /// using bevy's `Time` resource to get the delta between each update.
-fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
+fn print_when_completed(time: Res<Time>, mut query: Query<&mut PrintOnCompletionTimer>) {
     for mut timer in query.iter_mut() {
-        if timer.tick(time.delta()).just_finished() {
+        if timer.0.tick(time.delta()).just_finished() {
             info!("Entity timer just finished")
         }
     }
@@ -47,7 +52,7 @@ fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
 
 /// This system controls ticking the timer within the countdown resource and
 /// handling its state.
-fn countdown_system(time: Res<Time>, mut countdown: ResMut<Countdown>) {
+fn countdown(time: Res<Time>, mut countdown: ResMut<Countdown>) {
     countdown.main_timer.tick(time.delta());
 
     // The API encourages this kind of timer state checking (if you're only checking for one value)