Update codebase to use IntoIterator where possible. (#5269)

Remove unnecessary calls to `iter()`/`iter_mut()`.
Mainly updates the use of queries in our code, docs, and examples.

```rust
// From
for _ in list.iter() {
for _ in list.iter_mut() {

// To
for _ in &list {
for _ in &mut list {
```

We already enable the pedantic lint [clippy::explicit_iter_loop](https://rust-lang.github.io/rust-clippy/stable/) inside of Bevy. However, this only warns for a few known types from the standard library.

## Note for reviewers
As you can see the additions and deletions are exactly equal.
Maybe give it a quick skim to check I didn't sneak in a crypto miner, but you don't have to torture yourself by reading every line.
I already experienced enough pain making this PR :) 


Co-authored-by: devil-ira <[email protected]>

benches/benches/bevy_ecs/iteration/iter_simple_system.rs

@@ -30,7 +30,7 @@ impl Benchmark {
         }
 
         fn query_system(mut query: Query<(&Velocity, &mut Position)>) {
-            for (velocity, mut position) in query.iter_mut() {
+            for (velocity, mut position) in &mut query {
                 position.0 += velocity.0;
             }
         }

benches/benches/bevy_ecs/world/commands.rs

@@ -92,7 +92,7 @@ pub fn insert_commands(criterion: &mut Criterion) {
 
         bencher.iter(|| {
             let mut commands = Commands::new(&mut command_queue, &world);
-            for entity in entities.iter() {
+            for entity in &entities {
                 commands
                     .entity(*entity)
                     .insert_bundle((Matrix::default(), Vec3::default()));
@@ -112,7 +112,7 @@ pub fn insert_commands(criterion: &mut Criterion) {
         bencher.iter(|| {
             let mut commands = Commands::new(&mut command_queue, &world);
             let mut values = Vec::with_capacity(entity_count);
-            for entity in entities.iter() {
+            for entity in &entities {
                 values.push((*entity, (Matrix::default(), Vec3::default())));
             }
             commands.insert_or_spawn_batch(values);

benches/benches/bevy_reflect/struct.rs

@@ -43,7 +43,7 @@ fn concrete_struct_field(criterion: &mut Criterion) {
                     .collect::<Vec<_>>();
 
                 bencher.iter(|| {
-                    for name in field_names.iter() {
+                    for name in &field_names {
                         s.field(black_box(name));
                     }
                 });

crates/bevy_animation/src/lib.rs

@@ -183,7 +183,7 @@ pub fn animation_player(
     mut transforms: Query<&mut Transform>,
     children: Query<&Children>,
 ) {
-    for (entity, mut player) in animation_players.iter_mut() {
+    for (entity, mut player) in &mut animation_players {
         if let Some(animation_clip) = animations.get(&player.animation_clip) {
             // Continue if paused unless the `AnimationPlayer` was changed
             // This allow the animation to still be updated if the player.elapsed field was manually updated in pause

crates/bevy_asset/src/asset_server.rs

@@ -110,7 +110,7 @@ impl AssetServer {
     {
         let mut loaders = self.server.loaders.write();
         let loader_index = loaders.len();
-        for extension in loader.extensions().iter() {
+        for extension in loader.extensions() {
             self.server
                 .extension_to_loader_index
                 .write()

crates/bevy_core_pipeline/src/core_3d/mod.rs

@@ -236,7 +236,7 @@ pub fn prepare_core_3d_depth_textures(
     >,
 ) {
     let mut textures = HashMap::default();
-    for (entity, camera) in views_3d.iter() {
+    for (entity, camera) in &views_3d {
         if let Some(physical_target_size) = camera.physical_target_size {
             let cached_texture = textures
                 .entry(camera.target.clone())

crates/bevy_ecs/README.md

@@ -78,7 +78,7 @@ use bevy_ecs::prelude::*;
 struct Position { x: f32, y: f32 }
 
 fn print_position(query: Query<(Entity, &Position)>) {
-    for (entity, position) in query.iter() {
+    for (entity, position) in &query {
         println!("Entity {:?} is at position: x {}, y {}", entity, position.x, position.y);
     }
 }
@@ -130,7 +130,7 @@ struct Velocity { x: f32, y: f32 }
 
 // This system moves each entity with a Position and Velocity component
 fn movement(mut query: Query<(&mut Position, &Velocity)>) {
-    for (mut position, velocity) in query.iter_mut() {
+    for (mut position, velocity) in &mut query {
         position.x += velocity.x;
         position.y += velocity.y;
     }
@@ -176,7 +176,7 @@ struct Alive;
 // Gets the Position component of all Entities with Player component and without the Alive
 // component. 
 fn system(query: Query<&Position, (With<Player>, Without<Alive>)>) {
-    for position in query.iter() {
+    for position in &query {
     }
 }
 ```
@@ -197,13 +197,13 @@ struct Velocity { x: f32, y: f32 }
 
 // Gets the Position component of all Entities whose Velocity has changed since the last run of the System
 fn system_changed(query: Query<&Position, Changed<Velocity>>) {
-    for position in query.iter() {
+    for position in &query {
     }
 }
 
 // Gets the Position component of all Entities that had a Velocity component added since the last run of the System
 fn system_added(query: Query<&Position, Added<Velocity>>) {
-    for position in query.iter() {
+    for position in &query {
     }
 }
 ```

crates/bevy_ecs/examples/change_detection.rs

@@ -79,24 +79,24 @@ fn print_changed_entities(
     entity_with_added_component: Query<Entity, Added<Age>>,
     entity_with_mutated_component: Query<(Entity, &Age), Changed<Age>>,
 ) {
-    for entity in entity_with_added_component.iter() {
+    for entity in &entity_with_added_component {
         println!("    {:?} has it's first birthday!", entity);
     }
-    for (entity, value) in entity_with_mutated_component.iter() {
+    for (entity, value) in &entity_with_mutated_component {
         println!("    {:?} is now {:?} frames old", entity, value);
     }
 }
 
 // This system iterates over all entities and increases their age in every frame
 fn age_all_entities(mut entities: Query<&mut Age>) {
-    for mut age in entities.iter_mut() {
+    for mut age in &mut entities {
         age.frames += 1;
     }
 }
 
 // This system iterates over all entities in every frame and despawns entities older than 2 frames
 fn remove_old_entities(mut commands: Commands, entities: Query<(Entity, &Age)>) {
-    for (entity, age) in entities.iter() {
+    for (entity, age) in &entities {
         if age.frames > 2 {
             println!("    despawning {:?} due to age > 2", entity);
             commands.entity(entity).despawn();

crates/bevy_ecs/macros/src/fetch.rs

@@ -134,7 +134,7 @@ pub fn derive_world_query_impl(ast: DeriveInput) -> TokenStream {
     let mut field_idents = Vec::new();
     let mut field_types = Vec::new();
 
-    for field in fields.iter() {
+    for field in fields {
         let WorldQueryFieldInfo { is_ignored, attrs } = read_world_query_field_info(field);
 
         let field_ident = field.ident.as_ref().unwrap().clone();

crates/bevy_ecs/src/entity/mod.rs

@@ -84,7 +84,7 @@ use std::{
 /// # struct Expired;
 /// #
 /// fn dispose_expired_food(mut commands: Commands, query: Query<Entity, With<Expired>>) {
-///     for food_entity in query.iter() {
+///     for food_entity in &query {
 ///         commands.entity(food_entity).despawn();
 ///     }
 /// }

crates/bevy_ecs/src/query/fetch.rs

@@ -79,7 +79,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(query: Query<MyQuery>) {
-///     for q in query.iter() {
+///     for q in &query {
 ///         // Note the type of the returned item.
 ///         let q: MyQueryItem<'_> = q;
 ///         q.foo;
@@ -130,11 +130,11 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 ///
 /// fn my_system(mut health_query: Query<HealthQuery>) {
 ///     // Iterator's item is `HealthQueryReadOnlyItem`.
-///     for health in health_query.iter() {
+///     for health in &health_query {
 ///         println!("Total: {}", health.total());
 ///     }
 ///     // Iterator's item is `HealthQueryItem`.
-///     for mut health in health_query.iter_mut() {
+///     for mut health in &mut health_query {
 ///         health.damage(1.0);
 ///         println!("Total (mut): {}", health.total());
 ///     }
@@ -158,7 +158,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(mut my_query: Query<(FooReadOnly, FooReadOnly)>) {
-///     for (i1, i2) in my_query.iter_mut() {
+///     for (i1, i2) in &mut my_query {
 ///         let _: FooReadOnlyItem<'_> = i1;
 ///         let _: FooReadOnlyItem<'_> = i2;
 ///     }
@@ -254,7 +254,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 ///
 /// // You can also compose derived queries with regular ones in tuples.
 /// fn my_system(query: Query<(&Foo, MyQuery, FooQuery)>) {
-///     for (foo, my_query, foo_query) in query.iter() {
+///     for (foo, my_query, foo_query) in &query {
 ///         foo; my_query; foo_query;
 ///     }
 /// }
@@ -279,7 +279,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(query: Query<EmptyQuery>) {
-///     for _ in query.iter() {}
+///     for _ in &query {}
 /// }
 ///
 /// # bevy_ecs::system::assert_is_system(my_system);
@@ -311,7 +311,7 @@ use std::{cell::UnsafeCell, marker::PhantomData};
 /// }
 ///
 /// fn my_system(query: Query<Entity, MyFilter<Foo, Qux>>) {
-///     for _ in query.iter() {}
+///     for _ in &query {}
 /// }
 ///
 /// # bevy_ecs::system::assert_is_system(my_system);
@@ -1087,7 +1087,7 @@ unsafe impl<'w, T: Fetch<'w>> Fetch<'w> for OptionFetch<T> {
 /// # struct Transform {};
 /// #
 /// fn print_moving_objects_system(query: Query<(&Name, ChangeTrackers<Transform>)>) {
-///     for (name, tracker) in query.iter() {
+///     for (name, tracker) in &query {
 ///         if tracker.is_changed() {
 ///             println!("Entity moved: {:?}", name);
 ///         } else {

crates/bevy_ecs/src/query/filter.rs

@@ -36,7 +36,7 @@ use super::ReadOnlyWorldQuery;
 /// # struct Name { name: &'static str };
 /// #
 /// fn compliment_entity_system(query: Query<&Name, With<IsBeautiful>>) {
-///     for name in query.iter() {
+///     for name in &query {
 ///         println!("{} is looking lovely today!", name.name);
 ///     }
 /// }
@@ -177,7 +177,7 @@ impl<T> Copy for WithFetch<T> {}
 /// # struct Name { name: &'static str };
 /// #
 /// fn no_permit_system(query: Query<&Name, Without<Permit>>) {
-///     for name in query.iter() {
+///     for name in &query{
 ///         println!("{} has no permit!", name.name);
 ///     }
 /// }
@@ -324,7 +324,7 @@ impl<T> Copy for WithoutFetch<T> {}
 /// # struct Style {};
 /// #
 /// fn print_cool_entity_system(query: Query<Entity, Or<(Changed<Color>, Changed<Style>)>>) {
-///     for entity in query.iter() {
+///     for entity in &query {
 ///         println!("Entity {:?} got a new style or color", entity);
 ///     }
 /// }
@@ -685,7 +685,7 @@ impl_tick_filter!(
     /// # struct Name {};
     ///
     /// fn print_add_name_component(query: Query<&Name, Added<Name>>) {
-    ///     for name in query.iter() {
+    ///     for name in &query {
     ///         println!("Named entity created: {:?}", name)
     ///     }
     /// }
@@ -725,7 +725,7 @@ impl_tick_filter!(
     /// # struct Transform {};
     ///
     /// fn print_moving_objects_system(query: Query<&Name, Changed<Transform>>) {
-    ///     for name in query.iter() {
+    ///     for name in &query {
     ///         println!("Entity Moved: {:?}", name);
     ///     }
     /// }

crates/bevy_ecs/src/query/state.rs

@@ -264,7 +264,7 @@ impl<Q: WorldQuery, F: WorldQuery> QueryState<Q, F> {
     ///
     /// let mut mutable_component_values = query_state.get_many_mut(&mut world, entities).unwrap();
     ///
-    /// for mut a in mutable_component_values.iter_mut(){
+    /// for mut a in &mut mutable_component_values {
     ///     a.0 += 5;
     /// }
     ///
@@ -1074,7 +1074,7 @@ impl<Q: WorldQuery, F: WorldQuery> QueryState<Q, F> {
 
         let tables = &world.storages.tables;
 
-        for entity in entity_list.into_iter() {
+        for entity in entity_list {
             let location = match world.entities.get(*entity.borrow()) {
                 Some(location) => location,
                 None => continue,

crates/bevy_ecs/src/schedule/executor_parallel.rs

@@ -81,7 +81,7 @@ impl ParallelSystemExecutor for ParallelExecutor {
         self.should_run.grow(systems.len());
 
         // Construct scheduling data for systems.
-        for container in systems.iter() {
+        for container in systems {
             let dependencies_total = container.dependencies().len();
             let system = container.system();
             let (start_sender, start_receiver) = async_channel::bounded(1);

crates/bevy_ecs/src/storage/table.rs

@@ -492,7 +492,7 @@ impl Tables {
             .from_key(component_ids)
             .or_insert_with(|| {
                 let mut table = Table::with_capacity(0, component_ids.len());
-                for component_id in component_ids.iter() {
+                for component_id in component_ids {
                     table.add_column(components.get_info_unchecked(*component_id));
                 }
                 tables.push(table);

crates/bevy_ecs/src/system/commands/parallel_scope.rs

@@ -75,7 +75,7 @@ unsafe impl SystemParamState for ParallelCommandsState {
     }
 
     fn apply(&mut self, world: &mut World) {
-        for cq in self.thread_local_storage.iter_mut() {
+        for cq in &mut self.thread_local_storage {
             cq.get_mut().apply(world);
         }
     }

crates/bevy_ecs/src/system/exclusive_system.rs

@@ -128,7 +128,7 @@ mod tests {
             query: Query<Entity, With<Foo>>,
             mut counter: ResMut<usize>,
         ) {
-            for entity in query.iter() {
+            for entity in &query {
                 *counter += 1;
                 commands.entity(entity).remove::<Foo>();
             }

crates/bevy_ecs/src/system/function_system.rs

@@ -126,7 +126,7 @@ impl SystemMeta {
 /// world.resource_scope(|world, mut cached_state: Mut<CachedSystemState>| {
 ///     let mut event_reader = cached_state.event_state.get_mut(world);
 ///
-///     for events in event_reader.iter(){
+///     for events in event_reader.iter() {
 ///         println!("Hello World!");
 ///     };
 /// });

crates/bevy_ecs/src/system/mod.rs

@@ -23,7 +23,7 @@
 //!     mut query: Query<(&Player, &mut Score)>,
 //!     mut round: ResMut<Round>,
 //! ) {
-//!     for (player, mut score) in query.iter_mut() {
+//!     for (player, mut score) in &mut query {
 //!         if player.alive {
 //!             score.0 += round.0;
 //!         }
@@ -135,7 +135,7 @@ mod tests {
     #[test]
     fn simple_system() {
         fn sys(query: Query<&A>) {
-            for a in query.iter() {
+            for a in &query {
                 println!("{:?}", a);
             }
         }
@@ -598,7 +598,7 @@ mod tests {
             mut modified: ResMut<bool>,
         ) {
             assert_eq!(query.iter().count(), 1, "entity exists");
-            for entity in query.iter() {
+            for entity in &query {
                 let location = entities.get(entity).unwrap();
                 let archetype = archetypes.get(location.archetype_id).unwrap();
                 let archetype_components = archetype.components().collect::<Vec<_>>();