Update codebase to use IntoIterator where possible. (bevyengine#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]>

Author: tim-blackbird

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();
 ///     }
 /// }