From 6dc1d07cbc4a66c7c9f3a0a56ddce7628a9862a5 Mon Sep 17 00:00:00 2001
From: Carter Anderson <mcanders1@gmail.com>
Date: Mon, 20 Jul 2020 13:59:51 -0700
Subject: [PATCH] ecs: remove &mut requirement on query iterators

---
 crates/bevy_core/src/label.rs                 |  2 +-
 crates/bevy_core/src/time/timer.rs            |  2 +-
 crates/bevy_ecs/hecs/benches/bench.rs         |  2 +-
 crates/bevy_ecs/hecs/src/query.rs             | 22 +++++++++----------
 crates/bevy_ecs/hecs/src/world.rs             |  1 +
 crates/bevy_ecs/hecs/tests/tests.rs           | 11 ----------
 crates/bevy_ecs/src/system/into_system.rs     |  4 ++++
 .../bevy_render/src/camera/active_cameras.rs  |  2 +-
 crates/bevy_render/src/camera/camera.rs       |  2 +-
 .../src/camera/visible_entities.rs            |  4 ++--
 crates/bevy_render/src/draw.rs                |  2 +-
 crates/bevy_render/src/mesh/mesh.rs           |  2 +-
 .../src/pipeline/render_pipelines.rs          |  2 +-
 .../nodes/render_resources_node.rs            | 10 ++++-----
 crates/bevy_render/src/shader/shader_defs.rs  |  6 ++---
 crates/bevy_sprite/src/sprite.rs              |  2 +-
 .../hierarchy/hierarchy_maintenance_system.rs |  6 ++---
 .../src/local_transform_systems.rs            | 22 +++++++++----------
 .../src/transform_propagate_system.rs         |  2 +-
 .../bevy_transform/src/transform_systems.rs   | 22 +++++++++----------
 crates/bevy_ui/src/focus.rs                   |  7 +++---
 crates/bevy_ui/src/widget/text.rs             |  4 ++--
 examples/2d/sprite_sheet.rs                   |  2 +-
 examples/3d/parenting.rs                      |  2 +-
 examples/3d/spawner.rs                        |  2 +-
 examples/3d/z_sort_debug.rs                   |  4 ++--
 examples/ecs/ecs_guide.rs                     |  6 ++---
 examples/game/breakout.rs                     | 14 ++++++------
 examples/scene/load_scene.rs                  |  2 +-
 examples/ui/button.rs                         |  4 ++--
 examples/ui/font_atlas_debug.rs               |  2 +-
 examples/ui/text.rs                           |  2 +-
 examples/ui/ui_bench.rs                       |  2 +-
 33 files changed, 88 insertions(+), 93 deletions(-)

diff --git a/crates/bevy_core/src/label.rs b/crates/bevy_core/src/label.rs
index 185ada37fd..8ed0311351 100644
--- a/crates/bevy_core/src/label.rs
+++ b/crates/bevy_core/src/label.rs
@@ -68,7 +68,7 @@ pub fn entity_labels_system(
     mut query: Query<(Entity, &Labels)>,
 ) {
     let entity_labels = entity_labels.deref_mut();
-    for (entity, labels) in &mut query.iter() {
+    for (entity, labels) in query.iter() {
         let current_labels = entity_labels
             .entity_labels
             .entry(entity)
diff --git a/crates/bevy_core/src/time/timer.rs b/crates/bevy_core/src/time/timer.rs
index 2e0fff520d..c5b399ac28 100644
--- a/crates/bevy_core/src/time/timer.rs
+++ b/crates/bevy_core/src/time/timer.rs
@@ -38,7 +38,7 @@ impl Timer {
 }
 
 pub fn timer_system(time: Res<Time>, mut query: Query<&mut Timer>) {
-    for mut timer in &mut query.iter() {
+    for mut timer in query.iter() {
         timer.tick(time.delta_seconds);
     }
 }
diff --git a/crates/bevy_ecs/hecs/benches/bench.rs b/crates/bevy_ecs/hecs/benches/bench.rs
index 3a76340347..7beca441d6 100644
--- a/crates/bevy_ecs/hecs/benches/bench.rs
+++ b/crates/bevy_ecs/hecs/benches/bench.rs
@@ -68,7 +68,7 @@ fn iterate_100k(b: &mut Bencher) {
         world.spawn((Position(-(i as f32)), Velocity(i as f32)));
     }
     b.iter(|| {
-        for (mut pos, vel) in &mut world.query::<(&mut Position, &Velocity)>() {
+        for (mut pos, vel) in world.query::<(&mut Position, &Velocity)>() {
             pos.0 += vel.0;
         }
     })
diff --git a/crates/bevy_ecs/hecs/src/query.rs b/crates/bevy_ecs/hecs/src/query.rs
index d02401f75e..fb6c05fa48 100644
--- a/crates/bevy_ecs/hecs/src/query.rs
+++ b/crates/bevy_ecs/hecs/src/query.rs
@@ -321,7 +321,7 @@ impl<'w, Q: Query> QueryBorrow<'w, Q> {
     /// Execute the query
     ///
     /// Must be called only once per query.
-    pub fn iter<'q>(&'q mut self) -> QueryIter<'q, 'w, Q> {
+    pub fn iter(mut self) -> QueryIter<'w, Q> {
         self.borrow();
         QueryIter {
             borrow: self,
@@ -434,9 +434,9 @@ impl<'w, Q: Query> Drop for QueryBorrow<'w, Q> {
     }
 }
 
-impl<'q, 'w, Q: Query> IntoIterator for &'q mut QueryBorrow<'w, Q> {
-    type Item = <Q::Fetch as Fetch<'q>>::Item;
-    type IntoIter = QueryIter<'q, 'w, Q>;
+impl<'w, Q: Query> IntoIterator for QueryBorrow<'w, Q> {
+    type Item = <Q::Fetch as Fetch<'w>>::Item;
+    type IntoIter = QueryIter<'w, Q>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.iter()
@@ -444,17 +444,17 @@ impl<'q, 'w, Q: Query> IntoIterator for &'q mut QueryBorrow<'w, Q> {
 }
 
 /// Iterator over the set of entities with the components in `Q`
-pub struct QueryIter<'q, 'w, Q: Query> {
-    borrow: &'q mut QueryBorrow<'w, Q>,
+pub struct QueryIter<'w, Q: Query> {
+    borrow: QueryBorrow<'w, Q>,
     archetype_index: u32,
     iter: Option<ChunkIter<Q>>,
 }
 
-unsafe impl<'q, 'w, Q: Query> Send for QueryIter<'q, 'w, Q> {}
-unsafe impl<'q, 'w, Q: Query> Sync for QueryIter<'q, 'w, Q> {}
+unsafe impl<'w, Q: Query> Send for QueryIter<'w, Q> {}
+unsafe impl<'w, Q: Query> Sync for QueryIter<'w, Q> {}
 
-impl<'q, 'w, Q: Query> Iterator for QueryIter<'q, 'w, Q> {
-    type Item = <Q::Fetch as Fetch<'q>>::Item;
+impl<'w, Q: Query> Iterator for QueryIter<'w, Q> {
+    type Item = <Q::Fetch as Fetch<'w>>::Item;
 
     #[inline]
     fn next(&mut self) -> Option<Self::Item> {
@@ -489,7 +489,7 @@ impl<'q, 'w, Q: Query> Iterator for QueryIter<'q, 'w, Q> {
     }
 }
 
-impl<'q, 'w, Q: Query> ExactSizeIterator for QueryIter<'q, 'w, Q> {
+impl<'w, Q: Query> ExactSizeIterator for QueryIter<'w, Q> {
     fn len(&self) -> usize {
         self.borrow
             .archetypes
diff --git a/crates/bevy_ecs/hecs/src/world.rs b/crates/bevy_ecs/hecs/src/world.rs
index 4969db4f65..8c11b97298 100644
--- a/crates/bevy_ecs/hecs/src/world.rs
+++ b/crates/bevy_ecs/hecs/src/world.rs
@@ -481,6 +481,7 @@ impl World {
     ///
     /// See `remove`.
     pub fn remove_one<T: Component>(&mut self, entity: Entity) -> Result<T, ComponentError> {
+        std::println!("reomve {} ", std::any::type_name::<T>());
         self.remove::<(T,)>(entity).map(|(x,)| x)
     }
 
diff --git a/crates/bevy_ecs/hecs/tests/tests.rs b/crates/bevy_ecs/hecs/tests/tests.rs
index eff39ebc47..0f86f4c6d1 100644
--- a/crates/bevy_ecs/hecs/tests/tests.rs
+++ b/crates/bevy_ecs/hecs/tests/tests.rs
@@ -261,17 +261,6 @@ fn clear() {
     assert_eq!(world.iter().count(), 0);
 }
 
-#[test]
-#[should_panic(expected = "twice on the same borrow")]
-fn alias() {
-    let mut world = World::new();
-    world.spawn(("abc", 123));
-    world.spawn(("def", 456, true));
-    let mut q = world.query::<&mut i32>();
-    let _a = q.iter().collect::<Vec<_>>();
-    let _b = q.iter().collect::<Vec<_>>();
-}
-
 #[test]
 fn remove_missing() {
     let mut world = World::new();
diff --git a/crates/bevy_ecs/src/system/into_system.rs b/crates/bevy_ecs/src/system/into_system.rs
index 8fe00c09cf..fc661272f4 100644
--- a/crates/bevy_ecs/src/system/into_system.rs
+++ b/crates/bevy_ecs/src/system/into_system.rs
@@ -158,6 +158,10 @@ impl<'a, Q: HecsQuery> Query<'a, Q> {
                 .archetype_access
                 .immutable
                 .contains(location.archetype as usize)
+                || self
+                    .archetype_access
+                    .mutable
+                    .contains(location.archetype as usize)
             {
                 self.world
                     .get(entity)
diff --git a/crates/bevy_render/src/camera/active_cameras.rs b/crates/bevy_render/src/camera/active_cameras.rs
index 60115a7eb9..96a39eb6d1 100644
--- a/crates/bevy_render/src/camera/active_cameras.rs
+++ b/crates/bevy_render/src/camera/active_cameras.rs
@@ -27,7 +27,7 @@ pub fn active_cameras_system(
 ) {
     for (name, active_camera) in active_cameras.cameras.iter_mut() {
         if let None = active_camera {
-            for (camera_entity, camera) in &mut query.iter() {
+            for (camera_entity, camera) in query.iter() {
                 if let Some(ref current_name) = camera.name {
                     if current_name == name {
                         *active_camera = Some(camera_entity);
diff --git a/crates/bevy_render/src/camera/camera.rs b/crates/bevy_render/src/camera/camera.rs
index 2778290603..12b3017de5 100644
--- a/crates/bevy_render/src/camera/camera.rs
+++ b/crates/bevy_render/src/camera/camera.rs
@@ -62,7 +62,7 @@ pub fn camera_system<T: CameraProjection + Component>(
         }
     }
 
-    for (mut camera, mut camera_projection) in &mut query.iter() {
+    for (mut camera, mut camera_projection) in query.iter() {
         if let Some(window) = match camera.window {
             WindowReference::Id(id) => {
                 if changed_window_ids.contains(&id) {
diff --git a/crates/bevy_render/src/camera/visible_entities.rs b/crates/bevy_render/src/camera/visible_entities.rs
index ea55afb128..cf353b8098 100644
--- a/crates/bevy_render/src/camera/visible_entities.rs
+++ b/crates/bevy_render/src/camera/visible_entities.rs
@@ -26,13 +26,13 @@ pub fn visible_entities_system(
     mut draw_query: Query<(Entity, &Draw)>,
     draw_transform_query: Query<(&Draw, &Transform)>,
 ) {
-    for (_camera, camera_transform, mut visible_entities) in &mut camera_query.iter() {
+    for (_camera, camera_transform, mut visible_entities) in camera_query.iter() {
         visible_entities.value.clear();
         let camera_position = camera_transform.value.w_axis().truncate();
 
         let mut no_transform_order = 0.0;
         let mut transparent_entities = Vec::new();
-        for (entity, draw) in &mut draw_query.iter() {
+        for (entity, draw) in draw_query.iter() {
             if !draw.is_visible {
                 continue;
             }
diff --git a/crates/bevy_render/src/draw.rs b/crates/bevy_render/src/draw.rs
index c31f34cecc..ea5ed3fdea 100644
--- a/crates/bevy_render/src/draw.rs
+++ b/crates/bevy_render/src/draw.rs
@@ -366,7 +366,7 @@ pub trait Drawable {
 }
 
 pub fn clear_draw_system(mut query: Query<&mut Draw>) {
-    for mut draw in &mut query.iter() {
+    for mut draw in query.iter() {
         draw.clear_render_commands();
     }
 }
diff --git a/crates/bevy_render/src/mesh/mesh.rs b/crates/bevy_render/src/mesh/mesh.rs
index e3bc164afe..13b2710122 100644
--- a/crates/bevy_render/src/mesh/mesh.rs
+++ b/crates/bevy_render/src/mesh/mesh.rs
@@ -479,7 +479,7 @@ pub fn mesh_resource_provider_system(
     }
 
     // TODO: remove this once batches are pipeline specific and deprecate assigned_meshes draw target
-    for (handle, mut render_pipelines) in &mut query.iter() {
+    for (handle, mut render_pipelines) in query.iter() {
         if let Some(mesh) = meshes.get(&handle) {
             for render_pipeline in render_pipelines.pipelines.iter_mut() {
                 render_pipeline.specialization.primitive_topology = mesh.primitive_topology;
diff --git a/crates/bevy_render/src/pipeline/render_pipelines.rs b/crates/bevy_render/src/pipeline/render_pipelines.rs
index 1d7f1ba89f..5a608457bd 100644
--- a/crates/bevy_render/src/pipeline/render_pipelines.rs
+++ b/crates/bevy_render/src/pipeline/render_pipelines.rs
@@ -106,7 +106,7 @@ pub fn draw_render_pipelines_system(
     mut render_resource_bindings: ResMut<RenderResourceBindings>,
     mut query: Query<(&mut Draw, &mut RenderPipelines)>,
 ) {
-    for (mut draw, mut render_pipelines) in &mut query.iter() {
+    for (mut draw, mut render_pipelines) in query.iter() {
         let mut drawable = DrawableRenderPipelines {
             render_pipelines: &mut render_pipelines,
             render_resource_bindings: &mut render_resource_bindings,
diff --git a/crates/bevy_render/src/render_graph/nodes/render_resources_node.rs b/crates/bevy_render/src/render_graph/nodes/render_resources_node.rs
index 6f408c5106..6d9c831655 100644
--- a/crates/bevy_render/src/render_graph/nodes/render_resources_node.rs
+++ b/crates/bevy_render/src/render_graph/nodes/render_resources_node.rs
@@ -422,7 +422,7 @@ fn render_resources_node_system<T: RenderResources>(
     let render_resource_context = &**render_resource_context;
     state.uniform_buffer_arrays.reset_changed_item_counts();
     // update uniforms info
-    for (uniforms, draw, _render_pipelines) in &mut query.iter() {
+    for (uniforms, draw, _render_pipelines) in query.iter() {
         if !draw.is_visible {
             return;
         }
@@ -438,7 +438,7 @@ fn render_resources_node_system<T: RenderResources>(
         .uniform_buffer_arrays
         .update_staging_buffer(render_resource_context);
 
-    for (uniforms, draw, mut render_pipelines) in &mut query.iter() {
+    for (uniforms, draw, mut render_pipelines) in query.iter() {
         if !draw.is_visible {
             return;
         }
@@ -456,7 +456,7 @@ fn render_resources_node_system<T: RenderResources>(
             staging_buffer,
             0..state.uniform_buffer_arrays.staging_buffer_size as u64,
             &mut |mut staging_buffer, _render_resource_context| {
-                for (uniforms, draw, mut render_pipelines) in &mut query.iter() {
+                for (uniforms, draw, mut render_pipelines) in query.iter() {
                     if !draw.is_visible {
                         return;
                     }
@@ -479,7 +479,7 @@ fn render_resources_node_system<T: RenderResources>(
     } else {
         // TODO: can we just remove this?
         let mut staging_buffer: [u8; 0] = [];
-        for (uniforms, draw, mut render_pipelines) in &mut query.iter() {
+        for (uniforms, draw, mut render_pipelines) in query.iter() {
             if !draw.is_visible {
                 return;
             }
@@ -657,7 +657,7 @@ fn asset_render_resources_node_system<T: RenderResources>(
         }
     }
 
-    for (asset_handle, _draw, mut render_pipelines) in &mut query.iter() {
+    for (asset_handle, _draw, mut render_pipelines) in query.iter() {
         if let Some(asset_bindings) = asset_render_resource_bindings.get(*asset_handle) {
             render_pipelines.bindings.extend(asset_bindings);
         }
diff --git a/crates/bevy_render/src/shader/shader_defs.rs b/crates/bevy_render/src/shader/shader_defs.rs
index 509f39cdc1..f31847be38 100644
--- a/crates/bevy_render/src/shader/shader_defs.rs
+++ b/crates/bevy_render/src/shader/shader_defs.rs
@@ -59,7 +59,7 @@ pub fn shader_defs_system<T>(mut query: Query<(&T, &mut RenderPipelines)>)
 where
     T: ShaderDefs + Send + Sync + 'static,
 {
-    for (shader_defs, mut render_pipelines) in &mut query.iter() {
+    for (shader_defs, mut render_pipelines) in query.iter() {
         for shader_def in shader_defs.iter_shader_defs() {
             for render_pipeline in render_pipelines.pipelines.iter_mut() {
                 render_pipeline
@@ -73,7 +73,7 @@ where
 }
 
 pub fn clear_shader_defs_system(mut query: Query<&mut RenderPipelines>) {
-    for mut render_pipelines in &mut query.iter() {
+    for mut render_pipelines in query.iter() {
         for render_pipeline in render_pipelines.pipelines.iter_mut() {
             render_pipeline
                 .specialization
@@ -90,7 +90,7 @@ pub fn asset_shader_defs_system<T>(
 ) where
     T: ShaderDefs + Send + Sync + 'static,
 {
-    for (asset_handle, mut render_pipelines) in &mut query.iter() {
+    for (asset_handle, mut render_pipelines) in query.iter() {
         let shader_defs = assets.get(&asset_handle).unwrap();
         for shader_def in shader_defs.iter_shader_defs() {
             for render_pipeline in render_pipelines.pipelines.iter_mut() {
diff --git a/crates/bevy_sprite/src/sprite.rs b/crates/bevy_sprite/src/sprite.rs
index 2997d419a1..165aa973f1 100644
--- a/crates/bevy_sprite/src/sprite.rs
+++ b/crates/bevy_sprite/src/sprite.rs
@@ -23,7 +23,7 @@ pub fn sprite_system(
     textures: Res<Assets<Texture>>,
     mut query: Query<(&mut Sprite, &Handle<ColorMaterial>)>,
 ) {
-    for (mut sprite, handle) in &mut query.iter() {
+    for (mut sprite, handle) in query.iter() {
         let material = materials.get(&handle).unwrap();
         if let Some(texture_handle) = material.texture {
             if let Some(texture) = textures.get(&texture_handle) {
diff --git a/crates/bevy_transform/src/hierarchy/hierarchy_maintenance_system.rs b/crates/bevy_transform/src/hierarchy/hierarchy_maintenance_system.rs
index d769774843..e3c365efba 100644
--- a/crates/bevy_transform/src/hierarchy/hierarchy_maintenance_system.rs
+++ b/crates/bevy_transform/src/hierarchy/hierarchy_maintenance_system.rs
@@ -9,7 +9,7 @@ pub fn missing_previous_parent_system(
     mut query: Query<Without<PreviousParent, (Entity, &Parent)>>,
 ) {
     // Add missing `PreviousParent` components
-    for (entity, _parent) in &mut query.iter() {
+    for (entity, _parent) in query.iter() {
         log::trace!("Adding missing PreviousParent to {:?}", entity);
         commands.insert_one(entity, PreviousParent(None));
     }
@@ -24,7 +24,7 @@ pub fn parent_update_system(
 ) {
     // Entities with a missing `Parent` (ie. ones that have a `PreviousParent`), remove
     // them from the `Children` of the `PreviousParent`.
-    for (entity, previous_parent) in &mut removed_parent_query.iter() {
+    for (entity, previous_parent) in removed_parent_query.iter() {
         log::trace!("Parent was removed from {:?}", entity);
         if let Some(previous_parent_entity) = previous_parent.0 {
             if let Ok(mut previous_parent_children) =
@@ -40,7 +40,7 @@ pub fn parent_update_system(
     let mut children_additions = HashMap::<Entity, SmallVec<[Entity; 8]>>::with_capacity(16);
 
     // Entities with a changed Parent (that also have a PreviousParent, even if None)
-    for (entity, parent, mut previous_parent) in &mut changed_parent_query.iter() {
+    for (entity, parent, mut previous_parent) in changed_parent_query.iter() {
         log::trace!("Parent changed for {:?}", entity);
 
         // If the `PreviousParent` is not None.
diff --git a/crates/bevy_transform/src/local_transform_systems.rs b/crates/bevy_transform/src/local_transform_systems.rs
index 17439f5af1..6ef7dcd8fc 100644
--- a/crates/bevy_transform/src/local_transform_systems.rs
+++ b/crates/bevy_transform/src/local_transform_systems.rs
@@ -13,7 +13,7 @@ pub fn local_transform_translation_system(
         >,
     >,
 ) {
-    for (mut local, translation) in &mut query.iter() {
+    for (mut local, translation) in query.iter() {
         *local = LocalTransform(Mat4::from_translation(translation.0));
     }
 }
@@ -26,7 +26,7 @@ pub fn local_transform_rotation_system(
         >,
     >,
 ) {
-    for (mut local, rotation) in &mut query.iter() {
+    for (mut local, rotation) in query.iter() {
         *local = LocalTransform(Mat4::from_quat(rotation.0));
     }
 }
@@ -39,7 +39,7 @@ pub fn local_transform_scale_system(
         >,
     >,
 ) {
-    for (mut local, scale) in &mut query.iter() {
+    for (mut local, scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale(Vec3::new(scale.0, scale.0, scale.0)));
     }
 }
@@ -52,7 +52,7 @@ pub fn local_transform_non_uniform_scale_system(
         >,
     >,
 ) {
-    for (mut local, non_uniform_scale) in &mut query.iter() {
+    for (mut local, non_uniform_scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale(non_uniform_scale.0));
     }
 }
@@ -62,7 +62,7 @@ pub fn local_transform_translation_rotation_system(
         Without<Scale, Without<NonUniformScale, (&mut LocalTransform, &Translation, &Rotation)>>,
     >,
 ) {
-    for (mut local, translation, rotation) in &mut query.iter() {
+    for (mut local, translation, rotation) in query.iter() {
         *local = LocalTransform(Mat4::from_rotation_translation(rotation.0, translation.0));
     }
 }
@@ -72,7 +72,7 @@ pub fn local_transform_translation_scale_system(
         Without<Rotation, Without<NonUniformScale, (&mut LocalTransform, &Translation, &Scale)>>,
     >,
 ) {
-    for (mut local, translation, scale) in &mut query.iter() {
+    for (mut local, translation, scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale_rotation_translation(
             Vec3::new(scale.0, scale.0, scale.0),
             Quat::default(),
@@ -86,7 +86,7 @@ pub fn local_transform_translation_non_uniform_scale_system(
         Without<Rotation, Without<Scale, (&mut LocalTransform, &Translation, &NonUniformScale)>>,
     >,
 ) {
-    for (mut local, translation, non_uniform_scale) in &mut query.iter() {
+    for (mut local, translation, non_uniform_scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale_rotation_translation(
             non_uniform_scale.0,
             Quat::default(),
@@ -100,7 +100,7 @@ pub fn local_transform_rotation_scale_system(
         Without<Translation, Without<NonUniformScale, (&mut LocalTransform, &Rotation, &Scale)>>,
     >,
 ) {
-    for (mut local, rotation, scale) in &mut query.iter() {
+    for (mut local, rotation, scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale_rotation_translation(
             Vec3::new(scale.0, scale.0, scale.0),
             rotation.0,
@@ -114,7 +114,7 @@ pub fn local_transform_rotation_non_uniform_scale_system(
         Without<Translation, Without<Scale, (&mut LocalTransform, &Rotation, &NonUniformScale)>>,
     >,
 ) {
-    for (mut local, rotation, non_uniform_scale) in &mut query.iter() {
+    for (mut local, rotation, non_uniform_scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale_rotation_translation(
             non_uniform_scale.0,
             rotation.0,
@@ -128,7 +128,7 @@ pub fn local_transform_translation_rotation_scale_system(
         Without<NonUniformScale, (&mut LocalTransform, &Translation, &Rotation, &Scale)>,
     >,
 ) {
-    for (mut local, translation, rotation, scale) in &mut query.iter() {
+    for (mut local, translation, rotation, scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale_rotation_translation(
             Vec3::new(scale.0, scale.0, scale.0),
             rotation.0,
@@ -150,7 +150,7 @@ pub fn local_transform_translation_rotation_non_uniform_scale_system(
         >,
     >,
 ) {
-    for (mut local, translation, rotation, non_uniform_scale) in &mut query.iter() {
+    for (mut local, translation, rotation, non_uniform_scale) in query.iter() {
         *local = LocalTransform(Mat4::from_scale_rotation_translation(
             non_uniform_scale.0,
             rotation.0,
diff --git a/crates/bevy_transform/src/transform_propagate_system.rs b/crates/bevy_transform/src/transform_propagate_system.rs
index 30cfc9c463..7d3cd7c013 100644
--- a/crates/bevy_transform/src/transform_propagate_system.rs
+++ b/crates/bevy_transform/src/transform_propagate_system.rs
@@ -10,7 +10,7 @@ pub fn transform_propagate_system(
     mut children_query: Query<&Children>,
     mut local_transform_query: Query<&LocalTransform>,
 ) {
-    for (children, mut transform, local_transform) in &mut root_query.iter() {
+    for (children, mut transform, local_transform) in root_query.iter() {
         if let Some(local_transform) = local_transform {
             transform.value = local_transform.0;
         }
diff --git a/crates/bevy_transform/src/transform_systems.rs b/crates/bevy_transform/src/transform_systems.rs
index 3398ac95e8..9935730c60 100644
--- a/crates/bevy_transform/src/transform_systems.rs
+++ b/crates/bevy_transform/src/transform_systems.rs
@@ -10,7 +10,7 @@ pub fn transform_translation_system(
         Without<Rotation, Without<Scale, Without<NonUniformScale, (&mut Transform, &Translation)>>>,
     >,
 ) {
-    for (mut transform, translation) in &mut query.iter() {
+    for (mut transform, translation) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -24,7 +24,7 @@ pub fn transform_rotation_system(
         Without<Translation, Without<Scale, Without<NonUniformScale, (&mut Transform, &Rotation)>>>,
     >,
 ) {
-    for (mut transform, rotation) in &mut query.iter() {
+    for (mut transform, rotation) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -38,7 +38,7 @@ pub fn transform_scale_system(
         Without<Translation, Without<Rotation, Without<NonUniformScale, (&mut Transform, &Scale)>>>,
     >,
 ) {
-    for (mut transform, scale) in &mut query.iter() {
+    for (mut transform, scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -52,7 +52,7 @@ pub fn transform_non_uniform_scale_system(
         Without<Translation, Without<Rotation, Without<Scale, (&mut Transform, &NonUniformScale)>>>,
     >,
 ) {
-    for (mut transform, non_uniform_scale) in &mut query.iter() {
+    for (mut transform, non_uniform_scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -66,7 +66,7 @@ pub fn transform_translation_rotation_system(
         Without<Scale, Without<NonUniformScale, (&mut Transform, &Translation, &Rotation)>>,
     >,
 ) {
-    for (mut transform, translation, rotation) in &mut query.iter() {
+    for (mut transform, translation, rotation) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -80,7 +80,7 @@ pub fn transform_translation_scale_system(
         Without<Rotation, Without<NonUniformScale, (&mut Transform, &Translation, &Scale)>>,
     >,
 ) {
-    for (mut transform, translation, scale) in &mut query.iter() {
+    for (mut transform, translation, scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -98,7 +98,7 @@ pub fn transform_translation_non_uniform_scale_system(
         Without<Rotation, Without<Scale, (&mut Transform, &Translation, &NonUniformScale)>>,
     >,
 ) {
-    for (mut transform, translation, non_uniform_scale) in &mut query.iter() {
+    for (mut transform, translation, non_uniform_scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -116,7 +116,7 @@ pub fn transform_rotation_scale_system(
         Without<Translation, Without<NonUniformScale, (&mut Transform, &Rotation, &Scale)>>,
     >,
 ) {
-    for (mut transform, rotation, scale) in &mut query.iter() {
+    for (mut transform, rotation, scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -134,7 +134,7 @@ pub fn transform_rotation_non_uniform_scale_system(
         Without<Translation, Without<Scale, (&mut Transform, &Rotation, &NonUniformScale)>>,
     >,
 ) {
-    for (mut transform, rotation, non_uniform_scale) in &mut query.iter() {
+    for (mut transform, rotation, non_uniform_scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -150,7 +150,7 @@ pub fn transform_rotation_non_uniform_scale_system(
 pub fn transform_translation_rotation_scale_system(
     mut query: Query<Without<NonUniformScale, (&mut Transform, &Translation, &Rotation, &Scale)>>,
 ) {
-    for (mut transform, translation, rotation, scale) in &mut query.iter() {
+    for (mut transform, translation, rotation, scale) in query.iter() {
         if !transform.sync {
             continue;
         }
@@ -166,7 +166,7 @@ pub fn transform_translation_rotation_scale_system(
 pub fn transform_translation_rotation_non_uniform_scale_system(
     mut query: Query<Without<Scale, (&mut Transform, &Translation, &Rotation, &NonUniformScale)>>,
 ) {
-    for (mut transform, translation, rotation, non_uniform_scale) in &mut query.iter() {
+    for (mut transform, translation, rotation, non_uniform_scale) in query.iter() {
         if !transform.sync {
             continue;
         }
diff --git a/crates/bevy_ui/src/focus.rs b/crates/bevy_ui/src/focus.rs
index 3e4f0fdc6d..5f25846d97 100644
--- a/crates/bevy_ui/src/focus.rs
+++ b/crates/bevy_ui/src/focus.rs
@@ -69,7 +69,7 @@ pub fn ui_focus_system(
     }
 
     if mouse_button_input.just_released(MouseButton::Left) {
-        for (_entity, _node, _transform, click, _hover, _focus_policy) in &mut node_query.iter() {
+        for (_entity, _node, _transform, click, _hover, _focus_policy) in node_query.iter() {
             if let Some(mut click) = click {
                 if *click == Click::Pressed {
                     *click = Click::Released;
@@ -83,8 +83,9 @@ pub fn ui_focus_system(
     let mut hovered_entity = None;
 
     {
-        let mut query_iter = node_query.iter();
-        let mut moused_over_z_sorted_nodes = query_iter
+        // let mut query_iter = node_query.iter();
+        let mut moused_over_z_sorted_nodes = node_query
+            .iter()
             .iter()
             .filter_map(|(entity, node, transform, click, hover, focus_policy)| {
                 let position = transform.value.w_axis();
diff --git a/crates/bevy_ui/src/widget/text.rs b/crates/bevy_ui/src/widget/text.rs
index d4bb98dfab..1fcba454f3 100644
--- a/crates/bevy_ui/src/widget/text.rs
+++ b/crates/bevy_ui/src/widget/text.rs
@@ -24,7 +24,7 @@ pub fn text_system(
     mut texture_atlases: ResMut<Assets<TextureAtlas>>,
     mut query: Query<&Text>,
 ) {
-    for text in &mut query.iter() {
+    for text in query.iter() {
         let font_atlases = font_atlas_sets
             .get_or_insert_with(Handle::from_id(text.font.id), || {
                 FontAtlasSet::new(text.font)
@@ -54,7 +54,7 @@ pub fn draw_text_system(
     mut asset_render_resource_bindings: ResMut<AssetRenderResourceBindings>,
     mut query: Query<(&mut Draw, &Text, &Node, &Transform)>,
 ) {
-    for (mut draw, text, node, transform) in &mut query.iter() {
+    for (mut draw, text, node, transform) in query.iter() {
         let position = transform.value.w_axis().truncate() - (node.size / 2.0).extend(0.0);
 
         let mut drawable_text = DrawableText {
diff --git a/examples/2d/sprite_sheet.rs b/examples/2d/sprite_sheet.rs
index 5fb37661b6..e0cb0fb5bc 100644
--- a/examples/2d/sprite_sheet.rs
+++ b/examples/2d/sprite_sheet.rs
@@ -12,7 +12,7 @@ fn animate_sprite_system(
     texture_atlases: Res<Assets<TextureAtlas>>,
     mut query: Query<(&mut Timer, &mut TextureAtlasSprite, &Handle<TextureAtlas>)>,
 ) {
-    for (mut timer, mut sprite, texture_atlas_handle) in &mut query.iter() {
+    for (mut timer, mut sprite, texture_atlas_handle) in query.iter() {
         if timer.finished {
             let texture_atlas = texture_atlases.get(&texture_atlas_handle).unwrap();
             sprite.index = ((sprite.index as usize + 1) % texture_atlas.textures.len()) as u32;
diff --git a/examples/3d/parenting.rs b/examples/3d/parenting.rs
index 82126e0036..12eb8896ac 100644
--- a/examples/3d/parenting.rs
+++ b/examples/3d/parenting.rs
@@ -12,7 +12,7 @@ fn main() {
 
 /// rotates the parent, which will result in the child also rotating
 fn rotator_system(time: Res<Time>, mut query: Query<(&Rotator, &mut Rotation)>) {
-    for (_rotator, mut rotation) in &mut query.iter() {
+    for (_rotator, mut rotation) in query.iter() {
         rotation.0 = rotation.0 * Quat::from_rotation_x(3.0 * time.delta_seconds);
     }
 }
diff --git a/examples/3d/spawner.rs b/examples/3d/spawner.rs
index 9768b80ec8..9731ecfb9b 100644
--- a/examples/3d/spawner.rs
+++ b/examples/3d/spawner.rs
@@ -19,7 +19,7 @@ fn move_cubes(
     mut materials: ResMut<Assets<StandardMaterial>>,
     mut query: Query<(&mut Translation, &Handle<StandardMaterial>)>,
 ) {
-    for (mut translation, material_handle) in &mut query.iter() {
+    for (mut translation, material_handle) in query.iter() {
         let material = materials.get_mut(&material_handle).unwrap();
         translation.0 += Vec3::new(1.0, 0.0, 0.0) * time.delta_seconds;
         material.albedo += Color::rgb(-time.delta_seconds, -time.delta_seconds, time.delta_seconds);
diff --git a/examples/3d/z_sort_debug.rs b/examples/3d/z_sort_debug.rs
index a2851977ad..3d370f1072 100644
--- a/examples/3d/z_sort_debug.rs
+++ b/examples/3d/z_sort_debug.rs
@@ -19,7 +19,7 @@ fn main() {
 
 /// rotates the parent, which will result in the child also rotating
 fn rotator_system(time: Res<Time>, mut query: Query<(&Rotator, &mut Rotation)>) {
-    for (_rotator, mut rotation) in &mut query.iter() {
+    for (_rotator, mut rotation) in query.iter() {
         rotation.0 = rotation.0 * Quat::from_rotation_x(3.0 * time.delta_seconds);
     }
 }
@@ -29,7 +29,7 @@ fn camera_order_color_system(
     mut camera_query: Query<(&Camera, &VisibleEntities)>,
     material_query: Query<&Handle<StandardMaterial>>,
 ) {
-    for (_camera, visible_entities) in &mut camera_query.iter() {
+    for (_camera, visible_entities) in camera_query.iter() {
         for visible_entity in visible_entities.iter() {
             if let Ok(material_handle) =
                 material_query.get::<Handle<StandardMaterial>>(visible_entity.entity)
diff --git a/examples/ecs/ecs_guide.rs b/examples/ecs/ecs_guide.rs
index 3a8bf1f1d3..07d0f033f3 100644
--- a/examples/ecs/ecs_guide.rs
+++ b/examples/ecs/ecs_guide.rs
@@ -85,7 +85,7 @@ fn new_round_system(game_rules: Res<GameRules>, mut game_state: ResMut<GameState
 
 // This system updates the score for each entity with the "Player" and "Score" component.
 fn score_system(mut query: Query<(&Player, &mut Score)>) {
-    for (player, mut score) in &mut query.iter() {
+    for (player, mut score) in query.iter() {
         let scored_a_point = random::<bool>();
         if scored_a_point {
             score.value += 1;
@@ -112,7 +112,7 @@ fn score_check_system(
     mut game_state: ResMut<GameState>,
     mut query: Query<(&Player, &Score)>,
 ) {
-    for (player, score) in &mut query.iter() {
+    for (player, score) in query.iter() {
         if score.value == game_rules.winning_score {
             game_state.winning_player = Some(player.name.clone());
         }
@@ -238,7 +238,7 @@ struct State {
 // NOTE: this doesn't do anything relevant to our game, it is just here for illustrative purposes
 #[allow(dead_code)]
 fn local_state_system(mut state: Local<State>, mut query: Query<(&Player, &Score)>) {
-    for (player, score) in &mut query.iter() {
+    for (player, score) in query.iter() {
         println!("processed: {} {}", player.name, score.value);
     }
     println!("this system ran {} times", state.counter);
diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index cebee9b05e..40fd028e09 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -160,7 +160,7 @@ fn paddle_movement_system(
     keyboard_input: Res<Input<KeyCode>>,
     mut query: Query<(&Paddle, &mut Translation)>,
 ) {
-    for (paddle, mut translation) in &mut query.iter() {
+    for (paddle, mut translation) in query.iter() {
         let mut direction = 0.0;
         if keyboard_input.pressed(KeyCode::Left) {
             direction -= 1.0;
@@ -175,13 +175,13 @@ fn paddle_movement_system(
 }
 
 fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Translation)>) {
-    for (ball, mut translation) in &mut ball_query.iter() {
+    for (ball, mut translation) in ball_query.iter() {
         translation.0 += ball.velocity * time.delta_seconds;
     }
 }
 
 fn scoreboard_system(scoreboard: Res<Scoreboard>, mut query: Query<&mut Text>) {
-    for mut text in &mut query.iter() {
+    for mut text in query.iter() {
         text.value = format!("Score: {}", scoreboard.score);
     }
 }
@@ -194,13 +194,13 @@ fn ball_collision_system(
     mut brick_query: Query<(Entity, &Brick, &Translation, &Sprite)>,
     mut wall_query: Query<(&Wall, &Translation, &Sprite)>,
 ) {
-    for (mut ball, ball_translation, sprite) in &mut ball_query.iter() {
+    for (mut ball, ball_translation, sprite) in ball_query.iter() {
         let ball_size = sprite.size;
         let velocity = &mut ball.velocity;
         let mut collision = None;
 
         // check collision with walls
-        for (_wall, translation, sprite) in &mut wall_query.iter() {
+        for (_wall, translation, sprite) in wall_query.iter() {
             if collision.is_some() {
                 break;
             }
@@ -209,7 +209,7 @@ fn ball_collision_system(
         }
 
         // check collision with paddle(s)
-        for (_paddle, translation, sprite) in &mut paddle_query.iter() {
+        for (_paddle, translation, sprite) in paddle_query.iter() {
             if collision.is_some() {
                 break;
             }
@@ -218,7 +218,7 @@ fn ball_collision_system(
         }
 
         // check collision with bricks
-        for (brick_entity, _brick, translation, sprite) in &mut brick_query.iter() {
+        for (brick_entity, _brick, translation, sprite) in brick_query.iter() {
             if collision.is_some() {
                 break;
             }
diff --git a/examples/scene/load_scene.rs b/examples/scene/load_scene.rs
index 86fb4ec7b8..40c0037bb8 100644
--- a/examples/scene/load_scene.rs
+++ b/examples/scene/load_scene.rs
@@ -93,7 +93,7 @@ fn load_scene_right_now_system(world: &mut World, resources: &mut Resources) {
 // You should immediately see the changes appear in the console.
 fn print_system(mut query: Query<(Entity, &ComponentA)>) {
     println!("Current World State:");
-    for (entity, component_a) in &mut query.iter() {
+    for (entity, component_a) in query.iter() {
         println!("  Entity({})", entity.id());
         println!(
             "    ComponentA: {{ x: {} y: {} }}\n",
diff --git a/examples/ui/button.rs b/examples/ui/button.rs
index 3feef9d5e9..da5d545da8 100644
--- a/examples/ui/button.rs
+++ b/examples/ui/button.rs
@@ -44,7 +44,7 @@ fn button_system(
     )>,
     text_query: Query<&mut Text>,
 ) {
-    for (_button, hover, click, mut material, children) in &mut hover_query.iter() {
+    for (_button, hover, click, mut material, children) in hover_query.iter() {
         let mut text = text_query.get_mut::<Text>(children[0]).unwrap();
         match *hover {
             Hover::Hovered => {
@@ -65,7 +65,7 @@ fn button_system(
         }
     }
 
-    for (_button, click, hover, mut material, children) in &mut click_query.iter() {
+    for (_button, click, hover, mut material, children) in click_query.iter() {
         let mut text = text_query.get_mut::<Text>(children[0]).unwrap();
         match *click {
             Click::Pressed => {
diff --git a/examples/ui/font_atlas_debug.rs b/examples/ui/font_atlas_debug.rs
index bb116a0097..068b0d3792 100644
--- a/examples/ui/font_atlas_debug.rs
+++ b/examples/ui/font_atlas_debug.rs
@@ -51,7 +51,7 @@ fn atlas_render_system(
 }
 
 fn text_update_system(mut state: ResMut<State>, time: Res<Time>, mut query: Query<&mut Text>) {
-    for mut text in &mut query.iter() {
+    for mut text in query.iter() {
         state.timer.tick(time.delta_seconds);
         if state.timer.finished {
             text.value = format!("{}", rand::random::<u8>() as char);
diff --git a/examples/ui/text.rs b/examples/ui/text.rs
index bfb6331f68..e952734722 100644
--- a/examples/ui/text.rs
+++ b/examples/ui/text.rs
@@ -13,7 +13,7 @@ fn main() {
 }
 
 fn text_update_system(diagnostics: Res<Diagnostics>, mut query: Query<&mut Text>) {
-    for mut text in &mut query.iter() {
+    for mut text in query.iter() {
         if let Some(fps) = diagnostics.get(FrameTimeDiagnosticsPlugin::FPS) {
             if let Some(average) = fps.average() {
                 text.value = format!("FPS: {:.2}", average);
diff --git a/examples/ui/ui_bench.rs b/examples/ui/ui_bench.rs
index e65c3c2dee..76860549d1 100644
--- a/examples/ui/ui_bench.rs
+++ b/examples/ui/ui_bench.rs
@@ -13,7 +13,7 @@ fn placement_system(
     materials: Res<Assets<ColorMaterial>>,
     mut query: Query<(&mut Node, &Handle<ColorMaterial>)>,
 ) {
-    for (mut node, material_handle) in &mut query.iter() {
+    for (mut node, material_handle) in query.iter() {
         let material = materials.get(&material_handle).unwrap();
         if material.color.r > 0.2 {
             node.position += Vec2::new(0.1 * time.delta_seconds, 0.0);