Remove remnant EntityHash and related types from bevy_utils (#15039)

# Objective

`EntityHash` and related types were moved from `bevy_utils` to
`bevy_ecs` in #11498, but seemed to have been accidentally reintroduced
a week later in #11707.

## Solution

Remove the old leftover code.

---

## Migration Guide

- Uses of `bevy::utils::{EntityHash, EntityHasher, EntityHashMap,
EntityHashSet}` now have to be imported from `bevy::ecs::entity`.

crates/bevy_ecs/src/observer/mod.rs

@@ -7,11 +7,12 @@ mod trigger_event;
 pub use runner::*;
 pub use trigger_event::*;
 
+use crate::entity::EntityHashMap;
 use crate::observer::entity_observer::ObservedBy;
 use crate::{archetype::ArchetypeFlags, system::IntoObserverSystem, world::*};
 use crate::{component::ComponentId, prelude::*, world::DeferredWorld};
 use bevy_ptr::Ptr;
-use bevy_utils::{EntityHashMap, HashMap};
+use bevy_utils::HashMap;
 use std::{fmt::Debug, marker::PhantomData};
 
 /// Type containing triggered [`Event`] information for a given run of an [`Observer`]. This contains the
@@ -152,15 +153,15 @@ pub struct ObserverTrigger {
 }
 
 // Map between an observer entity and its runner
-type ObserverMap = EntityHashMap<Entity, ObserverRunner>;
+type ObserverMap = EntityHashMap<ObserverRunner>;
 
 /// Collection of [`ObserverRunner`] for [`Observer`] registered to a particular trigger targeted at a specific component.
 #[derive(Default, Debug)]
 pub struct CachedComponentObservers {
     // Observers listening to triggers targeting this component
     map: ObserverMap,
     // Observers listening to triggers targeting this component on a specific entity
-    entity_map: EntityHashMap<Entity, ObserverMap>,
+    entity_map: EntityHashMap<ObserverMap>,
 }
 
 /// Collection of [`ObserverRunner`] for [`Observer`] registered to a particular trigger.
@@ -171,7 +172,7 @@ pub struct CachedObservers {
     // Observers listening for this trigger fired at a specific component
     component_observers: HashMap<ComponentId, CachedComponentObservers>,
     // Observers listening for this trigger fired at a specific entity
-    entity_observers: EntityHashMap<Entity, ObserverMap>,
+    entity_observers: EntityHashMap<ObserverMap>,
 }
 
 /// Metadata for observers. Stores a cache mapping trigger ids to the registered observers.

crates/bevy_reflect/src/impls/std.rs

@@ -1029,7 +1029,6 @@ macro_rules! impl_reflect_for_hashset {
 }
 
 impl_type_path!(::bevy_utils::NoOpHash);
-impl_type_path!(::bevy_utils::EntityHash);
 impl_type_path!(::bevy_utils::FixedState);
 
 impl_reflect_for_hashset!(::std::collections::HashSet<V,S>);

crates/bevy_render/src/batching/gpu_preprocessing.rs

@@ -3,14 +3,13 @@
 use bevy_app::{App, Plugin};
 use bevy_derive::{Deref, DerefMut};
 use bevy_ecs::{
-    entity::Entity,
+    entity::{Entity, EntityHashMap},
     query::{Has, With},
     schedule::IntoSystemConfigs as _,
     system::{Query, Res, ResMut, Resource, StaticSystemParam},
     world::{FromWorld, World},
 };
 use bevy_encase_derive::ShaderType;
-use bevy_utils::EntityHashMap;
 use bytemuck::{Pod, Zeroable};
 use nonmax::NonMaxU32;
 use smallvec::smallvec;
@@ -99,7 +98,7 @@ where
     /// corresponds to each instance.
     ///
     /// This is keyed off each view. Each view has a separate buffer.
-    pub work_item_buffers: EntityHashMap<Entity, PreprocessWorkItemBuffer>,
+    pub work_item_buffers: EntityHashMap<PreprocessWorkItemBuffer>,
 
     /// The uniform data inputs for the current frame.
     ///

crates/bevy_render/src/view/visibility/range.rs

@@ -9,15 +9,15 @@ use std::{
 use bevy_app::{App, Plugin, PostUpdate};
 use bevy_ecs::{
     component::Component,
-    entity::Entity,
+    entity::{Entity, EntityHashMap},
     query::{Changed, With},
     schedule::IntoSystemConfigs as _,
     system::{Query, Res, ResMut, Resource},
 };
 use bevy_math::{vec4, FloatOrd, Vec4};
 use bevy_reflect::Reflect;
 use bevy_transform::components::GlobalTransform;
-use bevy_utils::{prelude::default, EntityHashMap, HashMap};
+use bevy_utils::{prelude::default, HashMap};
 use nonmax::NonMaxU16;
 use wgpu::{BufferBindingType, BufferUsages};
 
@@ -191,7 +191,7 @@ impl VisibilityRange {
 #[derive(Resource)]
 pub struct RenderVisibilityRanges {
     /// Information corresponding to each entity.
-    entities: EntityHashMap<Entity, RenderVisibilityEntityInfo>,
+    entities: EntityHashMap<RenderVisibilityEntityInfo>,
 
     /// Maps a [`VisibilityRange`] to its index within the `buffer`.
     ///
@@ -309,13 +309,13 @@ impl RenderVisibilityRanges {
 #[derive(Resource, Default)]
 pub struct VisibleEntityRanges {
     /// Stores which bit index each view corresponds to.
-    views: EntityHashMap<Entity, u8>,
+    views: EntityHashMap<u8>,
 
     /// Stores a bitmask in which each view has a single bit.
     ///
     /// A 0 bit for a view corresponds to "out of range"; a 1 bit corresponds to
     /// "in range".
-    entities: EntityHashMap<Entity, u32>,
+    entities: EntityHashMap<u32>,
 }
 
 impl VisibleEntityRanges {

crates/bevy_utils/src/lib.rs

@@ -276,85 +276,6 @@ impl<K: Hash + Eq + PartialEq + Clone, V> PreHashMapExt<K, V> for PreHashMap<K,
     }
 }
 
-/// A [`BuildHasher`] that results in a [`EntityHasher`].
-#[derive(Default, Clone)]
-pub struct EntityHash;
-
-impl BuildHasher for EntityHash {
-    type Hasher = EntityHasher;
-
-    fn build_hasher(&self) -> Self::Hasher {
-        EntityHasher::default()
-    }
-}
-
-/// A very fast hash that is only designed to work on generational indices
-/// like `Entity`. It will panic if attempting to hash a type containing
-/// non-u64 fields.
-///
-/// This is heavily optimized for typical cases, where you have mostly live
-/// entities, and works particularly well for contiguous indices.
-///
-/// If you have an unusual case -- say all your indices are multiples of 256
-/// or most of the entities are dead generations -- then you might want also to
-/// try [`AHasher`] for a slower hash computation but fewer lookup conflicts.
-#[derive(Debug, Default)]
-pub struct EntityHasher {
-    hash: u64,
-}
-
-impl Hasher for EntityHasher {
-    #[inline]
-    fn finish(&self) -> u64 {
-        self.hash
-    }
-
-    fn write(&mut self, _bytes: &[u8]) {
-        panic!("can only hash u64 using EntityHasher");
-    }
-
-    #[inline]
-    fn write_u64(&mut self, bits: u64) {
-        // SwissTable (and thus `hashbrown`) cares about two things from the hash:
-        // - H1: low bits (masked by `2ⁿ-1`) to pick the slot in which to store the item
-        // - H2: high 7 bits are used to SIMD optimize hash collision probing
-        // For more see <https://abseil.io/about/design/swisstables#metadata-layout>
-
-        // This hash function assumes that the entity ids are still well-distributed,
-        // so for H1 leaves the entity id alone in the low bits so that id locality
-        // will also give memory locality for things spawned together.
-        // For H2, take advantage of the fact that while multiplication doesn't
-        // spread entropy to the low bits, it's incredibly good at spreading it
-        // upward, which is exactly where we need it the most.
-
-        // While this does include the generation in the output, it doesn't do so
-        // *usefully*.  H1 won't care until you have over 3 billion entities in
-        // the table, and H2 won't care until something hits generation 33 million.
-        // Thus the comment suggesting that this is best for live entities,
-        // where there won't be generation conflicts where it would matter.
-
-        // The high 32 bits of this are ⅟φ for Fibonacci hashing.  That works
-        // particularly well for hashing for the same reason as described in
-        // <https://extremelearning.com.au/unreasonable-effectiveness-of-quasirandom-sequences/>
-        // It loses no information because it has a modular inverse.
-        // (Specifically, `0x144c_bc89_u32 * 0x9e37_79b9_u32 == 1`.)
-        //
-        // The low 32 bits make that part of the just product a pass-through.
-        const UPPER_PHI: u64 = 0x9e37_79b9_0000_0001;
-
-        // This is `(MAGIC * index + generation) << 32 + index`, in a single instruction.
-        self.hash = bits.wrapping_mul(UPPER_PHI);
-    }
-}
-
-/// A [`HashMap`] pre-configured to use [`EntityHash`] hashing.
-/// Iteration order only depends on the order of insertions and deletions.
-pub type EntityHashMap<K, V> = hashbrown::HashMap<K, V, EntityHash>;
-
-/// A [`HashSet`] pre-configured to use [`EntityHash`] hashing.
-/// Iteration order only depends on the order of insertions and deletions.
-pub type EntityHashSet<T> = hashbrown::HashSet<T, EntityHash>;
-
 /// A specialized hashmap type with Key of [`TypeId`]
 /// Iteration order only depends on the order of insertions and deletions.
 pub type TypeIdMap<V> = hashbrown::HashMap<TypeId, V, NoOpHash>;

examples/2d/mesh2d_manual.rs

@@ -8,6 +8,7 @@
 use bevy::{
     color::palettes::basic::YELLOW,
     core_pipeline::core_2d::{Transparent2d, CORE_2D_DEPTH_FORMAT},
+    ecs::entity::EntityHashMap,
     math::FloatOrd,
     prelude::*,
     render::{
@@ -33,7 +34,6 @@ use bevy::{
         Mesh2dPipelineKey, Mesh2dTransforms, MeshFlags, RenderMesh2dInstance, SetMesh2dBindGroup,
         SetMesh2dViewBindGroup, WithMesh2d,
     },
-    utils::EntityHashMap,
 };
 use std::f32::consts::PI;
 
@@ -291,7 +291,7 @@ pub const COLORED_MESH2D_SHADER_HANDLE: Handle<Shader> =
 
 /// Our custom pipeline needs its own instance storage
 #[derive(Resource, Deref, DerefMut, Default)]
-pub struct RenderColoredMesh2dInstances(EntityHashMap<Entity, RenderMesh2dInstance>);
+pub struct RenderColoredMesh2dInstances(EntityHashMap<RenderMesh2dInstance>);
 
 impl Plugin for ColoredMesh2dPlugin {
     fn build(&self, app: &mut App) {