Faster compilation of bevy_diagnostic (#1235)

* Remove AHashExt

There is little benefit of Hash*::new() over Hash*::default(), but it
does require more code that needs to be duplicated for every Hash* in
bevy_utils. It may also slightly increase compile times.

* Add StableHash* to bevy_utils

* Use StableHashMap instead of HashMap + BTreeSet for diagnostics

This is a significant reduction in the release mode compile times of
bevy_diagnostics

```
Benchmark #1: touch crates/bevy_diagnostic/src/lib.rs && cargo build --release -p bevy_diagnostic -j1
  Time (mean ± σ):      3.645 s ±  0.009 s    [User: 3.551 s, System: 0.094 s]
  Range (min … max):    3.632 s …  3.658 s    20 runs
```

```
Benchmark #1: touch crates/bevy_diagnostic/src/lib.rs && cargo build --release -p bevy_diagnostic -j1
  Time (mean ± σ):      2.938 s ±  0.012 s    [User: 2.850 s, System: 0.090 s]
  Range (min … max):    2.919 s …  2.969 s    20 runs
```

Author: bjorn3

crates/bevy_diagnostic/src/diagnostic.rs

@@ -1,5 +1,5 @@
-use bevy_utils::{Duration, HashMap, Instant, Uuid};
-use std::collections::{BTreeSet, VecDeque};
+use bevy_utils::{Duration, Instant, StableHashMap, Uuid};
+use std::collections::VecDeque;
 
 /// Unique identifier for a [Diagnostic]
 #[derive(Debug, Copy, Clone, Hash, Eq, PartialEq, PartialOrd, Ord)]
@@ -101,13 +101,13 @@ impl Diagnostic {
 /// A collection of [Diagnostic]s
 #[derive(Debug, Default)]
 pub struct Diagnostics {
-    diagnostics: HashMap<DiagnosticId, Diagnostic>,
-    ordered_diagnostics: BTreeSet<DiagnosticId>,
+    // This uses a [`StableHashMap`] to ensure that the iteration order is deterministic between
+    // runs when all diagnostics are inserted in the same order.
+    diagnostics: StableHashMap<DiagnosticId, Diagnostic>,
 }
 
 impl Diagnostics {
     pub fn add(&mut self, diagnostic: Diagnostic) {
-        self.ordered_diagnostics.insert(diagnostic.id);
         self.diagnostics.insert(diagnostic.id, diagnostic);
     }
 
@@ -134,10 +134,4 @@ impl Diagnostics {
     pub fn iter(&self) -> impl Iterator<Item = &Diagnostic> {
         self.diagnostics.values()
     }
-
-    pub fn ordered_iter(&self) -> impl Iterator<Item = &Diagnostic> {
-        self.ordered_diagnostics
-            .iter()
-            .filter_map(move |k| self.diagnostics.get(k))
-    }
 }

crates/bevy_diagnostic/src/log_diagnostics_plugin.rs

@@ -78,7 +78,7 @@ impl LogDiagnosticsPlugin {
                     Self::log_diagnostic(diagnostic);
                 }
             } else {
-                for diagnostic in diagnostics.ordered_iter() {
+                for diagnostic in diagnostics.iter() {
                     Self::log_diagnostic(diagnostic);
                 }
             }
@@ -96,7 +96,7 @@ impl LogDiagnosticsPlugin {
                     debug!("{:#?}\n", diagnostic);
                 }
             } else {
-                for diagnostic in diagnostics.ordered_iter() {
+                for diagnostic in diagnostics.iter() {
                     debug!("{:#?}\n", diagnostic);
                 }
             }

crates/bevy_input/src/axis.rs

@@ -1,4 +1,4 @@
-use bevy_utils::{AHashExt, HashMap};
+use bevy_utils::HashMap;
 use std::hash::Hash;
 
 #[derive(Debug)]
@@ -12,7 +12,7 @@ where
 {
     fn default() -> Self {
         Axis {
-            axis_data: HashMap::new(),
+            axis_data: HashMap::default(),
         }
     }
 }

crates/bevy_render/src/render_graph/nodes/texture_copy_node.rs

@@ -6,7 +6,7 @@ use crate::{
 use bevy_app::prelude::{EventReader, Events};
 use bevy_asset::{AssetEvent, Assets};
 use bevy_ecs::{Resources, World};
-use bevy_utils::{AHashExt, HashSet};
+use bevy_utils::HashSet;
 
 #[derive(Default)]
 pub struct TextureCopyNode {
@@ -24,7 +24,7 @@ impl Node for TextureCopyNode {
     ) {
         let texture_events = resources.get::<Events<AssetEvent<Texture>>>().unwrap();
         let textures = resources.get::<Assets<Texture>>().unwrap();
-        let mut copied_textures = HashSet::new();
+        let mut copied_textures = HashSet::default();
         for event in self.texture_event_reader.iter(&texture_events) {
             match event {
                 AssetEvent::Created { handle } | AssetEvent::Modified { handle } => {

crates/bevy_text/src/font_atlas_set.rs

@@ -6,7 +6,7 @@ use bevy_math::Vec2;
 use bevy_reflect::TypeUuid;
 use bevy_render::texture::Texture;
 use bevy_sprite::TextureAtlas;
-use bevy_utils::{AHashExt, HashMap};
+use bevy_utils::HashMap;
 
 type FontSizeKey = FloatOrd;
 
@@ -25,7 +25,7 @@ pub struct GlyphAtlasInfo {
 impl Default for FontAtlasSet {
     fn default() -> Self {
         FontAtlasSet {
-            font_atlases: HashMap::with_capacity(1),
+            font_atlases: HashMap::with_capacity_and_hasher(1, Default::default()),
         }
     }
 }

crates/bevy_utils/src/lib.rs

@@ -11,89 +11,45 @@ pub type BoxedFuture<'a, T> = Pin<Box<dyn Future<Output = T> + Send + 'a>>;
 #[cfg(target_arch = "wasm32")]
 pub type BoxedFuture<'a, T> = Pin<Box<dyn Future<Output = T> + 'a>>;
 
+/// A hasher builder that will create a fixed hasher.
+#[derive(Default)]
+pub struct FixedState;
+
+impl std::hash::BuildHasher for FixedState {
+    type Hasher = AHasher;
+
+    #[inline]
+    fn build_hasher(&self) -> AHasher {
+        AHasher::new_with_keys(0, 0)
+    }
+}
+
 /// A std hash map implementing AHash, a high speed keyed hashing algorithm
 /// intended for use in in-memory hashmaps.
 ///
 /// AHash is designed for performance and is NOT cryptographically secure.
 pub type HashMap<K, V> = std::collections::HashMap<K, V, RandomState>;
 
-pub trait AHashExt {
-    fn new() -> Self;
-
-    fn with_capacity(capacity: usize) -> Self;
-}
-
-impl<K, V> AHashExt for HashMap<K, V> {
-    /// Creates an empty `HashMap` with AHash.
-    ///
-    /// The hash map is initially created with a capacity of 0, so it will not
-    /// allocate until it is first inserted into.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use bevy_utils::{HashMap, AHashExt};
-    /// let mut map: HashMap<&str, i32> = HashMap::new();
-    /// ```
-    #[inline]
-    fn new() -> Self {
-        Default::default()
-    }
-
-    /// Creates an empty `HashMap` with the specified capacity with AHash.
-    ///
-    /// The hash map will be able to hold at least `capacity` elements without
-    /// reallocating. If `capacity` is 0, the hash map will not allocate.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use bevy_utils::{HashMap, AHashExt};
-    /// let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
-    /// ```
-    #[inline]
-    fn with_capacity(capacity: usize) -> Self {
-        HashMap::with_capacity_and_hasher(capacity, RandomState::default())
-    }
-}
+/// A stable std hash map implementing AHash, a high speed keyed hashing algorithm
+/// intended for use in in-memory hashmaps.
+///
+/// Unlike [`HashMap`] this has an iteration order that only depends on the order
+/// of insertions and deletions and not a random source.
+///
+/// AHash is designed for performance and is NOT cryptographically secure.
+pub type StableHashMap<K, V> = std::collections::HashMap<K, V, FixedState>;
 
 /// A std hash set implementing AHash, a high speed keyed hashing algorithm
 /// intended for use in in-memory hashmaps.
 ///
 /// AHash is designed for performance and is NOT cryptographically secure.
 pub type HashSet<K> = std::collections::HashSet<K, RandomState>;
 
-impl<K> AHashExt for HashSet<K> {
-    /// Creates an empty `HashSet` with AHash.
-    ///
-    /// The hash set is initially created with a capacity of 0, so it will not
-    /// allocate until it is first inserted into.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use bevy_utils::{HashSet, AHashExt};
-    /// let set: HashSet<i32> = HashSet::new();
-    /// ```
-    #[inline]
-    fn new() -> Self {
-        Default::default()
-    }
-
-    /// Creates an empty `HashSet` with the specified capacity with AHash.
-    ///
-    /// The hash set will be able to hold at least `capacity` elements without
-    /// reallocating. If `capacity` is 0, the hash set will not allocate.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use bevy_utils::{HashSet, AHashExt};
-    /// let set: HashSet<i32> = HashSet::with_capacity(10);
-    /// assert!(set.capacity() >= 10);
-    /// ```
-    #[inline]
-    fn with_capacity(capacity: usize) -> Self {
-        HashSet::with_capacity_and_hasher(capacity, RandomState::default())
-    }
-}
+/// A stable std hash set implementing AHash, a high speed keyed hashing algorithm
+/// intended for use in in-memory hashmaps.
+///
+/// Unlike [`HashSet`] this has an iteration order that only depends on the order
+/// of insertions and deletions and not a random source.
+///
+/// AHash is designed for performance and is NOT cryptographically secure.
+pub type StableHashSet<K> = std::collections::HashSet<K, FixedState>;