optimize Id::hash (#974)

Author: ibraheemdev

src/id.rs

@@ -1,5 +1,5 @@
 use std::fmt::Debug;
-use std::hash::Hash;
+use std::hash::{Hash, Hasher};
 use std::num::NonZeroU32;
 
 use crate::zalsa::Zalsa;
@@ -17,7 +17,7 @@ use crate::zalsa::Zalsa;
 ///
 /// As an end-user of `Salsa` you will generally not use `Id` directly,
 /// it is wrapped in new types.
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 #[cfg_attr(feature = "persistence", derive(serde::Serialize, serde::Deserialize))]
 pub struct Id {
     index: NonZeroU32,
@@ -126,6 +126,13 @@ impl Id {
     }
 }
 
+impl Hash for Id {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        // Convert to a `u64` to avoid dispatching multiple calls to `H::write`.
+        state.write_u64(self.as_bits());
+    }
+}
+
 impl Debug for Id {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         if self.generation() == 0 {

src/key.rs

@@ -1,4 +1,4 @@
-use core::fmt;
+use std::fmt;
 
 use crate::function::{VerifyCycleHeads, VerifyResult};
 use crate::zalsa::{IngredientIndex, Zalsa};