fix(primitives): make sure DefaultHashBuilder implements Clone (#748)

crates/primitives/src/map/fixed.rs

@@ -72,7 +72,7 @@ macro_rules! assert_eq_unchecked {
 /// Works best with `fxhash`, enabled by default with the "map-fxhash" feature.
 ///
 /// **NOTE:** this hasher accepts only `N`-length byte arrays! It is invalid to hash anything else.
-#[derive(Default)]
+#[derive(Clone, Default)]
 pub struct FbBuildHasher<const N: usize> {
     inner: DefaultHashBuilder,
     _marker: core::marker::PhantomData<[(); N]>,
@@ -98,7 +98,7 @@ impl<const N: usize> BuildHasher for FbBuildHasher<N> {
 /// Works best with `fxhash`, enabled by default with the "map-fxhash" feature.
 ///
 /// **NOTE:** this hasher accepts only `N`-length byte arrays! It is invalid to hash anything else.
-#[derive(Default)]
+#[derive(Clone, Default)]
 pub struct FbHasher<const N: usize> {
     inner: DefaultHasher,
     _marker: core::marker::PhantomData<[(); N]>,
@@ -201,5 +201,11 @@ mod tests {
         map.insert(Address::ZERO, true);
         assert_eq!(map.get(&Address::ZERO), Some(&true));
         assert_eq!(map.get(&Address::with_last_byte(1)), None);
+
+        let map2 = map.clone();
+        assert_eq!(map.len(), map2.len());
+        assert_eq!(map.len(), 1);
+        assert_eq!(map2.get(&Address::ZERO), Some(&true));
+        assert_eq!(map2.get(&Address::with_last_byte(1)), None);
     }
 }

crates/primitives/src/map/mod.rs

@@ -63,7 +63,40 @@ cfg_if! {
 
         cfg_if! {
             if #[cfg(all(feature = "std", feature = "rand"))] {
-                use rustc_hash::FxRandomState as FxBuildHasherInner;
+                // use rustc_hash::FxRandomState as FxBuildHasherInner;
+
+                // TODO: Polyfill for https://github.com/rust-lang/rustc-hash/pull/52/
+                #[allow(missing_debug_implementations, missing_copy_implementations)]
+                #[doc(hidden)]
+                #[derive(Clone)]
+                pub struct FxBuildHasherInner(usize);
+
+                impl Default for FxBuildHasherInner {
+                    // Copied from `FxRandomState::new`.
+                    fn default() -> Self {
+                        use rand::Rng;
+                        use std::{cell::Cell, thread_local};
+
+                        thread_local!(static SEED: Cell<usize> = {
+                            Cell::new(rand::thread_rng().gen())
+                        });
+
+                        SEED.with(|seed| {
+                            let s = seed.get();
+                            seed.set(s.wrapping_add(1));
+                            Self(s)
+                        })
+                    }
+                }
+
+                impl core::hash::BuildHasher for FxBuildHasherInner {
+                    type Hasher = rustc_hash::FxHasher;
+
+                    #[inline]
+                    fn build_hasher(&self) -> Self::Hasher {
+                        rustc_hash::FxHasher::with_seed(self.0)
+                    }
+                }
             } else {
                 use rustc_hash::FxBuildHasher as FxBuildHasherInner;
             }
@@ -127,3 +160,19 @@ cfg_if! {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_hasher_builder_traits() {
+        let hash_builder = <DefaultHashBuilder as Default>::default();
+        let _hash_builder2 = <DefaultHashBuilder as Clone>::clone(&hash_builder);
+        let mut hasher =
+            <DefaultHashBuilder as core::hash::BuildHasher>::build_hasher(&hash_builder);
+
+        <DefaultHasher as core::hash::Hasher>::write_u8(&mut hasher, 0);
+        let _hasher2 = <DefaultHasher as Clone>::clone(&hasher);
+    }
+}