feat: add optional support for hasbrown Map & Set

serde_with/Cargo.toml

@@ -66,6 +66,7 @@ time_0_3 = ["dep:time_0_3"]
 base64 = {version = "0.21.0", optional = true, default-features = false}
 chrono_0_4 = {package = "chrono", version = "0.4.20", optional = true, default-features = false, features = ["serde"]}
 doc-comment = {version = "0.3.3", optional = true}
+hashbrown = {version = "0.14.0", optional = true, features = ["serde"]}
 hex = {version = "0.4.3", optional = true, default-features = false}
 indexmap_1 = {package = "indexmap", version = "1.8", optional = true, default-features = false, features = ["serde-1"]}
 indexmap_2 = {package = "indexmap", version = "2.0", optional = true, default-features = false, features = ["serde"]}
@@ -112,6 +113,11 @@ name = "hex"
 path = "tests/hex.rs"
 required-features = ["hex", "macros"]
 
+[[test]]
+name = "hashbrown"
+path = "tests/hashbrown.rs"
+required-features = ["hashbrown", "macros"]
+
 [[test]]
 name = "indexmap_1"
 path = "tests/indexmap_1.rs"

serde_with/src/de/duplicates.rs

@@ -7,6 +7,8 @@ use crate::{
     prelude::*,
     MapFirstKeyWins, MapPreventDuplicates, SetLastValueWins, SetPreventDuplicates,
 };
+#[cfg(feature = "hashbrown")]
+use hashbrown::{HashMap as HashbrownMap, HashSet as HashbrownSet};
 #[cfg(feature = "indexmap_1")]
 use indexmap_1::{IndexMap, IndexSet};
 #[cfg(feature = "indexmap_2")]

serde_with/src/de/impls.rs

@@ -1,4 +1,6 @@
 use crate::{formats::*, prelude::*};
+#[cfg(feature = "hashbrown")]
+use hashbrown::{HashMap as HashbrownMap, HashSet as HashbrownSet};
 #[cfg(feature = "indexmap_1")]
 use indexmap_1::{IndexMap, IndexSet};
 #[cfg(feature = "indexmap_2")]
@@ -16,6 +18,8 @@ macro_rules! foreach_map {
         $m!(BTreeMap<K: Ord, V>);
         #[cfg(feature = "std")]
         $m!(HashMap<K: Eq + Hash, V, H: Sized>);
+        #[cfg(all(feature = "std", feature = "hashbrown"))]
+        $m!(HashbrownMap<K: Eq + Hash, V, H: Sized>);
         #[cfg(all(feature = "std", feature = "indexmap_1"))]
         $m!(IndexMap<K: Eq + Hash, V, H: Sized>);
         #[cfg(all(feature = "std", feature = "indexmap_2"))]
@@ -33,6 +37,11 @@ macro_rules! foreach_map_create {
             HashMap<K: Eq + Hash, V, S: BuildHasher + Default>,
             (|size| HashMap::with_capacity_and_hasher(size, Default::default()))
         );
+        #[cfg(feature = "hashbrown")]
+        $m!(
+            HashbrownMap<K: Eq + Hash, V, S: BuildHasher + Default>,
+            (|size| HashbrownMap::with_capacity_and_hasher(size, Default::default()))
+        );
         #[cfg(feature = "indexmap_1")]
         $m!(
             IndexMap<K: Eq + Hash, V, S: BuildHasher + Default>,
@@ -53,6 +62,8 @@ macro_rules! foreach_set {
         $m!(BTreeSet<(K, V): Ord>);
         #[cfg(feature = "std")]
         $m!(HashSet<(K, V): Eq + Hash>);
+        #[cfg(all(feature = "std", feature = "hashbrown"))]
+        $m!(HashbrownSet<(K, V): Eq + Hash>);
         #[cfg(all(feature = "std", feature = "indexmap_1"))]
         $m!(IndexSet<(K, V): Eq + Hash>);
         #[cfg(all(feature = "std", feature = "indexmap_2"))]
@@ -71,6 +82,12 @@ macro_rules! foreach_set_create {
             (|size| HashSet::with_capacity_and_hasher(size, S::default())),
             insert
         );
+        #[cfg(feature = "hashbrown")]
+        $m!(
+            HashbrownSet<T: Eq + Hash, S: BuildHasher + Default>,
+            (|size| HashbrownSet::with_capacity_and_hasher(size, S::default())),
+            insert
+        );
         #[cfg(feature = "indexmap_1")]
         $m!(
             IndexSet<T: Eq + Hash, S: BuildHasher + Default>,

serde_with/src/duplicate_key_impls/error_on_duplicate.rs

@@ -34,6 +34,26 @@ where
     }
 }
 
+#[cfg(feature = "hashbrown")]
+impl<T, S> PreventDuplicateInsertsSet<T> for hashbrown::HashSet<T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher + Default,
+{
+    #[inline]
+    fn new(size_hint: Option<usize>) -> Self {
+        match size_hint {
+            Some(size) => Self::with_capacity_and_hasher(size, S::default()),
+            None => Self::with_hasher(S::default()),
+        }
+    }
+
+    #[inline]
+    fn insert(&mut self, value: T) -> bool {
+        self.insert(value)
+    }
+}
+
 #[cfg(feature = "indexmap_1")]
 impl<T, S> PreventDuplicateInsertsSet<T> for indexmap_1::IndexSet<T, S>
 where
@@ -109,6 +129,26 @@ where
     }
 }
 
+#[cfg(feature = "hashbrown")]
+impl<K, V, S> PreventDuplicateInsertsMap<K, V> for hashbrown::HashMap<K, V, S>
+where
+    K: Eq + Hash,
+    S: BuildHasher + Default,
+{
+    #[inline]
+    fn new(size_hint: Option<usize>) -> Self {
+        match size_hint {
+            Some(size) => Self::with_capacity_and_hasher(size, S::default()),
+            None => Self::with_hasher(S::default()),
+        }
+    }
+
+    #[inline]
+    fn insert(&mut self, key: K, value: V) -> bool {
+        self.insert(key, value).is_none()
+    }
+}
+
 #[cfg(feature = "indexmap_1")]
 impl<K, V, S> PreventDuplicateInsertsMap<K, V> for indexmap_1::IndexMap<K, V, S>
 where

serde_with/src/duplicate_key_impls/first_value_wins.rs

@@ -35,6 +35,34 @@ where
     }
 }
 
+#[cfg(feature = "hashbrown")]
+impl<K, V, S> DuplicateInsertsFirstWinsMap<K, V> for hashbrown::HashMap<K, V, S>
+where
+    K: Eq + Hash,
+    S: BuildHasher + Default,
+{
+    #[inline]
+    fn new(size_hint: Option<usize>) -> Self {
+        match size_hint {
+            Some(size) => Self::with_capacity_and_hasher(size, S::default()),
+            None => Self::with_hasher(S::default()),
+        }
+    }
+
+    #[inline]
+    fn insert(&mut self, key: K, value: V) {
+        use hashbrown::hash_map::Entry;
+
+        match self.entry(key) {
+            // we want to keep the first value, so do nothing
+            Entry::Occupied(_) => {}
+            Entry::Vacant(vacant) => {
+                vacant.insert(value);
+            }
+        }
+    }
+}
+
 #[cfg(feature = "indexmap_1")]
 impl<K, V, S> DuplicateInsertsFirstWinsMap<K, V> for indexmap_1::IndexMap<K, V, S>
 where

serde_with/src/duplicate_key_impls/last_value_wins.rs

@@ -28,6 +28,27 @@ where
     }
 }
 
+#[cfg(feature = "hashbrown")]
+impl<T, S> DuplicateInsertsLastWinsSet<T> for hashbrown::HashSet<T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher + Default,
+{
+    #[inline]
+    fn new(size_hint: Option<usize>) -> Self {
+        match size_hint {
+            Some(size) => Self::with_capacity_and_hasher(size, S::default()),
+            None => Self::with_hasher(S::default()),
+        }
+    }
+
+    #[inline]
+    fn replace(&mut self, value: T) {
+        // Hashset already fulfils the contract
+        self.replace(value);
+    }
+}
+
 #[cfg(feature = "indexmap_1")]
 impl<T, S> DuplicateInsertsLastWinsSet<T> for indexmap_1::IndexSet<T, S>
 where

serde_with/src/guide/feature_flags.md

@@ -6,17 +6,19 @@ Each entry will explain the feature in more detail.
 `serde_with` is fully `no_std` compatible.
 Using it in a `no_std` environment requires using `default-features = false`, since `std` is enabled by default.
 
-1. [`alloc`](#alloc)
-2. [`std` (default)](#std-default)
-3. [`base64`](#base64)
-4. [`chrono_0_4`](#chrono_0_4)
-5. [`guide`](#guide)
-6. [`hex`](#hex)
-7. [`indexmap_1`](#indexmap_1)
-8. [`indexmap_2`](#indexmap_2)
-9. [`json`](#json)
-10. [`macros` (default)](#macros-default)
-11. [`time_0_3`](#time_0_3)
+- [Available Feature Flags](#available-feature-flags)
+  - [`alloc`](#alloc)
+  - [`std` (default)](#std-default)
+  - [`base64`](#base64)
+  - [`chrono_0_4`](#chrono_0_4)
+  - [`guide`](#guide)
+  - [`hashbrown`](#hashbrown)
+  - [`hex`](#hex)
+  - [`indexmap_1`](#indexmap_1)
+  - [`indexmap_2`](#indexmap_2)
+  - [`json`](#json)
+  - [`macros` (default)](#macros-default)
+  - [`time_0_3`](#time_0_3)
 
 ## `alloc`
 
@@ -49,6 +51,14 @@ This pulls in `chrono` v0.4 as a dependency.
 The `guide` feature enables inclusion of this user guide.
 The feature only changes the rustdoc output and enables no other effects.
 
+## `hashbrown`
+
+The `hashbrown` feature enables `hashbown::{HashMap, HashSet}` as supported containers.
+
+This pulls in `hashbrown` as a dependency.
+It enables the `alloc` feature.
+Some functionality is only available when `std` is enabled too.
+
 ## `hex`
 
 The `hex` feature enables serializing data in hex format.

serde_with/src/ser/duplicates.rs

@@ -2,6 +2,8 @@ use super::impls::{foreach_map, foreach_set};
 use crate::{
     prelude::*, MapFirstKeyWins, MapPreventDuplicates, SetLastValueWins, SetPreventDuplicates,
 };
+#[cfg(feature = "hashbrown")]
+use hashbrown::{HashMap as HashbrownMap, HashSet as HashbrownSet};
 #[cfg(feature = "indexmap_1")]
 use indexmap_1::{IndexMap, IndexSet};
 #[cfg(feature = "indexmap_2")]

serde_with/src/ser/impls.rs

@@ -1,4 +1,6 @@
 use crate::{formats, formats::Strictness, prelude::*};
+#[cfg(feature = "hashbrown")]
+use hashbrown::{HashMap as HashbrownMap, HashSet as HashbrownSet};
 #[cfg(feature = "indexmap_1")]
 use indexmap_1::{IndexMap, IndexSet};
 #[cfg(feature = "indexmap_2")]
@@ -17,9 +19,11 @@ macro_rules! foreach_map {
         $m!(BTreeMap<K, V>);
         #[cfg(feature = "std")]
         $m!(HashMap<K, V, H: Sized>);
-        #[cfg(all(feature = "indexmap_1"))]
+        #[cfg(feature = "hashbrown")]
+        $m!(HashbrownMap<K, V, H: Sized>);
+        #[cfg(feature = "indexmap_1")]
         $m!(IndexMap<K, V, H: Sized>);
-        #[cfg(all(feature = "indexmap_2"))]
+        #[cfg(feature = "indexmap_2")]
         $m!(IndexMap2<K, V, H: Sized>);
     };
 }
@@ -31,9 +35,11 @@ macro_rules! foreach_set {
         $m!(BTreeSet<$T>);
         #[cfg(feature = "std")]
         $m!(HashSet<$T, H: Sized>);
-        #[cfg(all(feature = "indexmap_1"))]
+        #[cfg(feature = "hashbrown")]
+        $m!(HashbrownSet<$T, H: Sized>);
+        #[cfg(feature = "indexmap_1")]
         $m!(IndexSet<$T, H: Sized>);
-        #[cfg(all(feature = "indexmap_2"))]
+        #[cfg(feature = "indexmap_2")]
         $m!(IndexSet2<$T, H: Sized>);
     };
     ($m:ident) => {