Replace "ahash" with "default-hasher" in Cargo features

This allows us to change the default hasher in the future without it
being a breaking change.

Author: Amanieu

Cargo.toml

@@ -22,6 +22,7 @@ serde = { version = "1.0.25", default-features = false, optional = true }
 rkyv = { version = "0.7.42", optional = true, default-features = false, features = [
     "alloc",
 ] }
+borsh = { version = "1.5.0", default-features = false, optional = true, features = ["derive"]}
 
 # When built as part of libstd
 core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }
@@ -36,9 +37,6 @@ allocator-api2 = { version = "0.2.9", optional = true, default-features = false,
 # Equivalent trait which can be shared with other hash table implementations.
 equivalent = { version = "1.0", optional = true, default-features = false }
 
-# borsh serde
-borsh = { version = "1.5.0", default-features = false, optional = true, features = ["derive"]}
-
 [dev-dependencies]
 lazy_static = "1.4"
 rand = { version = "0.8.3", features = ["small_rng"] }
@@ -50,27 +48,37 @@ bumpalo = { version = "3.13.0", features = ["allocator-api2"] }
 rkyv = { version = "0.7.42", features = ["validation"] }
 
 [features]
-default = ["ahash", "inline-more", "allocator-api2", "equivalent"]
+default = ["default-hasher", "inline-more", "allocator-api2", "equivalent"]
 
+# Enables use of nightly features. This is only guaranteed to work on the latest
+# version of nightly Rust.
 nightly = ["allocator-api2?/nightly", "bumpalo/allocator_api"]
 
+# Enables the RustcEntry API used to provide the standard library's Entry API.
 rustc-internal-api = []
+
+# Internal feature used when building as part of the standard library.
 rustc-dep-of-std = [
     "nightly",
     "core",
     "compiler_builtins",
     "alloc",
     "rustc-internal-api",
 ]
+
+# Enables the RawTable API.
 raw = []
 
+# Provides a default hasher. Currently this is AHash but this is subject to
+# change in the future. Note that the default hasher does *not* provide HashDoS
+# resistance, unlike the one in the standard library.
+default-hasher = ["dep:ahash"]
+
 # Enables usage of `#[inline]` on far more functions than by default in this
 # crate. This may lead to a performance increase but often comes at a compile
 # time cost.
 inline-more = []
 
-borsh = ["dep:borsh"]
-
 [package.metadata.docs.rs]
 features = ["nightly", "rayon", "serde", "raw"]
 rustdoc-args = ["--generate-link-to-definition"]

README.md

@@ -101,12 +101,14 @@ This crate has the following Cargo features:
 
 - `nightly`: Enables nightly-only features including: `#[may_dangle]`.
 - `serde`: Enables serde serialization support.
+- `borsh`: Enables borsh serialization support.
 - `rkyv`: Enables rkyv serialization support.
 - `rayon`: Enables rayon parallel iterator support.
+- `equivalent`: Allows comparisons to be customized with the `Equivalent` trait.
 - `raw`: Enables access to the experimental and unsafe `RawTable` API.
 - `inline-more`: Adds inline hints to most functions, improving run-time performance at the cost
   of compilation time. (enabled by default)
-- `ahash`: Compiles with ahash as default hasher. (enabled by default)
+- `default-hasher`: Compiles with ahash as default hasher. (enabled by default)
 - `allocator-api2`: Enables support for allocators that support `allocator-api2`. (enabled by default)
 
 ## License

src/map.rs

@@ -11,11 +11,11 @@ use core::mem;
 use core::ops::Index;
 
 /// Default hasher for `HashMap`.
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 pub type DefaultHashBuilder = core::hash::BuildHasherDefault<ahash::AHasher>;
 
 /// Dummy default hasher for `HashMap`.
-#[cfg(not(feature = "ahash"))]
+#[cfg(not(feature = "default-hasher"))]
 pub enum DefaultHashBuilder {}
 
 /// A hash map implemented with quadratic probing and SIMD lookup.
@@ -262,7 +262,7 @@ where
     hash_builder.hash_one(val)
 }
 
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 impl<K, V> HashMap<K, V, DefaultHashBuilder> {
     /// Creates an empty `HashMap`.
     ///
@@ -325,7 +325,7 @@ impl<K, V> HashMap<K, V, DefaultHashBuilder> {
     }
 }
 
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 impl<K, V, A: Allocator> HashMap<K, V, DefaultHashBuilder, A> {
     /// Creates an empty `HashMap` using the given allocator.
     ///
@@ -2258,7 +2258,7 @@ where
 }
 
 // The default hasher is used to match the std implementation signature
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 impl<K, V, A, const N: usize> From<[(K, V); N]> for HashMap<K, V, DefaultHashBuilder, A>
 where
     K: Eq + Hash,

src/set.rs

@@ -128,7 +128,7 @@ impl<T: Clone, S: Clone, A: Allocator + Clone> Clone for HashSet<T, S, A> {
     }
 }
 
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 impl<T> HashSet<T, DefaultHashBuilder> {
     /// Creates an empty `HashSet`.
     ///
@@ -192,7 +192,7 @@ impl<T> HashSet<T, DefaultHashBuilder> {
     }
 }
 
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 impl<T: Hash + Eq, A: Allocator> HashSet<T, DefaultHashBuilder, A> {
     /// Creates an empty `HashSet`.
     ///
@@ -1324,7 +1324,7 @@ where
 }
 
 // The default hasher is used to match the std implementation signature
-#[cfg(feature = "ahash")]
+#[cfg(feature = "default-hasher")]
 impl<T, A, const N: usize> From<[T; N]> for HashSet<T, DefaultHashBuilder, A>
 where
     T: Eq + Hash,