Stabilize BuildHasher::hash_one in Rust 1.71

Author: dtolnay

build.rs

@@ -4,6 +4,9 @@ use std::env;
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
+    if let Some(true) = version_check::is_min_version("1.71.0") {
+        println!("cargo:rustc-cfg=build_hasher_hash_one");
+    }
     if let Some(true) = version_check::supports_feature("specialize") {
         println!("cargo:rustc-cfg=feature=\"specialize\"");
     }

src/random_state.rs

@@ -453,7 +453,7 @@ impl BuildHasher for RandomState {
     /// implementation of [`Hash`].  The way to create a combined hash of
     /// multiple values is to call [`Hash::hash`] multiple times using the same
     /// [`Hasher`], not to call this method repeatedly and combine the results.
-    #[cfg(feature = "specialize")]
+    #[cfg(build_hasher_hash_one)]
     #[inline]
     fn hash_one<T: Hash>(&self, x: T) -> u64 {
         RandomState::hash_one(self, x)

tests/bench.rs

@@ -1,5 +1,3 @@
-#![cfg_attr(feature = "specialize", feature(build_hasher_simple_hash_one))]
-
 use ahash::{AHasher, RandomState};
 use criterion::*;
 use fxhash::FxHasher;

tests/map_tests.rs

@@ -1,5 +1,3 @@
-#![cfg_attr(feature = "specialize", feature(build_hasher_simple_hash_one))]
-
 use std::hash::{BuildHasher, Hash, Hasher};
 
 use ahash::RandomState;
@@ -151,13 +149,13 @@ fn check_for_collisions<H: Hash, B: BuildHasher>(build_hasher: &B, items: &[H],
     );
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(build_hasher_hash_one)]
 #[allow(unused)] // False positive
 fn hash<H: Hash, B: BuildHasher>(b: &H, build_hasher: &B) -> u64 {
     build_hasher.hash_one(b)
 }
 
-#[cfg(not(feature = "specialize"))]
+#[cfg(not(build_hasher_hash_one))]
 #[allow(unused)] // False positive
 fn hash<H: Hash, B: BuildHasher>(b: &H, build_hasher: &B) -> u64 {
     let mut hasher = build_hasher.build_hasher();