Require Cargo feature opt-in for min_specialize

This commit switches away from implicitly enabling the `min_specialize` Rust nightly feature whenever a Nightly compiler is used to instead requiring an explicit opt-in with a new Cargo feature `nightly-specialize`. The goal of this commit is to fix tkaitchuck#238 and has two primary motivations: 1. In tkaitchuck#238 I'm trying to build something that depends on this crate as part of the Rust bootstrap process but this crate fails to build due to `min_specialize` not being allowed but a nightly compiler is in use. This is due to the fact that the way `-Zallow-features` is managed in the bootstrap is different than the standard Cargo way of doing so. 2. This removes a failure mode where if one day the `min_specialize` feature changes this crate won't break when built on nightly. Users of Nightly compilers will be able to continue using this crate if the feature was not explicitly opted-in to.
alexcrichton · Jul 8, 2024 · 0f0fb48 · 0f0fb48
1 parent 7d5c661
commit 0f0fb48
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diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
@@ -46,6 +46,8 @@ jobs:
         run: cargo check --features serde
       - name: test serde
         run: cargo test --features serde
+      - name: check specialize
+        run: cargo check --features nightly-specialize
   linux_arm7:
     name: Linux ARMv7
     runs-on: ubuntu-latest
@@ -153,4 +155,4 @@ jobs:
     - uses: dtolnay/rust-toolchain@master
       with:
         toolchain: nightly
-    - run: cargo build --manifest-path=no_std_test/Cargo.toml
+    - run: cargo build --manifest-path=no_std_test/Cargo.toml
diff --git a/Cargo.toml b/Cargo.toml
@@ -47,6 +47,9 @@ atomic-polyfill = [ "dep:portable-atomic", "once_cell/critical-section"]
 # Nightly-only support for AES intrinsics on 32-bit ARM
 nightly-arm-aes = []
 
+# Nightly-only support for impls that work with `min_specialization`
+nightly-specialize = []
+
 [[bench]]
 name = "ahash"
 path = "tests/bench.rs"
@@ -75,9 +78,6 @@ lto = 'fat'
 debug-assertions = false
 codegen-units = 1
 
-[build-dependencies]
-version_check = "0.9.4"
-
 [dependencies]
 const-random = { version = "0.1.17", optional = true }
 serde = { version = "1.0.117", optional = true }

diff --git a/build.rs b/build.rs
@@ -4,9 +4,6 @@ use std::env;
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
-    if let Some(true) = version_check::supports_feature("specialize") {
-        println!("cargo:rustc-cfg=feature=\"specialize\"");
-    }
     let arch = env::var("CARGO_CFG_TARGET_ARCH").expect("CARGO_CFG_TARGET_ARCH was not set");
     if arch.eq_ignore_ascii_case("x86_64")
         || arch.eq_ignore_ascii_case("aarch64")

diff --git a/src/aes_hash.rs b/src/aes_hash.rs
@@ -94,7 +94,7 @@ impl AHasher {
     }
 
     #[inline]
-    #[cfg(feature = "specialize")]
+    #[cfg(feature = "nightly-specialize")]
     fn short_finish(&self) -> u64 {
         let combined = aesenc(self.sum, self.enc);
         let result: [u64; 2] = aesdec(combined, combined).convert();
@@ -214,14 +214,14 @@ impl Hasher for AHasher {
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 pub(crate) struct AHasherU64 {
     pub(crate) buffer: u64,
     pub(crate) pad: u64,
 }
 
 /// A specialized hasher for only primitives under 64 bits.
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl Hasher for AHasherU64 {
     #[inline]
     fn finish(&self) -> u64 {
@@ -264,11 +264,11 @@ impl Hasher for AHasherU64 {
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 pub(crate) struct AHasherFixed(pub AHasher);
 
 /// A specialized hasher for fixed size primitives larger than 64 bits.
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl Hasher for AHasherFixed {
     #[inline]
     fn finish(&self) -> u64 {
@@ -311,12 +311,12 @@ impl Hasher for AHasherFixed {
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 pub(crate) struct AHasherStr(pub AHasher);
 
 /// A specialized hasher for strings
 /// Note that the other types don't panic because the hash impl for String tacks on an unneeded call. (As does vec)
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl Hasher for AHasherStr {
     #[inline]
     fn finish(&self) -> u64 {

diff --git a/src/fallback_hash.rs b/src/fallback_hash.rs
@@ -115,7 +115,7 @@ impl AHasher {
     }
 
     #[inline]
-    #[cfg(feature = "specialize")]
+    #[cfg(feature = "nightly-specialize")]
     fn short_finish(&self) -> u64 {
         folded_multiply(self.buffer, self.pad)
     }
@@ -199,14 +199,14 @@ impl Hasher for AHasher {
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 pub(crate) struct AHasherU64 {
     pub(crate) buffer: u64,
     pub(crate) pad: u64,
 }
 
 /// A specialized hasher for only primitives under 64 bits.
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl Hasher for AHasherU64 {
     #[inline]
     fn finish(&self) -> u64 {
@@ -250,11 +250,11 @@ impl Hasher for AHasherU64 {
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 pub(crate) struct AHasherFixed(pub AHasher);
 
 /// A specialized hasher for fixed size primitives larger than 64 bits.
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl Hasher for AHasherFixed {
     #[inline]
     fn finish(&self) -> u64 {
@@ -297,12 +297,12 @@ impl Hasher for AHasherFixed {
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 pub(crate) struct AHasherStr(pub AHasher);
 
 /// A specialized hasher for a single string
 /// Note that the other types don't panic because the hash impl for String tacks on an unneeded call. (As does vec)
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl Hasher for AHasherStr {
     #[inline]
     fn finish(&self) -> u64 {

diff --git a/src/hash_quality_test.rs b/src/hash_quality_test.rs
@@ -407,7 +407,7 @@ mod fallback_tests {
     #[test]
     fn fallback_keys_affect_every_byte() {
         //For fallback second key is not used in every hash.
-        #[cfg(all(not(feature = "specialize"), feature = "folded_multiply"))]
+        #[cfg(all(not(feature = "nightly-specialize"), feature = "folded_multiply"))]
         test_keys_affect_every_byte(0, |a, b| AHasher::new_with_keys(a ^ b, a));
         test_keys_affect_every_byte("", |a, b| AHasher::new_with_keys(a ^ b, a));
         test_keys_affect_every_byte((0, 0), |a, b| AHasher::new_with_keys(a ^ b, a));
@@ -504,7 +504,7 @@ mod aes_tests {
 
     #[test]
     fn aes_keys_affect_every_byte() {
-        #[cfg(not(feature = "specialize"))]
+        #[cfg(not(feature = "nightly-specialize"))]
         test_keys_affect_every_byte(0, AHasher::test_with_keys);
         test_keys_affect_every_byte("", AHasher::test_with_keys);
         test_keys_affect_every_byte((0, 0), AHasher::test_with_keys);

diff --git a/src/lib.rs b/src/lib.rs
@@ -97,7 +97,7 @@ Note the import of [HashMapExt]. This is needed for the constructor.
 #![deny(clippy::correctness, clippy::complexity, clippy::perf)]
 #![allow(clippy::pedantic, clippy::cast_lossless, clippy::unreadable_literal)]
 #![cfg_attr(all(not(test), not(feature = "std")), no_std)]
-#![cfg_attr(feature = "specialize", feature(min_specialization))]
+#![cfg_attr(feature = "nightly-specialize", feature(min_specialization))]
 #![cfg_attr(feature = "nightly-arm-aes", feature(stdarch_arm_neon_intrinsics))]
 
 #[macro_use]
@@ -262,42 +262,42 @@ pub(crate) trait BuildHasherExt: BuildHasher {
 
 impl<B: BuildHasher> BuildHasherExt for B {
     #[inline]
-    #[cfg(feature = "specialize")]
+    #[cfg(feature = "nightly-specialize")]
     default fn hash_as_u64<T: Hash + ?Sized>(&self, value: &T) -> u64 {
         let mut hasher = self.build_hasher();
         value.hash(&mut hasher);
         hasher.finish()
     }
     #[inline]
-    #[cfg(not(feature = "specialize"))]
+    #[cfg(not(feature = "nightly-specialize"))]
     fn hash_as_u64<T: Hash + ?Sized>(&self, value: &T) -> u64 {
         let mut hasher = self.build_hasher();
         value.hash(&mut hasher);
         hasher.finish()
     }
     #[inline]
-    #[cfg(feature = "specialize")]
+    #[cfg(feature = "nightly-specialize")]
     default fn hash_as_fixed_length<T: Hash + ?Sized>(&self, value: &T) -> u64 {
         let mut hasher = self.build_hasher();
         value.hash(&mut hasher);
         hasher.finish()
     }
     #[inline]
-    #[cfg(not(feature = "specialize"))]
+    #[cfg(not(feature = "nightly-specialize"))]
     fn hash_as_fixed_length<T: Hash + ?Sized>(&self, value: &T) -> u64 {
         let mut hasher = self.build_hasher();
         value.hash(&mut hasher);
         hasher.finish()
     }
     #[inline]
-    #[cfg(feature = "specialize")]
+    #[cfg(feature = "nightly-specialize")]
     default fn hash_as_str<T: Hash + ?Sized>(&self, value: &T) -> u64 {
         let mut hasher = self.build_hasher();
         value.hash(&mut hasher);
         hasher.finish()
     }
     #[inline]
-    #[cfg(not(feature = "specialize"))]
+    #[cfg(not(feature = "nightly-specialize"))]
     fn hash_as_str<T: Hash + ?Sized>(&self, value: &T) -> u64 {
         let mut hasher = self.build_hasher();
         value.hash(&mut hasher);

diff --git a/src/random_state.rs b/src/random_state.rs
@@ -11,7 +11,7 @@ cfg_if::cfg_if! {
     }
 }
 cfg_if::cfg_if! {
-    if #[cfg(feature = "specialize")]{
+    if #[cfg(feature = "nightly-specialize")]{
         use crate::BuildHasherExt;
     }
 }
@@ -458,14 +458,14 @@ 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(feature = "nightly-specialize")]
     #[inline]
     fn hash_one<T: Hash>(&self, x: T) -> u64 {
         RandomState::hash_one(self, x)
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl BuildHasherExt for RandomState {
     #[inline]
     fn hash_as_u64<T: Hash + ?Sized>(&self, value: &T) -> u64 {

diff --git a/src/specialize.rs b/src/specialize.rs
@@ -7,11 +7,11 @@ extern crate alloc;
 #[cfg(feature = "std")]
 extern crate std as alloc;
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 use crate::BuildHasherExt;
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 use alloc::string::String;
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 use alloc::vec::Vec;
 
 /// Provides a way to get an optimized hasher for a given data type.
@@ -21,7 +21,7 @@ pub(crate) trait CallHasher {
     fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64;
 }
 
-#[cfg(not(feature = "specialize"))]
+#[cfg(not(feature = "nightly-specialize"))]
 impl<T> CallHasher for T
 where
     T: Hash + ?Sized,
@@ -34,7 +34,7 @@ where
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl<T> CallHasher for T
 where
     T: Hash + ?Sized,
@@ -49,7 +49,7 @@ where
 
 macro_rules! call_hasher_impl_u64 {
     ($typ:ty) => {
-        #[cfg(feature = "specialize")]
+        #[cfg(feature = "nightly-specialize")]
         impl CallHasher for $typ {
             #[inline]
             fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
@@ -77,7 +77,7 @@ call_hasher_impl_u64!(&i64);
 
 macro_rules! call_hasher_impl_fixed_length{
     ($typ:ty) => {
-        #[cfg(feature = "specialize")]
+        #[cfg(feature = "nightly-specialize")]
         impl CallHasher for $typ {
             #[inline]
             fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
@@ -96,31 +96,31 @@ call_hasher_impl_fixed_length!(&i128);
 call_hasher_impl_fixed_length!(&usize);
 call_hasher_impl_fixed_length!(&isize);
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl CallHasher for [u8] {
     #[inline]
     fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
         build_hasher.hash_as_str(value)
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl CallHasher for Vec<u8> {
     #[inline]
     fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
         build_hasher.hash_as_str(value)
     }
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 impl CallHasher for str {
     #[inline]
     fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
         build_hasher.hash_as_str(value)
     }
 }
 
-#[cfg(all(feature = "specialize"))]
+#[cfg(all(feature = "nightly-specialize"))]
 impl CallHasher for String {
     #[inline]
     fn get_hash<H: Hash + ?Sized, B: BuildHasher>(value: &H, build_hasher: &B) -> u64 {
@@ -134,7 +134,7 @@ mod test {
     use crate::*;
 
     #[test]
-    #[cfg(feature = "specialize")]
+    #[cfg(feature = "nightly-specialize")]
     pub fn test_specialized_invoked() {
         let build_hasher = RandomState::with_seeds(1, 2, 3, 4);
         let shortened = u64::get_hash(&0, &build_hasher);
@@ -186,7 +186,7 @@ mod test {
             str::get_hash(&"test", &build_hasher),
             String::get_hash(&"test".to_string(), &build_hasher)
         );
-        #[cfg(feature = "specialize")]
+        #[cfg(feature = "nightly-specialize")]
         assert_eq!(
             str::get_hash(&"test", &build_hasher),
             <[u8]>::get_hash("test".as_bytes(), &build_hasher)
@@ -206,7 +206,7 @@ mod test {
             str::get_hash(&&"test", &build_hasher),
             String::get_hash(&"test".to_string(), &build_hasher)
         );
-        #[cfg(feature = "specialize")]
+        #[cfg(feature = "nightly-specialize")]
         assert_eq!(
             str::get_hash(&&"test", &build_hasher),
             <[u8]>::get_hash(&"test".to_string().into_bytes(), &build_hasher)

diff --git a/tests/bench.rs b/tests/bench.rs
@@ -1,4 +1,4 @@
-#![cfg_attr(feature = "specialize", feature(build_hasher_simple_hash_one))]
+#![cfg_attr(feature = "nightly-specialize", feature(build_hasher_simple_hash_one))]
 
 use ahash::{AHasher, RandomState};
 use criterion::*;

diff --git a/tests/map_tests.rs b/tests/map_tests.rs
@@ -1,4 +1,4 @@
-#![cfg_attr(feature = "specialize", feature(build_hasher_simple_hash_one))]
+#![cfg_attr(feature = "nightly-specialize", feature(build_hasher_simple_hash_one))]
 
 use std::hash::{BuildHasher, Hash, Hasher};
 
@@ -151,13 +151,13 @@ fn check_for_collisions<H: Hash, B: BuildHasher>(build_hasher: &B, items: &[H],
     );
 }
 
-#[cfg(feature = "specialize")]
+#[cfg(feature = "nightly-specialize")]
 #[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(feature = "nightly-specialize"))]
 #[allow(unused)] // False positive
 fn hash<H: Hash, B: BuildHasher>(b: &H, build_hasher: &B) -> u64 {
     let mut hasher = build_hasher.build_hasher();