Import StableHasher, StableHasherResult and SipHasher128

as well as the `DebugStrictAdd` and `DebugStrictSub` from rustc.

.gitignore

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+/target

Cargo.toml

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+[package]
+name = "rustc-stable-hash"
+version = "0.1.0"
+authors = ["The Rust Project Developers"]
+description = "A stable hashing algorithm used by rustc"
+license = "Apache-2.0 OR MIT"
+readme = "README.md"
+repository = "https://github.com/rust-lang/rustc-stable-hash"
+edition = "2021"
+
+[features]
+nightly = [] # for feature(hasher_prefixfree_extras)

src/int_overflow.rs

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+// Weaker version of `-Coverflow-checks`.
+
+/// Addition, but only overflow checked when `cfg(debug_assertions)` is set
+/// instead of respecting `-Coverflow-checks`.
+///
+/// This exists for performance reasons, as we ship rustc with overflow checks.
+/// While overflow checks are perf neutral in almost all of the compiler, there
+/// are a few particularly hot areas where we don't want overflow checks in our
+/// dist builds. Overflow is still a bug there, so we want overflow check for
+/// builds with debug assertions.
+///
+/// That's a long way to say that this should be used in areas where overflow
+/// is a bug but overflow checking is too slow.
+pub trait DebugStrictAdd {
+    /// See [`DebugStrictAdd`].
+    fn debug_strict_add(self, other: Self) -> Self;
+}
+
+macro_rules! impl_debug_strict_add {
+    ($( $ty:ty )*) => {
+        $(
+            impl DebugStrictAdd for $ty {
+                fn debug_strict_add(self, other: Self) -> Self {
+                    if cfg!(debug_assertions) {
+                        self + other
+                    } else {
+                        self.wrapping_add(other)
+                    }
+                }
+            }
+        )*
+    };
+}
+
+/// See [`DebugStrictAdd`].
+pub trait DebugStrictSub {
+    /// See [`DebugStrictAdd`].
+    fn debug_strict_sub(self, other: Self) -> Self;
+}
+
+macro_rules! impl_debug_strict_sub {
+    ($( $ty:ty )*) => {
+        $(
+            impl DebugStrictSub for $ty {
+                fn debug_strict_sub(self, other: Self) -> Self {
+                    if cfg!(debug_assertions) {
+                        self - other
+                    } else {
+                        self.wrapping_sub(other)
+                    }
+                }
+            }
+        )*
+    };
+}
+
+impl_debug_strict_add! {
+    usize
+}
+
+/*
+impl_debug_strict_add! {
+    u8 u16 u32 u64 u128 usize
+    i8 i16 i32 i64 i128 isize
+}
+*/
+
+impl_debug_strict_sub! {
+    usize
+}
+
+/*
+impl_debug_strict_sub! {
+    u8 u16 u32 u64 u128 usize
+    i8 i16 i32 i64 i128 isize
+}
+*/

src/lib.rs

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+//! A stable hashing algorithm used by rustc
+
+#![cfg_attr(feature = "nightly", feature(hasher_prefixfree_extras))]
+
+mod int_overflow;
+mod sip128;
+mod stable_hasher;
+
+#[doc(inline)]
+pub use stable_hasher::StableHasher;
+
+#[doc(inline)]
+pub use stable_hasher::StableHasherResult;