1 files changed, 69 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/svh.rs b/compiler/rustc_data_structures/src/svh.rs
new file mode 100644
index 00000000000..02103de2e8d
--- /dev/null
+++ b/compiler/rustc_data_structures/src/svh.rs
@@ -0,0 +1,69 @@
+//! Calculation and management of a Strict Version Hash for crates
+//!
+//! The SVH is used for incremental compilation to track when HIR
+//! nodes have changed between compilations, and also to detect
+//! mismatches where we have two versions of the same crate that were
+//! compiled from distinct sources.
+
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+use std::fmt;
+use std::hash::{Hash, Hasher};
+
+use crate::stable_hasher;
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct Svh {
+    hash: u64,
+}
+
+impl Svh {
+    /// Creates a new `Svh` given the hash. If you actually want to
+    /// compute the SVH from some HIR, you want the `calculate_svh`
+    /// function found in `librustc_incremental`.
+    pub fn new(hash: u64) -> Svh {
+        Svh { hash }
+    }
+
+    pub fn as_u64(&self) -> u64 {
+        self.hash
+    }
+
+    pub fn to_string(&self) -> String {
+        format!("{:016x}", self.hash)
+    }
+}
+
+impl Hash for Svh {
+    fn hash<H>(&self, state: &mut H)
+    where
+        H: Hasher,
+    {
+        self.hash.to_le().hash(state);
+    }
+}
+
+impl fmt::Display for Svh {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad(&self.to_string())
+    }
+}
+
+impl<S: Encoder> Encodable<S> for Svh {
+    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_u64(self.as_u64().to_le())
+    }
+}
+
+impl<D: Decoder> Decodable<D> for Svh {
+    fn decode(d: &mut D) -> Result<Svh, D::Error> {
+        d.read_u64().map(u64::from_le).map(Svh::new)
+    }
+}
+
+impl<T> stable_hasher::HashStable<T> for Svh {
+    #[inline]
+    fn hash_stable(&self, ctx: &mut T, hasher: &mut stable_hasher::StableHasher) {
+        let Svh { hash } = *self;
+        hash.hash_stable(ctx, hasher);
+    }
+}