a faster hash for ActivationsKey

src/cargo/core/resolver/types.rs

@@ -167,7 +167,7 @@ impl ResolveOpts {
 /// A key that when stord in a hash map ensures that there is only one
 /// semver compatible version of each crate.
 /// Find the activated version of a crate based on the name, source, and semver compatibility.
-#[derive(Clone, PartialEq, Eq, Debug, Ord, PartialOrd, Hash)]
+#[derive(Clone, PartialEq, Eq, Debug, Ord, PartialOrd)]
 pub struct ActivationsKey(InternedString, SemverCompatibility, SourceId);
 
 impl ActivationsKey {
@@ -176,6 +176,14 @@ impl ActivationsKey {
     }
 }
 
+impl std::hash::Hash for ActivationsKey {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.0.fast_hash(state);
+        self.1.hash(state);
+        // self.2.hash(state); // Packages that only differ by SourceId are rare enough to not be worth hashing
+    }
+}
+
 /// A type that represents when cargo treats two Versions as compatible.
 /// Versions `a` and `b` are compatible if their left-most nonzero digit is the
 /// same.

src/cargo/util/interning.rs

@@ -90,6 +90,12 @@ impl InternedString {
     pub fn as_str(&self) -> &'static str {
         self.inner
     }
+
+    /// A faster implementation of hash that is completely compatible with HashMap,
+    /// but does not have a stable value between runs of the program.
+    pub fn fast_hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        std::ptr::NonNull::from(self.inner).hash(state);
+    }
 }
 
 impl Deref for InternedString {