a faster hash for ActivationsKey (rust-lang#14915)

This is a perf improvement I suggested
rust-lang#14665 (comment)

I mostly want this landed to make it easier to compare the cost and
benefits of more complicated changes. As this is the thing to compare
against.

src/cargo/core/resolver/context.rs

@@ -1,13 +1,12 @@
 use super::dep_cache::RegistryQueryer;
 use super::errors::ActivateResult;
-use super::types::{ConflictMap, ConflictReason, FeaturesSet, ResolveOpts};
+use super::types::{ActivationsKey, ConflictMap, ConflictReason, FeaturesSet, ResolveOpts};
 use super::RequestedFeatures;
-use crate::core::{Dependency, PackageId, SourceId, Summary};
+use crate::core::{Dependency, PackageId, Summary};
 use crate::util::interning::InternedString;
 use crate::util::Graph;
 use anyhow::format_err;
 use std::collections::HashMap;
-use std::num::NonZeroU64;
 use tracing::debug;
 
 // A `Context` is basically a bunch of local resolution information which is
@@ -39,39 +38,9 @@ pub type ContextAge = usize;
 /// By storing this in a hash map we ensure that there is only one
 /// semver compatible version of each crate.
 /// This all so stores the `ContextAge`.
-pub type ActivationsKey = (InternedString, SourceId, SemverCompatibility);
-
 pub type Activations =
     im_rc::HashMap<ActivationsKey, (Summary, ContextAge), rustc_hash::FxBuildHasher>;
 
-/// 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.
-#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug, PartialOrd, Ord)]
-pub enum SemverCompatibility {
-    Major(NonZeroU64),
-    Minor(NonZeroU64),
-    Patch(u64),
-}
-
-impl From<&semver::Version> for SemverCompatibility {
-    fn from(ver: &semver::Version) -> Self {
-        if let Some(m) = NonZeroU64::new(ver.major) {
-            return SemverCompatibility::Major(m);
-        }
-        if let Some(m) = NonZeroU64::new(ver.minor) {
-            return SemverCompatibility::Minor(m);
-        }
-        SemverCompatibility::Patch(ver.patch)
-    }
-}
-
-impl PackageId {
-    pub fn as_activations_key(self) -> ActivationsKey {
-        (self.name(), self.source_id(), self.version().into())
-    }
-}
-
 impl ResolverContext {
     pub fn new() -> ResolverContext {
         ResolverContext {
@@ -137,7 +106,8 @@ impl ResolverContext {
                 // versions came from a `[patch]` source.
                 if let Some((_, dep)) = parent {
                     if dep.source_id() != id.source_id() {
-                        let key = (id.name(), dep.source_id(), id.version().into());
+                        let key =
+                            ActivationsKey::new(id.name(), id.version().into(), dep.source_id());
                         let prev = self.activations.insert(key, (summary.clone(), age));
                         if let Some((previous_summary, _)) = prev {
                             return Err(

src/cargo/core/resolver/types.rs

@@ -1,10 +1,11 @@
 use super::features::{CliFeatures, RequestedFeatures};
-use crate::core::{Dependency, PackageId, Summary};
+use crate::core::{Dependency, PackageId, SourceId, Summary};
 use crate::util::errors::CargoResult;
 use crate::util::interning::InternedString;
 use crate::util::GlobalContext;
 use std::cmp::Ordering;
 use std::collections::{BTreeMap, BTreeSet};
+use std::num::NonZeroU64;
 use std::rc::Rc;
 use std::time::{Duration, Instant};
 
@@ -163,6 +164,58 @@ 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)]
+pub struct ActivationsKey(InternedString, SemverCompatibility, SourceId);
+
+impl ActivationsKey {
+    pub fn new(
+        name: InternedString,
+        ver: SemverCompatibility,
+        source_id: SourceId,
+    ) -> ActivationsKey {
+        ActivationsKey(name, ver, source_id)
+    }
+}
+
+impl std::hash::Hash for ActivationsKey {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.0.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.
+#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug, PartialOrd, Ord)]
+pub enum SemverCompatibility {
+    Major(NonZeroU64),
+    Minor(NonZeroU64),
+    Patch(u64),
+}
+
+impl From<&semver::Version> for SemverCompatibility {
+    fn from(ver: &semver::Version) -> Self {
+        if let Some(m) = NonZeroU64::new(ver.major) {
+            return SemverCompatibility::Major(m);
+        }
+        if let Some(m) = NonZeroU64::new(ver.minor) {
+            return SemverCompatibility::Minor(m);
+        }
+        SemverCompatibility::Patch(ver.patch)
+    }
+}
+
+impl PackageId {
+    pub fn as_activations_key(self) -> ActivationsKey {
+        ActivationsKey(self.name(), self.version().into(), self.source_id())
+    }
+}
+
 #[derive(Clone)]
 pub struct DepsFrame {
     pub parent: Summary,