Auto merge of #14260 - Eh2406:summary_sync, r=weihanglo

make summary sync by using Arc not Rc

### What does this PR try to resolve?

For my PubGrub testing work I want to be able to read the entire crates.io index into memory and then run lots of resolution questions against that data in parallel. Currently cargoes `Summary` and `Dependency` types use `Rc` internally which prevents this pattern. Using `Arc` in cargo makes my life a lot easier! It does not noticeably slow down single threaded performance. (Measured by running my PubGrub testing in single threaded mode before and after.)

The team largely agreed to this at a meeting and in discussions https://rust-lang.zulipchat.com/#narrow/stream/246057-t-cargo/topic/Make.20summary.20sync

### How should we test and review this PR?

Tests still pass

### Additional information

Should be add a test a this is sync?

src/cargo/core/dependency.rs

@@ -5,7 +5,7 @@ use serde::Serialize;
 use std::borrow::Cow;
 use std::fmt;
 use std::path::PathBuf;
-use std::rc::Rc;
+use std::sync::Arc;
 use tracing::trace;
 
 use crate::core::compiler::{CompileKind, CompileTarget};
@@ -18,7 +18,7 @@ use crate::util::OptVersionReq;
 /// Cheap to copy.
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
 pub struct Dependency {
-    inner: Rc<Inner>,
+    inner: Arc<Inner>,
 }
 
 /// The data underlying a `Dependency`.
@@ -152,7 +152,7 @@ impl Dependency {
 
         let mut ret = Dependency::new_override(name, source_id);
         {
-            let ptr = Rc::make_mut(&mut ret.inner);
+            let ptr = Arc::make_mut(&mut ret.inner);
             ptr.only_match_name = false;
             ptr.req = version_req;
             ptr.specified_req = specified_req;
@@ -163,7 +163,7 @@ impl Dependency {
     pub fn new_override(name: InternedString, source_id: SourceId) -> Dependency {
         assert!(!name.is_empty());
         Dependency {
-            inner: Rc::new(Inner {
+            inner: Arc::new(Inner {
                 name,
                 source_id,
                 registry_id: None,
@@ -241,7 +241,7 @@ impl Dependency {
     }
 
     pub fn set_registry_id(&mut self, registry_id: SourceId) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).registry_id = Some(registry_id);
+        Arc::make_mut(&mut self.inner).registry_id = Some(registry_id);
         self
     }
 
@@ -259,7 +259,7 @@ impl Dependency {
             // Setting 'public' only makes sense for normal dependencies
             assert_eq!(self.kind(), DepKind::Normal);
         }
-        Rc::make_mut(&mut self.inner).public = public;
+        Arc::make_mut(&mut self.inner).public = public;
         self
     }
 
@@ -286,7 +286,7 @@ impl Dependency {
             // Setting 'public' only makes sense for normal dependencies
             assert_eq!(kind, DepKind::Normal);
         }
-        Rc::make_mut(&mut self.inner).kind = kind;
+        Arc::make_mut(&mut self.inner).kind = kind;
         self
     }
 
@@ -295,44 +295,44 @@ impl Dependency {
         &mut self,
         features: impl IntoIterator<Item = impl Into<InternedString>>,
     ) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).features = features.into_iter().map(|s| s.into()).collect();
+        Arc::make_mut(&mut self.inner).features = features.into_iter().map(|s| s.into()).collect();
         self
     }
 
     /// Sets whether the dependency requests default features of the package.
     pub fn set_default_features(&mut self, default_features: bool) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).default_features = default_features;
+        Arc::make_mut(&mut self.inner).default_features = default_features;
         self
     }
 
     /// Sets whether the dependency is optional.
     pub fn set_optional(&mut self, optional: bool) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).optional = optional;
+        Arc::make_mut(&mut self.inner).optional = optional;
         self
     }
 
     /// Sets the source ID for this dependency.
     pub fn set_source_id(&mut self, id: SourceId) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).source_id = id;
+        Arc::make_mut(&mut self.inner).source_id = id;
         self
     }
 
     /// Sets the version requirement for this dependency.
     pub fn set_version_req(&mut self, req: OptVersionReq) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).req = req;
+        Arc::make_mut(&mut self.inner).req = req;
         self
     }
 
     pub fn set_platform(&mut self, platform: Option<Platform>) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).platform = platform;
+        Arc::make_mut(&mut self.inner).platform = platform;
         self
     }
 
     pub fn set_explicit_name_in_toml(
         &mut self,
         name: impl Into<InternedString>,
     ) -> &mut Dependency {
-        Rc::make_mut(&mut self.inner).explicit_name_in_toml = Some(name.into());
+        Arc::make_mut(&mut self.inner).explicit_name_in_toml = Some(name.into());
         self
     }
 
@@ -346,7 +346,7 @@ impl Dependency {
             self.source_id(),
             id
         );
-        let me = Rc::make_mut(&mut self.inner);
+        let me = Arc::make_mut(&mut self.inner);
         me.req.lock_to(id.version());
 
         // Only update the `precise` of this source to preserve other
@@ -361,7 +361,7 @@ impl Dependency {
     /// Mainly used in dependency patching like `[patch]` or `[replace]`, which
     /// doesn't need to lock the entire dependency to a specific [`PackageId`].
     pub fn lock_version(&mut self, version: &semver::Version) -> &mut Dependency {
-        let me = Rc::make_mut(&mut self.inner);
+        let me = Arc::make_mut(&mut self.inner);
         me.req.lock_to(version);
         self
     }
@@ -430,7 +430,7 @@ impl Dependency {
     }
 
     pub(crate) fn set_artifact(&mut self, artifact: Artifact) {
-        Rc::make_mut(&mut self.inner).artifact = Some(artifact);
+        Arc::make_mut(&mut self.inner).artifact = Some(artifact);
     }
 
     pub(crate) fn artifact(&self) -> Option<&Artifact> {
@@ -453,7 +453,7 @@ impl Dependency {
 /// This information represents a requirement in the package this dependency refers to.
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
 pub struct Artifact {
-    inner: Rc<Vec<ArtifactKind>>,
+    inner: Arc<Vec<ArtifactKind>>,
     is_lib: bool,
     target: Option<ArtifactTarget>,
 }
@@ -492,7 +492,7 @@ impl Artifact {
                 .collect::<Result<Vec<_>, _>>()?,
         )?;
         Ok(Artifact {
-            inner: Rc::new(kinds),
+            inner: Arc::new(kinds),
             is_lib,
             target: target.map(ArtifactTarget::parse).transpose()?,
         })

src/cargo/core/summary.rs

@@ -9,22 +9,22 @@ use std::collections::{BTreeMap, HashMap, HashSet};
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::mem;
-use std::rc::Rc;
+use std::sync::Arc;
 
 /// Subset of a `Manifest`. Contains only the most important information about
 /// a package.
 ///
 /// Summaries are cloned, and should not be mutated after creation
 #[derive(Debug, Clone)]
 pub struct Summary {
-    inner: Rc<Inner>,
+    inner: Arc<Inner>,
 }
 
 #[derive(Debug, Clone)]
 struct Inner {
     package_id: PackageId,
     dependencies: Vec<Dependency>,
-    features: Rc<FeatureMap>,
+    features: Arc<FeatureMap>,
     checksum: Option<String>,
     links: Option<InternedString>,
     rust_version: Option<RustVersion>,
@@ -82,10 +82,10 @@ impl Summary {
         }
         let feature_map = build_feature_map(features, &dependencies)?;
         Ok(Summary {
-            inner: Rc::new(Inner {
+            inner: Arc::new(Inner {
                 package_id: pkg_id,
                 dependencies,
-                features: Rc::new(feature_map),
+                features: Arc::new(feature_map),
                 checksum: None,
                 links: links.map(|l| l.into()),
                 rust_version,
@@ -124,12 +124,12 @@ impl Summary {
     }
 
     pub fn override_id(mut self, id: PackageId) -> Summary {
-        Rc::make_mut(&mut self.inner).package_id = id;
+        Arc::make_mut(&mut self.inner).package_id = id;
         self
     }
 
     pub fn set_checksum(&mut self, cksum: String) {
-        Rc::make_mut(&mut self.inner).checksum = Some(cksum);
+        Arc::make_mut(&mut self.inner).checksum = Some(cksum);
     }
 
     pub fn map_dependencies<F>(self, mut f: F) -> Summary
@@ -144,7 +144,7 @@ impl Summary {
         F: FnMut(Dependency) -> CargoResult<Dependency>,
     {
         {
-            let slot = &mut Rc::make_mut(&mut self.inner).dependencies;
+            let slot = &mut Arc::make_mut(&mut self.inner).dependencies;
             *slot = mem::take(slot)
                 .into_iter()
                 .map(f)
@@ -178,6 +178,12 @@ impl Hash for Summary {
     }
 }
 
+// A check that only compiles if Summary is Sync
+const _: fn() = || {
+    fn is_sync<T: Sync>() {}
+    is_sync::<Summary>();
+};
+
 /// Checks features for errors, bailing out a CargoResult:Err if invalid,
 /// and creates FeatureValues for each feature.
 fn build_feature_map(