feat: Add -Zmsrv-policy feature flag

crates/cargo-test-support/src/publish.rs

@@ -165,6 +165,7 @@ pub(crate) fn create_index_line(
     features: crate::registry::FeatureMap,
     yanked: bool,
     links: Option<String>,
+    rust_version: Option<&str>,
     v: Option<u32>,
 ) -> String {
     // This emulates what crates.io does to retain backwards compatibility.
@@ -185,6 +186,9 @@ pub(crate) fn create_index_line(
     if let Some(v) = v {
         json["v"] = serde_json::json!(v);
     }
+    if let Some(rust_version) = rust_version {
+        json["rust_version"] = serde_json::json!(rust_version);
+    }
 
     json.to_string()
 }

crates/cargo-test-support/src/registry.rs

@@ -1144,6 +1144,7 @@ fn save_new_crate(
         false,
         new_crate.links,
         None,
+        None,
     );
 
     write_to_index(registry_path, &new_crate.name, line, false);
@@ -1400,6 +1401,7 @@ impl Package {
             self.features.clone(),
             self.yanked,
             self.links.clone(),
+            self.rust_version.as_deref(),
             self.v,
         );
 

crates/resolver-tests/src/lib.rs

@@ -184,6 +184,7 @@ pub fn resolve_with_config_raw(
         deps,
         &BTreeMap::new(),
         None::<&String>,
+        None::<&String>,
     )
     .unwrap();
     let opts = ResolveOpts::everything();
@@ -585,6 +586,7 @@ pub fn pkg_dep<T: ToPkgId>(name: T, dep: Vec<Dependency>) -> Summary {
         dep,
         &BTreeMap::new(),
         link,
+        None::<&String>,
     )
     .unwrap()
 }
@@ -613,6 +615,7 @@ pub fn pkg_loc(name: &str, loc: &str) -> Summary {
         Vec::new(),
         &BTreeMap::new(),
         link,
+        None::<&String>,
     )
     .unwrap()
 }
@@ -627,6 +630,7 @@ pub fn remove_dep(sum: &Summary, ind: usize) -> Summary {
         deps,
         &BTreeMap::new(),
         sum.links().map(|a| a.as_str()),
+        None::<&String>,
     )
     .unwrap()
 }

src/cargo/core/features.rs

@@ -733,6 +733,7 @@ unstable_cli_options!(
     unstable_options: bool = ("Allow the usage of unstable options"),
     skip_rustdoc_fingerprint: bool = (HIDDEN),
     rustdoc_scrape_examples: bool = ("Allows Rustdoc to scrape code examples from reverse-dependencies"),
+    msrv_policy: bool = ("Enable rust-version aware policy within cargo"),
 );
 
 const STABILIZED_COMPILE_PROGRESS: &str = "The progress bar is now always \
@@ -1095,6 +1096,7 @@ impl CliUnstable {
             "timings" => stabilized_warn(k, "1.60", STABILIZED_TIMINGS),
             "codegen-backend" => self.codegen_backend = parse_empty(k, v)?,
             "profile-rustflags" => self.profile_rustflags = parse_empty(k, v)?,
+            "msrv-policy" => self.msrv_policy = parse_empty(k, v)?,
             _ => bail!("unknown `-Z` flag specified: {}", k),
         }
 

src/cargo/core/resolver/version_prefs.rs

@@ -100,7 +100,15 @@ mod test {
         let pkg_id = pkgid(name, version);
         let config = Config::default().unwrap();
         let features = BTreeMap::new();
-        Summary::new(&config, pkg_id, Vec::new(), &features, None::<&String>).unwrap()
+        Summary::new(
+            &config,
+            pkg_id,
+            Vec::new(),
+            &features,
+            None::<&String>,
+            None::<&String>,
+        )
+        .unwrap()
     }
 
     fn describe(summaries: &Vec<Summary>) -> String {

src/cargo/core/summary.rs

@@ -25,6 +25,7 @@ struct Inner {
     features: Rc<FeatureMap>,
     checksum: Option<String>,
     links: Option<InternedString>,
+    rust_version: Option<InternedString>,
 }
 
 impl Summary {
@@ -34,6 +35,7 @@ impl Summary {
         dependencies: Vec<Dependency>,
         features: &BTreeMap<InternedString, Vec<InternedString>>,
         links: Option<impl Into<InternedString>>,
+        rust_version: Option<impl Into<InternedString>>,
     ) -> CargoResult<Summary> {
         // ****CAUTION**** If you change anything here that may raise a new
         // error, be sure to coordinate that change with either the index
@@ -55,6 +57,7 @@ impl Summary {
                 features: Rc::new(feature_map),
                 checksum: None,
                 links: links.map(|l| l.into()),
+                rust_version: rust_version.map(|l| l.into()),
             }),
         })
     }
@@ -85,6 +88,10 @@ impl Summary {
         self.inner.links
     }
 
+    pub fn rust_version(&self) -> Option<InternedString> {
+        self.inner.rust_version
+    }
+
     pub fn override_id(mut self, id: PackageId) -> Summary {
         Rc::make_mut(&mut self.inner).package_id = id;
         self

src/cargo/sources/registry/index.rs

@@ -814,6 +814,7 @@ impl IndexSummary {
             features2,
             yanked,
             links,
+            rust_version,
             v,
         } = serde_json::from_slice(line)?;
         let v = v.unwrap_or(1);
@@ -828,7 +829,7 @@ impl IndexSummary {
                 features.entry(name).or_default().extend(values);
             }
         }
-        let mut summary = Summary::new(config, pkgid, deps, &features, links)?;
+        let mut summary = Summary::new(config, pkgid, deps, &features, links, rust_version)?;
         summary.set_checksum(cksum);
         Ok(IndexSummary {
             summary,

src/cargo/sources/registry/mod.rs

@@ -287,6 +287,13 @@ pub struct RegistryPackage<'a> {
     /// Added early 2018 (see <https://github.com/rust-lang/cargo/pull/4978>),
     /// can be `None` if published before then.
     links: Option<InternedString>,
+    /// Required version of rust
+    ///
+    /// Corresponds to `package.rust-version`.
+    ///
+    /// Added in 2023 (see <https://github.com/rust-lang/crates.io/pull/6267>),
+    /// can be `None` if published before then or if not set in the manifest.
+    rust_version: Option<InternedString>,
     /// The schema version for this entry.
     ///
     /// If this is None, it defaults to version 1. Entries with unknown

src/cargo/util/toml/mod.rs

@@ -2367,6 +2367,7 @@ impl TomlManifest {
             deps,
             me.features.as_ref().unwrap_or(&empty_features),
             package.links.as_deref(),
+            rust_version.as_deref().map(InternedString::new),
         )?;
 
         let metadata = ManifestMetadata {

src/doc/src/reference/unstable.md

@@ -69,6 +69,7 @@ Each new feature described below should explain how to use it.
     * [minimal-versions](#minimal-versions) --- Forces the resolver to use the lowest compatible version instead of the highest.
     * [direct-minimal-versions](#direct-minimal-versions) — Forces the resolver to use the lowest compatible version instead of the highest.
     * [public-dependency](#public-dependency) --- Allows dependencies to be classified as either public or private.
+    * [msrv-policy](#msrv-policy) --- MSRV-aware resolver and version selection
 * Output behavior
     * [out-dir](#out-dir) --- Adds a directory where artifacts are copied to.
     * [Different binary name](#different-binary-name) --- Assign a name to the built binary that is separate from the crate name.
@@ -300,6 +301,14 @@ my_dep = { version = "1.2.3", public = true }
 private_dep = "2.0.0" # Will be 'private' by default
 ```
 
+### msrv-policy
+- [#9930](https://github.com/rust-lang/cargo/issues/9930) (MSRV-aware resolver)
+- [#10653](https://github.com/rust-lang/cargo/issues/10653) (MSRV-aware cargo-add)
+- [#10903](https://github.com/rust-lang/cargo/issues/10903) (MSRV-aware cargo-install)
+
+The `msrv-policy` feature enables experiments in MSRV-aware policy for cargo in
+preparation for an upcoming RFC.
+
 ### build-std
 * Tracking Repository: <https://github.com/rust-lang/wg-cargo-std-aware>