feat: -Zmsrv-policy groundwork

Author: epage

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/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>