Include rust-version in publish request

crates.io reads rust-version from the tarball directly, but we can include it in
the publish request for the sake of consistency for third-party registries.

crates/crates-io/lib.rs

@@ -57,6 +57,7 @@ pub struct NewCrate {
  pub repository: Option<String>,
  pub badges: BTreeMap<String, BTreeMap<String, String>>,
  pub links: Option<String>,
+ pub rust_version: Option<String>,
 }
 
 #[derive(Serialize, Deserialize)]

src/cargo/core/manifest.rs

@@ -110,6 +110,7 @@ pub struct ManifestMetadata {
  pub documentation: Option<String>, // URL
  pub badges: BTreeMap<String, BTreeMap<String, String>>,
  pub links: Option<String>,
+ pub rust_version: Option<String>,
 }
 
 #[derive(Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]

src/cargo/ops/registry.rs

@@ -345,6 +345,7 @@ fn transmit(
  ref categories,
  ref badges,
  ref links,
+ ref rust_version,
  } = *manifest.metadata();
  let readme_content = readme
  .as_ref()
@@ -398,6 +399,7 @@ fn transmit(
  license_file: license_file.clone(),
  badges: badges.clone(),
  links: links.clone(),
+ rust_version: rust_version.clone(),
  },
  tarball,
  )

src/cargo/util/toml/mod.rs

@@ -2433,6 +2433,11 @@ impl TomlManifest {
  .transpose()?
  .unwrap_or_default(),
  links: package.links.clone(),
+ rust_version: package
+ .rust_version
+ .clone()
+ .map(|mw| mw.resolve("rust-version", || inherit()?.rust_version()))
+ .transpose()?,
  };
  package.description = metadata
  .description