config: extract setting of toolchain override in rustup help mode

Author: djc

src/cli/rustup_mode.rs

@@ -585,6 +585,11 @@ pub async fn main(
             write!(process.stdout().lock(), "{err}")?;
             info!("This is the version for the rustup toolchain manager, not the rustc compiler.");
             let mut cfg = Cfg::from_env(current_dir, true, process)?;
+            cfg.toolchain_override = cfg
+                .process
+                .args()
+                .find_map(|arg| arg.strip_prefix('+').map(ResolvableToolchainName::try_from))
+                .transpose()?;
             match cfg.active_rustc_version().await {
                 Ok(Some(version)) => info!("The currently active `rustc` version is `{version}`"),
                 Ok(None) => info!("No `rustc` is currently active"),

src/config.rs

@@ -700,11 +700,6 @@ impl<'a> Cfg<'a> {
 
     #[tracing::instrument(level = "trace")]
     pub(crate) async fn active_rustc_version(&mut self) -> Result<Option<String>> {
-        if let Some(t) = self.process.args().find(|x| x.starts_with('+')) {
-            trace!("Fetching rustc version from toolchain `{}`", t);
-            self.toolchain_override = Some(ResolvableToolchainName::try_from(&t[1..])?);
-        }
-
         let Some((name, _)) = self.maybe_ensure_active_toolchain(None).await? else {
             return Ok(None);
         };