fix(errors)!: improve error messages for RustupError::ToolchainNotInstalled

Author: rami3l

src/config.rs

@@ -672,17 +672,13 @@ impl<'a> Cfg<'a> {
 
                     // XXX: this awkwardness deals with settings file being locked already
                     let toolchain_name = toolchain_name.resolve(&default_host_triple)?;
-                    match Toolchain::new(self, (&toolchain_name).into()) {
-                        Err(RustupError::ToolchainNotInstalled { .. }) => {
-                            if matches!(toolchain_name, ToolchainName::Custom(_)) {
-                                bail!(
-                                    "custom toolchain specified in override file '{}' is not installed",
-                                    toolchain_file.display()
-                                )
-                            }
-                        }
-                        Ok(_) => {}
-                        Err(e) => Err(e)?,
+                    if !Toolchain::exists(self, &(&toolchain_name).into())?
+                        && matches!(toolchain_name, ToolchainName::Custom(_))
+                    {
+                        bail!(
+                            "custom toolchain specified in override file '{}' is not installed",
+                            toolchain_file.display()
+                        )
                     }
                 }
 

src/errors.rs

@@ -98,12 +98,16 @@ pub enum RustupError {
     #[error(
         "toolchain '{name}' is not installed{}",
         if let ToolchainName::Official(t) = name {
-            format!("\nhelp: run `rustup toolchain install {t}` to install it")
+            let t = if *is_active { "" } else { &format!(" {t}") };
+            format!("\nhelp: run `rustup toolchain install{t}` to install it")
         } else {
             String::new()
         },
     )]
-    ToolchainNotInstalled { name: ToolchainName },
+    ToolchainNotInstalled {
+        name: ToolchainName,
+        is_active: bool,
+    },
     #[error("path '{0}' not found")]
     PathToolchainNotInstalled(PathBasedToolchainName),
     #[error(

src/toolchain.rs

@@ -53,6 +53,7 @@ impl<'a> Toolchain<'a> {
             Ok(tc) => Ok(tc),
             Err(RustupError::ToolchainNotInstalled {
                 name: ToolchainName::Official(desc),
+                ..
             }) if install_if_missing => {
                 Ok(
                     DistributableToolchain::install(cfg, &desc, &[], &[], cfg.get_profile()?, true)
@@ -107,7 +108,10 @@ impl<'a> Toolchain<'a> {
         let path = cfg.toolchain_path(&name);
         if !Toolchain::exists(cfg, &name)? {
             return Err(match name {
-                LocalToolchainName::Named(name) => RustupError::ToolchainNotInstalled { name },
+                LocalToolchainName::Named(name) => {
+                    let is_active = matches!(cfg.active_toolchain(), Ok(Some((t, _))) if t == name);
+                    RustupError::ToolchainNotInstalled { name, is_active }
+                }
                 LocalToolchainName::Path(name) => RustupError::PathToolchainNotInstalled(name),
             });
         }

tests/suite/cli_exact.rs

@@ -5,6 +5,7 @@ use rustup::for_host;
 use rustup::test::{
     CROSS_ARCH1, CROSS_ARCH2, CliTestContext, MULTI_ARCH1, Scenario, this_host_triple,
 };
+use rustup::utils::raw;
 
 #[tokio::test]
 async fn update_once() {
@@ -699,6 +700,35 @@ help: run `rustup toolchain install nightly-{0}` to install it
         .await;
 }
 
+// issue #4212
+#[tokio::test]
+async fn show_suggestion_for_missing_toolchain_with_components() {
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+
+    let cwd = cx.config.current_dir();
+    let toolchain_file = cwd.join("rust-toolchain.toml");
+    raw::write_file(
+        &toolchain_file,
+        r#"
+[toolchain]
+channel = "stable"
+components = [ "rust-src" ]
+"#,
+    )
+    .unwrap();
+    cx.config
+        .expect_err_env(
+            &["cargo", "fmt"],
+            &[("RUSTUP_AUTO_INSTALL", "0")],
+            for_host!(
+                r"error: toolchain 'stable-{0}' is not installed
+help: run `rustup toolchain install` to install it
+"
+            ),
+        )
+        .await;
+}
+
 // issue #927
 #[tokio::test]
 async fn undefined_linked_toolchain() {