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

Author: rami3l

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

@@ -107,7 +107,10 @@ 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),
             });
         }