Show available profiles on error

src/bootstrap/flags.rs

@@ -542,7 +542,14 @@ Arguments:
                         |path| format!("{} is not a valid UTF8 string", path.to_string_lossy())
                     ));
 
-                    profile_string.parse().expect("unknown profile")
+                    profile_string.parse().unwrap_or_else(|_| {
+                        eprintln!("error: unknown profile {}", profile_string);
+                        eprintln!("help: the available profiles are:");
+                        for choice in Profile::all() {
+                            eprintln!("- {}", choice);
+                        }
+                        std::process::exit(1);
+                    })
                 } else {
                     t!(crate::setup::interactive_path())
                 };

src/bootstrap/setup.rs

@@ -18,6 +18,10 @@ impl Profile {
     fn include_path(&self, src_path: &Path) -> PathBuf {
         PathBuf::from(format!("{}/src/bootstrap/defaults/config.{}.toml", src_path.display(), self))
     }
+
+    pub fn all() -> impl Iterator<Item = Self> {
+        [Profile::Compiler, Profile::Codegen, Profile::Library, Profile::User].iter().copied()
+    }
 }
 
 #[derive(Debug)]