feat: error when recipe-dir is not a directory

src/opt.rs

@@ -251,7 +251,7 @@ pub struct BuildOpts {
     pub recipe: Vec<PathBuf>,
 
     /// The directory that contains recipes.
-    #[arg(long)]
+    #[arg(long, value_parser = is_dir)]
     pub recipe_dir: Option<PathBuf>,
 
     /// Build recipes up to the specified package.
@@ -332,6 +332,17 @@ pub struct BuildOpts {
     pub skip_existing: SkipExisting,
 }
 
+fn is_dir(dir: &str) -> Result<PathBuf, String> {
+    let path = PathBuf::from(dir);
+    if path.is_dir() {
+        Ok(path)
+    } else {
+        Err(format!(
+            "Path '{dir}' needs to exist on disk and be a directory.",
+        ))
+    }
+}
+
 /// Test options.
 #[derive(Parser)]
 pub struct TestOpts {