handle single error

Signed-off-by: Bugen Zhao <[email protected]>

src/meta/src/barrier/rpc.rs

@@ -541,6 +541,7 @@ fn merge_node_rpc_errors<E: Error + Send + Sync + 'static>(
     errors: impl IntoIterator<Item = (WorkerId, E)>,
 ) -> MetaError {
     use std::error::request_value;
+    use std::fmt::Write;
 
     use risingwave_common::error::tonic::extra::Score;
 
@@ -550,6 +551,18 @@ fn merge_node_rpc_errors<E: Error + Send + Sync + 'static>(
         return anyhow!(message.to_owned()).into();
     }
 
+    // Create the error from the single error.
+    let single_error = |(worker_id, e)| {
+        anyhow::Error::from(e)
+            .context(format!("{message}, in worker node {worker_id}"))
+            .into()
+    };
+
+    if errors.len() == 1 {
+        return single_error(errors.into_iter().next().unwrap());
+    }
+
+    // Find the error with the highest score.
     let max_score = errors
         .iter()
         .map(|(_, e)| request_value::<Score>(e))
@@ -558,23 +571,20 @@ fn merge_node_rpc_errors<E: Error + Send + Sync + 'static>(
 
     if let Some(max_score) = max_score {
         let mut errors = errors;
-        let (worker_id, error) = errors
+        let max_scored = errors
             .extract_if(|(_, e)| request_value::<Score>(e) == Some(max_score))
             .next()
             .unwrap();
 
-        anyhow::Error::from(error)
-            .context(format!("{message}, in worker node {worker_id}"))
-            .into()
-    } else {
-        use std::fmt::Write;
-
-        let concat: String = errors
-            .into_iter()
-            .fold(format!("{message}: "), |mut s, (w, e)| {
-                write!(&mut s, " in worker node {}, {};", w, e.as_report()).unwrap();
-                s
-            });
-        anyhow!(concat).into()
+        return single_error(max_scored);
     }
+
+    // The errors do not have scores, so simply concatenate them.
+    let concat: String = errors
+        .into_iter()
+        .fold(format!("{message}: "), |mut s, (w, e)| {
+            write!(&mut s, " in worker node {}, {};", w, e.as_report()).unwrap();
+            s
+        });
+    anyhow!(concat).into()
 }