Change: remove AddLearnerError::Exists, which is not actually used

Author: drmingdrmer

openraft/src/error.rs

@@ -115,9 +115,6 @@ pub enum AddLearnerError {
     #[error(transparent)]
     ForwardToLeader(#[from] ForwardToLeader),
 
-    #[error("node {0} is already a learner")]
-    Exists(NodeId),
-
     #[error(transparent)]
     Fatal(#[from] Fatal),
 }

openraft/src/raft.rs

@@ -317,10 +317,6 @@ impl<D: AppData, R: AppDataResponse, N: RaftNetwork<D>, S: RaftStorage<D, R>> Ra
                 AddLearnerError::ForwardToLeader(forward_err) => {
                     return Err(ClientWriteError::ForwardToLeader(forward_err))
                 }
-                AddLearnerError::Exists(node_id) => {
-                    tracing::info!(%node_id, "add learner: already exists");
-                    continue;
-                }
                 AddLearnerError::Fatal(f) => return Err(ClientWriteError::Fatal(f)),
             }
         }