Fix: Prevent panic when calling Raft::change_membership() on uninit…

…ialized node

Previously, `change_membership()` assumed the current membership config was
always non-empty and used the last config entry. However, uninitialized
nodes lack a membership config, leading to panics.

This commit adds checks to prevent `change_membership()` from panicking

openraft/src/membership/membership.rs

@@ -277,7 +277,7 @@ where C: RaftTypeConfig
     pub(crate) fn change(mut self, change: ChangeMembers<C>, retain: bool) -> Result<Self, ChangeMembershipError<C>> {
         tracing::debug!(change = debug(&change), "{}", func_name!());
 
-        let last = self.get_joint_config().last().unwrap().clone();
+        let last = self.get_joint_config().last().cloned().unwrap_or_default();
 
         let new_membership = match change {
             ChangeMembers::AddVoterIds(add_voter_ids) => {

openraft/src/quorum/coherent_impl.rs

@@ -69,7 +69,12 @@ where
         if self.is_coherent_with(&other) {
             Joint::from(vec![other])
         } else {
-            Joint::from(vec![self.children().last().unwrap().clone(), other])
+            let last = self.children().last();
+            if let Some(last) = last {
+                Joint::from(vec![last.clone(), other])
+            } else {
+                Joint::from(vec![other])
+            }
         }
     }
 }

tests/tests/membership/main.rs

@@ -19,6 +19,7 @@ mod t31_add_remove_follower;
 mod t31_remove_leader;
 mod t31_removed_follower;
 mod t51_remove_unreachable_follower;
+mod t52_change_membership_on_uninitialized_node;
 mod t99_issue_471_adding_learner_uses_uninit_leader_id;
 mod t99_issue_584_replication_state_reverted;
 mod t99_new_leader_auto_commit_uniform_config;

tests/tests/membership/t52_change_membership_on_uninitialized_node.rs

@@ -0,0 +1,37 @@
+use std::sync::Arc;
+
+use anyhow::Result;
+use maplit::btreemap;
+use openraft::ChangeMembers;
+use openraft::Config;
+
+use crate::fixtures::ut_harness;
+use crate::fixtures::RaftRouter;
+
+/// Call `Raft::change_membership()` on an uninitialized node should not panic due to empty
+/// membership.
+#[tracing::instrument]
+#[test_harness::test(harness = ut_harness)]
+async fn change_membership_on_uninitialized_node() -> Result<()> {
+    let config = Arc::new(
+        Config {
+            enable_heartbeat: false,
+            ..Default::default()
+        }
+        .validate()?,
+    );
+
+    let mut router = RaftRouter::new(config.clone());
+    router.new_raft_node(0).await;
+
+    let n0 = router.get_raft_handle(&0)?;
+    let res = n0.change_membership(ChangeMembers::AddVoters(btreemap! {0=>()}), false).await;
+    tracing::info!("{:?}", res);
+
+    let err = res.unwrap_err();
+    tracing::info!("{}", err);
+
+    assert!(err.to_string().contains("forward request to"));
+
+    Ok(())
+}