From 5f262198d22b71750c7bb83b32f91d21e54d0e63 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=BC=A0=E7=82=8E=E6=B3=BC?= <drdr.xp@gmail.com>
Date: Fri, 17 Nov 2023 12:37:40 +0800
Subject: [PATCH] Fix: avoid panic with "loosen-follower-log-revert" enabled

Problem:

When "loosen-follower-log-revert" enabled, and a follower log gets
reverted, e.g., all raft-logs are removed from that follower, the leader
encounters a panic due to a `debug_assert()`.

Solution:

- Disable the assertion when this feature is enabled.

- The test `feature_loosen_follower_log_revert` is also revised to reveal this
  bug.
---
 openraft/src/replication/mod.rs                 | 17 ++++++++++++++++-
 .../t60_feature_loosen_follower_log_revert.rs   |  2 ++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/openraft/src/replication/mod.rs b/openraft/src/replication/mod.rs
index 7e4fc651a..c020f65cf 100644
--- a/openraft/src/replication/mod.rs
+++ b/openraft/src/replication/mod.rs
@@ -466,7 +466,22 @@ where
             func_name!()
         );
 
-        debug_assert!(self.matching <= new_matching);
+        if cfg!(feature = "loosen-follower-log-revert") {
+            if self.matching > new_matching {
+                tracing::warn!(
+                "follower log is reverted from {} to {}; with 'loosen-follower-log-revert' enabled, this is allowed",
+                self.matching.display(),
+                new_matching.display(),
+            );
+            }
+        } else {
+            debug_assert!(
+                self.matching <= new_matching,
+                "follower log is reverted from {} to {}",
+                self.matching.display(),
+                new_matching.display(),
+            );
+        }
 
         self.matching = new_matching;
 
diff --git a/tests/tests/replication/t60_feature_loosen_follower_log_revert.rs b/tests/tests/replication/t60_feature_loosen_follower_log_revert.rs
index e5d7e01ff..ab1f8f110 100644
--- a/tests/tests/replication/t60_feature_loosen_follower_log_revert.rs
+++ b/tests/tests/replication/t60_feature_loosen_follower_log_revert.rs
@@ -17,6 +17,8 @@ async fn feature_loosen_follower_log_revert() -> Result<()> {
         Config {
             enable_tick: false,
             enable_heartbeat: false,
+            // Make sure the replication is done in more than one steps
+            max_payload_entries: 1,
             ..Default::default()
         }
         .validate()?,