From c5aab9fe29aa8ad6eed7691f0fef032933b15beb Mon Sep 17 00:00:00 2001
From: Yuya Nishihara <yuya@tcha.org>
Date: Wed, 31 Aug 2022 17:56:37 +0900
Subject: [PATCH] cli: fix crash on "jj merge whatever root"

---
 src/commands.rs           | 7 +++++++
 tests/test_new_command.rs | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/src/commands.rs b/src/commands.rs
index 200d4da00..f3d950907 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -3495,6 +3495,13 @@ fn cmd_new(ui: &mut Ui, command: &CommandHelper, args: &NewArgs) -> Result<(), C
         parent_ids.push(commit.id().clone());
         commits.push(commit);
     }
+    if parent_ids.len() >= 2
+        && parent_ids.contains(workspace_command.repo().store().root_commit_id())
+    {
+        return Err(CommandError::UserError(
+            "Cannot merge with root revision".to_owned(),
+        ));
+    }
     let mut tx = workspace_command.start_transaction("new empty commit");
     let merged_tree = merge_commit_trees(workspace_command.repo().as_repo_ref(), &commits);
     let new_commit = CommitBuilder::for_new_commit(ui.settings(), merged_tree.id().clone())
diff --git a/tests/test_new_command.rs b/tests/test_new_command.rs
index 9e680e7ad..4b19e488c 100644
--- a/tests/test_new_command.rs
+++ b/tests/test_new_command.rs
@@ -92,6 +92,9 @@ fn test_new_merge() {
     insta::assert_snapshot!(stderr, @r###"
     Error: Revset "@" and "c34d" resolved to the same revision c34d60aa3322
     "###);
+
+    // merge with root
+    test_env.jj_cmd_failure(&repo_path, &["new", "@", "root"]);
 }
 
 fn get_log_output(test_env: &TestEnvironment, repo_path: &Path) -> String {