Mention --multi in hint when one revset resolves to multiple revisions

src/cli_util.rs

@@ -1398,7 +1398,9 @@ pub fn resolve_base_revs(
         }
     } else {
         for revision_str in revisions {
-            let commit = workspace_command.resolve_single_rev(revision_str)?;
+            let commit = workspace_command
+                .resolve_single_rev(revision_str)
+                .map_err(add_multi_message_to_hint_if_mutliple_revisions)?;
             let commit_hash = short_commit_hash(commit.id());
             if !commits.insert(commit) {
                 return Err(user_error(format!(
@@ -1416,6 +1418,22 @@ pub fn resolve_base_revs(
     }
 }
 
+fn add_multi_message_to_hint_if_mutliple_revisions(err: CommandError) -> CommandError {
+    if let CommandError::UserError { message, hint } = err {
+        let hint = if message.contains("more than one revision") {
+            let hint = hint.map(|h| format!("{h}\n")).unwrap_or_default();
+            Some(format!(
+                "{hint}If this was intentional, specify the `--multi` argument"
+            ))
+        } else {
+            hint
+        };
+        CommandError::UserError { message, hint }
+    } else {
+        err
+    }
+}
+
 pub fn update_working_copy(
     ui: &mut Ui,
     repo: &Arc<ReadonlyRepo>,

tests/test_rebase_command.rs

@@ -320,6 +320,7 @@ fn test_rebase_multiple_destinations() {
     Hint: The revset "b|c" resolved to these revisions:
     fe2e8e8b50b3 c
     d370aee184ba b
+    If this was intentional, specify the `--multi` argument
     "###);
     let stdout =
         test_env.jj_cmd_success(&repo_path, &["rebase", "--multi", "-r", "a", "-d", "b|c"]);