From 7cfd32bac198758caf32ce649176a1b7156422fd Mon Sep 17 00:00:00 2001
From: Yuya Nishihara <yuya@tcha.org>
Date: Mon, 8 Jan 2024 11:59:08 +0900
Subject: [PATCH] cli: disallow gc run from non-head operation

It doesn't make sense to do gc from a non-head operation because that means
either the head operation would be corrupted or the --at-op argument is
ignored.
---
 cli/src/commands/util.rs       |  5 +++++
 cli/tests/test_util_command.rs | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/cli/src/commands/util.rs b/cli/src/commands/util.rs
index 43d68ebc1..357ed28ed 100644
--- a/cli/src/commands/util.rs
+++ b/cli/src/commands/util.rs
@@ -108,6 +108,11 @@ fn cmd_util_gc(
     command: &CommandHelper,
     _args: &UtilGcArgs,
 ) -> Result<(), CommandError> {
+    if command.global_args().at_operation != "@" {
+        return Err(user_error(
+            "Cannot garbage collect from a non-head operation",
+        ));
+    }
     let workspace_command = command.workspace_helper(ui)?;
     let store = workspace_command.repo().store();
     store.gc().map_err(|err| user_error(err.to_string()))?;
diff --git a/cli/tests/test_util_command.rs b/cli/tests/test_util_command.rs
index ad57aa1dd..1509e57f7 100644
--- a/cli/tests/test_util_command.rs
+++ b/cli/tests/test_util_command.rs
@@ -37,3 +37,22 @@ fn test_util_config_schema() {
         "###)
     });
 }
+
+#[test]
+fn test_gc_args() {
+    let test_env = TestEnvironment::default();
+    // Use the local backend because GitBackend::gc() depends on the git CLI.
+    test_env.jj_cmd_ok(
+        test_env.env_root(),
+        &["init", "repo", "--config-toml=ui.allow-init-native=true"],
+    );
+    let repo_path = test_env.env_root().join("repo");
+
+    let (_stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["util", "gc"]);
+    insta::assert_snapshot!(stderr, @"");
+
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["util", "gc", "--at-op=@-"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Error: Cannot garbage collect from a non-head operation
+    "###);
+}