git: preserve HEAD when possible

Closes: jj-vcs#2210
isinyaaa · Oct 30, 2023 · 07ccfca · 07ccfca
1 parent 19a658e
commit 07ccfca
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Showing 2 changed files with 32 additions and 2 deletions.
diff --git a/cli/tests/test_git_colocated.rs b/cli/tests/test_git_colocated.rs
@@ -410,6 +410,32 @@ fn test_git_colocated_conflicting_git_refs() {
     "###);
 }
 
+#[test]
+fn test_git_colocated_checkout_non_empty_working_copy() {
+    let test_env = TestEnvironment::default();
+    let workspace_root = test_env.env_root().join("repo");
+    git2::Repository::init(&workspace_root).unwrap();
+    test_env.jj_cmd_ok(&workspace_root, &["init", "--git-repo", "."]);
+    test_env.jj_cmd_ok(&workspace_root, &["new", "-m", "foo"]);
+
+    std::fs::write(workspace_root.join("one"), "x").unwrap();
+
+    test_env.jj_cmd_ok(&workspace_root, &["co", "@-"]);
+    let (_, stderr) = test_env.jj_cmd_ok(&workspace_root, &["describe", "-m", "bar"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Working copy now at: kkmpptxz c3a22cf1 (empty) bar
+    Parent commit      : qpvuntsm 230dd059 (empty) (no description set)
+    "###);
+
+    insta::assert_snapshot!(get_log_output(&test_env, &workspace_root), @r###"
+    @  c3a22cf1b56281238683d897419c0f09f10331e2 bar
+    │ ◉  96d5d16db6ff3cf2bcb066137c2490090eb9f88b foo
+    ├─╯
+    ◉  230dd059e1b059aefc0da06a2e5a7dbf22362f22 HEAD@git
+    ◉  0000000000000000000000000000000000000000
+    "###);
+}
+
 #[test]
 fn test_git_colocated_fetch_deleted_or_moved_branch() {
     let test_env = TestEnvironment::default();

diff --git a/lib/src/git.rs b/lib/src/git.rs
@@ -809,11 +809,15 @@ pub fn reset_head(
 ) -> Result<(), git2::Error> {
     let first_parent_id = &wc_commit.parent_ids()[0];
     if first_parent_id != mut_repo.store().root_commit_id() {
+        let first_parent = RefTarget::normal(first_parent_id.clone());
+        let git_head = mut_repo.view().git_head();
         let new_git_commit_id = Oid::from_bytes(first_parent_id.as_bytes()).unwrap();
         let new_git_commit = git_repo.find_commit(new_git_commit_id)?;
-        git_repo.set_head_detached(new_git_commit_id)?;
+        if git_head != &first_parent {
+            git_repo.set_head_detached(new_git_commit_id)?;
+            mut_repo.set_git_head_target(first_parent);
+        }
         git_repo.reset(new_git_commit.as_object(), git2::ResetType::Mixed, None)?;
-        mut_repo.set_git_head_target(RefTarget::normal(first_parent_id.clone()));
     } else {
         // Can't detach HEAD without a commit. Use placeholder ref to nullify the HEAD.
         // We can't set_head() an arbitrary unborn ref, so use reference_symbolic()