git: Add CHERRY_PICK_HEAD to the list of merge heads (#26145)

Attempt to fix an issue where conflicts from a cherry-pick don't get
cleared out of the git panel after being resolved.

Release Notes:

- Git Beta: Fixed resolution of conflicts from cherry-picks not being
reflected in the git panel

crates/worktree/src/worktree_tests.rs

@@ -5,6 +5,7 @@ use crate::{
 use anyhow::Result;
 use fs::{FakeFs, Fs, RealFs, RemoveOptions};
 use git::{
+    repository::RepoPath,
     status::{
         FileStatus, GitSummary, StatusCode, TrackedStatus, TrackedSummary, UnmergedStatus,
         UnmergedStatusCode,
@@ -3307,6 +3308,87 @@ async fn test_propagate_statuses_for_nested_repos(cx: &mut TestAppContext) {
     );
 }
 
+#[gpui::test]
+async fn test_conflicted_cherry_pick(cx: &mut TestAppContext) {
+    init_test(cx);
+    cx.executor().allow_parking();
+
+    let root = TempTree::new(json!({
+        "project": {
+            "a.txt": "a",
+        },
+    }));
+    let root_path = root.path();
+
+    let tree = Worktree::local(
+        root_path,
+        true,
+        Arc::new(RealFs::default()),
+        Default::default(),
+        &mut cx.to_async(),
+    )
+    .await
+    .unwrap();
+
+    let repo = git_init(&root_path.join("project"));
+    git_add("a.txt", &repo);
+    git_commit("init", &repo);
+
+    cx.read(|cx| tree.read(cx).as_local().unwrap().scan_complete())
+        .await;
+
+    tree.flush_fs_events(cx).await;
+
+    git_branch("other-branch", &repo);
+    git_checkout("refs/heads/other-branch", &repo);
+    std::fs::write(root_path.join("project/a.txt"), "A").unwrap();
+    git_add("a.txt", &repo);
+    git_commit("capitalize", &repo);
+    let commit = repo
+        .head()
+        .expect("Failed to get HEAD")
+        .peel_to_commit()
+        .expect("HEAD is not a commit");
+    git_checkout("refs/heads/master", &repo);
+    std::fs::write(root_path.join("project/a.txt"), "b").unwrap();
+    git_add("a.txt", &repo);
+    git_commit("improve letter", &repo);
+    git_cherry_pick(&commit, &repo);
+    std::fs::read_to_string(root_path.join("project/.git/CHERRY_PICK_HEAD"))
+        .expect("No CHERRY_PICK_HEAD");
+    pretty_assertions::assert_eq!(
+        git_status(&repo),
+        collections::HashMap::from_iter([("a.txt".to_owned(), git2::Status::CONFLICTED)])
+    );
+    tree.flush_fs_events(cx).await;
+    let conflicts = tree.update(cx, |tree, _| {
+        let entry = tree.git_entries().nth(0).expect("No git entry").clone();
+        entry
+            .current_merge_conflicts
+            .iter()
+            .cloned()
+            .collect::<Vec<_>>()
+    });
+    pretty_assertions::assert_eq!(conflicts, [RepoPath::from("a.txt")]);
+
+    git_add("a.txt", &repo);
+    // Attempt to manually simulate what `git cherry-pick --continue` would do.
+    git_commit("whatevs", &repo);
+    std::fs::remove_file(root.path().join("project/.git/CHERRY_PICK_HEAD"))
+        .expect("Failed to remove CHERRY_PICK_HEAD");
+    pretty_assertions::assert_eq!(git_status(&repo), collections::HashMap::default());
+    tree.flush_fs_events(cx).await;
+    let conflicts = tree.update(cx, |tree, _| {
+        let entry = tree.git_entries().nth(0).expect("No git entry").clone();
+        entry
+            .current_merge_conflicts
+            .iter()
+            .cloned()
+            .collect::<Vec<_>>()
+    });
+    pretty_assertions::assert_eq!(conflicts, []);
+}
+
 #[gpui::test]
 async fn test_private_single_file_worktree(cx: &mut TestAppContext) {
     init_test(cx);
@@ -3405,6 +3487,11 @@ fn git_commit(msg: &'static str, repo: &git2::Repository) {
     }
 }
 
+#[track_caller]
+fn git_cherry_pick(commit: &git2::Commit<'_>, repo: &git2::Repository) {
+    repo.cherrypick(commit, None).expect("Failed to cherrypick");
+}
+
 #[track_caller]
 fn git_stash(repo: &mut git2::Repository) {
     use git2::Signature;
@@ -3430,6 +3517,22 @@ fn git_reset(offset: usize, repo: &git2::Repository) {
         .expect("Could not reset");
 }
 
+#[track_caller]
+fn git_branch(name: &str, repo: &git2::Repository) {
+    let head = repo
+        .head()
+        .expect("Couldn't get repo head")
+        .peel_to_commit()
+        .expect("HEAD is not a commit");
+    repo.branch(name, &head, false).expect("Failed to commit");
+}
+
+#[track_caller]
+fn git_checkout(name: &str, repo: &git2::Repository) {
+    repo.set_head(name).expect("Failed to set head");
+    repo.checkout_head(None).expect("Failed to check out head");
+}
+
 #[allow(dead_code)]
 #[track_caller]
 fn git_status(repo: &git2::Repository) -> collections::HashMap<String, git2::Status> {