cli: reorder import of git head/refs and snapshot

Since import_git_refs() may check out new working-copy commit, it shouldn't be
triggered before the snapshot.

Fixes #2876

CHANGELOG.md

@@ -42,6 +42,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Fixed snapshots of symlinks in `gitignore`-d directory.
   [#2878](https://github.com/martinvonz/jj/issues/2878)
 
+* Fixed data loss in dirty working copy when checked-out branch is rebased or
+  abandoned by Git.
+  [#2876](https://github.com/martinvonz/jj/issues/2876)
+
 
 ## [0.13.0] - 2024-01-03
 

cli/src/cli_util.rs

@@ -813,9 +813,16 @@ impl WorkspaceCommandHelper {
         if self.may_update_working_copy {
             if self.working_copy_shared_with_git {
                 self.import_git_head(ui)?;
+            }
+            // Because the Git refs (except HEAD) aren't imported yet, the ref
+            // pointing to the new working-copy commit might not be exported.
+            // In that situation, the ref would be conflicted anyway, so export
+            // failure is okay.
+            self.snapshot_working_copy(ui)?;
+            // import_git_refs() can rebase the working-copy commit.
+            if self.working_copy_shared_with_git {
                 self.import_git_refs(ui)?;
             }
-            self.snapshot_working_copy(ui)?;
         }
         Ok(())
     }

cli/tests/test_git_colocated.rs

@@ -520,6 +520,54 @@ fn test_git_colocated_fetch_deleted_or_moved_branch() {
     "###);
 }
 
+#[test]
+fn test_git_colocated_rebase_dirty_working_copy() {
+    let test_env = TestEnvironment::default();
+    let repo_path = test_env.env_root().join("repo");
+    let git_repo = git2::Repository::init(&repo_path).unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["init", "--git-repo=."]);
+
+    std::fs::write(repo_path.join("file"), "base").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file"), "old").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "feature"]);
+
+    // Make the working-copy dirty, delete the checked out branch.
+    std::fs::write(repo_path.join("file"), "new").unwrap();
+    git_repo
+        .find_reference("refs/heads/feature")
+        .unwrap()
+        .delete()
+        .unwrap();
+
+    // Because the working copy is dirty, the new working-copy commit will be
+    // diverged. Therefore, the feature branch has change-delete conflict.
+    let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["status"]);
+    insta::assert_snapshot!(stdout, @r###"
+    Working copy changes:
+    M file
+    Working copy : rlvkpnrz d6c5e664 feature?? | (no description set)
+    Parent commit: qpvuntsm 5973d373 (no description set)
+    These branches have conflicts:
+      feature
+      Use `jj branch list` to see details. Use `jj branch set <name> -r <rev>` to resolve.
+    "###);
+    insta::assert_snapshot!(stderr, @r###"
+    Failed to export some branches:
+      feature: Modified ref had been deleted in Git
+    Done importing changes from the underlying Git repo.
+    "###);
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
+    @  d6c5e66473426f5ed3a24ecce8ce8b44ff23cf81 feature??
+    ◉  5973d3731aba9dd86c00b4a765fbc4cc13f1e14b HEAD@git
+    ◉  0000000000000000000000000000000000000000
+    "###);
+
+    // The working-copy content shouldn't be lost.
+    insta::assert_snapshot!(
+        std::fs::read_to_string(repo_path.join("file")).unwrap(), @"new");
+}
+
 #[test]
 fn test_git_colocated_external_checkout() {
     let test_env = TestEnvironment::default();