revset: allow checking out git-tracking (@git) branches

CHANGELOG.md

@@ -102,8 +102,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   setting the `revsets.short-prefixes` config to a different revset.
 
 * The last seen state of branches in the underlying git repo is now presented by
-  `jj branch list` as a remote called `git` (e.g. `main@git`). Such branches
+  `jj branch list` as a remote called `git` (e.g. `main@git`). They can also be
-  exist in colocated repos or if you use `jj git export`.
+  referenced in revsets. Such branches exist in colocated repos or if you use
+  `jj git export`.
 
 ### Fixed bugs
 

lib/src/git.rs

@@ -70,6 +70,10 @@ pub fn git_tracking_branches(view: &View) -> impl Iterator<Item = (&str, &RefTar
     })
 }
 
+pub fn get_git_tracking_branch<'a>(view: &'a View, branch: &str) -> Option<&'a RefTarget> {
+    view.git_refs().get(&local_branch_name_to_ref_name(branch))
+}
+
 fn prevent_gc(git_repo: &git2::Repository, id: &CommitId) -> Result<(), git2::Error> {
     // If multiple processes do git::import_refs() in parallel, this can fail to
     // acquire a lock file even with force=true.

lib/src/revset.rs

@@ -31,6 +31,7 @@ use thiserror::Error;
 
 use crate::backend::{BackendError, BackendResult, ChangeId, CommitId, ObjectId};
 use crate::commit::Commit;
+use crate::git::get_git_tracking_branch;
 use crate::hex_util::to_forward_hex;
 use crate::index::{HexPrefix, PrefixResolution};
 use crate::op_store::WorkspaceId;
@@ -1640,6 +1641,12 @@ fn resolve_branch(repo: &dyn Repo, symbol: &str) -> Option<Vec<CommitId>> {
                 return Some(target.adds());
             }
         }
+        // A remote with name "git" will shadow local-git tracking branches
+        if remote_name == "git" {
+            if let Some(target) = get_git_tracking_branch(repo.view(), name) {
+                return Some(target.adds());
+            }
+        }
     }
     None
 }

tests/test_git_import_export.rs

@@ -20,6 +20,53 @@ use crate::common::{get_stderr_string, TestEnvironment};
 
 pub mod common;
 
+#[test]
+fn test_resolution_of_git_tracking_branches() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "main"]);
+    test_env.jj_cmd_success(&repo_path, &["describe", "-r", "main", "-m", "old_message"]);
+
+    // Create local-git tracking branch
+    let stdout = test_env.jj_cmd_success(&repo_path, &["git", "export"]);
+    insta::assert_snapshot!(stdout, @"");
+    // Move the local branch somewhere else
+    test_env.jj_cmd_success(&repo_path, &["describe", "-r", "main", "-m", "new_message"]);
+    insta::assert_snapshot!(get_branch_output(&test_env, &repo_path), @r###"
+    main: 3af370264cdc new_message
+      @git (ahead by 1 commits, behind by 1 commits): 16d541ca40f4 old_message
+    "###);
+
+    // Test that we can address both revisions
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "-r=main",
+            "-T",
+            r#"commit_id ++ " " ++ description"#,
+            "--no-graph",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    3af370264cdcbba791762f8ef6bc79b456dcbf3b new_message
+    "###);
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "-r=main@git",
+            "-T",
+            r#"commit_id ++ " " ++ description"#,
+            "--no-graph",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    16d541ca40f42baf2dea41aa61a0b5f1cbf1f91b old_message
+    "###);
+}
+
 #[test]
 fn test_git_export_conflicting_git_refs() {
     let test_env = TestEnvironment::default();