info: Report actual checked-out HEAD revision

When `repo info` runs, the reported "Current revision" is resolved using
the manifest's target branch tracking ref (e.g. refs/remotes/goog/main).

Introduce Project.GetHeadRevisionId(), which gets the checked-out HEAD
commit in the worktree, and use it in `repo info` with a fallback to the
old behavior if the project is not checked out.

Bug: 526685287
Change-Id: I72280ce27daa210cada27d722a94e365644f06e0
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/599481
Reviewed-by: Brian Gan <brgan@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>

tests/test_project.py

@@ -104,6 +104,28 @@ class ProjectTests(unittest.TestCase):
             "abcd00%21%21_%2b",
         )
 
+    def test_get_head_revision_id(self):
+        """Check GetHeadRevisionId behavior."""
+        with utils_for_test.TempGitTree() as tempdir:
+            proj = _create_mock_project(tempdir)
+
+            # Initially unborn HEAD should return None.
+            self.assertIsNone(proj.GetHeadRevisionId())
+
+            # Create a commit.
+            with open(os.path.join(tempdir, "readme"), "w") as fp:
+                fp.write("hello")
+            proj.work_git.add("readme")
+            proj.work_git.commit("-m", "initial commit")
+
+            # HEAD should resolve to the commit SHA.
+            commit_sha = proj.work_git.rev_parse("HEAD")
+            self.assertEqual(commit_sha, proj.GetHeadRevisionId())
+
+            # Even if worktree is detached.
+            proj.work_git.checkout("HEAD~0")
+            self.assertEqual(commit_sha, proj.GetHeadRevisionId())
+
     @unittest.skipUnless(
         utils_for_test.supports_reftable(),
         "git reftable support is required for this test",

tests/test_subcmds_info.py

@@ -199,3 +199,27 @@ def test_text_enables_pager() -> None:
     cmd = _get_cmd()
     opts, _ = cmd.OptionParser.parse_args([])
     assert cmd.WantPager(opts)
+
+
+def test_get_project_data_uses_head_revision() -> None:
+    """_getProjectData should use GetHeadRevisionId if available."""
+    cmd = _get_cmd()
+    project = mock.MagicMock()
+    project.name = "foo"
+    project.worktree = "/path/to/foo"
+    project.revisionExpr = "refs/heads/main"
+    project.GetBranches.return_value = []
+
+    # GetHeadRevisionId() returns a SHA, it should be used.
+    project.GetHeadRevisionId.return_value = "head_sha_12345"
+    project.GetRevisionId.return_value = "manifest_sha_54321"
+
+    data = cmd._getProjectData(project)
+    assert data["current_revision"] == "head_sha_12345"
+    project.GetHeadRevisionId.assert_called_once()
+
+    # GetHeadRevisionId() is None, fall back to GetRevisionId().
+    project.GetHeadRevisionId.reset_mock()
+    project.GetHeadRevisionId.return_value = None
+    data = cmd._getProjectData(project)
+    assert data["current_revision"] == "manifest_sha_54321"