upload: reuse the worker current-branch result

Carry the current branch through _GatherOne so the parent can report a
failed current-branch upload without resolving HEAD a second time.

Bug: 553599402
Change-Id: I3fc54be6c10c30470e14f792ff68c0a396519327
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/623905
Reviewed-by: Brian Gan <brgan@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>

subcmds/upload.py

@@ -721,13 +721,14 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
     def _GatherOne(cls, opt, project_idx):
         """Figure out the upload status for |project|."""
         project = cls.get_parallel_context()["projects"][project_idx]
+        cbr = None
         if opt.current_branch:
             cbr = project.CurrentBranch
             up_branch = project.GetUploadableBranch(cbr)
             avail = [up_branch] if up_branch else None
         else:
             avail = project.GetUploadableBranches(opt.branch)
-        return (project_idx, avail)
+        return (project_idx, avail, cbr)
 
     def Execute(self, opt, args):
         projects = self.GetProjects(
@@ -737,7 +738,7 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
         def _ProcessResults(_pool, _out, results):
             pending = []
             for result in results:
-                project_idx, avail = result
+                project_idx, avail, current_branch = result
                 project = projects[project_idx]
                 if avail is None:
                     logger.error(
@@ -745,7 +746,7 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
                         "You might be able to fix the branch by running:\n"
                         "  git branch --set-upstream-to m/%s",
                         project.RelPath(local=opt.this_manifest_only),
-                        project.CurrentBranch,
+                        current_branch,
                         project.manifest.branch,
                     )
                 elif avail:

tests/test_subcmds_upload.py

@@ -97,3 +97,23 @@ def test_GetMergeBranch_none_when_no_branch(cmd: upload.Upload) -> None:
 
     res = cmd._GetMergeBranch(mock_project, local_branch=None)
     assert res == ""
+
+
+def test_GatherOne_returns_resolved_current_branch(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Upload error reporting reuses the branch gathered by the worker."""
+    project = mock.MagicMock()
+    project.CurrentBranch = "topic"
+    branch = mock.sentinel.branch
+    project.GetUploadableBranch.return_value = branch
+    monkeypatch.setattr(
+        upload.Upload,
+        "get_parallel_context",
+        lambda: {"projects": [project]},
+    )
+    opt = mock.MagicMock(current_branch=True)
+
+    assert upload.Upload._GatherOne(opt, 0) == (0, [branch], "topic")
+
+    project.GetUploadableBranch.assert_called_once_with("topic")