rebase: delegate automatic stashing to Git

Git --autostash predates repo's minimum supported client. Pass it
directly to rebase instead of probing the index and separately running
stash and stash pop, reducing the dirty path from four Git processes to
one and correctly covering staged-only changes.

Bug: 553599402
Change-Id: I0d6d59b17996576310498e9378e49380d355236e
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/623902
Tested-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Brian Gan <brgan@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

subcmds/rebase.py

@@ -139,6 +139,8 @@ branch but need to incorporate new upstream changes "underneath" them.
             common_args.append("--autosquash")
         if opt.interactive:
             common_args.append("-i")
+        if opt.auto_stash:
+            common_args.append("--autostash")
 
         config = self.manifest.manifestProject.config
         out = RebaseColoring(config)
@@ -188,29 +190,10 @@ branch but need to incorporate new upstream changes "underneath" them.
             out.nl()
             out.flush()
 
-            needs_stash = False
-            if opt.auto_stash:
-                stash_args = ["update-index", "--refresh", "-q"]
-
-                if GitCommand(project, stash_args).Wait() != 0:
-                    needs_stash = True
-                    # Dirty index, requires stash...
-                    stash_args = ["stash"]
-
-                    if GitCommand(project, stash_args).Wait() != 0:
-                        ret += 1
-                        continue
-
             if GitCommand(project, args).Wait() != 0:
                 ret += 1
                 continue
 
-            if needs_stash:
-                stash_args.append("pop")
-                stash_args.append("--quiet")
-                if GitCommand(project, stash_args).Wait() != 0:
-                    ret += 1
-
         if ret:
             msg_fmt = "%d projects had errors"
             self.git_event_log.ErrorEvent(msg_fmt % (ret), msg_fmt)

tests/test_subcmds_rebase.py

@@ -14,6 +14,9 @@
 
 """Unittests for the subcmds/rebase.py module."""
 
+import contextlib
+import io
+from types import SimpleNamespace
 from unittest import mock
 
 from error import GitError
@@ -48,3 +51,41 @@ def test_resolve_onto_manifest_fallback() -> None:
     assert res == "main"
     project.GetRemote.assert_called_once()
     remote.ToLocal.assert_called_once_with("main")
+
+
+def test_execute_delegates_autostash_to_rebase() -> None:
+    """--auto-stash is one rebase process, including staged-only changes."""
+    cmd = rebase.Rebase()
+    cmd.manifest = mock.MagicMock()
+    cmd.git_event_log = mock.MagicMock()
+    project = mock.MagicMock()
+    project.CurrentBranch = "topic"
+    project.RelPath.return_value = "project"
+    branch = mock.MagicMock()
+    branch.LocalMerge = "refs/remotes/origin/main"
+    project.GetBranch.return_value = branch
+    cmd.GetProjects = mock.MagicMock(return_value=[project])
+    opt = SimpleNamespace(
+        interactive=False,
+        fail_fast=False,
+        whitespace=None,
+        quiet=False,
+        force_rebase=False,
+        ff=True,
+        autosquash=False,
+        auto_stash=True,
+        onto_manifest=False,
+        this_manifest_only=False,
+    )
+    git_command = mock.MagicMock()
+    git_command.Wait.return_value = 0
+
+    with mock.patch.object(
+        rebase, "GitCommand", return_value=git_command
+    ) as run_git, contextlib.redirect_stdout(io.StringIO()):
+        assert cmd.Execute(opt, []) == 0
+
+    run_git.assert_called_once_with(
+        project,
+        ["rebase", "--autostash", "refs/remotes/origin/main"],
+    )