project: check upstream ref ancestry for non-shallow clones

In _CheckForImmutableRevision, commit d9cc0a15 restricted upstream ref
validation strictly to superprojects (if use_superproject) to prevent
shallow clones with an upstream attribute from failing ancestry checks
and falling back to full clones.

However, restricting this check exclusively to superprojects broke
non-shallow projects with pinned immutable revisions (such as in Smart
Sync, `repo sync -t <BUILD_ID>`, or pinned manifests): When the target
commit already exists in the local Git object store (for instance,
prefetched into refs/prefetch/ by a background daemon or via shared
object dirs), _CheckForImmutableRevision returned True without verifying
that the local tracking ref (refs/remotes/<remote>/<upstream>) is
present and reaches the revision. As a result, _RemoteFetch skipped
fetching the upstream branch, leaving the local tracking ref stale or
missing. Subsequent `repo start` branches tracking that remote branch
diverged, causing `repo upload` to attempt uploading all intermediate
commits between the stale tracking ref and HEAD.

Restore upstream ancestry validation in _CheckForImmutableRevision for
non-shallow projects when upstream is specified. Also pass the sync
depth into _CheckForImmutableRevision call sites so shallow checkouts
continue to skip upstream verification and avoid triggering un-shallow
fallbacks.

Test: PYTHONPATH=. pytest tests/test_project.py
Change-Id: Ib5bdf41810bb06c8ed053447209ddc2e488f3913
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/624361
Tested-by: Rahul Yadav <yadavrah@google.com>
Commit-Queue: Rahul Yadav <yadavrah@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

completion.zsh

@@ -400,6 +400,7 @@ _repo() {
         '--no-verify[Do not verify]' \
         '--verify[Verify]' \
         '--ignore-hooks[Ignore hooks]' \
+        '--fix[Automatically fix]' \
         '*: :->project'
       ;;
     version)

docs/repo-hooks.md

@@ -88,7 +88,14 @@ be useful when deploying automatic fixes.
 If the repo command that triggered the hook supports a "yes" option (e.g.,
 `repo upload --yes`), this option is propagated to the hook's `main` function
 as `yes` parameter (defaulting to `False`).  Hooks can use this to bypass
-interactive confirmation prompts when they can automatically fix issues.
+interactive confirmation prompts for safe non-modifying operations.
+
+### Automated Fixes
+
+If the repo command that triggered the hook supports a "fix" option (e.g.,
+`repo upload --fix`), this option is propagated to the hook's `main` function
+as `fix` parameter (defaulting to `False`).  Hooks can use this to automatically
+apply fixes without prompting the user.
 
 ### Shebang Handling
 
@@ -126,7 +133,7 @@ This hook runs when people run `repo upload`.
 The `pre-upload.py` file should be defined like:
 
 ```py
-def main(project_list, worktree_list=None, yes=False, **kwargs):
+def main(project_list, worktree_list=None, fix=False, yes=False, **kwargs):
     """Main function invoked directly by repo.
 
     We must use the name "main" as that is what repo requires.
@@ -137,6 +144,7 @@ def main(project_list, worktree_list=None, yes=False, **kwargs):
           project_list, so that each entry in project_list matches with a
           directory in worktree_list.  If None, we will attempt to calculate
           the directories automatically.
+      fix: Whether to automatically apply fixes without prompting.
       yes: Whether to answer yes to all safe prompts (see
           [Safe Prompts](#safe-prompts)).
       kwargs: Leave this here for forward-compatibility.

git_command.py

@@ -70,6 +70,19 @@ class _GitCall:
 git = _GitCall()
 
 
+def IsValidBranchName(name: str) -> bool:
+    """Return whether |name| is valid where Git expects a branch name."""
+    p = GitCommand(
+        None,
+        ["check-ref-format", "--branch", name],
+        capture_stdout=True,
+        capture_stderr=True,
+        add_event_log=False,
+        log_as_error=False,
+    )
+    return p.Wait() == 0
+
+
 def RepoSourceVersion():
     """Return the version of the repo.git tree."""
     ver = getattr(RepoSourceVersion, "version", None)

git_config.py

@@ -40,7 +40,7 @@ from repo_trace import Trace
 # that is saved in the config.
 SYNC_STATE_PREFIX = "repo.syncstate."
 
-ID_RE = re.compile(r"^[0-9a-f]{40,64}$")
+ID_RE = re.compile(r"^(?:[0-9a-f]{40}|[0-9a-f]{64})$")
 
 REVIEW_CACHE = {}
 

git_refs.py

@@ -14,6 +14,7 @@
 
 import os
 
+from git_command import git_require
 from git_command import GitCommand
 import platform_utils
 from repo_trace import Trace
@@ -41,6 +42,17 @@ class GitRefs:
         self._EnsureLoaded()
         return self._phyref
 
+    @property
+    def head(self) -> str:
+        """Return HEAD's symbolic target or detached object ID."""
+        self._EnsureLoaded()
+        return self._symref.get(HEAD) or self._phyref.get(HEAD, "")
+
+    @property
+    def is_loaded(self) -> bool:
+        """Whether a ref snapshot has already been loaded."""
+        return self._phyref is not None
+
     def get(self, name):
         try:
             return self.all[name]
@@ -87,8 +99,12 @@ class GitRefs:
             self._symref = {}
             self._mtime = {}
 
-            self._ReadRefs()
+            root_refs_loaded = self._ReadRefs()
-            self._ReadSymbolicRef(HEAD)
+            if not root_refs_loaded or (
+                HEAD not in self._phyref and HEAD not in self._symref
+            ):
+                # --include-root-refs does not report an unborn HEAD.
+                self._ReadSymbolicRef(HEAD)
 
             scan = self._symref
             attempts = 0
@@ -113,18 +129,32 @@ class GitRefs:
         """Check if a ref_id is a null object ID."""
         return ref_id and all(ch == "0" for ch in ref_id)
 
-    def _ReadRefs(self) -> None:
+    def _ReadRefs(self) -> bool:
-        """Read all references using git for-each-ref."""
+        """Read all references using git for-each-ref.
+
+        Returns:
+            Whether root refs, including HEAD when it exists, were loaded.
+        """
+        include_root_refs = git_require((2, 45, 0))
+        cmd = [
+            "for-each-ref",
+            "--format=%(objectname)%00%(refname)%00%(symref)",
+        ]
+        if include_root_refs:
+            cmd.insert(1, "--include-root-refs")
+            # Avoid caching volatile root refs such as ORIG_HEAD.  HEAD and
+            # refs/* are the only namespaces GitRefs exposes to callers.
+            cmd.extend([HEAD, "refs"])
         p = GitCommand(
             None,
-            ["for-each-ref", "--format=%(objectname)%00%(refname)%00%(symref)"],
+            cmd,
             capture_stdout=True,
             capture_stderr=True,
             bare=True,
             gitdir=self._gitdir,
         )
         if p.Wait() != 0:
-            return
+            return False
 
         for line in p.stdout.splitlines():
             ref_id, name, symref = line.split("\0")
@@ -132,6 +162,7 @@ class GitRefs:
                 self._symref[name] = symref
             elif ref_id and not self._IsNullRef(ref_id):
                 self._phyref[name] = ref_id
+        return include_root_refs
 
     def _ReadSymbolicRef(self, name: str) -> None:
         """Read a symbolic reference."""

git_superproject.py

@@ -36,7 +36,6 @@ from git_command import git_require
 from git_command import GitCommand
 from git_config import IsId
 from git_config import RepoConfig
-from git_refs import GitRefs
 import platform_utils
 
 
@@ -189,7 +188,7 @@ class Superproject:
             if netloc:
                 parts = netloc.split("-review", 1)
                 host = parts[0]
-                rev = GitRefs(self._work_git).get("HEAD")
+                rev = self._GetRef("HEAD")
                 return f"{host}/{self.name}@{rev}"
         return None
 
@@ -314,7 +313,10 @@ class Superproject:
         # We use --negotiation-tip to speed up the fetch. Superproject branches
         # do not share commits. So this lets git know it only needs to send
         # commits reachable from the specified local refs.
-        rev_commit = GitRefs(self._work_git).get(f"refs/heads/{self.revision}")
+        negotiation_ref = self.revision
+        if negotiation_ref and not negotiation_ref.startswith("refs/"):
+            negotiation_ref = f"refs/heads/{negotiation_ref}"
+        rev_commit = self._GetRef(negotiation_ref) if negotiation_ref else ""
         if rev_commit:
             cmd.extend(["--negotiation-tip", rev_commit])
 
@@ -347,6 +349,21 @@ class Superproject:
             return False
         return True
 
+    def _GetRef(self, ref: str) -> str:
+        """Resolve one local ref without loading the entire ref namespace."""
+        p = GitCommand(
+            None,
+            ["rev-parse", "--verify", "--quiet", ref],
+            gitdir=self._work_git,
+            bare=True,
+            capture_stdout=True,
+            capture_stderr=True,
+            log_as_error=False,
+        )
+        if p.Wait() == 0:
+            return p.stdout.strip()
+        return ""
+
     def _LsTree(self):
         """Gets the commit ids for all projects.
 

hooks.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import optparse
 import os
 import re
 import sys
@@ -69,6 +70,7 @@ class RepoHook:
         ignore_hooks=False,
         abort_if_user_denies=False,
         yes=False,
+        fix=False,
     ):
         """RepoHook constructor.
 
@@ -91,6 +93,7 @@ class RepoHook:
             abort_if_user_denies: If True, we'll abort running the hook if the
                 user doesn't allow us to run the hook.
             yes: If True, then 'Yes' is assumed for any prompts.
+            fix: If True, then 'Fix' is assumed for any fixup prompts.
         """
         self._hook_type = hook_type
         self._hooks_project = hooks_project
@@ -102,6 +105,7 @@ class RepoHook:
         self._ignore_hooks = ignore_hooks
         self._abort_if_user_denies = abort_if_user_denies
         self._yes = yes
+        self._fix = fix
 
         # Store the full path to the script for convenience.
         self._script_fullpath = None
@@ -380,6 +384,7 @@ class RepoHook:
             kwargs = {
                 **kwargs,
                 "hook_should_take_kwargs": True,
+                "fix": self._fix,
                 "yes": self._yes,
             }
 
@@ -504,12 +509,17 @@ class RepoHook:
                 ).url,
                 "bug_url": manifest.contactinfo.bugurl,
                 "yes": getattr(opt, "yes", False),
+                "fix": getattr(opt, "fix", False),
             }
         )
         return cls(*args, **kwargs)
 
     @staticmethod
-    def AddOptionGroup(parser, name):
+    def AddOptionGroup(
+        parser: optparse.OptionParser,
+        name: str,
+        allow_fix: bool = False,
+    ) -> None:
         """Help options relating to the various hooks."""
 
         # Note that verify and no-verify are NOT opposites of each other, which
@@ -533,3 +543,10 @@ class RepoHook:
             action="store_true",
             help="Do not abort if %s hooks fail." % name,
         )
+        if allow_fix:
+            group.add_option(
+                "--fix",
+                action="store_true",
+                default=False,
+                help="Automatically apply %s fixes without prompting." % name,
+            )

man/repo-upload.1

@@ -1,5 +1,5 @@
 .\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
-.TH REPO "1" "June 2026" "repo upload" "Repo Manual"
+.TH REPO "1" "August 2026" "repo upload" "Repo Manual"
 .SH NAME
 repo \- repo upload - manual page for repo upload
 .SH SYNOPSIS
@@ -112,6 +112,9 @@ Run the pre\-upload hook without prompting.
 .TP
 \fB\-\-ignore\-hooks\fR
 Do not abort if pre\-upload hooks fail.
+.TP
+\fB\-\-fix\fR
+Automatically apply pre\-upload fixes without prompting.
 .PP
 Run `repo help upload` to view the detailed manual.
 .SH DETAILS

manifest_xml.py

@@ -692,9 +692,9 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
                 e.setAttribute("remote", remoteName)
             if peg_rev:
                 if self.IsMirror:
-                    value = p.bare_git.rev_parse(p.revisionExpr + "^0")
+                    value = p.bare_git.ResolveCommit(p.revisionExpr)
                 else:
-                    value = p.work_git.rev_parse(HEAD + "^0")
+                    value = p.work_git.ResolveCommit(HEAD)
                 e.setAttribute("revision", value)
                 if peg_rev_upstream:
                     if p.upstream:

project.py

@@ -195,6 +195,10 @@ class ReviewableBranch:
     def name(self):
         return self.branch.name
 
+    @property
+    def current(self) -> bool:
+        return getattr(self.branch, "current", False)
+
     @property
     def commits(self):
         if self._commit_cache is None:
@@ -239,6 +243,12 @@ class ReviewableBranch:
             "--pretty=format:%cd", "-n", "1", R_HEADS + self.name, "--"
         )
 
+    @property
+    def modified_files(self) -> List[str]:
+        return self.project.bare_git.diff(
+            "--name-only", f"{self.base}...{R_HEADS}{self.name}"
+        ).splitlines()
+
     @property
     def base_exists(self):
         """Whether the branch we're tracking exists.
@@ -271,7 +281,8 @@ class ReviewableBranch:
         validate_certs=True,
         push_options=None,
         patchset_description=None,
-    ):
+        git_event_log: Optional[EventLog] = None,
+    ) -> None:
         self.project.UploadForReview(
             branch=self.name,
             people=people,
@@ -287,6 +298,7 @@ class ReviewableBranch:
             validate_certs=validate_certs,
             push_options=push_options,
             patchset_description=patchset_description,
+            git_event_log=git_event_log,
         )
 
     def GetPublishedRefs(self):
@@ -568,6 +580,7 @@ class Project:
         parent=None,
         use_git_worktrees=False,
         is_derived=False,
+        gitlink_path: Optional[str] = None,
         dest_branch=None,
         optimized_fetch=False,
         retry_fetches=0,
@@ -597,6 +610,8 @@ class Project:
             use_git_worktrees: Whether to use `git worktree` for this project.
             is_derived: False if the project was explicitly defined in the
                 manifest; True if the project is a discovered submodule.
+            gitlink_path: For a discovered submodule, its path inside the
+                parent project.
             dest_branch: The branch to which to push changes for review by
                 default.
             optimized_fetch: If True, when a project is set to a sha1 revision,
@@ -624,6 +639,7 @@ class Project:
         # See the XmlManifest init code for more info.
         self.use_git_worktrees = use_git_worktrees
         self.is_derived = is_derived
+        self.gitlink_path = gitlink_path
         self.optimized_fetch = optimized_fetch
         self.retry_fetches = max(0, retry_fetches)
         self.subprojects = []
@@ -758,15 +774,28 @@ class Project:
         work_git is otheriwse inaccessible (e.g. an incomplete sync).
         """
         try:
-            b = self.work_git.GetHead()
+            b = self._GetHead()
         except NoManifestException:
             # If the local checkout is in a bad state, don't barf.  Let the
             # callers process this like the head is unreadable.
             return None
-        if b.startswith(R_HEADS):
+        if b and b.startswith(R_HEADS):
             return b[len(R_HEADS) :]
         return None
 
+    def _GetHead(self) -> Optional[str]:
+        """Return worktree HEAD, reusing a compatible loaded ref snapshot."""
+        if not self.work_git:
+            return None
+        # Git worktrees keep the checkout's HEAD in the worktree admin dir,
+        # while bare_ref reads the shared repository.  Its HEAD is not the
+        # checked-out worktree's HEAD and must not be reused here.
+        if not self.use_git_worktrees and self.bare_ref.is_loaded:
+            head = self.bare_ref.head
+            if head:
+                return head
+        return self.work_git.GetHead()
+
     def IsRebaseInProgress(self):
         """Returns true if a rebase or "am" is in progress"""
         # "rebase-apply" is used for "git rebase".
@@ -865,8 +894,8 @@ class Project:
 
     def GetBranches(self):
         """Get all existing local branches."""
-        current = self.CurrentBranch
         all_refs = self._allrefs
+        current = self.CurrentBranch
         heads = {}
 
         for name, ref_id in all_refs.items():
@@ -1142,24 +1171,37 @@ class Project:
 
     def GetUploadableBranches(self, selected_branch=None):
         """List any branches which can be uploaded for review."""
-        heads = {}
+        if selected_branch:
-        pubed = {}
+            branch = self.GetBranch(selected_branch)
+            if not branch.LocalMerge:
+                return []
+            head_id = self.bare_ref.get(R_HEADS + selected_branch)
+            if not head_id:
+                return []
+            pub_id = self.bare_ref.get(R_PUB + selected_branch)
+            if pub_id and pub_id == head_id:
+                return []
+            rb = self.GetUploadableBranch(selected_branch)
+            if rb:
+                rb.branch.current = selected_branch == self.CurrentBranch
+                return [rb]
+            return []
 
-        for name, ref_id in self._allrefs.items():
+        # Optimization: Skip scanning _allrefs (which spawns git processes)
-            if name.startswith(R_HEADS):
+        # if no local branches with upstream tracking exist in .git/config.
-                heads[name[len(R_HEADS) :]] = ref_id
+        if not any(self.config.GetSubSections("branch")):
-            elif name.startswith(R_PUB):
+            return []
-                pubed[name[len(R_PUB) :]] = ref_id
+
+        branches = self.GetBranches()
 
         ready = []
-        for branch, ref_id in heads.items():
+        for branch, branch_config in branches.items():
-            if branch in pubed and pubed[branch] == ref_id:
+            if branch_config.published == branch_config.revision:
-                continue
-            if selected_branch and branch != selected_branch:
                 continue
 
             rb = self.GetUploadableBranch(branch)
             if rb:
+                rb.branch.current = branch_config.current
                 ready.append(rb)
         return ready
 
@@ -1189,7 +1231,8 @@ class Project:
         validate_certs=True,
         push_options=None,
         patchset_description=None,
-    ):
+        git_event_log: Optional[EventLog] = None,
+    ) -> None:
         """Uploads the named branch for code review."""
         if branch is None:
             branch = self.CurrentBranch
@@ -1278,14 +1321,47 @@ class Project:
             ref_spec = ref_spec + "%" + ",".join(opts)
         cmd.append(ref_spec)
 
-        GitCommand(self, cmd, bare=True, verify_command=True).Wait()
+        push_cmd = GitCommand(
+            self,
+            cmd,
+            bare=True,
+            verify_command=True,
+        )
+        push_cmd.Wait()
 
+        cls_urls = self._FindGerritUrls(push_cmd.stderr)
+
+        try:
+            rb = ReviewableBranch(self, branch, branch.LocalMerge)
+            modified_files_list = rb.modified_files
+            if git_event_log:
+                git_event_log.LogDataConfigEvents(
+                    {
+                        "cls": ",".join(cls_urls),
+                        "remote": branch.remote.name,
+                        "branch": branch.name,
+                        "files": ",".join(modified_files_list),
+                    },
+                    "repo.uploadstate",
+                )
+        except Exception as e:
+            logger.error("Tracing failed: %s", str(e))
         if not dryrun:
             msg = f"posted to {branch.remote.review} for {dest_branch}"
             self.bare_git.UpdateRef(
                 R_PUB + branch.name, R_HEADS + branch.name, message=msg
             )
 
+    @staticmethod
+    def _FindGerritUrls(stderr: Optional[str]) -> List[str]:
+        """Extracts Gerrit review URLs from git push output."""
+        if not stderr:
+            return []
+        return [
+            match.group(1)
+            for match in re.finditer(r"(https?://[^/]+/c/.+?/\+/\d+)", stderr)
+        ]
+
     @staticmethod
     def _encode_patchset_description(original):
         """Applies percent-encoding for strings sent as patchset description.
@@ -1547,11 +1623,7 @@ class Project:
 
         # If the project has been manually unshallowed (e.g. via
         # `git fetch --unshallow`), don't re-shallow it during sync.
-        if (
+        if depth and not is_new and not self._HasShallow():
-            depth
-            and not is_new
-            and not os.path.exists(os.path.join(self.gitdir, "shallow"))
-        ):
             depth = None
 
         if depth and clone_filter_for_depth:
@@ -1587,17 +1659,15 @@ class Project:
                 )
         else:
             # See if we can skip the standard network fetch entirely.
-            has_shallow = os.path.exists(os.path.join(self.gitdir, "shallow"))
+            has_shallow = self._HasShallow()
             skip_fetch = (
                 optimized_fetch
                 and IsId(self.revisionExpr)
                 and self._CheckForImmutableRevision(
-                    use_superproject=use_superproject
+                    use_superproject=use_superproject,
-                )
+                    depth=depth,
-                and (
-                    has_shallow
-                    or (not depth and not self._SharingProjectHasShallow())
                 )
+                and (has_shallow or not self._IsShallow(depth))
             )
 
             if not skip_fetch:
@@ -1679,7 +1749,9 @@ class Project:
         for linkfile in self.linkfiles:
             linkfile._Link()
 
-    def GetCommitRevisionId(self):
+    def GetCommitRevisionId(
+        self, all_refs: Optional[Dict[str, str]] = None
+    ) -> str:
         """Get revisionId of a commit.
 
         Use this method instead of GetRevisionId to get the id of the commit
@@ -1689,10 +1761,12 @@ class Project:
         if self.revisionId:
             return self.revisionId
         if not self.revisionExpr.startswith(R_TAGS):
-            return self.GetRevisionId(self._allrefs)
+            if all_refs is None:
+                all_refs = self._allrefs
+            return self.GetRevisionId(all_refs)
 
         try:
-            return self.bare_git.rev_list(self.revisionExpr, "-1")[0]
+            return self.bare_git.ResolveCommit(self.revisionExpr)
         except GitError:
             raise ManifestInvalidRevisionError(
                 f"revision {self.revisionExpr} in {self.name} not found"
@@ -1704,6 +1778,10 @@ class Project:
         Returns None if worktree is not checked out or HEAD cannot be resolved.
         """
         if self.work_git:
+            if not self.use_git_worktrees and self.bare_ref.is_loaded:
+                head = self.bare_ref.get(HEAD)
+                if head:
+                    return head
             try:
                 return self.work_git.rev_parse("HEAD")
             except GitError:
@@ -1721,7 +1799,7 @@ class Project:
             return all_refs[rev]
 
         try:
-            return self.bare_git.rev_parse("--verify", "%s^0" % rev)
+            return self.bare_git.ResolveCommit(rev)
         except GitError:
             raise ManifestInvalidRevisionError(
                 f"revision {self.revisionExpr} in {self.name} not found"
@@ -1817,8 +1895,8 @@ class Project:
             if p.Wait() != 0:
                 logger.warning("warn: %s: stateless gc failed", self.name)
 
-        head = self.work_git.GetHead()
+        head = self._GetHead()
-        if head.startswith(R_HEADS):
+        if head and head.startswith(R_HEADS):
             branch = head[len(R_HEADS) :]
             try:
                 head = all_refs[head]
@@ -2349,7 +2427,7 @@ class Project:
             # Doesn't exist
             return None
 
-        head = self.work_git.GetHead()
+        head = self._GetHead()
         if head == rev:
             # We can't destroy the branch while we are sitting
             # on it.  Switch to a detached HEAD.
@@ -2371,9 +2449,9 @@ class Project:
 
     def PruneHeads(self):
         """Prune any topic branches already merged into upstream."""
-        cb = self.CurrentBranch
         kill = []
         left = self._allrefs
+        cb = self.CurrentBranch
         for name in left.keys():
             if name.startswith(R_HEADS):
                 name = name[len(R_HEADS) :]
@@ -2385,17 +2463,25 @@ class Project:
         if not kill and not cb:
             return []
 
-        rev = self.GetRevisionId(left)
+        rev = self.GetCommitRevisionId(left)
+        head = left.get(R_HEADS + cb) if cb is not None else None
         if (
             cb is not None
-            and not self._revlist(HEAD + "..." + rev)
+            and head == rev
             and not self.IsDirty(consider_untracked=False)
         ):
             self.work_git.DetachHead(HEAD)
             kill.append(cb)
 
         if kill:
-            old = self.bare_git.GetHead()
+            if not self.use_git_worktrees:
+                old = (
+                    head
+                    if cb in kill
+                    else (self.bare_ref.head or self.bare_git.GetHead())
+                )
+            else:
+                old = self.bare_git.GetHead()
 
             try:
                 self.bare_git.DetachHead(rev)
@@ -2410,7 +2496,11 @@ class Project:
                 if IsId(old):
                     self.bare_git.DetachHead(old)
                 else:
-                    self.bare_git.SetHead(old)
+                    branch = (
+                        old[len(R_HEADS) :] if old.startswith(R_HEADS) else old
+                    )
+                    if branch not in kill:
+                        self.bare_git.SetHead(old)
                 left = self._allrefs
 
             for branch in kill:
@@ -2426,6 +2516,7 @@ class Project:
         for branch in kill:
             if R_HEADS + branch in left:
                 branch = self.GetBranch(branch)
+                branch.current = branch.name == cb
                 base = branch.LocalMerge
                 if not base:
                     base = rev
@@ -2573,6 +2664,37 @@ class Project:
             return []
         return get_submodules(self.gitdir, rev)
 
+    def GetSubmoduleRevisions(self) -> Optional[Dict[str, str]]:
+        """Read the gitlinks of our submodules at our current revision.
+
+        Discovered submodules are derived from the revision their parent was
+        at when the manifest was loaded, which is before it gets fetched.
+        Once it is up-to-date, its gitlinks have to be read again, otherwise
+        the submodules would be synced to the revisions of the previous sync.
+
+        Returns:
+            The revision of every submodule, keyed by its path inside this
+            project, or None if our revision is not available locally. A
+            revision that is merely set does not have to be fetched yet, and
+            without its objects a removed submodule cannot be told apart from
+            one that was never fetched.
+        """
+        try:
+            rev = self.GetRevisionId()
+            self.bare_git.rev_list(
+                "-1",
+                "--missing=allow-any",
+                f"{rev}^0",
+                "--",
+                log_as_error=False,
+            )
+        except (GitError, ManifestInvalidRevisionError):
+            return None
+
+        return {
+            path: sha for sha, path, _url, _shallow in self._GetSubmodules()
+        }
+
     def GetDerivedSubprojects(self):
         result = []
         if not self.Exists:
@@ -2620,6 +2742,7 @@ class Project:
                 parent=self,
                 clone_depth=clone_depth,
                 is_derived=True,
+                gitlink_path=path,
             )
             result.append(subproject)
             result.extend(subproject.GetDerivedSubprojects())
@@ -2668,19 +2791,22 @@ class Project:
         return None
 
     def _CheckForImmutableRevision(
-        self, use_superproject: Optional[bool] = None
+        self,
+        use_superproject: Optional[bool] = None,
+        depth: Optional[int] = None,
     ) -> bool:
         try:
             # if revision (sha or tag) is not present then following function
             # throws an error.
             revs = [f"{self.revisionExpr}^0"]
             upstream_rev = None
-            use_superproject_for_upstream = self.upstream and (
+            verify_upstream = self._ShouldVerifyUpstream(
-                self._UseSuperprojectForUpstream(use_superproject)
+                use_superproject=use_superproject,
+                depth=depth,
             )
 
-            # Only check upstream when using superproject.
+            # Ensure the local upstream tracking ref also exists in the ODB.
-            if use_superproject_for_upstream:
+            if verify_upstream:
                 upstream_rev = self.GetRemote().ToLocal(self.upstream)
                 revs.append(upstream_rev)
 
@@ -2692,9 +2818,8 @@ class Project:
                 log_as_error=False,
             )
 
-            # Only verify upstream relationship for superproject scenarios
+            # Verify revision is an ancestor of the upstream tracking ref.
-            # without affecting plain usage.
+            if verify_upstream:
-            if use_superproject_for_upstream:
                 self.bare_git.merge_base(
                     "--is-ancestor",
                     self.revisionExpr,
@@ -2706,6 +2831,31 @@ class Project:
             # There is no such persistent revision. We have to fetch it.
             return False
 
+    def _HasShallow(self) -> bool:
+        """Check if this project has a shallow file in its gitdir."""
+        return bool(
+            self.gitdir and os.path.exists(os.path.join(self.gitdir, "shallow"))
+        )
+
+    def _IsShallow(self, depth: Optional[int] = None) -> bool:
+        """Check if the project is shallow or sharing shallow objects."""
+        return bool(
+            self._HasShallow() or self._SharingProjectHasShallow() or depth
+        )
+
+    def _ShouldVerifyUpstream(
+        self,
+        use_superproject: Optional[bool] = None,
+        depth: Optional[int] = None,
+    ) -> bool:
+        """Whether to verify upstream ancestry during immutable revision
+        check."""
+        if not (IsId(self.revisionExpr) and self.upstream):
+            return False
+        if self._UseSuperprojectForUpstream(use_superproject):
+            return True
+        return not self._IsShallow(depth)
+
     def _SharingProjectHasShallow(self) -> bool:
         """Check if another project sharing this objdir has a "shallow" file.
 
@@ -2719,18 +2869,14 @@ class Project:
         )
         for proj in other_projects:
             if proj.objdir == self.objdir and proj.gitdir != self.gitdir:
-                if os.path.exists(os.path.join(proj.gitdir, "shallow")):
+                if proj._HasShallow():
                     return True
         return False
 
     def _UseSuperprojectForUpstream(
         self, use_superproject: Optional[bool] = None
     ) -> bool:
-        """Whether to include upstream in the immutability check.
+        """Whether to check upstream for superprojects."""
-
-        The upstream ancestry check is only meaningful for projects
-        that participate in a superproject relationship.
-        """
         return git_superproject.UseSuperproject(use_superproject, self.manifest)
 
     def _FetchArchive(self, tarpath, cwd=None):
@@ -2858,14 +3004,16 @@ class Project:
         return True
 
     def _GetUpstreamFallback(self) -> Optional[str]:
-        """Resolve a fallback upstream ref when revisionExpr is a SHA-1."""
+        """Resolve a fallback upstream branch when revisionExpr is a SHA-1.
-        for cand in (
+
-            self.dest_branch,
+        Returns manifest default upstream or revision if it names a branch,
-            self.manifest.default.upstreamExpr,
+        or None to fall back to fetching all heads.
-            self.manifest.default.destBranchExpr,
+        """
-            self.manifest.default.revisionExpr,
+        default = self.manifest.default
-        ):
+        if not default:
-            if cand and not IsId(cand):
+            return None
+        for cand in (default.upstreamExpr, default.revisionExpr):
+            if cand and not IsId(cand) and not cand.startswith(R_TAGS):
                 return cand
         return None
 
@@ -2929,15 +3077,11 @@ class Project:
                 tag_name = upstream[len(R_TAGS) :]
 
             if is_sha1 or tag_name is not None:
-                has_shallow = os.path.exists(
+                has_shallow = self._HasShallow()
-                    os.path.join(self.gitdir, "shallow")
-                )
                 if self._CheckForImmutableRevision(
-                    use_superproject=use_superproject
+                    use_superproject=use_superproject,
-                ) and (
+                    depth=depth,
-                    has_shallow
+                ) and (has_shallow or not self._IsShallow(depth)):
-                    or (not depth and not self._SharingProjectHasShallow())
-                ):
                     if verbose:
                         print(
                             "Skipped fetching project %s (already have "
@@ -3003,7 +3147,7 @@ class Project:
             # have shallow objects or not. Tell git to unshallow all fetched
             # refs.  Don't do this with projects that don't have shallow
             # objects, since it is less efficient.
-            if os.path.exists(os.path.join(self.gitdir, "shallow")):
+            if self._HasShallow():
                 cmd.append("--depth=2147483647")
 
         # Use clone-depth="1" as a heuristic for repositories containing
@@ -3246,7 +3390,8 @@ class Project:
             # got what we wanted, else trigger a second run of all
             # refs.
             if not self._CheckForImmutableRevision(
-                use_superproject=use_superproject
+                use_superproject=use_superproject,
+                depth=depth,
             ):
                 # Sync the current branch only with depth set to None.
                 # We always pass depth=None down to avoid infinite recursion.
@@ -4384,8 +4529,52 @@ class Project:
 
             return dotgit if subpath is None else os.path.join(dotgit, subpath)
 
+        @staticmethod
+        def _ParseHead(line: str) -> Optional[str]:
+            """Parse the content of a .git/HEAD file.
+
+            Handles both symbolic refs (e.g. 'ref: refs/heads/...') and raw
+            commit IDs (40-hex SHA-1 or 64-hex SHA-256).
+
+            Returns:
+                The ref name (e.g. 'refs/heads/main') or lowercase commit hash
+                if valid, or None if empty or invalid.
+            """
+            line = line.strip()
+            if line.startswith("ref:"):
+                ref = line[4:].strip()
+                # Ensure the ref is not empty, pure whitespace, or the
+                # "refs/heads/.invalid" placeholder used for unborn branches,
+                # empty repositories, or when the reftables backend is used
+                # (which will be the default in Git 3.0).
+                if not ref or ref == R_HEADS + ".invalid":
+                    return None
+                return ref
+            else:
+                # Normalize commit IDs to canonical lowercase hexadecimal,
+                # matching the output format of `git rev-parse`.
+                line_lower = line.lower()
+                if IsId(line_lower):
+                    return line_lower
+            return None
+
         def GetHead(self):
             """Return the ref that HEAD points to."""
+            path = None
+            try:
+                # Catch AssertionError raised by GetDotgitPath when worktree
+                # .git pointer file is malformed (e.g. missing 'gitdir:').
+                path = self.GetDotgitPath(subpath=HEAD)
+                if not platform_utils.islink(path):
+                    with open(
+                        path, "r", encoding="utf-8", errors="replace"
+                    ) as fd:
+                        ref = self._ParseHead(fd.readline())
+                    if ref:
+                        return ref
+            except (OSError, AssertionError):
+                pass
+
             try:
                 return self.symbolic_ref("-q", HEAD, log_as_error=False)
             except GitError:
@@ -4405,24 +4594,38 @@ class Project:
 
                 # Fallback to direct file reading for compatibility with broken
                 # repos, e.g. if HEAD points to an unborn branch.
-                path = self.GetDotgitPath(subpath=HEAD)
+                if not path:
+                    raise NoManifestException(
+                        self._project.RelPath(local=False), str(e)
+                    )
                 try:
-                    with open(path) as fd:
+                    with open(
-                        line = fd.readline()
+                        path, "r", encoding="utf-8", errors="replace"
+                    ) as fd:
+                        ref = self._ParseHead(fd.readline())
                 except OSError:
-                    raise NoManifestException(path, str(e))
+                    raise NoManifestException(
-                try:
+                        self._project.RelPath(local=False), str(e)
-                    line = line.decode()
+                    )
-                except AttributeError:
+                if not ref:
-                    pass
+                    raise NoManifestException(
-                if line.startswith("ref: "):
+                        self._project.RelPath(local=False), str(e)
-                    ref = line[5:-1]
+                    )
-                else:
-                    ref = line[:-1]
-                if ref == R_HEADS + ".invalid":
-                    raise NoManifestException(path, str(e))
                 return ref
 
+        def ResolveCommit(self, revision: str) -> str:
+            """Resolve |revision| to a commit without option ambiguity."""
+            cmdv = ["--verify", "--quiet"]
+            if git_require((2, 30, 0)):
+                cmdv.append("--end-of-options")
+            elif revision.startswith("-"):
+                raise GitError(
+                    f"invalid revision: {revision}",
+                    project=self._project.name,
+                )
+            cmdv.append(f"{revision}^{{commit}}")
+            return self.rev_parse(*cmdv, log_as_error=False)
+
         def SetHead(self, ref, message=None):
             cmdv = []
             if message is not None:
@@ -4695,9 +4898,11 @@ def _DefaultBranchFallback() -> str:
         )
         return p.stdout.strip() if p.Wait() == 0 else ""
 
-    branch = _git(["var", "GIT_DEFAULT_BRANCH"]) or _git(
+    branch = ""
-        ["config", "--get", "init.defaultBranch"]
+    if git_require((2, 35, 0)):
-    )
+        branch = _git(["var", "GIT_DEFAULT_BRANCH"])
+    if not branch:
+        branch = _git(["config", "--get", "init.defaultBranch"])
     return f"refs/heads/{branch or 'master'}"
 
 
@@ -4737,6 +4942,30 @@ class MetaProject(Project):
         # before manifest.xml has been linked into .repo/.
         return False
 
+    def _GetUpstreamFallback(self) -> Optional[str]:
+        # MetaProjects (the manifest repo and repo itself) do not have
+        # defaults in a manifest. Returning None here also avoids
+        # loading the manifest during `repo init`, before manifest.xml
+        # has been linked into .repo/.
+        return None
+
+    def _SharingProjectHasShallow(self) -> bool:
+        # MetaProjects (the manifest repo and repo itself) are never
+        # shared with other projects in the manifest. Returning False
+        # here also avoids loading the manifest during `repo init`,
+        # before manifest.xml has been linked into .repo/.
+        return False
+
+    def _ShouldVerifyUpstream(
+        self,
+        use_superproject: Optional[bool] = None,
+        depth: Optional[int] = None,
+    ) -> bool:
+        """MetaProjects (manifest repo and repo itself) do not verify upstream
+        ancestry.
+        """
+        return False
+
     @property
     def HasChanges(self):
         """Has the remote received new commits not yet checked out?"""
@@ -4745,8 +4974,8 @@ class MetaProject(Project):
 
         all_refs = self.bare_ref.all
         revid = self.GetRevisionId(all_refs)
-        head = self.work_git.GetHead()
+        head = self._GetHead()
-        if head.startswith(R_HEADS):
+        if head and head.startswith(R_HEADS):
             try:
                 head = all_refs[head]
             except KeyError:
@@ -4754,7 +4983,7 @@ class MetaProject(Project):
 
         if revid == head:
             return False
-        elif self._revlist(not_rev(HEAD), revid):
+        elif self._revlist("-1", not_rev(HEAD), revid):
             return True
         return False
 

subcmds/abandon.py

@@ -20,7 +20,7 @@ from command import Command
 from command import DEFAULT_LOCAL_JOBS
 from error import RepoError
 from error import RepoExitError
-from git_command import git
+from git_command import IsValidBranchName
 from progress import Progress
 from repo_logging import RepoLogger
 
@@ -58,9 +58,7 @@ It is equivalent to "git branch -D <branchname>".
 
         if not opt.all:
             branches = args[0].split()
-            invalid_branches = [
+            invalid_branches = [x for x in branches if not IsValidBranchName(x)]
-                x for x in branches if not git.check_ref_format(f"heads/{x}")
-            ]
 
             if invalid_branches:
                 self.OptionParser.error(

subcmds/cherry_pick.py

@@ -14,6 +14,7 @@
 
 import re
 import sys
+from typing import Tuple
 
 from command import Command
 from error import GitError
@@ -43,36 +44,8 @@ change id will be added.
 
     def Execute(self, opt, args):
         reference = args[0]
-
+        sha1, commit = self._ResolveReference(reference)
-        p = GitCommand(
+        old_msg = self._StripHeader(commit)
-            None,
-            ["rev-parse", "--verify", reference],
-            capture_stdout=True,
-            capture_stderr=True,
-            verify_command=True,
-        )
-        try:
-            p.Wait()
-        except GitError:
-            logger.error(p.stderr)
-            raise
-
-        sha1 = p.stdout.strip()
-
-        p = GitCommand(
-            None,
-            ["cat-file", "commit", sha1],
-            capture_stdout=True,
-            verify_command=True,
-        )
-
-        try:
-            p.Wait()
-        except GitError:
-            logger.error("error: Failed to retrieve old commit message")
-            raise
-
-        old_msg = self._StripHeader(p.stdout)
 
         p = GitCommand(
             None,
@@ -117,6 +90,48 @@ change id will be added.
             logger.error("error: Failed to update commit message")
             raise
 
+    def _ResolveReference(self, reference: str) -> Tuple[str, str]:
+        """Resolve a commit and read it through one cat-file batch request."""
+        expression = f"{reference}^{{commit}}"
+        p = GitCommand(
+            None,
+            ["cat-file", "--batch"],
+            input=expression + "\n",
+            capture_stdout=True,
+            capture_stderr=True,
+            verify_command=True,
+        )
+        try:
+            p.Wait()
+            header, separator, output = p.stdout.partition("\n")
+            if not separator:
+                raise ValueError("missing cat-file header")
+            if header.endswith(" missing") or header.endswith(" ambiguous"):
+                raise GitError(f"commit {reference} not found")
+
+            parts = header.split(" ", 2)
+            if len(parts) != 3 or parts[1] != "commit":
+                raise ValueError(
+                    f"unexpected object type {parts[1]!r}"
+                    if len(parts) >= 2
+                    else "invalid header"
+                )
+            sha1, _object_type, _size = parts
+
+            if not output.endswith("\n"):
+                raise ValueError("truncated cat-file object")
+
+            commit = output[:-1]
+        except (GitError, ValueError) as e:
+            logger.error(
+                "error: Failed to resolve or read commit %s", reference
+            )
+            if isinstance(e, GitError):
+                raise
+            raise GitError(str(e)) from e
+
+        return sha1, commit
+
     def _IsChangeId(self, line):
         return CHANGE_ID_RE.match(line)
 

subcmds/overview.py

@@ -59,10 +59,15 @@ are displayed.
         for project in self.GetProjects(
             args, all_manifests=not opt.this_manifest_only
         ):
-            br = [project.GetUploadableBranch(x) for x in project.GetBranches()]
+            local_branches = project.GetBranches()
-            br = [x for x in br if x]
+            br = []
+            for name, branch in local_branches.items():
+                uploadable = project.GetUploadableBranch(name)
+                if uploadable:
+                    uploadable.branch.current = branch.current
+                    br.append(uploadable)
             if opt.current_branch:
-                br = [x for x in br if x.name == project.CurrentBranch]
+                br = [x for x in br if x.current]
             all_branches.extend(br)
 
         if not all_branches:
@@ -97,7 +102,7 @@ are displayed.
             print(
                 "%s %-33s (%2d commit%s, %s)"
                 % (
-                    branch.name == project.CurrentBranch and "*" or " ",
+                    branch.current and "*" or " ",
                     branch.name,
                     len(commits),
                     len(commits) != 1 and "s" or " ",

subcmds/prune.py

@@ -80,7 +80,7 @@ class Prune(PagedCommand):
             print(
                 "%s %-33s "
                 % (
-                    branch.name == project.CurrentBranch and "*" or " ",
+                    branch.current and "*" or " ",
                     branch.name,
                 ),
                 end="",

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)

subcmds/start.py

@@ -18,7 +18,7 @@ from typing import NamedTuple
 from command import Command
 from command import DEFAULT_LOCAL_JOBS
 from error import RepoExitError
-from git_command import git
+from git_command import IsValidBranchName
 from git_config import IsImmutable
 from progress import Progress
 from repo_logging import RepoLogger
@@ -75,7 +75,7 @@ revision specified in the manifest.
             self.Usage()
 
         nb = args[0]
-        if not git.check_ref_format("heads/%s" % nb):
+        if not IsValidBranchName(nb):
             self.OptionParser.error("'%s' is not a valid name" % nb)
 
     @classmethod

subcmds/sync.py

@@ -28,7 +28,7 @@ import subprocess
 import sys
 import tempfile
 import time
-from typing import List, NamedTuple, Optional, Set, Tuple, Union
+from typing import Dict, List, NamedTuple, Optional, Set, Tuple, Union
 import urllib.error
 import urllib.parse
 import urllib.request
@@ -156,6 +156,83 @@ def _SafeCheckoutOrder(checkouts: List[Project]) -> List[List[Project]]:
     return res
 
 
+def _ParentFirstBatches(projects: List[Project]) -> List[List[Project]]:
+    """Group |projects| so that a parent is fetched before its submodules.
+
+    A discovered submodule can only be fetched at the right revision once the
+    project holding its gitlink has been fetched, so it is held back to a later
+    batch than its parent. Projects that are not discovered submodules all end
+    up in the first batch, which keeps manifests without submodules on a single
+    batch.
+    """
+    batches = collections.defaultdict(list)
+    for project in projects:
+        depth = 0
+        ancestor = project
+        while ancestor.Derived and ancestor.parent:
+            depth += 1
+            ancestor = ancestor.parent
+        batches[depth].append(project)
+    return [batches[depth] for depth in sorted(batches)]
+
+
+def _RefreshDerivedRevisions(
+    projects: List[Project],
+    submodule_revisions: Optional[Dict[Project, Dict[str, str]]] = None,
+) -> List[Project]:
+    """Re-resolve the gitlinks of the discovered submodules in |projects|.
+
+    The revision of a discovered submodule is read from its parent when the
+    manifest is loaded, so it is stale as soon as the parent gets fetched. It
+    has to be resolved again once the parent is up-to-date, and before the
+    submodule itself is fetched and checked out.
+
+    Args:
+        projects: The projects whose discovered submodules to resolve.
+        submodule_revisions: Gitlinks already read, keyed by the project
+            holding them. Passing the same dict for project sets that follow
+            the same fetches, e.g. the levels of one checkout order, keeps a
+            project from being read more than once.
+
+    Returns:
+        The submodules that their parent no longer holds a gitlink for.
+    """
+    if submodule_revisions is None:
+        submodule_revisions = {}
+
+    subprojects_by_parent = collections.defaultdict(list)
+    for project in projects:
+        if project.Derived and project.parent:
+            subprojects_by_parent[project.parent].append(project)
+
+    removed = []
+    for parent, subprojects in subprojects_by_parent.items():
+        revisions = submodule_revisions.get(parent)
+        if revisions is None:
+            revisions = parent.GetSubmoduleRevisions()
+            if revisions is None:
+                # Leave the submodules of a parent we cannot read alone.
+                continue
+            submodule_revisions[parent] = revisions
+        for subproject in subprojects:
+            rev = revisions.get(subproject.gitlink_path)
+            if rev:
+                subproject.SetRevision(rev, revisionId=rev)
+            else:
+                removed.append(subproject)
+    return removed
+
+
+def _WithoutProjects(
+    projects: List[Project], unwanted: List[Project]
+) -> List[Project]:
+    """Return |projects| without the projects in |unwanted|."""
+    if not unwanted:
+        return projects
+    dropped = set(unwanted)
+    return [p for p in projects if p not in dropped]
+
+
 def _chunksize(projects: int, jobs: int) -> int:
     """Calculate chunk size for the given number of projects and jobs."""
     return min(max(1, projects // jobs), WORKER_BATCH_SIZE)
@@ -224,7 +301,8 @@ class _SyncResult(NamedTuple):
 
     Attributes:
       project_index (int): The index of the project in the shared list.
-      relpath (str): The project's relative path from the repo client top.
+      relpath (str): The project's path relative to the tree being synced.
+          Unlike Project.relpath, it is unique across submanifests.
       remote_fetched (bool): True if the remote was actually queried.
       fetch_success (bool): True if the fetch operation was successful.
       fetch_errors (List[Exception]): The Exceptions from a failed fetch.
@@ -1067,6 +1145,40 @@ later is required to fix a server side protocol bug.
 
         return _FetchResult(ret, fetched)
 
+    def _FetchParentFirst(
+        self,
+        projects: List[Project],
+        opt: optparse.Values,
+        err_event: _threading.Event,
+        ssh_proxy: ssh.ProxyManager,
+        errors: List[Exception],
+    ) -> _FetchResult:
+        """Fetch |projects|, holding submodules back until their parent is done.
+
+        Args:
+            projects: Projects to fetch.
+            opt: Program options returned from optparse. See _Options().
+            err_event: Whether an error was hit while processing.
+            ssh_proxy: SSH manager for clients & masters.
+            errors: A list to accumulate errors.
+
+        Returns:
+            _FetchResult for all the batches combined.
+        """
+        success = True
+        fetched = set()
+        for batch in _ParentFirstBatches(projects):
+            batch = _WithoutProjects(batch, _RefreshDerivedRevisions(batch))
+            if not batch:
+                continue
+            batch.sort(key=self._fetch_times.Get, reverse=True)
+            result = self._Fetch(batch, opt, err_event, ssh_proxy, errors)
+            success = success and result.success
+            fetched.update(result.projects)
+            if not success and opt.fail_fast:
+                break
+        return _FetchResult(success, fetched)
+
     def _FetchMain(
         self, opt, args, all_projects, err_event, ssh_proxy, manifest, errors
     ):
@@ -1083,12 +1195,10 @@ later is required to fix a server side protocol bug.
         Returns:
             List of all projects that should be checked out.
         """
-        to_fetch = []
-        to_fetch.extend(all_projects)
-        to_fetch.sort(key=self._fetch_times.Get, reverse=True)
-
         try:
-            result = self._Fetch(to_fetch, opt, err_event, ssh_proxy, errors)
+            result = self._FetchParentFirst(
+                all_projects, opt, err_event, ssh_proxy, errors
+            )
             success = result.success
             fetched = result.projects
             if not success:
@@ -1131,7 +1241,9 @@ later is required to fix a server side protocol bug.
                 if previously_missing_set == missing_set:
                     break
                 previously_missing_set = missing_set
-                result = self._Fetch(missing, opt, err_event, ssh_proxy, errors)
+                result = self._FetchParentFirst(
+                    missing, opt, err_event, ssh_proxy, errors
+                )
                 success = result.success
                 new_fetched = result.projects
                 if not success:
@@ -2758,7 +2870,7 @@ later is required to fix a server side protocol bug.
 
         return _SyncResult(
             project_index=project_index,
-            relpath=project.relpath,
+            relpath=project.RelPath(local=opt.this_manifest_only),
             fetch_success=fetch_success,
             remote_fetched=remote_fetched,
             checkout_success=checkout_success,
@@ -2906,6 +3018,10 @@ later is required to fix a server side protocol bug.
         self._interleaved_err_checkout = False
         self._interleaved_err_checkout_results = []
 
+        # Project.relpath is relative to its own (sub)manifest, so it does not
+        # tell apart projects of different manifests being synced together.
+        _RelPath = lambda p: p.RelPath(local=opt.this_manifest_only)
+
         err_event = multiprocessing.Event()
         finished_relpaths = set()
         project_list = list(all_projects)
@@ -2942,13 +3058,13 @@ later is required to fix a server side protocol bug.
                             projects_to_sync = [
                                 p
                                 for p in project_list
-                                if p.relpath not in finished_relpaths
+                                if _RelPath(p) not in finished_relpaths
                             ]
                             if not projects_to_sync:
                                 break
 
                             pending_relpaths = {
-                                p.relpath for p in projects_to_sync
+                                _RelPath(p) for p in projects_to_sync
                             }
                             if previously_pending_relpaths == pending_relpaths:
                                 stalled_projects_str = "\n".join(
@@ -2977,12 +3093,22 @@ later is required to fix a server side protocol bug.
                             # projects in one level can be processed in
                             # parallel, but we must wait for a level to complete
                             # before starting the next.
+                            submodule_revisions = {}
                             for level_projects in _SafeCheckoutOrder(
                                 projects_to_sync
                             ):
                                 if not level_projects:
                                     continue
 
+                                level_projects = _WithoutProjects(
+                                    level_projects,
+                                    _RefreshDerivedRevisions(
+                                        level_projects, submodule_revisions
+                                    ),
+                                )
+                                if not level_projects:
+                                    continue
+
                                 objdir_project_map = collections.defaultdict(
                                     list
                                 )

subcmds/upload.py

@@ -25,7 +25,6 @@ from editor import Editor
 from error import GitError
 from error import SilentRepoExitError
 from error import UploadError
-from git_command import GitCommand
 from git_refs import R_HEADS
 import git_superproject
 from hooks import RepoHook
@@ -379,7 +378,7 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
             default=True,
             help="disable verifying ssl certs (unsafe)",
         )
-        RepoHook.AddOptionGroup(p, "pre-upload")
+        RepoHook.AddOptionGroup(p, "pre-upload", allow_fix=True)
 
     def _SingleBranch(self, opt, branch, people):
         project = branch.project
@@ -649,6 +648,7 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
             validate_certs=opt.validate_certs,
             push_options=push_options,
             patchset_description=opt.patchset_description,
+            git_event_log=self.git_event_log,
         )
 
         branch.uploaded = True
@@ -704,36 +704,31 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
             raise UploadExitError(aggregate_errors=aggregate_errors)
 
     def _GetMergeBranch(self, project, local_branch=None):
+        """Get the merge branch name for a local branch.
+
+        Resolves the merge branch in-memory via project configuration to
+        avoid git subprocess overhead during upload.
+        """
         if local_branch is None:
-            p = GitCommand(
+            local_branch = project.CurrentBranch
-                project,
+        if local_branch:
-                ["rev-parse", "--abbrev-ref", "HEAD"],
+            branch = project.GetBranch(local_branch)
-                capture_stdout=True,
+            if branch.merge:
-                capture_stderr=True,
+                return branch.merge
-            )
+        return ""
-            p.Wait()
-            local_branch = p.stdout.strip()
-        p = GitCommand(
-            project,
-            ["config", "--get", "branch.%s.merge" % local_branch],
-            capture_stdout=True,
-            capture_stderr=True,
-        )
-        p.Wait()
-        merge_branch = p.stdout.strip()
-        return merge_branch
 
     @classmethod
     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(
@@ -743,7 +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(
@@ -751,7 +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:

subcmds/version.py

@@ -14,10 +14,12 @@
 
 import platform
 import sys
+from typing import Any, Tuple
 
 from command import Command
 from command import MirrorSafeCommand
 from git_command import git
+from git_command import git_require
 from git_command import RepoSourceVersion
 from git_command import user_agent
 from git_refs import HEAD
@@ -34,6 +36,22 @@ class Version(Command, MirrorSafeCommand):
 %prog
 """
 
+    @staticmethod
+    def _RepoVersion(project: Any) -> Tuple[str, str]:
+        """Return repo's describe string and commit date."""
+        if git_require((2, 32, 0)):
+            output = project.bare_git.log(
+                "-1", "--format=%(describe)%n%cD", HEAD
+            )
+            description, commit_date = output.rstrip("\n").split("\n", 1)
+            if description:
+                return description, commit_date
+
+        return (
+            project.bare_git.describe(HEAD),
+            project.bare_git.log("-1", "--format=%cD", HEAD),
+        )
+
     def Execute(self, opt, args):
         rp = self.manifest.repoProject
         rem = rp.GetRemote()
@@ -41,11 +59,11 @@ class Version(Command, MirrorSafeCommand):
 
         # These might not be the same.  Report them both.
         src_ver = RepoSourceVersion()
-        rp_ver = rp.bare_git.describe(HEAD)
+        rp_ver, commit_date = self._RepoVersion(rp)
         print(f"repo version {rp_ver}")
         print(f"       (from {rem.url})")
         print(f"       (tracking {branch.merge})")
-        print(f"       ({rp.bare_git.log('-1', '--format=%cD', HEAD)})")
+        print(f"       ({commit_date})")
 
         if self.wrapper_path is not None:
             print(f"repo launcher version {self.wrapper_version}")

tests/test_git_command.py

@@ -231,6 +231,24 @@ class GitCommandStreamLogsTest(unittest.TestCase):
 class GitCallUnitTest(unittest.TestCase):
     """Tests the _GitCall class (via git_command.git)."""
 
+    def test_valid_branch_name_uses_branch_mode(self) -> None:
+        """Branch validation applies Git's branch-specific restrictions."""
+        command = mock.MagicMock()
+        command.Wait.return_value = 1
+        with mock.patch.object(
+            git_command, "GitCommand", return_value=command
+        ) as check:
+            self.assertFalse(git_command.IsValidBranchName("-topic"))
+
+        check.assert_called_once_with(
+            None,
+            ["check-ref-format", "--branch", "-topic"],
+            capture_stdout=True,
+            capture_stderr=True,
+            add_event_log=False,
+            log_as_error=False,
+        )
+
     def test_version_tuple(self):
         """Check git.version_tuple() handling."""
         ver = git_command.git.version_tuple()

tests/test_git_config.py

@@ -256,8 +256,8 @@ def test_remote_save_with_push_url_without_projectname(
         ("0" * 64, True),
         ("f" * 64, True),
         ("a" * 39, False),
-        ("a" * 41, True),
+        ("a" * 41, False),
-        ("a" * 63, True),
+        ("a" * 63, False),
         ("a" * 65, False),
         ("g" * 40, False),
         ("g" * 64, False),

tests/test_git_refs.py

@@ -17,6 +17,8 @@
 import os
 from pathlib import Path
 import subprocess
+from typing import Any, List
+from unittest import mock
 
 import pytest
 import utils_for_test
@@ -24,7 +26,7 @@ import utils_for_test
 import git_refs
 
 
-def _run(repo, *args):
+def _run(repo: str, *args: str) -> str:
     return subprocess.run(
         ["git", "-C", repo, *args],
         stdout=subprocess.PIPE,
@@ -34,7 +36,7 @@ def _run(repo, *args):
     ).stdout.strip()
 
 
-def _init_repo(tmp_path, reftable=False):
+def _init_repo(tmp_path: Path, reftable: bool = False) -> str:
     repo = os.path.join(tmp_path, "repo")
     ref_format = "reftable" if reftable else "files"
     utils_for_test.init_git_tree(repo, ref_format=ref_format)
@@ -57,10 +59,154 @@ def test_reads_refs(tmp_path, reftable):
     branch = _run(repo, "symbolic-ref", "--short", "HEAD")
     head = _run(repo, "rev-parse", "HEAD")
     assert refs.symref("HEAD") == f"refs/heads/{branch}"
+    assert refs.head == f"refs/heads/{branch}"
     assert refs.get("HEAD") == head
     assert refs.get(f"refs/heads/{branch}") == head
 
 
+@pytest.mark.parametrize("reftable", [False, True])
+def test_reads_detached_head(tmp_path: Path, reftable: bool) -> None:
+    if reftable and not utils_for_test.supports_reftable():
+        pytest.skip("reftable not supported")
+
+    repo = _init_repo(tmp_path, reftable=reftable)
+    head = _run(repo, "rev-parse", "HEAD")
+    _run(repo, "checkout", "--detach", head)
+    refs = git_refs.GitRefs(os.path.join(repo, ".git"))
+
+    assert refs.symref("HEAD") == ""
+    assert refs.head == head
+    assert refs.get("HEAD") == head
+
+
+def test_reads_head_with_root_refs_in_one_command(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Git 2.45 and newer include HEAD in the ref snapshot."""
+    head = "1" * 40
+    commands = []
+
+    class FakeGitCommand:
+        def __init__(
+            self, _project: Any, cmdv: List[str], **_kwargs: Any
+        ) -> None:
+            commands.append(cmdv)
+            self.stdout = (
+                f"{head}\0HEAD\0refs/heads/main\n"
+                f"{head}\0refs/heads/main\0\n"
+            )
+
+        def Wait(self) -> int:
+            return 0
+
+    monkeypatch.setattr(git_refs, "GitCommand", FakeGitCommand)
+    monkeypatch.setattr(git_refs, "git_require", lambda _version: True)
+    refs = git_refs.GitRefs("/nonexistent")
+    with mock.patch.object(refs, "_ReadSymbolicRef") as read_head:
+        assert refs.get("HEAD") == head
+
+    assert commands == [
+        [
+            "for-each-ref",
+            "--include-root-refs",
+            "--format=%(objectname)%00%(refname)%00%(symref)",
+            "HEAD",
+            "refs",
+        ]
+    ]
+    read_head.assert_not_called()
+
+
+def test_root_ref_snapshot_falls_back_for_unborn_head(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """An unborn HEAD still uses symbolic-ref after the ref snapshot."""
+
+    class FakeGitCommand:
+        def __init__(
+            self, _project: Any, _cmdv: List[str], **_kwargs: Any
+        ) -> None:
+            self.stdout = ""
+
+        def Wait(self) -> int:
+            return 0
+
+    monkeypatch.setattr(git_refs, "GitCommand", FakeGitCommand)
+    monkeypatch.setattr(git_refs, "git_require", lambda _version: True)
+    refs = git_refs.GitRefs("/nonexistent")
+
+    def read_head(name: str) -> None:
+        assert name == "HEAD"
+        refs._symref[name] = "refs/heads/main"
+
+    monkeypatch.setattr(refs, "_ReadSymbolicRef", read_head)
+
+    assert refs.symref("HEAD") == "refs/heads/main"
+
+
+def test_old_git_keeps_separate_head_fallback(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Git before 2.45 uses the original for-each-ref and HEAD calls."""
+    head = "1" * 40
+    commands = []
+
+    class FakeGitCommand:
+        def __init__(
+            self, _project: Any, cmdv: List[str], **_kwargs: Any
+        ) -> None:
+            commands.append(cmdv)
+            self.stdout = f"{head}\0refs/heads/main\0\n"
+
+        def Wait(self) -> int:
+            return 0
+
+    monkeypatch.setattr(git_refs, "GitCommand", FakeGitCommand)
+    monkeypatch.setattr(git_refs, "git_require", lambda _version: False)
+    refs = git_refs.GitRefs("/nonexistent")
+
+    def read_head(name: str) -> None:
+        assert name == "HEAD"
+        refs._symref[name] = "refs/heads/main"
+
+    monkeypatch.setattr(refs, "_ReadSymbolicRef", read_head)
+
+    assert refs.get("HEAD") == head
+    assert commands == [
+        [
+            "for-each-ref",
+            "--format=%(objectname)%00%(refname)%00%(symref)",
+        ]
+    ]
+
+
+def test_for_each_ref_failure_falls_back_to_symbolic_ref(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """When for-each-ref fails, HEAD is still resolved via symbolic-ref."""
+
+    class FakeGitCommand:
+        def __init__(
+            self, _project: Any, _cmdv: List[str], **_kwargs: Any
+        ) -> None:
+            self.stdout = ""
+
+        def Wait(self) -> int:
+            return 1
+
+    monkeypatch.setattr(git_refs, "GitCommand", FakeGitCommand)
+    monkeypatch.setattr(git_refs, "git_require", lambda _version: True)
+    refs = git_refs.GitRefs("/nonexistent")
+
+    def read_head(name: str) -> None:
+        assert name == "HEAD"
+        refs._symref[name] = "refs/heads/main"
+
+    monkeypatch.setattr(refs, "_ReadSymbolicRef", read_head)
+
+    assert refs.symref("HEAD") == "refs/heads/main"
+
+
 @pytest.mark.parametrize("reftable", [False, True])
 def test_updates_when_refs_change(tmp_path, reftable):
     if reftable and not utils_for_test.supports_reftable():

tests/test_git_superproject.py

@@ -542,14 +542,15 @@ class SuperprojectTestCase(unittest.TestCase):
             with mock.patch(
                 "git_superproject.GitCommand", autospec=True
             ) as mock_git_command:
-                with mock.patch(
+                with mock.patch.object(
-                    "git_superproject.GitRefs.get", autospec=True
+                    self._superproject, "_GetRef"
-                ) as mock_git_refs:
+                ) as get_ref:
                     instance = mock_git_command.return_value
                     instance.Wait.return_value = 0
-                    mock_git_refs.side_effect = ["", "1234"]
+                    get_ref.side_effect = ["", "1234"]
 
                     self.assertTrue(self._superproject._Fetch())
+                    get_ref.assert_called_with("refs/heads/main")
                     self.assertEqual(
                         # TODO: Once we require Python 3.8+,
                         #  use 'mock_git_command.call_args.args'.
@@ -572,6 +573,7 @@ class SuperprojectTestCase(unittest.TestCase):
 
                     # If branch for revision exists, set as --negotiation-tip.
                     self.assertTrue(self._superproject._Fetch())
+                    get_ref.assert_called_with("refs/heads/main")
                     self.assertEqual(
                         # TODO: Once we require Python 3.8+,
                         #  use 'mock_git_command.call_args.args'.
@@ -593,3 +595,21 @@ class SuperprojectTestCase(unittest.TestCase):
                             ],
                         ),
                     )
+
+    def test_GetRef_resolves_only_the_requested_ref(self) -> None:
+        command = mock.MagicMock(stdout="1234\n")
+        command.Wait.return_value = 0
+        with mock.patch(
+            "git_superproject.GitCommand", return_value=command
+        ) as git_command:
+            self.assertEqual("1234", self._superproject._GetRef("HEAD"))
+
+        git_command.assert_called_once_with(
+            None,
+            ["rev-parse", "--verify", "--quiet", "HEAD"],
+            gitdir=self._superproject._work_git,
+            bare=True,
+            capture_stdout=True,
+            capture_stderr=True,
+            log_as_error=False,
+        )

tests/test_hooks.py

@@ -15,6 +15,7 @@
 """Unittests for the hooks.py module."""
 
 from io import StringIO
+from pathlib import Path
 import sys
 
 import pytest
@@ -108,11 +109,11 @@ def test_post_sync_argument_validation() -> None:
 
 
 @pytest.mark.parametrize("yes_val", (True, False))
-def test_repo_upload_yes_arg(tmp_path, yes_val: bool) -> None:
+def test_repo_upload_yes_arg(tmp_path: Path, yes_val: bool) -> None:
     """Test that yes is passed in kwargs during hook execution."""
 
     class FakeProject:
-        def __init__(self, worktree):
+        def __init__(self, worktree: str) -> None:
             self.worktree = worktree
             self.enabled_repo_hooks = ["pre-upload"]
             self.config = None
@@ -139,3 +140,64 @@ def main(project_list, **kwargs):
 
     assert res is True
     assert project_list == [yes_val]
+
+
+@pytest.mark.parametrize("fix_val", (True, False))
+def test_repo_upload_fix_arg(tmp_path: Path, fix_val: bool) -> None:
+    """Test that fix is passed in kwargs during hook execution."""
+
+    class FakeProject:
+        def __init__(self, worktree: str) -> None:
+            self.worktree = worktree
+            self.enabled_repo_hooks = ["pre-upload"]
+            self.config = None
+
+    hook_file = tmp_path / "pre-upload.py"
+
+    hook_content = """
+def main(project_list, **kwargs):
+    project_list.append(kwargs.get("fix"))
+"""
+    hook_file.write_text(hook_content)
+
+    hook = hooks.RepoHook(
+        hook_type="pre-upload",
+        hooks_project=FakeProject(str(tmp_path)),
+        repo_topdir=str(tmp_path),
+        manifest_url="https://gerrit",
+        allow_all_hooks=True,
+        fix=fix_val,
+    )
+
+    project_list = []
+    res = hook.Run(project_list=project_list, worktree_list=[])
+
+    assert res is True
+    assert project_list == [fix_val]
+
+
+def test_from_subcmd_without_fix_option() -> None:
+    """Test that FromSubcmd works when opt does not have fix attribute."""
+
+    class Remote:
+        url = "https://gerrit"
+
+    class FakeManifest:
+        repo_hooks_project = None
+        topdir = "/fake/topdir"
+
+        class manifestProject:
+            @staticmethod
+            def GetRemote(name: str) -> "Remote":
+                return Remote()
+
+        class contactinfo:
+            bugurl = "https://bugs"
+
+    class FakeOpt:
+        bypass_hooks = False
+        allow_all_hooks = False
+        ignore_hooks = False
+
+    hook = hooks.RepoHook.FromSubcmd(FakeManifest(), FakeOpt(), "post-sync")
+    assert hook._fix is False

tests/test_subcmds_cherry_pick.py

@@ -0,0 +1,85 @@
+# Copyright (C) 2026 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for subcmds/cherry_pick.py."""
+
+from unittest import mock
+
+import pytest
+
+from error import GitError
+from git_command import GitCommand
+from subcmds import cherry_pick
+
+
+def test_resolve_reference_uses_one_typed_batch_request(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    oid = "1" * 40
+    commit = "tree " + "2" * 40 + "\n\nSubject 🚀\n\nBody\n"
+    output = oid + " commit " + str(len(commit.encode("utf-8"))) + "\n"
+    output += commit + "\n"
+    command = mock.create_autospec(GitCommand, instance=True)
+    command.stdout = output
+    command.stderr = ""
+    command.Wait.return_value = 0
+    run_git = mock.create_autospec(GitCommand, return_value=command)
+    monkeypatch.setattr(cherry_pick, "GitCommand", run_git)
+
+    resolved, contents = cherry_pick.CherryPick()._ResolveReference("topic")
+
+    assert resolved == oid
+    assert contents == commit
+    run_git.assert_called_once_with(
+        None,
+        ["cat-file", "--batch"],
+        input="topic^{commit}\n",
+        capture_stdout=True,
+        capture_stderr=True,
+        verify_command=True,
+    )
+
+
+def test_resolve_reference_rejects_missing_object(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    command = mock.create_autospec(GitCommand, instance=True)
+    command.stdout = "topic^{commit} missing\n"
+    command.stderr = ""
+    command.Wait.return_value = 0
+    monkeypatch.setattr(
+        cherry_pick,
+        "GitCommand",
+        mock.create_autospec(GitCommand, return_value=command),
+    )
+
+    with pytest.raises(GitError, match="commit topic not found"):
+        cherry_pick.CherryPick()._ResolveReference("topic")
+
+
+def test_resolve_reference_rejects_ambiguous_object(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    command = mock.create_autospec(GitCommand, instance=True)
+    command.stdout = "topic^{commit} ambiguous\n"
+    command.stderr = ""
+    command.Wait.return_value = 0
+    monkeypatch.setattr(
+        cherry_pick,
+        "GitCommand",
+        mock.create_autospec(GitCommand, return_value=command),
+    )
+
+    with pytest.raises(GitError, match="commit topic not found"):
+        cherry_pick.CherryPick()._ResolveReference("topic")

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"],
+    )

tests/test_subcmds_sync.py

@@ -14,11 +14,13 @@
 """Unittests for the subcmds/sync.py module."""
 
 import json
+import optparse
 import os
 from pathlib import Path
 import shutil
 import tempfile
 import time
+from typing import Dict, List, Optional
 import unittest
 from unittest import mock
 
@@ -491,12 +493,26 @@ class LocalSyncState(unittest.TestCase):
 
 
 class FakeProject:
-    def __init__(self, relpath, name=None, objdir=None):
+    def __init__(
+        self,
+        relpath: str,
+        name: Optional[str] = None,
+        objdir: Optional[str] = None,
+        parent: Optional["FakeProject"] = None,
+        is_derived: bool = False,
+        revisionId: Optional[str] = None,
+        gitlink_path: Optional[str] = None,
+        path_prefix: str = "",
+    ) -> None:
         self.relpath = relpath
+        self.path_prefix = path_prefix
         self.name = name or relpath
         self.objdir = objdir or relpath
         self.worktree = relpath
-        self.parent = None
+        self.parent = parent
+        self.is_derived = is_derived
+        self.revisionId = revisionId
+        self.gitlink_path = gitlink_path
 
         self.use_git_worktrees = False
         self.UseAlternates = False
@@ -505,8 +521,20 @@ class FakeProject:
         self.config = mock.MagicMock()
         self.EnableRepositoryExtension = mock.MagicMock()
 
-    def RelPath(self, local=None):
+    @property
-        return self.relpath
+    def Derived(self) -> bool:
+        return self.is_derived
+
+    def SetRevision(
+        self, revisionExpr: str, revisionId: Optional[str] = None
+    ) -> None:
+        self.revisionExpr = revisionExpr
+        self.revisionId = revisionId or revisionExpr
+
+    def RelPath(self, local: bool = True) -> str:
+        if local:
+            return self.relpath
+        return os.path.join(self.path_prefix, self.relpath)
 
     def __str__(self):
         return f"project: {self.relpath}"
@@ -614,6 +642,159 @@ class SafeCheckoutOrder(unittest.TestCase):
         )
 
 
+class ParentFirstBatches(unittest.TestCase):
+    def test_no_submodules(self) -> None:
+        p_a = FakeProject("a")
+        p_a_b = FakeProject("a/b")
+        out = sync._ParentFirstBatches([p_a, p_a_b])
+        self.assertEqual(out, [[p_a, p_a_b]])
+
+    def test_submodules_follow_their_parent(self) -> None:
+        p_a = FakeProject("a")
+        p_a_b = FakeProject("a/b", parent=p_a, is_derived=True)
+        p_a_b_c = FakeProject("a/b/c", parent=p_a_b, is_derived=True)
+        out = sync._ParentFirstBatches([p_a_b_c, p_a, p_a_b])
+        self.assertEqual(out, [[p_a], [p_a_b], [p_a_b_c]])
+
+
+class RefreshDerivedRevisions(unittest.TestCase):
+    def _parent_with_submodules(self, **gitlinks: str) -> FakeProject:
+        p_a = FakeProject("a")
+        p_a.GetSubmoduleRevisions = mock.Mock(return_value=gitlinks)
+        return p_a
+
+    def _submodule(self, parent: FakeProject, path: str) -> FakeProject:
+        return FakeProject(
+            f"a/{path}", parent=parent, is_derived=True, gitlink_path=path
+        )
+
+    def test_reads_each_parent_once(self) -> None:
+        p_a = self._parent_with_submodules(b="beef1234", c="cafe1234")
+        p_a_b = self._submodule(p_a, "b")
+        p_a_c = self._submodule(p_a, "c")
+
+        sync._RefreshDerivedRevisions([p_a, p_a_b, p_a_c])
+
+        p_a.GetSubmoduleRevisions.assert_called_once_with()
+        self.assertEqual(p_a_b.revisionId, "beef1234")
+        self.assertEqual(p_a_c.revisionId, "cafe1234")
+
+    def test_reuses_gitlinks_read_for_an_earlier_level(self) -> None:
+        p_a = self._parent_with_submodules(b="beef1234", c="cafe1234")
+        p_a_b = self._submodule(p_a, "b")
+        p_a_c = self._submodule(p_a, "c")
+        submodule_revisions = {}
+
+        sync._RefreshDerivedRevisions([p_a_b], submodule_revisions)
+        sync._RefreshDerivedRevisions([p_a_c], submodule_revisions)
+
+        p_a.GetSubmoduleRevisions.assert_called_once_with()
+        self.assertEqual(p_a_c.revisionId, "cafe1234")
+
+    def test_tells_apart_projects_with_the_same_path(self) -> None:
+        # Paths are relative to their own (sub)manifest, so two projects can
+        # share one.
+        first = self._parent_with_submodules(b="beef1234")
+        second = self._parent_with_submodules(b="cafe1234")
+        first_sub = self._submodule(first, "b")
+        second_sub = self._submodule(second, "b")
+        submodule_revisions = {}
+
+        sync._RefreshDerivedRevisions([first_sub], submodule_revisions)
+        sync._RefreshDerivedRevisions([second_sub], submodule_revisions)
+
+        self.assertEqual(first_sub.revisionId, "beef1234")
+        self.assertEqual(second_sub.revisionId, "cafe1234")
+
+    def test_ignores_projects_from_the_manifest(self) -> None:
+        p_a = self._parent_with_submodules()
+
+        sync._RefreshDerivedRevisions([p_a])
+
+        p_a.GetSubmoduleRevisions.assert_not_called()
+
+    def test_reports_submodules_removed_from_their_parent(self) -> None:
+        p_a = self._parent_with_submodules(b="beef1234")
+        p_a_c = self._submodule(p_a, "c")
+
+        removed = sync._RefreshDerivedRevisions([p_a, p_a_c])
+
+        self.assertEqual(removed, [p_a_c])
+
+    def test_keeps_submodules_of_an_unreadable_parent(self) -> None:
+        p_a = FakeProject("a")
+        p_a.GetSubmoduleRevisions = mock.Mock(return_value=None)
+        p_a_b = FakeProject(
+            "a/b",
+            parent=p_a,
+            is_derived=True,
+            revisionId="stale",
+            gitlink_path="b",
+        )
+
+        removed = sync._RefreshDerivedRevisions([p_a, p_a_b])
+
+        self.assertEqual(removed, [])
+        self.assertEqual(p_a_b.revisionId, "stale")
+
+
+class FetchParentFirst(unittest.TestCase):
+    def test_submodules_are_fetched_after_their_parent(self) -> None:
+        cmd = sync.Sync()
+        cmd._fetch_times = mock.Mock()
+        cmd._fetch_times.Get = mock.Mock(return_value=0)
+
+        calls = []
+        p_a = FakeProject("a")
+
+        def fake_read() -> Dict[str, str]:
+            calls.append(("read gitlinks of", p_a.relpath))
+            return {"b": "beef1234"}
+
+        p_a.GetSubmoduleRevisions = mock.Mock(side_effect=fake_read)
+        p_a_b = FakeProject(
+            "a/b", parent=p_a, is_derived=True, gitlink_path="b"
+        )
+
+        def fake_fetch(
+            projects: List[FakeProject], *_args: object
+        ) -> sync._FetchResult:
+            calls.append(("fetch", [p.relpath for p in projects]))
+            return sync._FetchResult(True, {p.objdir for p in projects})
+
+        opt = mock.Mock(fail_fast=False)
+        with mock.patch.object(cmd, "_Fetch", side_effect=fake_fetch):
+            result = cmd._FetchParentFirst([p_a_b, p_a], opt, None, None, [])
+
+        self.assertTrue(result.success)
+        self.assertEqual(result.projects, {"a", "a/b"})
+        self.assertEqual(
+            calls,
+            [
+                ("fetch", ["a"]),
+                ("read gitlinks of", "a"),
+                ("fetch", ["a/b"]),
+            ],
+        )
+
+
+class WithoutProjects(unittest.TestCase):
+    def test_drops_the_unwanted_projects(self) -> None:
+        p_a = FakeProject("a")
+        p_a_b = FakeProject("a/b")
+        self.assertEqual(sync._WithoutProjects([p_a, p_a_b], [p_a_b]), [p_a])
+        self.assertEqual(sync._WithoutProjects([p_a, p_a_b], []), [p_a, p_a_b])
+
+    def test_keeps_projects_with_the_same_path(self) -> None:
+        # Paths are relative to their own (sub)manifest, so two projects can
+        # share one.
+        first = FakeProject("a/b")
+        second = FakeProject("a/b")
+        self.assertEqual(
+            sync._WithoutProjects([first, second], [second]), [first]
+        )
+
+
 class Chunksize(unittest.TestCase):
     """Tests for _chunksize."""
 
@@ -1158,6 +1339,203 @@ class InterleavedSyncTest(unittest.TestCase):
 
         execute_mock.assert_called_once()
 
+    def test_interleaved_refreshes_submodule_revision(self) -> None:
+        """Test submodules are synced at the revision of the fetched parent."""
+        opt, args = self.cmd.OptionParser.parse_args(["--interleaved", "-j4"])
+        opt.quiet = True
+
+        submodule = FakeProject(
+            "projA/sub",
+            name="projA_sub",
+            objdir="objA_sub",
+            parent=self.projA,
+            is_derived=True,
+            revisionId="stale",
+            gitlink_path="sub",
+        )
+        all_projects = [self.projA, submodule]
+        mock.patch.object(
+            self.cmd, "GetProjects", return_value=all_projects
+        ).start()
+
+        self.projA.GetSubmoduleRevisions = mock.Mock(
+            return_value={"sub": "fetched"}
+        )
+
+        synced = []
+
+        def execute_side_effect(
+            jobs: int,
+            target: object,
+            work_items: List[List[int]],
+            **kwargs: object,
+        ) -> bool:
+            synced_relpaths_set = kwargs["callback"].args[0]
+            projects_in_pass = self.cmd.get_parallel_context()["projects"]
+            for item in work_items:
+                for project_idx in item:
+                    project = projects_in_pass[project_idx]
+                    synced.append((project.relpath, project.revisionId))
+                    synced_relpaths_set.add(project.relpath)
+            return True
+
+        mock.patch.object(
+            self.cmd, "ExecuteInParallel", side_effect=execute_side_effect
+        ).start()
+
+        self.cmd._SyncInterleaved(
+            opt,
+            args,
+            [],
+            self.manifest,
+            self.manifest.manifestProject,
+            all_projects,
+            {},
+        )
+
+        self.assertIn(("projA/sub", "fetched"), synced)
+
+    def test_interleaved_skips_removed_submodule(self) -> None:
+        """Test submodules dropped by their parent are not checked out."""
+        opt, args = self.cmd.OptionParser.parse_args(["--interleaved", "-j4"])
+        opt.quiet = True
+
+        submodule = FakeProject(
+            "projA/sub",
+            name="projA_sub",
+            objdir="objA_sub",
+            parent=self.projA,
+            is_derived=True,
+            revisionId="stale",
+            gitlink_path="sub",
+        )
+        # The parent no longer holds a gitlink for the submodule.
+        self.projA.GetSubmoduleRevisions = mock.Mock(return_value={})
+        # The reloaded manifest no longer derives the removed submodule.
+        mock.patch.object(
+            self.cmd, "GetProjects", return_value=[self.projA]
+        ).start()
+
+        synced = []
+
+        def execute_side_effect(
+            jobs: int,
+            target: object,
+            work_items: List[List[int]],
+            **kwargs: object,
+        ) -> bool:
+            synced_relpaths_set = kwargs["callback"].args[0]
+            projects_in_pass = self.cmd.get_parallel_context()["projects"]
+            for item in work_items:
+                for project_idx in item:
+                    project = projects_in_pass[project_idx]
+                    synced.append(project.relpath)
+                    synced_relpaths_set.add(project.relpath)
+            return True
+
+        mock.patch.object(
+            self.cmd, "ExecuteInParallel", side_effect=execute_side_effect
+        ).start()
+
+        self.cmd._SyncInterleaved(
+            opt,
+            args,
+            [],
+            self.manifest,
+            self.manifest.manifestProject,
+            [self.projA, submodule],
+            {},
+        )
+
+        self.assertEqual(synced, ["projA"])
+
+    def _make_syncable(self, project: FakeProject) -> FakeProject:
+        project.Sync_NetworkHalf = mock.Mock(
+            return_value=SyncNetworkHalfResult(error=None, remote_fetched=True)
+        )
+        project.Sync_LocalHalf = mock.Mock()
+        return project
+
+    def _run_interleaved(
+        self,
+        opt: optparse.Values,
+        initial_projects: List[FakeProject],
+        reloaded_projects: List[FakeProject],
+    ) -> None:
+        """Run _SyncInterleaved with the real workers and callback.
+
+        |initial_projects| make up the first pass, |reloaded_projects| every
+        later one, the way reloading the manifest between passes does.
+        """
+        mock.patch.object(
+            self.cmd, "GetProjects", return_value=reloaded_projects
+        ).start()
+        mock.patch.object(self.cmd, "event_log").start()
+
+        def execute_side_effect(
+            jobs: int,
+            target: object,
+            work_items: List[List[int]],
+            **kwargs: object,
+        ) -> bool:
+            results = [target(item) for item in work_items]
+            return kwargs["callback"](None, kwargs["output"], results)
+
+        mock.patch.object(
+            self.cmd, "ExecuteInParallel", side_effect=execute_side_effect
+        ).start()
+
+        with mock.patch("subcmds.sync.SyncBuffer") as mock_sync_buffer:
+            mock_sync_buffer.return_value.Finish.return_value = True
+            mock_sync_buffer.return_value.errors = []
+            self.cmd._SyncInterleaved(
+                opt,
+                [],
+                [],
+                self.manifest,
+                self.manifest.manifestProject,
+                initial_projects,
+                {},
+            )
+
+    def test_interleaved_syncs_same_path_projects_of_every_manifest(
+        self,
+    ) -> None:
+        """Test a project is not skipped because another shares its path."""
+        opt = self._get_opts(["--interleaved", "-j4"])
+        outer = self._make_syncable(
+            FakeProject("foo", name="outer", objdir="a")
+        )
+        sub = self._make_syncable(
+            FakeProject("foo", name="sub", objdir="b", path_prefix="sub")
+        )
+
+        # |sub| is only discovered once the manifest is reloaded after the
+        # first pass has synced |outer|.
+        self._run_interleaved(opt, [outer], [outer, sub])
+
+        outer.Sync_LocalHalf.assert_called_once()
+        sub.Sync_LocalHalf.assert_called_once()
+
+    def test_interleaved_reports_failures_by_a_unique_path(self) -> None:
+        """Test failing projects are listed by a path that is theirs alone."""
+        opt = self._get_opts(["--interleaved", "-j4"])
+        outer = self._make_syncable(
+            FakeProject("foo", name="outer", objdir="a")
+        )
+        sub = self._make_syncable(
+            FakeProject("foo", name="sub", objdir="b", path_prefix="sub")
+        )
+        sub.Sync_LocalHalf.side_effect = GitError("checkout failed")
+        self.cmd.git_event_log = mock.MagicMock()
+
+        with self.assertRaises(sync.SyncError):
+            self._run_interleaved(opt, [outer, sub], [outer, sub])
+
+        self.assertEqual(
+            self.cmd._interleaved_err_checkout_results, ["sub/foo"]
+        )
+
     def test_interleaved_shared_objdir_serial(self):
         """Test that projects with shared objdir are processed serially."""
         opt, args = self.cmd.OptionParser.parse_args(["--interleaved", "-j4"])
@@ -1252,6 +1630,23 @@ class InterleavedSyncTest(unittest.TestCase):
             project.Sync_NetworkHalf.assert_called_once()
             project.Sync_LocalHalf.assert_called_once()
 
+    def test_worker_reports_a_path_unique_across_manifests(self) -> None:
+        """Test _SyncResult.relpath tells apart same-path projects."""
+        project = FakeProject("foo", objdir="objA", path_prefix="sub")
+        self._make_syncable(project)
+        self.mock_context["projects"] = [project]
+
+        for this_manifest_only, expected in ((False, "sub/foo"), (True, "foo")):
+            with self.subTest(this_manifest_only=this_manifest_only):
+                opt = self._get_opts()
+                opt.this_manifest_only = this_manifest_only
+                with mock.patch("subcmds.sync.SyncBuffer") as mock_sync_buffer:
+                    mock_sync_buffer.return_value.Finish.return_value = True
+                    mock_sync_buffer.return_value.errors = []
+                    result_obj = self.cmd._SyncProjectList(opt, [0])
+
+                self.assertEqual(result_obj.results[0].relpath, expected)
+
     def test_worker_fetch_fails(self):
         """Test _SyncProjectList with a failed fetch."""
         opt = self._get_opts()

tests/test_subcmds_upload.py

@@ -63,3 +63,57 @@ def test_UploadAndReport_UnhandledError(cmd: upload.Upload) -> None:
     with mock.patch.object(cmd, "_UploadBranch", side_effect=UnexpectedError):
         with pytest.raises(UnexpectedError):
             cmd._UploadAndReport(opt, [mock.MagicMock()], _STUB_PEOPLE)
+
+
+def test_GetMergeBranch_explicit_branch(cmd: upload.Upload) -> None:
+    """Verify _GetMergeBranch reads branch.merge for explicit local_branch."""
+    mock_project = mock.MagicMock()
+    mock_branch = mock.MagicMock()
+    mock_branch.merge = "refs/heads/main"
+    mock_project.GetBranch.return_value = mock_branch
+
+    res = cmd._GetMergeBranch(mock_project, local_branch="feature")
+    assert res == "refs/heads/main"
+    mock_project.GetBranch.assert_called_once_with("feature")
+
+
+def test_GetMergeBranch_current_branch(cmd: upload.Upload) -> None:
+    """Verify _GetMergeBranch falls back to project.CurrentBranch."""
+    mock_project = mock.MagicMock()
+    mock_project.CurrentBranch = "auto-cbr"
+    mock_branch = mock.MagicMock()
+    mock_branch.merge = "refs/heads/upstream-main"
+    mock_project.GetBranch.return_value = mock_branch
+
+    res = cmd._GetMergeBranch(mock_project, local_branch=None)
+    assert res == "refs/heads/upstream-main"
+    mock_project.GetBranch.assert_called_once_with("auto-cbr")
+
+
+def test_GetMergeBranch_none_when_no_branch(cmd: upload.Upload) -> None:
+    """Verify _GetMergeBranch returns empty string when detached HEAD."""
+    mock_project = mock.MagicMock()
+    mock_project.CurrentBranch = 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")

tests/test_subcmds_version.py

@@ -0,0 +1,52 @@
+# Copyright (C) 2026 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for subcmds/version.py."""
+
+from unittest import mock
+
+import pytest
+
+from subcmds import version
+
+
+def test_repo_version_uses_one_pretty_format_call(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    project = mock.MagicMock()
+    project.bare_git.log.return_value = "v2.0-1-g12345678\nTue, 25 Aug\n"
+    monkeypatch.setattr(version, "git_require", lambda _version: True)
+
+    result = version.Version._RepoVersion(project)
+
+    assert result == ("v2.0-1-g12345678", "Tue, 25 Aug")
+    project.bare_git.log.assert_called_once_with(
+        "-1", "--format=%(describe)%n%cD", "HEAD"
+    )
+    project.bare_git.describe.assert_not_called()
+
+
+def test_repo_version_keeps_old_git_fallback(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    project = mock.MagicMock()
+    project.bare_git.describe.return_value = "v2.0"
+    project.bare_git.log.return_value = "Tue, 25 Aug"
+    monkeypatch.setattr(version, "git_require", lambda _version: False)
+
+    result = version.Version._RepoVersion(project)
+
+    assert result == ("v2.0", "Tue, 25 Aug")
+    project.bare_git.describe.assert_called_once_with("HEAD")
+    project.bare_git.log.assert_called_once_with("-1", "--format=%cD", "HEAD")