sync: Add --superproject-rev flag to sync to specific revision

Allow syncing the outer manifest to a state defined by a specific
superproject revision. It updates the superproject, reads the manifest
commit from .supermanifest, and checks out the outer manifest project
to that commit.

Submanifests are then processed normally, allowing them to be updated
to the revisions specified in the new outer manifest state.

Bug: 416589884
Change-Id: I304c37a2b8794f9b74cb7e5e209a8a93762bdb52
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/576321
Commit-Queue: Gavin Mak <gavinmak@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

git_superproject.py

@@ -34,6 +34,7 @@ import urllib.parse
 
 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
@@ -132,6 +133,10 @@ class Superproject:
         """Set the _print_messages attribute."""
         self._print_messages = value
 
+    def SetRevisionId(self, revision_id: str) -> None:
+        """Set the revisionId of the superproject to sync to."""
+        self.revision = revision_id
+
     @property
     def commit_id(self):
         """Returns the commit ID of the superproject checkout."""
@@ -314,7 +319,14 @@ class Superproject:
             cmd.extend(["--negotiation-tip", rev_commit])
 
         if self.revision:
-            cmd += [self.revision + ":" + self.revision]
+            # If revision is a commit hash, fetch it directly to avoid
+            # creating a local branch of the same name.
+            refspec = (
+                self.revision
+                if IsId(self.revision)
+                else f"{self.revision}:{self.revision}"
+            )
+            cmd.append(refspec)
         p = GitCommand(
             None,
             cmd,
@@ -401,6 +413,8 @@ class Superproject:
 
         if not self._Init():
             return SyncResult(False, should_exit)
+        if IsId(self.revision) and self.commit_id:
+            return SyncResult(True, False)
         if not self._Fetch():
             return SyncResult(False, should_exit)
         if not self._quiet: