sync: support post-sync hook in <repo-hooks>

Add support for a new hook type "post-sync" declared in the manifest using
<repo-hooks>. This allows executing a script automatically after a successful
`repo sync`.

This is useful for initializing developer environments, installing project-wide
Git hooks, generating configs, and other post-sync automation tasks.

Example manifest usage:

  <project name="myorg/repo-hooks" path="hooks" revision="main" />
  <repo-hooks in-project="myorg/repo-hooks" enabled-list="post-sync">
    <hook name="post-sync" />
  </repo-hooks>

The hook script must be named `post-sync.py` and located at the root of the
hook project.

The post-sync hook does not block `repo sync`; if the script fails, the sync
still completes successfully with a warning.

Test: Added `post-sync.py` in hook project and verified it runs after `repo sync`

Bug: b/421694721
Change-Id: I69f3158f0fc319d73a85028d6e90fea02c1dc8c8
Signed-off-by: Kenny Cheng <chao.shun.cheng.tw@gmail.com>
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/480581
Reviewed-by: Scott Lee <ddoman@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

subcmds/sync.py

@@ -68,6 +68,7 @@ from git_config import GetUrlCookieFile
 from git_refs import HEAD
 from git_refs import R_HEADS
 import git_superproject
+from hooks import RepoHook
 import platform_utils
 from progress import elapsed_str
 from progress import jobs_str
@@ -623,6 +624,7 @@ later is required to fix a server side protocol bug.
             action="store_true",
             help=optparse.SUPPRESS_HELP,
         )
+        RepoHook.AddOptionGroup(p, "post-sync")
 
     def _GetBranch(self, manifest_project):
         """Returns the branch name for getting the approved smartsync manifest.
@@ -1847,6 +1849,21 @@ later is required to fix a server side protocol bug.
         except (KeyboardInterrupt, Exception) as e:
             raise RepoUnhandledExceptionError(e, aggregate_errors=errors)
 
+        # Run post-sync hook only after successful sync
+        self._RunPostSyncHook(opt)
+
+    def _RunPostSyncHook(self, opt):
+        """Run post-sync hook if configured in manifest <repo-hooks>."""
+        hook = RepoHook.FromSubcmd(
+            hook_type="post-sync",
+            manifest=self.manifest,
+            opt=opt,
+            abort_if_user_denies=False,
+        )
+        success = hook.Run(repo_topdir=self.client.topdir)
+        if not success:
+            print("Warning: post-sync hook reported failure.")
+
     def _ExecuteHelper(self, opt, args, errors):
         manifest = self.outer_manifest
         if not opt.outer_manifest: