Fix invalid reference: refs/remotes/origin/HEAD error

Change-Id: Iac298a7a14b5c0b55fd199ec120fe5c37ef88fdc
Bug: 1178944
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2757129Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>

recipes/recipe_modules/bot_update/resources/bot_update.py

@@ -770,6 +770,7 @@ def _git_checkout(sln, sln_dir, revisions, refs, no_fetch_tags, git_cache_dir,
   # Step 2: populate a checkout from local cache. All operations are local.
   mirror_dir = git(
       'cache', 'exists', '--quiet', '--cache-dir', git_cache_dir, url).strip()
+  _set_remote_head(mirror_dir)
   first_try = True
   while True:
     try:
@@ -789,6 +790,7 @@ def _git_checkout(sln, sln_dir, revisions, refs, no_fetch_tags, git_cache_dir,
         git('remote', 'set-url', 'origin', mirror_dir, cwd=sln_dir)
         git('fetch', 'origin', cwd=sln_dir)
       git('remote', 'set-url', '--push', 'origin', url, cwd=sln_dir)
+      _set_remote_head(sln_dir)
       for ref in refs:
         refspec = '%s:%s' % (ref, ref_to_remote_ref(ref.lstrip('+')))
         git('fetch', 'origin', refspec, cwd=sln_dir)
@@ -821,6 +823,19 @@ def _git_disable_gc(cwd):
   git('config', 'gc.autopacklimit', '0', cwd=cwd)
 
 
+def _set_remote_head(cwd):
+  if len(git('ls-remote', 'origin', 'HEAD', cwd=cwd)) > 0:
+    return
+  try:
+    git('remote', 'set-head', 'origin', '--auto', cwd=cwd)
+  except SubprocessFailed:
+    # If remote HEAD cannot be set automatically, prefer main over master.
+    try:
+      git('remote', 'set-head', 'origin', 'main', cwd=cwd)
+    except SubprocessFailed:
+      git('remote', 'set-head', 'origin', 'master', cwd=cwd)
+
+
 def get_commit_position(git_path, revision='HEAD'):
   """Dumps the 'git' log for a specific revision and parses out the commit
   position.