Allow 'git cl patch' when not on a branch.

R=agable@chromium.org,tandrii@chromium.org

Bug:
Change-Id: I83c285c333a21f2ed0138723a1cd5347e65f41ae
Reviewed-on: https://chromium-review.googlesource.com/710742
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>

git_cl.py

@@ -2828,11 +2828,19 @@ class _GerritChangelistImpl(_ChangelistCodereviewBase):
             'uploading changes based on top of this branch difficult.\n'
             'If you want to do that, use "git cl patch --force" instead.')
 
+    if self.GetBranch():
       self.SetIssue(parsed_issue_arg.issue)
       self.SetPatchset(patchset)
       fetched_hash = RunGit(['rev-parse', 'FETCH_HEAD']).strip()
       self._GitSetBranchConfigValue('last-upload-hash', fetched_hash)
       self._GitSetBranchConfigValue('gerritsquashhash', fetched_hash)
+    else:
+      print('WARNING: You are in detached HEAD state.\n'
+            'The patch has been applied to your checkout, but you will not be '
+            'able to upload a new patch set to the gerrit issue.\n'
+            'Try using the \'-b\' option if you would like to work on a '
+            'branch and/or upload a new patch set.')
+
     return 0
 
   @staticmethod
@@ -5402,8 +5410,6 @@ def CMDpatch(parser, args):
       RunGit(['branch', '-D', options.newbranch],
              stderr=subprocess2.PIPE, error_ok=True)
     RunGit(['new-branch', options.newbranch])
-  elif not GetCurrentBranch():
-    DieWithError('A branch is required to apply patch. Hint: use -b option.')
 
   cl = Changelist(**cl_kwargs)
 

tests/git_cl_test.py

@@ -2068,8 +2068,6 @@ class TestGitCl(TestCase):
 
     if new_branch:
       self.calls = [((['git', 'new-branch', 'master'],), ''),]
-    else:
-      self.calls = [((['git', 'symbolic-ref', 'HEAD'],), 'master')]
 
     if default_codereview:
       if not force_codereview:
@@ -2267,7 +2265,6 @@ class TestGitCl(TestCase):
     self.mock(git_cl.gerrit_util, 'GetChangeDetail', notExists)
 
     self.calls = [
-      ((['git', 'symbolic-ref', 'HEAD'],), 'master'),
       ((['git', 'symbolic-ref', 'HEAD'],), 'master'),
       ((['git', 'config', 'branch.master.rietveldissue'],), CERR1),
       ((['git', 'config', 'branch.master.gerritissue'],), CERR1),