Revert "git-cl: turn GERRIT_SQUASH_UPLOADS into a warning"

This reverts commit 31a538a3a9.

Reason for revert:
Breaks ANGLE's workflow.

Original change's description:
> git-cl: turn GERRIT_SQUASH_UPLOADS into a warning
> 
> Now that repos have dropped this from their codereview.settings file,
> change this logic to issue a warning if it's ever seen again.
> 
> Drop checking local gerrit.override-squash-uploads config too since
> it's no longer relevant.
> 
> Bug: 993518
> Change-Id: Id91bbc94b0890ca21c51a274f6acc41f2ae19b78
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1756159
> Commit-Queue: Mike Frysinger <vapier@chromium.org>
> Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>

TBR=vapier@chromium.org,ehmaldonado@chromium.org,infra-scoped@luci-project-accounts.iam.gserviceaccount.com

Change-Id: Iaa8b3341b189f356082ae25a1557898e25820566
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 993518
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2182019
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

git_cl.py

@@ -766,12 +766,27 @@ class Settings(object):
 
   def GetSquashGerritUploads(self):
     """Returns True if uploads to Gerrit should be squashed by default."""
+    if self.squash_gerrit_uploads is None:
+      self.squash_gerrit_uploads = self.GetSquashGerritUploadsOverride()
     if self.squash_gerrit_uploads is None:
       # Default is squash now (http://crbug.com/611892#c23).
       self.squash_gerrit_uploads = self._GetConfig(
           'gerrit.squash-uploads').lower() != 'false'
     return self.squash_gerrit_uploads
 
+  def GetSquashGerritUploadsOverride(self):
+    """Return True or False if codereview.settings should be overridden.
+
+    Returns None if no override has been defined.
+    """
+    # See also http://crbug.com/611892#c23
+    result = self._GetConfig('gerrit.override-squash-uploads').lower()
+    if result == 'true':
+      return True
+    if result == 'false':
+      return False
+    return None
+
   def GetGerritSkipEnsureAuthenticated(self):
     """Return True if EnsureAuthenticated should not be done for Gerrit
     uploads."""
@@ -2740,8 +2755,8 @@ def LoadCodereviewSettingsFromFile(fileobj):
     RunGit(['config', 'gerrit.host', keyvals['GERRIT_HOST']])
 
   if 'GERRIT_SQUASH_UPLOADS' in keyvals:
-    print('WARNING: GERRIT_SQUASH_UPLOADS in codereview.settings is no longer '
-          'supported.  Please delete it and update your ~/.gitconfig instead.')
+    RunGit(['config', 'gerrit.squash-uploads',
+            keyvals['GERRIT_SQUASH_UPLOADS']])
 
   if 'GERRIT_SKIP_ENSURE_AUTHENTICATED' in keyvals:
     RunGit(['config', 'gerrit.skip-ensure-authenticated',

tests/git_cl_test.py

@@ -694,6 +694,10 @@ class TestGitCl(unittest.TestCase):
 
     calls = []
 
+    if squash_mode in ('override_squash', 'override_nosquash'):
+      self.mockGit.config['gerrit.override-squash-uploads'] = (
+          'true' if squash_mode == 'override_squash' else 'false')
+
     if not git_footers.get_footer_change_id(description) and not squash:
       calls += [
         (('DownloadGerritHook', False), ''),
@@ -1104,38 +1108,52 @@ class TestGitCl(unittest.TestCase):
         post_amend_description='desc ✔\n\nBUG=\n\nChange-Id: Ixxx',
         change_id='Ixxx')
 
+  def test_gerrit_upload_without_change_id_override_nosquash(self):
+    self._run_gerrit_upload_test(
+        [],
+        'desc ✔\n\nBUG=\n',
+        [],
+        squash=False,
+        squash_mode='override_nosquash',
+        post_amend_description='desc ✔\n\nBUG=\n\nChange-Id: Ixxx',
+        change_id='Ixxx')
+
   def test_gerrit_no_reviewer(self):
     self._run_gerrit_upload_test(
-        ['--no-squash'],
+        [],
         'desc ✔\n\nBUG=\n\nChange-Id: I123456789\n',
         [],
         squash=False,
+        squash_mode='override_nosquash',
         change_id='I123456789')
 
   def test_gerrit_no_reviewer_non_chromium_host(self):
     # TODO(crbug/877717): remove this test case.
     self._run_gerrit_upload_test(
-        ['--no-squash'],
+        [],
         'desc ✔\n\nBUG=\n\nChange-Id: I123456789\n',
         [],
         squash=False,
+        squash_mode='override_nosquash',
         short_hostname='other',
         change_id='I123456789')
 
   def test_gerrit_patchset_title_special_chars_nosquash(self):
     self._run_gerrit_upload_test(
-        ['--no-squash', '-f', '-t', 'We\'ll escape ^_ ^ special chars...@{u}'],
+        ['-f', '-t', 'We\'ll escape ^_ ^ special chars...@{u}'],
         'desc ✔\n\nBUG=\n\nChange-Id: I123456789',
         squash=False,
+        squash_mode='override_nosquash',
         change_id='I123456789',
         title='We\'ll escape ^_ ^ special chars...@{u}')
 
   def test_gerrit_reviewers_cmd_line(self):
     self._run_gerrit_upload_test(
-        ['--no-squash', '-r', 'foo@example.com', '--send-mail'],
+        ['-r', 'foo@example.com', '--send-mail'],
         'desc ✔\n\nBUG=\n\nChange-Id: I123456789',
         reviewers=['foo@example.com'],
         squash=False,
+        squash_mode='override_nosquash',
         notify=True,
         change_id='I123456789',
         final_description=(