PRESUBMIT: Be resilient to changes with no Code-Review label

Bug: 750694
Change-Id: I69778c3ea0789795ad7e50d11bf677df8f7bc262
Reviewed-on: https://chromium-review.googlesource.com/594839
Reviewed-by: Daniel Jacques <dnj@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

presubmit_support.py

@@ -247,10 +247,19 @@ class GerritAccessor(object):
     return self.GetChangeInfo(issue)['owner']['email']
 
   def GetChangeReviewers(self, issue, approving_only=True):
-    cr = self.GetChangeInfo(issue)['labels']['Code-Review']
-    max_value = max(int(k) for k in cr['values'].keys())
-    return [r.get('email') for r in cr.get('all', [])
-            if not approving_only or r.get('value', 0) == max_value]
+    changeinfo = self.GetChangeInfo(issue)
+    if approving_only:
+      labelinfo = changeinfo.get('labels', {}).get('Code-Review', {})
+      values = labelinfo.get('values', {}).keys()
+      try:
+        max_value = max(int(v) for v in values)
+        reviewers = [r for r in labelinfo.get('all', [])
+                     if r.get('value', 0) == max_value]
+      except ValueError:  # values is the empty list
+        reviewers = []
+    else:
+      reviewers = changeinfo.get('reviewers', {}).get('REVIEWER', [])
+    return [r.get('email') for r in reviewers]
 
 
 class OutputApi(object):

tests/presubmit_unittest.py

@@ -2387,6 +2387,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
                     u'-1': u"I would prefer that you didn't submit this",
                     u'-2': u'Do not submit'}
       }},
+      "reviewers": {"REVIEWER": [{u'email': u'ben@example.com'}]},
     }
     self.AssertOwnersWorks(approvers=set(['ben@example.com']),
         gerrit_response=response,
@@ -2414,6 +2415,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
                     u'+1': u'Looks good to me',
                     u'-1': u"I would prefer that you didn't submit this"}
       }},
+      "reviewers": {"REVIEWER": [{u'email': u'ben@example.com'}]},
     }
     self.AssertOwnersWorks(approvers=set(['ben@example.com']),
         gerrit_response=response,
@@ -2462,6 +2464,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
                     u'-1': u"I would prefer that you didn't submit this",
                     u'-2': u'Do not submit'}
       }},
+      "reviewers": {"REVIEWER": [{u'email': u'ben@example.com'}]},
     }
     self.AssertOwnersWorks(
         approvers=set(),
@@ -2494,6 +2497,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
                     u'+1': u'Looks good to me',
                     u'-1': u"I would prefer that you didn't submit this"}
       }},
+      "reviewers": {"REVIEWER": [{u'email': u'ben@example.com'}]},
     }
     self.AssertOwnersWorks(
         approvers=set(),