pw_presubmit: Ignore reverts in commit message check

Change-Id: I4b25120e9fc4181fbbd783b3ecb202692fa1e4fd
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/37329
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Rob Mohr <mohrr@google.com>
diff --git a/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py b/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
index d136b77..a0ec61f 100755
--- a/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
+++ b/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
@@ -473,6 +473,13 @@
     for line in lines:
         _LOG.debug(line)
 
+    # Ignore Gerrit-generated reverts.
+    if ('Revert' in lines[0]
+            and 'This reverts commit ' in git_repo.commit_message()
+            and 'Reason for revert: ' in git_repo.commit_message()):
+        _LOG.warning('Ignoring apparent Gerrit-generated revert')
+        return
+
     if not lines:
         _LOG.error('The commit message is too short!')
         raise PresubmitFailure