Once every week or so we receive questions on IRC asking why a patch hasn't been enqueued to gate-and-submit and many times the answer is that there are dependent patch sets that haven't been merged.
In the zuul logs I see things like:
2018-06-11 00:38:28,496 DEBUG zuul.DependentPipelineManager: Considering adding change <Change 1,1> DEBUG zuul.DependentPipelineManager: Checking for changes needed by <Change 1,1>: DEBUG zuul.DependentPipelineManager: Change <Change 1,1> needs change <Change 2,1>: DEBUG zuul.DependentPipelineManager: Change <Change 2,1> is needed but can not be merged DEBUG zuul.DependentPipelineManager: Failed to enqueue changes ahead of <Change 1,1>
It would be nice if zuul could comment on the gerrit patch in this instance