In SERVER-103133 we noticed that the subpipeline for unionWith is referenced in dependency analysis and stage constraints but for sharded views the view resolution is only discovered during execution (code link), after dependency analysis has finished. This means that we perform dependency analysis and finding the strictest stage constraint with an incomplete view of the subpipeline we are going to execute. We did a small investigation during SERVER-103133 and we could not find a case where not knowing the full pipeline would cause a bug, but we also noticed there are were not many tests around this.

This ticket would involve adding more tests where $unionWith is in a subpipeline and is followed by stages that participate in dependency analysis.