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    Type:Improvement 
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    Resolution: Unresolved
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    Priority:Major - P3 
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    Affects Version/s: None
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    Component/s: None
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        Query Optimization
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Before SERVER-45620 we would allow a nested pipeline with an illegal stage. For example, $facet is not allowed in a $facet. However, we would allow $facet inside a $lookup inside a $facet. This is no longer allowed, but the error message is misleading – in the above example we would report "$lookup is not allowed in $facet". We should look into making the correct information available, or making the error message more generic.
- is related to
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                    SERVER-45620 Have $union introspect the sub-pipeline to allow for more liberal constraints if the sub-pipeline is not constrained -         
- Closed
 
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