CQL Translator produces Double List Promotion at Retrieve Codes

After updating from 1.3.10 to 1.3.14, the following CQL example translates to different ELM:

library Test
using FHIR version '4.0.0'
codesystem test: 'test'
code T0: '0' from test

define Observations: [Observation: T0]

The relevant part is the Retrieve Expression. Here you have the double list promotion:

{
  "dataType" : "{http://hl7.org/fhir}Observation",
  "codeProperty" : "code",
  "type" : "Retrieve",
  "codes" : {
    "type" : "ToList",
    "operand" : {
      "type" : "ToList",
      "operand" : {
        "name" : "T0",
        "type" : "CodeRef"
      }
    }
  }
}

With version 1.3.10 I get:

{
  "dataType" : "{http://hl7.org/fhir}Observation",
  "codeProperty" : "code",
  "type" : "Retrieve",
  "codes" : {
    "type" : "ToList",
    "operand" : {
      "name" : "T0",
      "type" : "CodeRef"
    }
  }
}

With disabled list promotion, I get no lists with both versions.

[brynrhodes]

Hi @alexanderkiel , thank you for the report. I have confirmed this behavior, it is a byproduct of list promotion, as well as some fixes to type resolution that were included in the 1.3.14 release.

In detail, what’s happening is that within the retrieve, when the terminology target is a direct reference code, the translator will attempt to resolve equality in to validate the terminology target. The type resolution in 1.3.14 is tighter, so that resolution results in a failure if list-promotion is disabled (which shows up as a warning when resolving terminology targets). But with list-promotion enabled, the translator will opt to promote both sides to a list and allow the comparison (effectively pushing the equality determination to a run-time operation). And finally, because it’s a direct-reference code, the translator assumes it needs to automatically promote the code to a list because the retrieve is expecting a list of codes (the failure here is that it is not checking whether the equality resolution actually resulted in a list promotion).

So the internal part about not resolving code equality correctly is actually an issue that is scheduled to be addressed in the first 1.4 release.

The other issue (not checking whether equality resolution resulted in list promotion, producing double-list promotion) I will address in this release.

[alexanderkiel]

Thanks. I rewrote my queries and was able to update to v1.3.15. Only my comments about the equal tests and the TestEqualNull are still relevant. Should I open separate issues on that?