Initial support (R4B) to handle multiple source rules in a group

[brianpos]

Add support for rules that have multiple source variables
(as noted in the spec here: https://www.hl7.org/fhir/mapping-language.html#7.8.0.8.1 )
e.g.

item.linkId as itemId, itemAnswer.value as coding
     -> condition.id = ('condition_' + %itemId.substring(1) + '_'+ %coding.code

The unit test requires some test files that are in the fhir-test-cases repo here:
FHIR/fhir-test-cases@master...brianpos:fhir-test-cases:master

This is only draft as I've only ported the change to the R4B branch, once conceptually approved, I will copy this change (and test) into R4 and R5.

[brianpos]

Note that the test testMultipleSourceVariables passes and works.
However the very similar testMultipleSourceVariablesCopyId doesn't and gets a weird can't cast a StringType to an Id message: this is the rule that has the issue

item.linkId as itemId, itemAnswer.value as coding
   -> condition.id = ('condition_' + %itemId.substring(1) + '_'+ %coding.code)

[bvdh]

Note that the test testMultipleSourceVariables passes and works. However the very similar testMultipleSourceVariablesCopyId doesn't and gets a weird can't cast a StringType to an Id message: this is the rule that has the issue

item.linkId as itemId, itemAnswer.value as coding
   -> condition.id = ('condition_' + %itemId.substring(1) + '_'+ %coding.code)

This might be caused by an issue in org.hl7.fhir.r5.model.TypeConvertor.
This class does not accept primitive types for many data classes. Updating castToId to

public static IdType castToId(Base b) throws FHIRException {
    if (b == null) {
      return null;
    }

    if (b instanceof IdType)
      return (IdType) b;
    else if ( b instanceof StringType )
      return ( new IdType( b.primitiveValue() ));
    else if (b.hasPrimitiveValue())
      return new IdType( b.primitiveValue() );
    else
      throw new FHIRException("Unable to convert a "+b.fhirType()+"("+b.getClass().getName()+") to a Id");
  }

might fix this.

[stale]

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