Cross-version conversion doesn't check modifierExtension for future modifier elements

[jwjahns]

Cross-version converters like ActorDefinition40_50.java will check for any cross-version extensions when converting to a newer FHIR version.

However, they only check the extension element, not modifierExtension. Future modifier elements (like R5's ActorDefinition.status) are modifier extensions when expressed in previous versions, so won't be found by the converter.

org.hl7.fhir.core/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv40_50/resources40_50/ActorDefinition40_50.java

Lines 124 to 126 in e862f23

	if (src.hasExtension(STATUS_EXTENSION_URL)) {
	tgt.setStatus(PublicationStatus.fromCode(src.getExtensionByUrl(STATUS_EXTENSION_URL).getValue().primitiveValue()));
	}

---

Validators and SUSHI will reject resources that incorrectly place a modifier extension within extension. So this issue is notable when trying to construct an ActorDefinition in an R4 IG, because the IG Publisher requires canonical resources like ActorDefinition to have a status, but SUSHI will refuse to generate the associated extension anywhere but modifierExtension.

---

Examples for converting R4 Basic to R5 ActorDefinition:

ex_Basic_modifierExtension.json

java -jar validator_cli.jar ./ex_Basic_modifierExtension.json -version 4.0 -to-version 5.0 -output ./result.json -do-native:
=>
{"resourceType":"ActorDefinition","id":"example","modifierExtension":[{"url":"http://hl7.org/fhir/5.0/StructureDefinition/extension-ActorDefinition.status","valueCode":"active"}],"type":"system"}

vs. throwing everything in extension:
ex_Basic_no_modifierExtension.json

java -jar validator_cli.jar ./ex_Basic_no_modifierExtension.json -version 4.0 -to-version 5.0 -output ./result.json -do-native
=>
{"resourceType":"ActorDefinition","id":"example","status":"active","type":"system"}