FI-2673 Add Primitive Extension handling (#166)

* generate metadata for must_supports.extensions.path

* Update navigator to handle primitive extension

* Fix fhir_navigator when the result is false

* coding style

* rubocop

* Add two unit test for primitive extension

* add another unit test

* handles if source_hash does not have specified key

* rubocop

* rubocop

* remove .rubocop.yml

* Update gitignore

* add unit tests for non primitive element

---------

Co-authored-by: Yunwei Wang <>

.gitignore

@@ -19,3 +19,4 @@
 /docs/yard
 .yardoc
 node_modules
+.rubocop.yml

lib/us_core_test_kit/fhir_resource_navigation.rb

@@ -1,6 +1,7 @@
 module USCoreTestKit
   module FHIRResourceNavigation
     DAR_EXTENSION_URL = 'http://hl7.org/fhir/StructureDefinition/data-absent-reason'.freeze
+    PRIMITIVE_DATA_TYPES = FHIR::PRIMITIVES.keys
 
     def resolve_path(elements, path)
       elements = Array.wrap(elements)
@@ -64,12 +65,21 @@ def get_next_value(element, property)
         slice = find_slice_via_discriminator(element, property)
         slice
       else
-        element.send(property)
+        result = element.send(property)
+        result = find_primitive_extension(element, property) if result.nil?
+        result
       end
     rescue NoMethodError
       nil
     end
 
+    def find_primitive_extension(element, property)
+      type = element.class::METADATA[property.to_s]['type']
+      source_value = element.source_hash["_#{property}"]
+
+      PRIMITIVE_DATA_TYPES.include?(type) && source_value.present? ? FHIR::Element.new(source_value) : nil
+    end
+
     def find_slice_via_discriminator(element, property)
       element_name = property.to_s.split(':')[0].gsub(/^class$/, 'local_class')
       slice_name = property.to_s.split(':')[1].gsub(/^class$/, 'local_class')