Use Element as primary data type for polymorphic elements [STU3]

src/Hl7.Fhir.Specification.Tests/Snapshot/SnapshotGeneratorTest.cs

@@ -7431,6 +7431,36 @@ public async T.Task SnapshotSucceedsWithExtendedVariantElementDef()
 
             structureDef.Snapshot.Element.Where(element => element.Path == "Observation.value[x].extension").Should().HaveCount(2, "Elements are in the snapshot");
             structureDef.Snapshot.Element.Where(element => element.Path == "Observation.extension").Should().HaveCount(1, "Only the root extension should be there");
-        }       
+        }
+
+        [TestMethod]
+        public async T.Task TestExtensionValueXCommentShouldBeNull()
+        {
+            const string ElementId = "Extension.value[x]";
+
+            var zipSource = ZipSource.CreateValidationSource();
+            var resolver = new MultiResolver(zipSource);
+            var sd = await resolver.FindStructureDefinitionForCoreTypeAsync(nameof(Extension));
+
+            var element = sd.Snapshot.Element.Single(x => x.ElementId == ElementId);
+            element.Comment.Should().BeNull();
+
+            var generator = new SnapshotGenerator(resolver, SnapshotGeneratorSettings.CreateDefault());
+
+            generator.PrepareElement += (sender, e) =>
+            {
+                if (e.Element.Path == ElementId)
+                {                   
+                    Debug.WriteLine($"Element:{ElementId} BaseElement:{e?.BaseElement?.ElementId}");
+                }
+            };
+
+            // Act
+            await generator.UpdateAsync(sd);
+
+            // Assert
+            element = sd.Snapshot.Element.Single(x => x.ElementId == ElementId);
+            element.Comment.Should().BeNull();
+        }
     }
 }

src/Hl7.Fhir.Specification/Specification/Navigation/ProfileNavigationExtensions.cs

@@ -7,7 +7,7 @@
  */
 
 using Hl7.Fhir.Model;
-using Hl7.Fhir.Specification.Navigation;
+using Hl7.Fhir.Utility;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -104,7 +104,16 @@ public static bool InRange(this ElementDefinition defn, int count)
         /// <returns>A <see cref="ElementDefinition.TypeRefComponent"/> instance, or <c>null</c>.</returns>
         public static ElementDefinition.TypeRefComponent PrimaryType(this ElementDefinition defn)
         {
-            return defn.Type != null && defn.Type.Count > 0 ? defn.Type[0] : null;
+            if (defn.Type.IsNullOrEmpty())
+                return null;
+            else if (defn.Type.Count == 1)
+                return defn.Type[0];
+            else  //if there are multiple types (value[x]), try to get a common type, otherwise, use Element as the common datatype             
+            {
+                var distinctTypeCode = defn.CommonTypeCode() ?? FHIRAllTypes.Element.GetLiteral();
+                return new ElementDefinition.TypeRefComponent() { Code = distinctTypeCode };
+            }
+
         }
 
         /// <summary>Returns the type profile reference of the primary element type, if it exists, or <c>null</c></summary>

src/Hl7.Fhir.Specification/Specification/Snapshot/SnapshotGenerator.cs

@@ -718,13 +718,7 @@ private async T.Task createNewElement(ElementDefinitionNavigator snap, ElementDe
             {
                 var newElement = (ElementDefinition)baseElement.DeepCopy();
                 newElement.Path = ElementDefinitionNavigator.ReplacePathRoot(newElement.Path, diff.Path);
-                newElement.Base = null;
-
-                //Remove type specific constraints on polymorph type elements.
-                if(diff.Current.Type.Count > 1)
-                {
-                    removeNewTypeConstraint(newElement, typeStructure);
-                }
+                newElement.Base = null;               
 
                 // [WMR 20160915] NEW: Notify subscribers
                 OnPrepareElement(newElement, typeStructure, baseElement);