Fixed element definition element.id not being merged by the snapshot generator

src/Hl7.Fhir.Conformance/Specification/Snapshot/ElementDefnMerger.cs

@@ -156,7 +156,7 @@ void merge(ElementDefinition snap, ElementDefinition diff, bool mergeElementId,
                 // Constraints are cumulative, so they are always "new" (hence a constant false for the comparer)
                 // [WMR 20160917] Note: constraint keys must be unique. The validator will detect duplicate keys, so the derived
                 // profile author can correct the conflicting constraint key.
-                // [WMR 20160918] MUST merge indentical constraints, otherwise each derived profile accumulates
+                // [WMR 20160918] MUST merge identical constraints, otherwise each derived profile accumulates
                 // additional identical constraints inherited from e.g. BackboneElement.
                 // snap.Constraint = mergeCollection(snap.Constraint, diff.Constraint, (a, b) => false);
                 // [WMR 20190723] R4 NEW: Initialize Constraint.source property
@@ -283,7 +283,7 @@ ElementDefinition.TypeRefComponent mergeElementType(ElementDefinition.TypeRefCom
                         // TODO: Move logic to MergeTo method on partial class TypeRefComponent
 
                         // TODO: Copy diff annotations...?
-                        if (diff.ElementId != null) { result.ElementId = diff.ElementId; }
+                        result.ElementId = mergeString(snap.ElementId, diff.ElementId);
                         result.Extension = mergeExtensions(snap.Extension, diff.Extension);
                         result.CodeElement = mergePrimitiveElement(snap.CodeElement, diff.CodeElement);
 
@@ -366,6 +366,7 @@ private ElementDefinition.ElementDefinitionBindingComponent mergeBinding(Element
                         snap.StrengthElement = mergePrimitiveElement(snap.StrengthElement, diff.StrengthElement);
                         snap.DescriptionElement = mergePrimitiveElement(snap.DescriptionElement, diff.DescriptionElement);
                         snap.ValueSetElement = mergeComplexAttribute(snap.ValueSetElement, diff.ValueSetElement);
+                        snap.ElementId = mergeString(snap.ElementId, diff.ElementId);
                         snap.Extension = mergeExtensions(snap.Extension, diff.Extension);
                         snap.Additional = mergeCollection(snap.Additional, diff.Additional, matchExactly);
                         onConstraint(result);
@@ -670,7 +671,8 @@ T mergePrimitiveElement<T>(T snap, T diff, bool allowAppend = false) where T : P
                         {
                             result.ObjectValue = diffValue;
                         }
-                        // Also merge extensions on primitives
+                        // Also merge element id and extensions on primitives
+                        result.ElementId = mergeString(snap.ElementId, diff.ElementId);
                         result.Extension = mergeExtensions(snap.Extension, diff.Extension);
                         onConstraint(result);
                     }
@@ -692,21 +694,21 @@ static string mergeId(ElementDefinition snap, ElementDefinition diff, bool merge
                     }
                     // Newly introduced named slices NEVER inherit element id
                     // Must always regenerate new unique identifier for named slices
-                    else if (!IsEqualName(diff.SliceName, snap.SliceName))
+                    if (!IsEqualName(diff.SliceName, snap.SliceName))
                     {
                         // Regenerate; don't inherit from snap
                         return null;
                     }
                     // Otherwise inherit existing element id from snap
                     return snap.ElementId;
                 }
-                else
-                {
-                    // Don't merge elementId, e.g. for type profiles
-                    return null;
-                }
+
+                // Don't merge elementId, e.g. for type profiles
+                return null;
             }
 
+            static string mergeString(string snap, string diff) => diff ?? snap;
+
             // Functions to match snap collection items to diff collection items
             // Matching key depends on collection type
 

src/Hl7.Fhir.STU3/Specification/Snapshot/ElementDefnMerger.cs

@@ -246,8 +246,9 @@ T mergePrimitiveAttribute<T>(T snap, T diff, bool allowAppend = false) where T :
 
                         result.ObjectValue = diffText;
                     }
-                    // Also merge extensions on primitives
+                    // Also merge element id and extensions on primitives
                     // [Backported from R4] 
+                    result.ElementId = mergeString(snap?.ElementId, diff.ElementId);
                     result.Extension = mergeExtensions(snap?.Extension, diff.Extension);
                     onConstraint(result);
                     return result;
@@ -509,6 +510,7 @@ private ElementDefinition.ElementDefinitionBindingComponent mergeBinding(Element
                         snap.StrengthElement = mergePrimitiveAttribute(snap.StrengthElement, diff.StrengthElement);
                         snap.DescriptionElement = mergePrimitiveAttribute(snap.DescriptionElement, diff.DescriptionElement);
                         snap.ValueSet = mergeComplexAttribute(snap.ValueSet, diff.ValueSet);
+                        snap.ElementId = mergeString(snap.ElementId, diff.ElementId);
                         snap.Extension = mergeExtensions(snap.Extension, diff.Extension);
                         onConstraint(result);
                     }
@@ -535,21 +537,21 @@ string mergeId(ElementDefinition snap, ElementDefinition diff, bool mergeElement
                     }
                     // Newly introduced named slices NEVER inherit element id
                     // Must always regenerate new unique identifier for named slices
-                    else if (diff.SliceName != snap.SliceName)
+                    if (diff.SliceName != snap.SliceName)
                     {
                         // Regenerate; don't inherit from snap
                         return null;
                     }
                     // Otherwise inherit existing element id from snap
                     return snap.ElementId;
                 }
-                else
-                {
-                    // Don't merge elementId, e.g. for type profiles
-                    return null;
-                }
+
+                // Don't merge elementId, e.g. for type profiles
+                return null;
             }
 
+            static string mergeString(string snap, string diff) => diff ?? snap;
+
             // [WMR 20180611] NEW
             static bool isEqualCoding(Coding c, Coding d)
             {

src/Hl7.Fhir.Specification.STU3.Tests/Snapshot/ElementDefinitionPropertyProxy.cs

@@ -12,14 +12,18 @@ namespace Hl7.Fhir.Specification.Tests
     /// The property can also be a specific item from a property list.
     /// The property name is specified in the constructor.
     /// 
-    /// The name is either the name of the property (e.g. "Binding") or the name of the property list
-    /// with a item selector (e.g. "Constraint[Key:dom-2]").
+    /// The name can be
+    /// - the name of the property (e.g. "Binding")
+    /// - the name of the property list with an index (e.g. "Type[0]").
+    /// - the name of the property list with an item selector (e.g. "Constraint[Key:dom-2]").
     /// </summary>
     internal class ElementDefinitionPropertyProxy
     {
+        private bool _isList;
         private string _propertyName;
-        private string _selectorPropertyName;
-        private string _selectorValue;
+        private string _listSelectorPropertyName;
+        private string _listSelectorValue;
+        private int? _listIndex;
         private PropertyInfo _propertyInfo;
         private PropertyInfo _selectorPropertyInfo;
 
@@ -38,7 +42,7 @@ public object CreateInstance(Element element)
         {
             var instance = Activator.CreateInstance(_propertyInfo.PropertyType);
 
-            if (_selectorPropertyInfo == null)
+            if (!_isList)
                 return instance; // Primitive property
 
             // Create item for property list
@@ -47,8 +51,8 @@ public object CreateInstance(Element element)
             // Initialize with specified element
             element?.CopyTo(item);
 
-            // Set key value
-            _selectorPropertyInfo.SetValue(item, _selectorValue);
+            if (_selectorPropertyInfo != null)
+                _selectorPropertyInfo.SetValue(item, _listSelectorValue); // Set key value
 
             // Add item to property list
             if (instance is IList items)
@@ -74,18 +78,29 @@ public void SetValue(object instance, object value)
         /// <returns>The property value as an Element type.</returns>
         public Element GetValueAsElement(object instance)
         {
-            if (_selectorPropertyInfo == null)
+            if (!_isList)
                 return (Element)_propertyInfo.GetValue(instance);
 
             if (_propertyInfo.GetValue(instance, null) is not IList items)
                 return null;
 
-            foreach (var item in items)
+            if (_selectorPropertyInfo != null)
             {
-                var value = _selectorPropertyInfo.GetValue(item)?.ToString();
+                foreach (var item in items)
+                {
+                    var value = _selectorPropertyInfo.GetValue(item)?.ToString();
 
-                if (_selectorValue.Equals(value))
-                    return (Element)item;
+                    if (_listSelectorValue.Equals(value))
+                        return (Element)item;
+                }
+
+                return null;
+            }
+
+            if (_listIndex.HasValue)
+            {
+                _listIndex.Value.Should().BeInRange(0, items.Count - 1);
+                return (Element)items[_listIndex.Value];
             }
 
             return null;
@@ -98,34 +113,60 @@ private void getPropertyInfo(string propertyName)
             _propertyInfo = typeof(ElementDefinition).GetProperty(_propertyName);
             _propertyInfo.Should().NotBeNull(); // Check property exists
 
-            // ReSharper disable once PossibleNullReferenceException
-            if (!isList(_propertyInfo.PropertyType))
+            _isList = isList(_propertyInfo.PropertyType);
+
+            if (!_isList)
             {
                 _propertyInfo.PropertyType.IsAssignableTo(typeof(Element)).Should().BeTrue(); // Property type should be derived from Element
                 return;
             }
 
             _propertyInfo.PropertyType.GenericTypeArguments[0].IsAssignableTo(typeof(Element)).Should().BeTrue(); // Property type should be derived from Element
 
-            _selectorPropertyInfo = _propertyInfo.PropertyType.GenericTypeArguments[0].GetProperty(_selectorPropertyName);
+            if (_listSelectorPropertyName == null)
+                return;
+
+            _selectorPropertyInfo = _propertyInfo.PropertyType.GenericTypeArguments[0].GetProperty(_listSelectorPropertyName);
             _selectorPropertyInfo.Should().NotBeNull(); // Check property exists
         }
 
         private void parsePropertyName(string propertyName)
         {
             _propertyName = propertyName;
 
-            var regex = new Regex("(.*)\\[(.*):(.*)\\]|(.*)");
+            if (!tryParseListKey(propertyName))
+                tryParseListIndex(propertyName);
+        }
+
+        private static bool isList(Type type) => typeof(IList).IsAssignableFrom(type);
+
+        private bool tryParseListKey(string propertyName)
+        {
+            var regex = new Regex("(.+)\\[(.+):(.+)\\]");
             var result = regex.Match(propertyName);
 
-            if (!result.Success || result.Groups[4].Success)
-                return;
+            if (!result.Success)
+                return false;
 
             _propertyName = result.Groups[1].Value;
-            _selectorPropertyName = result.Groups[2].Value;
-            _selectorValue = result.Groups[3].Value;
+            _listSelectorPropertyName = result.Groups[2].Value;
+            _listSelectorValue = result.Groups[3].Value;
+
+            return true;
         }
 
-        private static bool isList(Type type) => typeof(IList).IsAssignableFrom(type);
+        private bool tryParseListIndex(string propertyName)
+        {
+            var regex = new Regex("(.+)\\[(\\d+)\\]");
+            var result = regex.Match(propertyName);
+
+            if (!result.Success)
+                return false;
+
+            _propertyName = result.Groups[1].Value;
+            _listIndex = int.Parse(result.Groups[2].Value);
+
+            return true;
+        }
     }
 }