Fix serialization when the primitive's complex part would be filtered out

src/Hl7.Fhir.Base/Serialization/BaseFhirJsonPocoSerializer.cs

@@ -15,6 +15,7 @@
 using Hl7.Fhir.Specification;
 using Hl7.Fhir.Utility;
 using System;
+using System.Buffers;
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
@@ -271,12 +272,35 @@ private void serializeFhirPrimitive(string elementName, PrimitiveType value, Utf
 
             if (value.HasElements)
             {
-                // Write a property with '_elementName'
-                writer.WritePropertyName("_" + elementName);
-                serializeInternal(value, writer, skipValue: true);
+                deferSerializeForFilter(elementName, value, writer);
             }
         }
 
+        private void deferSerializeForFilter(string elementName, PrimitiveType value, Utf8JsonWriter writer)
+        {
+#if NETSTANDARD2_0
+            var data = new MemoryStream();
+#else
+            var data = new ArrayBufferWriter<byte>();
+#endif
+            using (var deferredWriter = new Utf8JsonWriter(data, writer.Options))
+            {
+                serializeInternal(value, deferredWriter, skipValue: true);
+            }
+
+#if NETSTANDARD2_0
+            var bytes = data.ToArray(); 
+#else
+            var bytes = data.WrittenSpan;
+#endif
+            if(bytes.Length < 3) return;
+
+            // Write a property with '_elementName'
+            writer.WritePropertyName("_" + elementName);
+            // write the deferred value
+            writer.WriteRawValue(bytes, skipInputValidation: true);
+        }
+
         /// <summary>
         /// Serialize a primitive .NET value that may occur in the POCOs into Json.
         /// </summary>

src/Hl7.Fhir.Support.Poco.Tests/NewPocoSerializers/SummaryFilterIntegrationTests.cs

@@ -4,6 +4,7 @@
 using Hl7.Fhir.Model;
 using Hl7.Fhir.Serialization;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
@@ -15,6 +16,20 @@ namespace Hl7.Fhir.Support.Poco.Tests
     [TestClass]
     public class SummaryFilterIntegrationTests
     {
+        [TestMethod]
+        public void SummaryHasNoEmptyObject()
+        {
+            var patient = new Patient
+            {
+                BirthDateElement = new Date("1990")
+                {
+                    Extension = [new Extension("birthTime", new Instant(DateTimeOffset.Now))]
+                }
+            };
+            var (original, summarized) = runSummarize(patient, SerializationFilter.ForSummary());
+            summarized.Extension.Should().BeEmpty();
+        }
+
         [TestMethod]
         public void Basics()
         {
@@ -152,14 +167,12 @@ public void SummaryCount()
             // check if result contains the link
             traverse(summarized).Should().ContainKey("link");
         }
-
-        private (T full, T summarized) runSummarize<T>(string filename, SerializationFilter filter) where T : Resource
+
+
+        private (T full, T summarized) runSummarize<T>(T full, SerializationFilter filter) where T : Resource
         {
-            var fullXml = File.ReadAllText(Path.Combine("TestData", filename));
-            var full = FhirXmlNode.Parse(fullXml).ToPoco<T>(ModelInspector.ForType<T>());
-
             var options = new JsonSerializerOptions()
-                .ForFhir(typeof(Patient).Assembly, new FhirJsonPocoSerializerSettings { SummaryFilter = filter })
+                .ForFhir(typeof(Patient).Assembly, new FhirJsonPocoSerializerSettings() { SummaryFilter = filter })
                 .Pretty();
             string summarizedJson = JsonSerializer.Serialize(full, options);
 
@@ -168,6 +181,14 @@ public void SummaryCount()
             return (full, summarized);
         }
 
+        private (T full, T summarized) runSummarize<T>(string filename, SerializationFilter filter) where T : Resource
+        {
+            var fullXml = File.ReadAllText(Path.Combine("TestData", filename));
+            var full = FhirXmlNode.Parse(fullXml).ToPoco<T>();
+
+            return runSummarize(full, filter);
+        }
+
         private static IEnumerable<KeyValuePair<string, object>> traverse(Base x)
         {
             return childrenAndMe(KeyValuePair.Create("(root)", (object)x));