Allow using nullable complex types (and arrays) in the message types (#6004)

Author: SzymonPobiega

src/NServiceBus.Core.Tests/MessageMapper/MessageMapperTests.cs

@@ -46,16 +46,29 @@ public void CreateInstance_WhenMessageInitialized_ShouldBeThreadsafe()
             });
         }
 
+#if NETCOREAPP
+#nullable enable
         [Test]
         public void Should_handle_messages_with_nullable_reference_types()
         {
             var mapper = new MessageMapper();
 
-            // Type defined in separate assembly as a workaround
-            // because we can't use nullable refeference types yet
-            mapper.CreateInstance<WithDodgyNullable.IMyMessage>();
+            mapper.CreateInstance<IMessageWithNullableProperties>();
         }
 
+        public interface IMessageWithNullableProperties : NServiceBus.ICommand, NServiceBus.IMessage
+        {
+            string? NullableString { get; set; }
+            object[]? NullableArray { get; set; }
+            List<NullableComplexTypeItem>? NullableList { get; set; }
+        }
+
+        public class NullableComplexTypeItem
+        {
+        }
+#nullable disable
+#endif
+
         [Test]
         public void CreateInstance_WhenMessageNotInitialized_ShouldBeThreadsafe()
         {
@@ -253,5 +266,6 @@ public interface IMessageInterfaceWithNullablePropertyAttribute
             object Value { get; set; }
         }
 
+
     }
 }

src/NServiceBus.Core.Tests/NServiceBus.Core.Tests.csproj

@@ -16,12 +16,6 @@
     <Reference Include="System.Transactions" />
   </ItemGroup>
 
-  <!-- Workaround reference because we can't use nullable reference types yet -->
-  <ItemGroup>
-    <Reference Include="WithDodgyNullable" HintPath="TestDlls\WithDodgyNullable.dll" />
-  </ItemGroup>
-  <!-- End workaround -->
-
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.6.1" />
     <PackageReference Include="Mono.Cecil" Version="0.10.4" />

src/NServiceBus.Core.Tests/TestDlls/WithDodgyNullable.dll

@@ -2,6 +2,7 @@ namespace NServiceBus
 {
     using System;
     using System.Collections.Generic;
+    using System.Collections.ObjectModel;
     using System.Linq;
     using System.Reflection;
     using System.Reflection.Emit;
@@ -99,26 +100,39 @@ static void AddCustomAttributeToProperty(CustomAttributeData attributeData, Prop
         {
             var namedArguments = attributeData.NamedArguments;
 
+            object[] constructorArgs = attributeData.ConstructorArguments.Select(ExtractValue).ToArray();
             if (namedArguments == null)
             {
                 var attributeBuilder = new CustomAttributeBuilder(
                     attributeData.Constructor,
-                    attributeData.ConstructorArguments.Select(x => x.Value).ToArray());
+                    constructorArgs);
 
                 propBuilder.SetCustomAttribute(attributeBuilder);
             }
             else
             {
+                PropertyInfo[] namedProperties = namedArguments.Select(x => (PropertyInfo)x.MemberInfo).ToArray();
+                object[] propertyValues = namedArguments.Select(x => x.TypedValue.Value).ToArray();
+
                 var attributeBuilder = new CustomAttributeBuilder(
                     attributeData.Constructor,
-                    attributeData.ConstructorArguments.Select(x => x.Value).ToArray(),
-                    namedArguments.Select(x => (PropertyInfo)x.MemberInfo).ToArray(),
-                    namedArguments.Select(x => x.TypedValue.Value).ToArray());
+                    constructorArgs,
+                    namedProperties,
+                    propertyValues);
 
                 propBuilder.SetCustomAttribute(attributeBuilder);
             }
         }
 
+        static object ExtractValue(CustomAttributeTypedArgument arg)
+        {
+            if (arg.Value is ReadOnlyCollection<CustomAttributeTypedArgument> nestedValue)
+            {
+                return nestedValue.Select(x => x.Value).ToArray();
+            }
+            return arg.Value;
+        }
+
         /// <summary>
         /// Returns all properties on the given type, going up the inheritance hierarchy.
         /// </summary>