Fixed a bug where nullable enum like classes could not be deserialized correctly (#564)

* Fixed a bug where nullable enum like classes could not be deserialized correctly

* Updated sample project version

* Added test for null cases as well

Author: david-driscoll

sample/SampleServer/SampleServer.csproj

@@ -5,7 +5,7 @@
         <IsPackable>false</IsPackable>
         <TargetFramework>netcoreapp3.1</TargetFramework>
         <RuntimeIdentifier>win7-x64</RuntimeIdentifier>
-        <LangVersion>8.0</LangVersion>
+        <LangVersion>latest</LangVersion>
     </PropertyGroup>
 
     <ItemGroup>

src/JsonRpc/Serialization/Converters/EnumLikeStringConverter.cs

@@ -13,9 +13,11 @@ public override IEnumLikeString ReadJson(
             bool hasExistingValue,
             JsonSerializer serializer
         ) =>
-            reader.TokenType switch {
-                JsonToken.String => (IEnumLikeString) Activator.CreateInstance(objectType, (string) reader.Value),
-                _                => (IEnumLikeString) Activator.CreateInstance(objectType, null)
+            ( reader.TokenType, Nullable.GetUnderlyingType(objectType) ) switch {
+                (JsonToken.String, null)         => (IEnumLikeString) Activator.CreateInstance(objectType, (string) reader.Value),
+                (JsonToken.String, { } realType) => (IEnumLikeString) Activator.CreateInstance(realType, (string) reader.Value),
+                (_, { })                         => (IEnumLikeString) Activator.CreateInstance(objectType, null),
+                _                                => null
             };
 
         public override bool CanRead => true;

test/Dap.Tests/EnumLikeConverterTests.cs

@@ -0,0 +1,36 @@
+using System;
+using FluentAssertions;
+using OmniSharp.Extensions.DebugAdapter.Client;
+using OmniSharp.Extensions.DebugAdapter.Protocol;
+using OmniSharp.Extensions.DebugAdapter.Protocol.Models;
+using OmniSharp.Extensions.DebugAdapter.Protocol.Requests;
+using Xunit;
+
+namespace Dap.Tests
+{
+    public class EnumLikeConverterTests
+    {
+        [Fact]
+        public void PathFormat_Should_Be_Serializable()
+        {
+            var options = new InitializeRequestArguments() {
+                PathFormat = PathFormat.Uri
+            };
+
+            Action a = () => new DapSerializer().SerializeObject(options);
+            a.Should().NotThrow();
+        }
+        [Fact]
+        public void PathFormat_Should_Be_Deserializable()
+        {
+            Func<InitializeRequestArguments> a = () => new DapSerializer().DeserializeObject<InitializeRequestArguments>("{\"pathformat\": \"Uri\"}");
+            a.Should().NotThrow().Subject.PathFormat.Should().NotBeNull();
+        }
+        [Fact]
+        public void PathFormat_Should_Be_Deserializable_When_Null()
+        {
+            var a = new DapSerializer().DeserializeObject<InitializeRequestArguments>("{\"pathformat\":null}");
+            a.PathFormat.Should().BeNull();
+        }
+    }
+}