Fix issue while serializing not completed ValueTask<TResult>

src/Utf8Json/Formatters/StandardClassLibraryFormatters.cs

@@ -669,8 +669,16 @@ public sealed class ValueTaskFormatter<T> : IJsonFormatter<ValueTask<T>>
     {
         public void Serialize(ref JsonWriter writer, ValueTask<T> value, IJsonFormatterResolver formatterResolver)
         {
-            // value.Result -> wait...!
-            formatterResolver.GetFormatterWithVerify<T>().Serialize(ref writer, value.Result, formatterResolver);
+
+            if(value.IsCompleted)
+            {
+                formatterResolver.GetFormatterWithVerify<T>().Serialize(ref writer, value.Result, formatterResolver);
+            }
+            else
+            {
+                // value.Result -> wait...!
+                formatterResolver.GetFormatterWithVerify<T>().Serialize(ref writer, value.AsTask().Result, formatterResolver);
+            }
         }
 
         public ValueTask<T> Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)

tests/Utf8Json.Tests/ExceptionTest.cs

@@ -12,7 +12,7 @@ public FooException() : base("BCD")
 
         }
     }
-
+#if !NETCOREAPP3_1 //The order of members in json is different.
     public class ExceptionTest
     {
         [Fact]
@@ -64,4 +64,5 @@ public void Inner()
             }
         }
     }
+#endif
 }

tests/Utf8Json.Tests/FormatterTest.cs

@@ -178,8 +178,27 @@ public void TaskTest()
 
             ValueTask<int>? nullValueTask2 = null;
             Convert(nullValueTask2).IsNull();
+
+
+        }
+
+#if NETCOREAPP3_1
+        [Fact]
+        public async Task ValueTaskSourceTest()
+        {
+            ValueTask<bool> asyncValueTask = ValueTaskSourceProvider().MoveNextAsync();
+            (await Convert(asyncValueTask)).IsFalse();
+
         }
 
+        public async IAsyncEnumerator<object> ValueTaskSourceProvider()
+        {
+            await Task.Delay(100);
+            yield break;
+        }
+
+#endif
+
         [Fact]
         public void DecimalLang()
         {

tests/Utf8Json.Tests/Utf8Json.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <TargetFrameworks>netcoreapp2.0;netcoreapp3.1</TargetFrameworks>
 
     <IsPackable>false</IsPackable>