Removed need for Nullable converters in Json serialization (dotnet/co…

…refx#35754)

Added support for Nullable<T> properties where a Nullable converter is no longer required.
Enum converter has generic constraint to `Enum` type.

Commit migrated from dotnet/corefx@b0751dc

src/libraries/System.Text.Json/src/System.Text.Json.csproj

@@ -46,42 +46,30 @@
     <Compile Include="System\Text\Json\Serialization\ClassType.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\DefaultArrayConverter.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\DefaultConverters.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\DefaultEnumConverter.cs" />
+    <Compile Include="System\Text\Json\Serialization\Converters\DefaultConvertersOfTValue.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterBoolean.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterBooleanNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterByte.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterByteNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterChar.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterCharNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterDateTime.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterDateTimeNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterDecimal.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterDecimalNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterDouble.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterDoubleNullable.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInfoInt16.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInt16Nullable.cs" />
+    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterEnum.cs" />
+    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInt16.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInt32.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInt32Nullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInt64.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterInt64Nullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterSByte.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterSByteNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterSingle.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterSingleNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterString.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt16.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt16Nullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt32.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt32Nullable.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt64.cs" />
-    <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt64Nullable.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonClassInfo.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonClassInfo.AddProperty.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonEnumerableConverter.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfo.cs" />
-    <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoOfTClassTProperty.cs" />
-    <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoOfTProperty.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoNotNullable.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoNullable.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoOfTClassTPropertyTUnderlying.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleArray.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.Stream.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleValue.cs" />

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/DefaultConverters.cs

@@ -2,75 +2,58 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Reflection;
+
 namespace System.Text.Json.Serialization.Converters
 {
     internal static class DefaultConverters
     {
-        private const int MaxTypeCode = 18;
-
-        private static readonly object[] s_Converters = new object[MaxTypeCode + 1] {
-            null,   // Empty 
-            null,   // Object
-            null,   // DBNull
-            new JsonValueConverterBoolean(),
-            new JsonValueConverterChar(),
-            new JsonValueConverterSByte(),
-            new JsonValueConverterByte(),
-            new JsonValueConverterInt16(),
-            new JsonValueConverterUInt16(),
-            new JsonValueConverterInt32(),
-            new JsonValueConverterUInt32(),
-            new JsonValueConverterInt64(),
-            new JsonValueConverterUInt64(),
-            new JsonValueConverterSingle(),
-            new JsonValueConverterDouble(),
-            new JsonValueConverterDecimal(),
-            new JsonValueConverterDateTime(),
-            null,   // (not a value)
-            new JsonValueConverterString()
-        };
-
-        private static readonly object[] s_NullableConverters = new object[MaxTypeCode + 1]
-        {
-            null,
-            null,
-            null,
-            new JsonValueConverterBooleanNullable(),
-            new JsonValueConverterCharNullable(),
-            new JsonValueConverterSByteNullable(),
-            new JsonValueConverterByteNullable(),
-            new JsonValueConverterInt16Nullable(),
-            new JsonValueConverterUInt16Nullable(),
-            new JsonValueConverterInt32Nullable(),
-            new JsonValueConverterUInt32Nullable(),
-            new JsonValueConverterInt64Nullable(),
-            new JsonValueConverterUInt64Nullable(),
-            new JsonValueConverterSingleNullable(),
-            new JsonValueConverterDoubleNullable(),
-            new JsonValueConverterDecimalNullable(),
-            new JsonValueConverterDateTimeNullable(),
-            null,
-            new JsonValueConverterString()
-        };
-
-        internal static object GetDefaultPropertyValueConverter(Type propertyType, bool isNullable)
+        internal static object Create(Type type)
         {
-            object converter = null;
-
-            int typeCode = (int)Type.GetTypeCode(propertyType);
-            if (typeCode <= MaxTypeCode)
+            if (type.IsEnum)
             {
-                if (isNullable)
-                {
-                    converter = s_NullableConverters[typeCode];
-                }
-                else
-                {
-                    converter = s_Converters[typeCode];
-                }
+                return Activator.CreateInstance(
+                    typeof(JsonValueConverterEnum<>).MakeGenericType(type),
+                    BindingFlags.Instance | BindingFlags.NonPublic,
+                    binder: null,
+                    new object[] { false },
+                    culture: null);
             }
-
-            return converter;
+            TypeCode typeCode = Type.GetTypeCode(type);
+            switch (typeCode)
+            {
+                case TypeCode.Boolean:
+                    return new JsonValueConverterBoolean();
+                case TypeCode.Char:
+                    return new JsonValueConverterChar();
+                case TypeCode.SByte:
+                    return new JsonValueConverterSByte();
+                case TypeCode.Byte:
+                    return new JsonValueConverterByte();
+                case TypeCode.Int16:
+                    return new JsonValueConverterInt16();
+                case TypeCode.UInt16:
+                    return new JsonValueConverterUInt16();
+                case TypeCode.Int32:
+                    return new JsonValueConverterInt32();
+                case TypeCode.UInt32:
+                    return new JsonValueConverterUInt32();
+                case TypeCode.Int64:
+                    return new JsonValueConverterInt64();
+                case TypeCode.UInt64:
+                    return new JsonValueConverterUInt64();
+                case TypeCode.Single:
+                    return new JsonValueConverterSingle();
+                case TypeCode.Double:
+                    return new JsonValueConverterDouble();
+                case TypeCode.Decimal:
+                    return new JsonValueConverterDecimal();
+                case TypeCode.DateTime:
+                    return new JsonValueConverterDateTime();
+                case TypeCode.String:
+                    return new JsonValueConverterString();
+            }
+            return null;
         }
     }
 }

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Converters/DefaultConvertersOfTValue.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Text.Json.Serialization.Policies;
+
+namespace System.Text.Json.Serialization.Converters
+{
+    internal static class DefaultConverters<TValue>
+    {
+        internal static readonly JsonValueConverter<TValue> s_converter = (JsonValueConverter<TValue>)DefaultConverters.Create(typeof(TValue));
+    }
+}