Add JsonIncludeAttribute & support for non-public accessors

src/libraries/System.Text.Json/ref/System.Text.Json.cs

@@ -508,6 +508,11 @@ public sealed partial class JsonIgnoreAttribute : System.Text.Json.Serialization
         public JsonIgnoreAttribute() { }
         public System.Text.Json.Serialization.JsonIgnoreCondition Condition { get { throw null; } set { } }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple = false)]
+    public sealed partial class JsonIncludeAttribute : System.Text.Json.Serialization.JsonAttribute
+    {
+        public JsonIncludeAttribute() { }
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple=false)]
     public sealed partial class JsonPropertyNameAttribute : System.Text.Json.Serialization.JsonAttribute
     {

src/libraries/System.Text.Json/src/Resources/Strings.resx

@@ -512,4 +512,7 @@
   <data name="SerializeTypeInstanceNotSupported" xml:space="preserve">
     <value>Serialization and deserialization of 'System.Type' instances are not supported and should be avoided since they can lead to security issues.</value>
   </data>
-</root>
+  <data name="JsonIncludeOnNonPublicInvalid" xml:space="preserve">
+    <value>The non-public property '{0}' on type '{1}' is annotated with 'JsonIncludeAttribute' which is invalid.</value>
+  </data>
+</root>

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

@@ -140,6 +140,7 @@
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfo.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoOfTTypeToConvert.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyNameAttribute.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonIncludeAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonResumableConverterOfT.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleMetadata.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandlePropertyName.cs" />

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.Cache.cs

@@ -77,7 +77,7 @@ public Dictionary<string, JsonParameterInfo> CreateParameterCache(int capacity,
             }
         }
 
-        public static JsonPropertyInfo AddProperty(Type propertyType, PropertyInfo propertyInfo, Type parentClassType, JsonSerializerOptions options)
+        public static JsonPropertyInfo AddProperty(PropertyInfo propertyInfo, Type parentClassType, JsonSerializerOptions options)
         {
             JsonIgnoreCondition? ignoreCondition = JsonPropertyInfo.GetAttribute<JsonIgnoreAttribute>(propertyInfo)?.Condition;
 
@@ -86,6 +86,8 @@ public static JsonPropertyInfo AddProperty(Type propertyType, PropertyInfo prope
                 return JsonPropertyInfo.CreateIgnoredPropertyPlaceholder(propertyInfo, options);
             }
 
+            Type propertyType = propertyInfo.PropertyType;
+
             JsonConverter converter = GetConverter(
                 propertyType,
                 parentClassType,

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs

@@ -95,12 +95,9 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
             {
                 case ClassType.Object:
                     {
-                        // Create the policy property.
-                        PropertyInfoForClassInfo = CreatePropertyInfoForClassInfo(type, runtimeType, converter!, options);
-
                         CreateObject = options.MemberAccessorStrategy.CreateConstructor(type);
 
-                        PropertyInfo[] properties = type.GetProperties(BindingFlags.Instance | BindingFlags.Public);
+                        PropertyInfo[] properties = type.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
 
                         Dictionary<string, JsonPropertyInfo> cache = CreatePropertyCache(properties.Length);
 
@@ -112,11 +109,22 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
                                 continue;
                             }
 
+                            if (IsNonPublicProperty(propertyInfo))
+                            {
+                                if (JsonPropertyInfo.GetAttribute<JsonIncludeAttribute>(propertyInfo) != null)
+                                {
+                                    ThrowHelper.ThrowInvalidOperationException_JsonIncludeOnNonPublicInvalid(propertyInfo, Type);
+                                }
+
+                                // Non-public properties should not be included for (de)serialization.
+                                continue;
+                            }
+
                             // For now we only support public getters\setters
                             if (propertyInfo.GetMethod?.IsPublic == true ||
                                 propertyInfo.SetMethod?.IsPublic == true)
                             {
-                                JsonPropertyInfo jsonPropertyInfo = AddProperty(propertyInfo.PropertyType, propertyInfo, type, options);
+                                JsonPropertyInfo jsonPropertyInfo = AddProperty(propertyInfo, type, options);
                                 Debug.Assert(jsonPropertyInfo != null && jsonPropertyInfo.NameAsString != null);
 
                                 // If the JsonPropertyNameAttribute or naming policy results in collisions, throw an exception.
@@ -189,6 +197,13 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
             }
         }
 
+        private static bool IsNonPublicProperty(PropertyInfo propertyInfo)
+        {
+            MethodInfo? getMethod = propertyInfo.GetMethod;
+            MethodInfo? setMethod = propertyInfo.SetMethod;
+            return !((getMethod != null && getMethod.IsPublic) || (setMethod != null && setMethod.IsPublic));
+        }
+
         private void InitializeConstructorParameters(ConstructorInfo constructorInfo)
         {
             ParameterInfo[] parameters = constructorInfo!.GetParameters();

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonIncludeAttribute.cs

@@ -0,0 +1,21 @@
+// 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.
+
+namespace System.Text.Json.Serialization
+{
+    /// <summary>
+    /// Indicates that the member should be included for serialization and deserialization.
+    /// </summary>
+    /// <remarks>
+    /// When applied to a property, indicates that non-public getters and setters can be used for serialization and deserialization.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
+    public sealed class JsonIncludeAttribute : JsonAttribute
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="JsonIncludeAttribute"/>.
+        /// </summary>
+        public JsonIncludeAttribute() { }
+    }
+}

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoOfTTypeToConvert.cs

@@ -40,13 +40,17 @@ public override void Initialize(
 
             if (propertyInfo != null)
             {
-                if (propertyInfo.GetMethod?.IsPublic == true)
+                bool useNonPublicAccessors = GetAttribute<JsonIncludeAttribute>(propertyInfo) != null;
+
+                MethodInfo? getMethod = propertyInfo.GetMethod;
+                if (getMethod != null && (getMethod.IsPublic || useNonPublicAccessors))
                 {
                     HasGetter = true;
                     Get = options.MemberAccessorStrategy.CreatePropertyGetter<TTypeToConvert>(propertyInfo);
                 }
 
-                if (propertyInfo.SetMethod?.IsPublic == true)
+                MethodInfo? setMethod = propertyInfo.SetMethod;
+                if (setMethod != null && (setMethod.IsPublic || useNonPublicAccessors))
                 {
                     HasSetter = true;
                     Set = options.MemberAccessorStrategy.CreatePropertySetter<TTypeToConvert>(propertyInfo);

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandlePropertyName.cs

@@ -38,7 +38,7 @@ internal static JsonPropertyInfo LookupProperty(
             if (jsonPropertyInfo == JsonPropertyInfo.s_missingProperty)
             {
                 JsonPropertyInfo? dataExtProperty = state.Current.JsonClassInfo.DataExtensionProperty;
-                if (dataExtProperty != null)
+                if (dataExtProperty != null && dataExtProperty.HasGetter && dataExtProperty.HasSetter)
                 {
                     state.Current.JsonPropertyNameAsString = JsonHelpers.Utf8GetString(unescapedPropertyName);
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReflectionEmitMemberAccessor.cs

@@ -232,7 +232,7 @@ public override Func<IEnumerable<KeyValuePair<string, TElement>>, TCollection> C
 
         private static Delegate CreatePropertyGetter(PropertyInfo propertyInfo, Type classType, Type propertyType)
         {
-            MethodInfo? realMethod = propertyInfo.GetGetMethod();
+            MethodInfo? realMethod = propertyInfo.GetMethod;
             Type objectType = typeof(object);
 
             Debug.Assert(realMethod != null);
@@ -268,7 +268,7 @@ private static Delegate CreatePropertyGetter(PropertyInfo propertyInfo, Type cla
 
         private static Delegate CreatePropertySetter(PropertyInfo propertyInfo, Type classType, Type propertyType)
         {
-            MethodInfo? realMethod = propertyInfo.GetSetMethod();
+            MethodInfo? realMethod = propertyInfo.SetMethod;
             Type objectType = typeof(object);
 
             Debug.Assert(realMethod != null);

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/ReflectionMemberAccessor.cs

@@ -145,7 +145,7 @@ public override Func<IEnumerable<KeyValuePair<string, TElement>>, TCollection> C
 
         public override Func<object, TProperty> CreatePropertyGetter<TProperty>(PropertyInfo propertyInfo)
         {
-            MethodInfo getMethodInfo = propertyInfo.GetGetMethod()!;
+            MethodInfo getMethodInfo = propertyInfo.GetMethod!;
 
             return delegate (object obj)
             {
@@ -155,7 +155,7 @@ public override Func<object, TProperty> CreatePropertyGetter<TProperty>(Property
 
         public override Action<object, TProperty> CreatePropertySetter<TProperty>(PropertyInfo propertyInfo)
         {
-            MethodInfo setMethodInfo = propertyInfo.GetSetMethod()!;
+            MethodInfo setMethodInfo = propertyInfo.SetMethod!;
 
             return delegate (object obj, TProperty value)
             {

src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs

@@ -203,6 +203,13 @@ public static void ThrowInvalidOperationException_ExtensionDataCannotBindToCtorP
             throw new InvalidOperationException(SR.Format(SR.ExtensionDataCannotBindToCtorParam, propertyInfo, classType, constructorInfo));
         }
 
+        [DoesNotReturn]
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        public static void ThrowInvalidOperationException_JsonIncludeOnNonPublicInvalid(PropertyInfo propertyInfo, Type parentType)
+        {
+            throw new InvalidOperationException(SR.Format(SR.JsonIncludeOnNonPublicInvalid, propertyInfo.Name, parentType));
+        }
+
         [DoesNotReturn]
         [MethodImpl(MethodImplOptions.NoInlining)]
         public static void ThrowNotSupportedException_ObjectWithParameterizedCtorRefMetadataNotHonored(