JsonSerializerOptions API update and ignore property features

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

@@ -118,9 +118,9 @@ public override void GetObjectData(System.Runtime.Serialization.SerializationInf
     public partial struct JsonReaderOptions
     {
         private int _dummyPrimitive;
+        public bool AllowTrailingCommas { get { throw null; } set { } }
         public System.Text.Json.JsonCommentHandling CommentHandling { get { throw null; } set { } }
         public int MaxDepth { get { throw null; } set { } }
-        public bool AllowTrailingCommas { get { throw null; } set { } }
     }
     public partial struct JsonReaderState
     {
@@ -311,6 +311,15 @@ public void WriteStringValue(string value, bool escape = true) { }
 }
 namespace System.Text.Json.Serialization
 {
+    public abstract partial class JsonAttribute : System.Attribute
+    {
+        protected JsonAttribute() { }
+    }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple=false)]
+    public sealed partial class JsonIgnoreAttribute : System.Text.Json.Serialization.JsonAttribute
+    {
+        public JsonIgnoreAttribute() { }
+    }
     public static partial class JsonSerializer
     {
         public static object Parse(System.ReadOnlySpan<byte> utf8Json, System.Type returnType, System.Text.Json.Serialization.JsonSerializerOptions options = null) { throw null; }
@@ -329,10 +338,12 @@ public static partial class JsonSerializer
     public sealed partial class JsonSerializerOptions
     {
         public JsonSerializerOptions() { }
+        public bool AllowTrailingCommas { get { throw null; } set { } }
         public int DefaultBufferSize { get { throw null; } set { } }
-        public bool IgnoreNullPropertyValueOnRead { get { throw null; } set { } }
-        public bool IgnoreNullPropertyValueOnWrite { get { throw null; } set { } }
-        public System.Text.Json.JsonReaderOptions ReaderOptions { get { throw null; } set { } }
-        public System.Text.Json.JsonWriterOptions WriterOptions { get { throw null; } set { } }
+        public bool IgnoreNullValues { get { throw null; } set { } }
+        public bool IgnoreReadOnlyProperties { get { throw null; } set { } }
+        public int MaxDepth { get { throw null; } set { } }
+        public System.Text.Json.JsonCommentHandling ReadCommentHandling { get { throw null; } set { } }
+        public bool WriteIndented { get { throw null; } set { } }
     }
 }

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

@@ -321,4 +321,7 @@
   <data name="TrailingCommaNotAllowedBeforeObjectEnd" xml:space="preserve">
     <value>The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options.</value>
   </data>
+  <data name="SerializerOptionsImmutable" xml:space="preserve">
+    <value>Serializer options cannot be changed once serialization or deserialization has occurred.</value>
+  </data>
 </root>

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

@@ -65,14 +65,17 @@
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt16.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt32.cs" />
     <Compile Include="System\Text\Json\Serialization\Converters\JsonValueConverterUInt64.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonAttribute.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\JsonIgnoreAttribute.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfo.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoCommon.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoNotNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonPropertyInfoNullable.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleArray.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.Helpers.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.Stream.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleValue.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Read.HandleObject.cs" />

src/System.Text.Json/src/System/Text/Json/Reader/JsonReaderOptions.cs

@@ -15,7 +15,7 @@ public struct JsonReaderOptions
 
         /// <summary>
         /// Defines how the <see cref="Utf8JsonReader"/> should handle comments when reading through the JSON.
-        /// By default the reader will throw a <exception cref="JsonReaderException"/> if it encounters a comment.
+        /// By default <exception cref="JsonReaderException"/> is thrown if a comment is encountered.
         /// </summary>
         public JsonCommentHandling CommentHandling { get; set; }
 
@@ -37,8 +37,8 @@ public int MaxDepth
 
         /// <summary>
         /// Defines whether an extra comma at the end of a list of JSON values in an object or array
-        /// are allowed (and ignored) within the JSON payload being read.
-        /// By default, it's set to false, and the reader will throw a <exception cref="JsonReaderException"/> if it encounters a trailing comma.
+        /// is allowed (and ignored) within the JSON payload being read.
+        /// By default, it's set to false, and <exception cref="JsonReaderException"/> is thrown if a trailing comma is encountered.
         /// </summary>
         public bool AllowTrailingCommas { get; set; }
     }

src/System.Text.Json/src/System/Text/Json/Serialization/JsonAttribute.cs

@@ -0,0 +1,11 @@
+// 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>
+    /// The base class of serialization attributes.
+    /// </summary>
+    public abstract class JsonAttribute : Attribute { }
+}

src/System.Text.Json/src/System/Text/Json/Serialization/JsonIgnoreAttribute.cs

@@ -0,0 +1,15 @@
+// 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>
+    /// Prevents a property from being serialized or deserialized.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
+    public sealed class JsonIgnoreAttribute : JsonAttribute
+    {
+        public JsonIgnoreAttribute() { }
+    }
+}

src/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections;
+using System.Diagnostics;
 using System.Reflection;
 using System.Text.Json.Serialization.Converters;
 using System.Text.Json.Serialization.Policies;
@@ -11,15 +12,22 @@ namespace System.Text.Json.Serialization
 {
     internal abstract class JsonPropertyInfo
     {
+        // Cache the array and enumerable converters so they don't get created for every enumerable property.
+        private static readonly JsonEnumerableConverter s_jsonArrayConverter = new DefaultArrayConverter();
+        private static readonly JsonEnumerableConverter s_jsonEnumerableConverter = new DefaultEnumerableConverter();
+
         internal ClassType ClassType;
 
         internal byte[] _name = default;
         internal byte[] _escapedName = default;
 
         internal bool HasGetter { get; set; }
         internal bool HasSetter { get; set; }
+        internal bool ShouldSerialize { get; private set; }
+        internal bool ShouldDeserialize { get; private set; }
+
+        internal bool IgnoreNullValues { get; private set; }
 
-        public ReadOnlySpan<byte> EscapedName => _escapedName;
         public ReadOnlySpan<byte> Name => _name;
 
         // todo: to minimize hashtable lookups, cache JsonClassInfo:
@@ -43,6 +51,7 @@ internal JsonPropertyInfo(
             ClassType = JsonClassInfo.GetClassType(runtimePropertyType);
             if (elementType != null)
             {
+                Debug.Assert(ClassType == ClassType.Enumerable);
                 ElementClassInfo = options.GetOrAddClass(elementType);
             }
 
@@ -66,31 +75,80 @@ internal JsonPropertyInfo(
 
         internal virtual void GetPolicies(JsonSerializerOptions options)
         {
-            if (RuntimePropertyType.IsArray)
+            DetermineSerializationCapabilities(options);
+            IgnoreNullValues = options.IgnoreNullValues;
+        }
+
+        private void DetermineSerializationCapabilities(JsonSerializerOptions options)
+        {
+            bool hasIgnoreAttribute = (GetAttribute<JsonIgnoreAttribute>() != null);
+
+            if (hasIgnoreAttribute)
             {
-                EnumerableConverter = new DefaultArrayConverter();
+                // We don't serialize or deserialize.
+                return;
             }
-            else if (typeof(IEnumerable).IsAssignableFrom(RuntimePropertyType))
+
+            if (ClassType != ClassType.Enumerable)
             {
-                Type elementType = JsonClassInfo.GetElementType(RuntimePropertyType);
+                // We serialize if there is a getter + no [Ignore] attribute + not ignoring readonly properties.
+                ShouldSerialize = HasGetter && (HasSetter || !options.IgnoreReadOnlyProperties);
 
-                if (RuntimePropertyType.IsAssignableFrom(typeof(JsonEnumerableT<>).MakeGenericType(elementType)))
+                // We deserialize if there is a setter + no [Ignore] attribute. 
+                ShouldDeserialize = HasSetter;
+            }
+            else
+            {
+                if (HasGetter)
                 {
-                    EnumerableConverter = new DefaultEnumerableConverter();
+                    if (HasSetter)
+                    {
+                        ShouldDeserialize = true;
+                    }
+                    else if (RuntimePropertyType.IsAssignableFrom(typeof(IList)))
+                    {
+                        ShouldDeserialize = true;
+                    }
+                    //else
+                    //{
+                    //    // todo: future feature that allows non-List types (e.g. from System.Collections.Immutable) to have converters.
+                    //}
+                }
+                //else if (HasSetter)
+                //{
+                //    // todo: Special case where there is no getter but a setter (and an EnumerableConverter)
+                //}
+
+                if (ShouldDeserialize)
+                {
+                    ShouldSerialize = HasGetter;
+
+                    if (RuntimePropertyType.IsArray)
+                    {
+                        EnumerableConverter = s_jsonArrayConverter;
+                    }
+                    else if (typeof(IEnumerable).IsAssignableFrom(RuntimePropertyType))
+                    {
+                        Type elementType = JsonClassInfo.GetElementType(RuntimePropertyType);
+
+                        if (RuntimePropertyType.IsAssignableFrom(typeof(JsonEnumerableT<>).MakeGenericType(elementType)))
+                        {
+                            EnumerableConverter = s_jsonEnumerableConverter;
+                        }
+                    }
+                }
+                else
+                {
+                    ShouldSerialize = HasGetter && !options.IgnoreReadOnlyProperties;
                 }
             }
         }
 
         internal abstract object GetValueAsObject(object obj, JsonSerializerOptions options);
 
-        internal bool IgnoreNullPropertyValueOnRead(JsonSerializerOptions options)
-        {
-            return options.IgnoreNullPropertyValueOnRead;
-        }
-
-        internal bool IgnoreNullPropertyValueOnWrite(JsonSerializerOptions options)
+        internal TAttribute GetAttribute<TAttribute>() where TAttribute : Attribute
         {
-            return options.IgnoreNullPropertyValueOnWrite;
+            return (TAttribute)PropertyInfo?.GetCustomAttribute(typeof(TAttribute), inherit: false);
         }
 
         internal abstract void Read(JsonTokenType tokenType, JsonSerializerOptions options, ref ReadStack state, ref Utf8JsonReader reader);

src/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoCommon.cs

@@ -78,7 +78,7 @@ internal override void SetValueAsObject(object obj, object value, JsonSerializer
             Debug.Assert(Set != null);
             TDeclaredProperty typedValue = (TDeclaredProperty)value;
 
-            if (typedValue != null || !IgnoreNullPropertyValueOnWrite(options))
+            if (typedValue != null || !IgnoreNullValues)
             {
                 Set((TClass)obj, (TDeclaredProperty)value);
             }

src/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoNotNullable.cs

@@ -36,7 +36,7 @@ internal override void Read(JsonTokenType tokenType, JsonSerializerOptions optio
                 JsonPropertyInfo propertyInfo = ElementClassInfo.GetPolicyProperty();
                 propertyInfo.ReadEnumerable(tokenType, options, ref state, ref reader);
             }
-            else if (HasSetter)
+            else if (ShouldDeserialize)
             {
                 if (ValueConverter != null)
                 {
@@ -48,10 +48,10 @@ internal override void Read(JsonTokenType tokenType, JsonSerializerOptions optio
                         }
                         else
                         {
-                            if (value != null || !IgnoreNullPropertyValueOnRead(options))
-                            {
-                                Set((TClass)state.Current.ReturnValue, value);
-                            }
+                            // Null values were already handled.
+                            Debug.Assert(value != null);
+
+                            Set((TClass)state.Current.ReturnValue, value);
                         }
 
                         return;
@@ -85,7 +85,7 @@ internal override void Write(JsonSerializerOptions options, ref WriteStackFrame
                 JsonPropertyInfo propertyInfo = ElementClassInfo.GetPolicyProperty();
                 propertyInfo.WriteEnumerable(options, ref current, ref writer);
             }
-            else if (HasGetter)
+            else if (ShouldSerialize)
             {
                 TRuntimeProperty value;
                 if (_isPropertyPolicy)
@@ -103,7 +103,7 @@ internal override void Write(JsonSerializerOptions options, ref WriteStackFrame
                     {
                         writer.WriteNullValue();
                     }
-                    else if (!IgnoreNullPropertyValueOnWrite(options))
+                    else if (!IgnoreNullValues)
                     {
                         writer.WriteNull(_escapedName);
                     }

src/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfoNullable.cs

@@ -36,7 +36,7 @@ internal override void Read(JsonTokenType tokenType, JsonSerializerOptions optio
                 JsonPropertyInfo propertyInfo = ElementClassInfo.GetPolicyProperty();
                 propertyInfo.ReadEnumerable(tokenType, options, ref state, ref reader);
             }
-            else if (HasSetter)
+            else if (ShouldDeserialize)
             {
                 if (ValueConverter != null)
                 {
@@ -82,7 +82,7 @@ internal override void Write(JsonSerializerOptions options, ref WriteStackFrame
                 JsonPropertyInfo propertyInfo = ElementClassInfo.GetPolicyProperty();
                 propertyInfo.WriteEnumerable(options, ref current, ref writer);
             }
-            else if (HasGetter)
+            else if (ShouldSerialize)
             {
                 TProperty? value;
                 if (_isPropertyPolicy)
@@ -100,7 +100,7 @@ internal override void Write(JsonSerializerOptions options, ref WriteStackFrame
                     {
                         writer.WriteNullValue();
                     }
-                    else if (!IgnoreNullPropertyValueOnWrite(options))
+                    else if (!IgnoreNullValues)
                     {
                         writer.WriteNull(_escapedName);
                     }

src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleArray.cs

@@ -15,15 +15,17 @@ private static void HandleStartArray(
             ref Utf8JsonReader reader,
             ref ReadStack state)
         {
-            if (state.Current.Skip())
+            JsonPropertyInfo jsonPropertyInfo = state.Current.JsonPropertyInfo;
+
+            bool skip = jsonPropertyInfo != null && !jsonPropertyInfo.ShouldDeserialize;
+            if (skip || state.Current.Skip())
             {
                 // The array is not being applied to the object.
                 state.Push();
                 state.Current.Drain = true;
                 return;
             }
 
-            JsonPropertyInfo jsonPropertyInfo = state.Current.JsonPropertyInfo;
             if (jsonPropertyInfo == null || state.Current.JsonClassInfo.ClassType == ClassType.Unknown)
             {
                 jsonPropertyInfo = state.Current.JsonClassInfo.CreatePolymorphicProperty(jsonPropertyInfo, typeof(object), options);
@@ -53,8 +55,10 @@ private static void HandleStartArray(
                     state.Current.EnumerableCreated = true;
                 }
 
+                jsonPropertyInfo = state.Current.JsonPropertyInfo;
+
                 // If current property is already set (from a constructor, for example) leave as-is
-                if (state.Current.JsonPropertyInfo.GetValueAsObject(state.Current.ReturnValue, options) == null)
+                if (jsonPropertyInfo.GetValueAsObject(state.Current.ReturnValue, options) == null)
                 {
                     // Create the enumerable.
                     object value = ReadStackFrame.CreateEnumerableValue(ref reader, ref state, options);

src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleNull.cs

@@ -41,7 +41,7 @@ private static bool HandleNull(ref Utf8JsonReader reader, ref ReadStack state, J
                 return true;
             }
 
-            if (!propertyInfo.IgnoreNullPropertyValueOnRead(options))
+            if (!propertyInfo.IgnoreNullValues)
             {
                 state.Current.JsonPropertyInfo.SetValueAsObject(state.Current.ReturnValue, null, options);
             }

src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Helpers.cs

@@ -0,0 +1,24 @@
+// 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
+{
+    public static partial class JsonSerializer
+    {
+        private static object ReadCore(
+            Type returnType,
+            JsonSerializerOptions options,
+            ref Utf8JsonReader reader)
+        {
+            options ??= JsonSerializerOptions.s_defaultOptions;
+
+            ReadStack state = default;
+            state.Current.Initialize(returnType, options);
+
+            ReadCore(options, ref reader, ref state);
+
+            return state.Current.ReturnValue;
+        }
+    }
+}