Added field support to JSON serializer

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

@@ -218,6 +218,8 @@ public JsonSerializerOptions(System.Text.Json.JsonSerializerDefaults defaults) {
         public System.Text.Encodings.Web.JavaScriptEncoder? Encoder { get { throw null; } set { } }
         public bool IgnoreNullValues { get { throw null; } set { } }
         public bool IgnoreReadOnlyProperties { get { throw null; } set { } }
+        public bool IgnoreReadOnlyFields { get { throw null; } set { } }
+        public bool IncludeFields { get { throw null; } set { } }
         public int MaxDepth { get { throw null; } set { } }
         public bool PropertyNameCaseInsensitive { get { throw null; } set { } }
         public System.Text.Json.JsonNamingPolicy? PropertyNamingPolicy { get { throw null; } set { } }
@@ -479,7 +481,7 @@ public abstract partial class JsonConverter
         internal JsonConverter() { }
         public abstract bool CanConvert(System.Type typeToConvert);
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Enum | System.AttributeTargets.Property | System.AttributeTargets.Struct, AllowMultiple=false)]
+    [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Struct | System.AttributeTargets.Enum | System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple=false)]
     public partial class JsonConverterAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         protected JsonConverterAttribute() { }
@@ -506,23 +508,23 @@ public sealed partial class JsonConstructorAttribute : System.Text.Json.Serializ
     {
         public JsonConstructorAttribute() { }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple=false)]
+    [System.AttributeUsageAttribute(System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple=false)]
     public sealed partial class JsonExtensionDataAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         public JsonExtensionDataAttribute() { }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple=false)]
+    [System.AttributeUsageAttribute(System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple=false)]
     public sealed partial class JsonIgnoreAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         public JsonIgnoreAttribute() { }
         public System.Text.Json.Serialization.JsonIgnoreCondition Condition { get { throw null; } set { } }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple = false)]
+    [System.AttributeUsageAttribute(System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple = false)]
     public sealed partial class JsonIncludeAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         public JsonIncludeAttribute() { }
     }
-    [System.AttributeUsageAttribute(System.AttributeTargets.Property, AllowMultiple=false)]
+    [System.AttributeUsageAttribute(System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple=false)]
     public sealed partial class JsonPropertyNameAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         public JsonPropertyNameAttribute(string name) { }

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonConverterAttribute.cs

@@ -5,16 +5,16 @@
 namespace System.Text.Json.Serialization
 {
     /// <summary>
-    /// When placed on a property or type, specifies the converter type to use.
+    /// When placed on a property, field, or type, specifies the converter type to use.
     /// </summary>
     /// <remarks>
     /// The specified converter type must derive from <see cref="JsonConverter"/>.
-    /// When placed on a property, the specified converter will always be used.
+    /// When placed on a property or field, the specified converter will always be used.
     /// When placed on a type, the specified converter will be used unless a compatible converter is added to
-    /// <see cref="JsonSerializerOptions.Converters"/> or there is another <see cref="JsonConverterAttribute"/> on a property
+    /// <see cref="JsonSerializerOptions.Converters"/> or there is another <see cref="JsonConverterAttribute"/> on a member
     /// of the same type.
     /// </remarks>
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Struct, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
     public class JsonConverterAttribute : JsonAttribute
     {
         /// <summary>

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonExtensionDataAttribute.cs

@@ -5,22 +5,22 @@
 namespace System.Text.Json.Serialization
 {
     /// <summary>
-    /// When placed on a property of type <see cref="System.Collections.Generic.IDictionary{TKey, TValue}"/>, any
-    /// properties that do not have a matching member are added to that Dictionary during deserialization and written during serialization.
+    /// When placed on a property or field of type <see cref="System.Collections.Generic.IDictionary{TKey, TValue}"/>, any
+    /// properties that do not have a matching property or field are added to that Dictionary during deserialization and written during serialization.
     /// </summary>
     /// <remarks>
     /// The TKey value must be <see cref="string"/> and TValue must be <see cref="JsonElement"/> or <see cref="object"/>.
     ///
     /// During deserializing, when using <see cref="object"/> a "null" JSON value is treated as a <c>null</c> object reference, and when using
     /// <see cref="JsonElement"/> a "null" is treated as a JsonElement with <see cref="JsonElement.ValueKind"/> set to <see cref="JsonValueKind.Null"/>.
     ///
-    /// During serializing, the name of the extension data property is not included in the JSON;
+    /// During serializing, the name of the extension data member is not included in the JSON;
     /// the data contained within the extension data is serialized as properties of the JSON object.
     ///
-    /// If there is more than one extension property on a type, or it the property is not of the correct type,
+    /// If there is more than one extension member on a type, or it the member is not of the correct type,
     /// an <see cref="InvalidOperationException"/> is thrown during the first serialization or deserialization of that type.
     /// </remarks>
-    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
     public sealed class JsonExtensionDataAttribute : JsonAttribute
     {
     }

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

@@ -5,13 +5,13 @@
 namespace System.Text.Json.Serialization
 {
     /// <summary>
-    /// Prevents a property from being serialized or deserialized.
+    /// Prevents a property or field from being serialized or deserialized.
     /// </summary>
-    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
     public sealed class JsonIgnoreAttribute : JsonAttribute
     {
         /// <summary>
-        /// Specifies the condition that must be met before a property will be ignored.
+        /// Specifies the condition that must be met before a property or field will be ignored.
         /// </summary>
         /// <remarks>The default value is <see cref="JsonIgnoreCondition.Always"/>.</remarks>
         public JsonIgnoreCondition Condition { get; set; } = JsonIgnoreCondition.Always;

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

@@ -10,7 +10,7 @@ namespace System.Text.Json.Serialization
     /// <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)]
+    [AttributeUsage(AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple = false)]
     public sealed class JsonIncludeAttribute : JsonAttribute
     {
         /// <summary>

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Attributes/JsonPropertyNameAttribute.cs

@@ -8,7 +8,7 @@ namespace System.Text.Json.Serialization
     /// Specifies the property name that is present in the JSON when serializing and deserializing.
     /// This overrides any naming policy specified by <see cref="JsonNamingPolicy"/>.
     /// </summary>
-    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
     public sealed class JsonPropertyNameAttribute : JsonAttribute
     {
         /// <summary>

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

@@ -53,28 +53,26 @@ internal sealed partial class JsonClassInfo
         // Use an array (instead of List<T>) for highest performance.
         private volatile PropertyRef[]? _propertyRefsSorted;
 
-        public static JsonPropertyInfo AddProperty(PropertyInfo propertyInfo, Type parentClassType, JsonSerializerOptions options)
+        public static JsonPropertyInfo AddProperty(MemberInfo memberInfo, Type memberType, Type parentClassType, JsonSerializerOptions options)
         {
-            JsonIgnoreCondition? ignoreCondition = JsonPropertyInfo.GetAttribute<JsonIgnoreAttribute>(propertyInfo)?.Condition;
+            JsonIgnoreCondition? ignoreCondition = JsonPropertyInfo.GetAttribute<JsonIgnoreAttribute>(memberInfo)?.Condition;
 
             if (ignoreCondition == JsonIgnoreCondition.Always)
             {
-                return JsonPropertyInfo.CreateIgnoredPropertyPlaceholder(propertyInfo, options);
+                return JsonPropertyInfo.CreateIgnoredPropertyPlaceholder(memberInfo, options);
             }
 
-            Type propertyType = propertyInfo.PropertyType;
-
             JsonConverter converter = GetConverter(
-                propertyType,
+                memberType,
                 parentClassType,
-                propertyInfo,
+                memberInfo,
                 out Type runtimeType,
                 options);
 
             return CreateProperty(
-                declaredPropertyType: propertyType,
+                declaredPropertyType: memberType,
                 runtimePropertyType: runtimeType,
-                propertyInfo,
+                memberInfo,
                 parentClassType,
                 converter,
                 options,
@@ -84,7 +82,7 @@ public static JsonPropertyInfo AddProperty(PropertyInfo propertyInfo, Type paren
         internal static JsonPropertyInfo CreateProperty(
             Type declaredPropertyType,
             Type? runtimePropertyType,
-            PropertyInfo? propertyInfo,
+            MemberInfo? memberInfo,
             Type parentClassType,
             JsonConverter converter,
             JsonSerializerOptions options,
@@ -98,7 +96,7 @@ internal static JsonPropertyInfo CreateProperty(
                 declaredPropertyType,
                 runtimePropertyType,
                 runtimeClassType: converter.ClassType,
-                propertyInfo,
+                memberInfo,
                 converter,
                 ignoreCondition,
                 options);
@@ -119,7 +117,7 @@ internal static JsonPropertyInfo CreatePropertyInfoForClassInfo(
             JsonPropertyInfo jsonPropertyInfo = CreateProperty(
                 declaredPropertyType: declaredPropertyType,
                 runtimePropertyType: runtimePropertyType,
-                propertyInfo: null, // Not a real property so this is null.
+                memberInfo: null, // Not a real property so this is null.
                 parentClassType: JsonClassInfo.ObjectType, // a dummy value (not used)
                 converter: converter,
                 options);