Added field support to JSON serializer

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

@@ -732,7 +732,7 @@ 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.Enum | System.AttributeTargets.Property | System.AttributeTargets.Field | System.AttributeTargets.Struct, AllowMultiple=false)]
     public partial class JsonConverterAttribute : System.Text.Json.Serialization.JsonAttribute
     {
         protected JsonConverterAttribute() { }
@@ -752,17 +752,17 @@ protected internal JsonConverter() { }
         public abstract T Read(ref System.Text.Json.Utf8JsonReader reader, System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options);
         public abstract void Write(System.Text.Json.Utf8JsonWriter writer, T value, System.Text.Json.JsonSerializerOptions options);
     }
-    [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() { }
     }
-    [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/JsonClassInfo.AddProperty.cs

@@ -13,7 +13,7 @@ namespace System.Text.Json
 {
     internal partial class JsonClassInfo
     {
-        private JsonPropertyInfo AddProperty(Type propertyType, PropertyInfo propertyInfo, Type parentClassType, JsonSerializerOptions options)
+        private JsonPropertyInfo AddProperty(Type propertyType, MemberInfo propertyInfo, Type parentClassType, JsonSerializerOptions options)
         {
             bool hasIgnoreAttribute = (JsonPropertyInfo.GetAttribute<JsonIgnoreAttribute>(propertyInfo) != null);
             if (hasIgnoreAttribute)
@@ -50,7 +50,7 @@ private JsonPropertyInfo AddProperty(Type propertyType, PropertyInfo propertyInf
         internal static JsonPropertyInfo CreateProperty(
             Type declaredPropertyType,
             Type runtimePropertyType,
-            PropertyInfo? propertyInfo,
+            MemberInfo? propertyInfo,
             Type parentClassType,
             Type? collectionElementType,
             Type? nullableUnderlyingType,

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

@@ -139,6 +139,7 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
                         CreateObject = options.MemberAccessorStrategy.CreateConstructor(type);
 
                         PropertyInfo[] properties = type.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
+                        FieldInfo[] fields = type.GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
 
                         Dictionary<string, JsonPropertyInfo> cache = CreatePropertyCache(properties.Length);
 
@@ -176,6 +177,35 @@ public JsonClassInfo(Type type, JsonSerializerOptions options)
                             }
                         }
 
+                        foreach (FieldInfo fieldInfo in fields)
+                        {
+                            if (fieldInfo.GetCustomAttribute(typeof(CompilerGeneratedAttribute)) is { })
+                            {
+                                // Ignore compiler generated fields
+                                continue;
+                            }
+
+                            JsonPropertyInfo jsonPropertyInfo = AddProperty(fieldInfo.FieldType, fieldInfo, type, options);
+                            Debug.Assert(jsonPropertyInfo != null && jsonPropertyInfo.NameAsString != null);
+
+                            // If the JsonPropertyNameAttribute or naming policy results in collisions, throw an exception.
+                            if (!JsonHelpers.TryAdd(cache, jsonPropertyInfo.NameAsString, jsonPropertyInfo))
+                            {
+                                JsonPropertyInfo other = cache[jsonPropertyInfo.NameAsString];
+
+                                if (other.ShouldDeserialize == false && other.ShouldSerialize == false)
+                                {
+                                    // Overwrite the one just added since it has [JsonIgnore].
+                                    cache[jsonPropertyInfo.NameAsString] = jsonPropertyInfo;
+                                }
+                                else if (jsonPropertyInfo.ShouldDeserialize == true || jsonPropertyInfo.ShouldSerialize == true)
+                                {
+                                    ThrowHelper.ThrowInvalidOperationException_SerializerPropertyNameConflict(this, jsonPropertyInfo);
+                                }
+                                // else ignore jsonPropertyInfo since it has [JsonIgnore].
+                            }
+                        }
+
                         JsonPropertyInfo[] cacheArray;
                         if (DetermineExtensionDataProperty(cache))
                         {
@@ -521,7 +551,7 @@ public static ulong GetKey(ReadOnlySpan<byte> propertyName)
         public static ClassType GetClassType(
             Type type,
             Type parentClassType,
-            PropertyInfo? propertyInfo,
+            MemberInfo? propertyInfo,
             out Type runtimeType,
             out Type? elementType,
             out Type? nullableUnderlyingType,

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

@@ -14,7 +14,7 @@ namespace System.Text.Json.Serialization
     /// <see cref="JsonSerializerOptions.Converters"/> or there is another <see cref="JsonConverterAttribute"/> on a property
     /// of the same type.
     /// </remarks>
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Struct, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Struct, AllowMultiple = false)]
     public class JsonConverterAttribute : JsonAttribute
     {
         /// <summary>

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

@@ -5,7 +5,7 @@
 namespace System.Text.Json.Serialization
 {
     /// <summary>
-    /// When placed on a property of type <see cref="System.Collections.Generic.IDictionary{TKey, TValue}"/>, any
+    /// When placed on a property or a field 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.
     /// </summary>
     /// <remarks>
@@ -14,13 +14,13 @@ namespace System.Text.Json.Serialization
     /// 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 property or field on a type, or if 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/JsonIgnoreAttribute.cs

@@ -5,9 +5,9 @@
 namespace System.Text.Json.Serialization
 {
     /// <summary>
-    /// Prevents a property from being serialized or deserialized.
+    /// Prevents a property or a 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>

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

@@ -62,7 +62,7 @@ public void CopyRuntimeSettingsTo(JsonPropertyInfo other)
 
         // Create a property that is ignored at run-time. It uses the same type (typeof(sbyte)) to help
         // prevent issues with unsupported types and helps ensure we don't accidently (de)serialize it.
-        public static JsonPropertyInfo CreateIgnoredPropertyPlaceholder(PropertyInfo? propertyInfo, JsonSerializerOptions options)
+        public static JsonPropertyInfo CreateIgnoredPropertyPlaceholder(MemberInfo? propertyInfo, JsonSerializerOptions options)
         {
             JsonPropertyInfo jsonPropertyInfo = new JsonPropertyInfoNotNullable<sbyte, sbyte, sbyte, sbyte>();
             jsonPropertyInfo.Options = options;
@@ -238,7 +238,7 @@ public JsonClassInfo? ElementClassInfo
         // Use a field here (not a property) to avoid value semantics.
         public JsonEncodedText? EscapedName;
 
-        public static TAttribute? GetAttribute<TAttribute>(PropertyInfo propertyInfo) where TAttribute : Attribute
+        public static TAttribute? GetAttribute<TAttribute>(MemberInfo propertyInfo) where TAttribute : Attribute
         {
             return (TAttribute?)propertyInfo.GetCustomAttribute(typeof(TAttribute), inherit: false);
         }
@@ -293,7 +293,7 @@ public virtual void Initialize(
             Type declaredPropertyType,
             Type runtimePropertyType,
             ClassType runtimeClassType,
-            PropertyInfo? propertyInfo,
+            MemberInfo? propertyInfo,
             Type? elementType,
             JsonConverter? converter,
             bool treatAsNullable,
@@ -357,7 +357,7 @@ protected virtual void OnWriteDictionary(ref WriteStackFrame current, Utf8JsonWr
 
         public Type ParentClassType { get; private set; } = null!;
 
-        public PropertyInfo? PropertyInfo { get; private set; }
+        public MemberInfo? PropertyInfo { get; private set; }
 
         public void Read(JsonTokenType tokenType, ref ReadStack state, ref Utf8JsonReader reader)
         {

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

@@ -7,6 +7,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
+using System.Runtime.CompilerServices;
 using System.Text.Json.Serialization;
 
 namespace System.Text.Json
@@ -26,7 +27,7 @@ public override void Initialize(
             Type declaredPropertyType,
             Type runtimePropertyType,
             ClassType runtimeClassType,
-            PropertyInfo? propertyInfo,
+            MemberInfo? propertyInfo,
             Type? elementType,
             JsonConverter? converter,
             bool treatAsNullable,
@@ -45,17 +46,27 @@ public override void Initialize(
 
             if (propertyInfo != null)
             {
-                if (propertyInfo.GetMethod?.IsPublic == true)
+                Debug.Assert(
+                    propertyInfo is PropertyInfo ||
+                    propertyInfo is FieldInfo);
+
+                if (propertyInfo is PropertyInfo property)
                 {
-                    HasGetter = true;
-                    Get = options.MemberAccessorStrategy.CreatePropertyGetter<TClass, TDeclaredProperty>(propertyInfo);
+                    Get = property.GetMethod?.IsPublic == true
+                        ? options.MemberAccessorStrategy.CreateGetter<TClass, TDeclaredProperty>(property)
+                        : null;
+                    Set = property.SetMethod?.IsPublic == true
+                        ? options.MemberAccessorStrategy.CreateSetter<TClass, TDeclaredProperty>(property)
+                        : null;
                 }
-
-                if (propertyInfo.SetMethod?.IsPublic == true)
+                else
                 {
-                    HasSetter = true;
-                    Set = options.MemberAccessorStrategy.CreatePropertySetter<TClass, TDeclaredProperty>(propertyInfo);
+                    Get = options.MemberAccessorStrategy.CreateGetter<TClass, TDeclaredProperty>(Unsafe.As<FieldInfo>(propertyInfo));
+                    Set = options.MemberAccessorStrategy.CreateSetter<TClass, TDeclaredProperty>(Unsafe.As<FieldInfo>(propertyInfo));
                 }
+
+                HasGetter = Get is { };
+                HasSetter = Set is { };
             }
             else
             {

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/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 | System.AttributeTargets.Field, AllowMultiple = false)]
     public sealed class JsonPropertyNameAttribute : JsonAttribute
     {
         /// <summary>

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

@@ -65,7 +65,7 @@ private static List<JsonConverter> GetDefaultConverters()
         /// </remarks>
         public IList<JsonConverter> Converters { get; }
 
-        internal JsonConverter? DetermineConverterForProperty(Type parentClassType, Type runtimePropertyType, PropertyInfo? propertyInfo)
+        internal JsonConverter? DetermineConverterForProperty(Type parentClassType, Type runtimePropertyType, MemberInfo? propertyInfo)
         {
             JsonConverter? converter = null;
 
@@ -189,7 +189,7 @@ internal bool HasConverter(Type typeToConvert)
             return GetConverter(typeToConvert) != null;
         }
 
-        private JsonConverter GetConverterFromAttribute(JsonConverterAttribute converterAttribute, Type typeToConvert, Type classTypeAttributeIsOn, PropertyInfo? propertyInfo)
+        private JsonConverter GetConverterFromAttribute(JsonConverterAttribute converterAttribute, Type typeToConvert, Type classTypeAttributeIsOn, MemberInfo? propertyInfo)
         {
             JsonConverter? converter;
 
@@ -223,7 +223,7 @@ private JsonConverter GetConverterFromAttribute(JsonConverterAttribute converter
             return converter;
         }
 
-        private static Attribute? GetAttributeThatCanHaveMultiple(Type classType, Type attributeType, PropertyInfo propertyInfo)
+        private static Attribute? GetAttributeThatCanHaveMultiple(Type classType, Type attributeType, MemberInfo propertyInfo)
         {
             object[] attributes = propertyInfo.GetCustomAttributes(attributeType, inherit: false);
             return GetAttributeThatCanHaveMultiple(attributeType, classType, propertyInfo, attributes);
@@ -235,7 +235,7 @@ private JsonConverter GetConverterFromAttribute(JsonConverterAttribute converter
             return GetAttributeThatCanHaveMultiple(attributeType, classType, null, attributes);
         }
 
-        private static Attribute? GetAttributeThatCanHaveMultiple(Type attributeType, Type classType, PropertyInfo? propertyInfo, object[] attributes)
+        private static Attribute? GetAttributeThatCanHaveMultiple(Type attributeType, Type classType, MemberInfo? propertyInfo, object[] attributes)
         {
             if (attributes.Length == 0)
             {

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

@@ -50,8 +50,10 @@ private MethodInfo FindImmutableCreateRangeMethod(Type constructingType)
             return null!;
         }
 
-        public abstract Func<object?, TProperty> CreatePropertyGetter<TClass, TProperty>(PropertyInfo propertyInfo);
+        public abstract Func<object?, TProperty> CreateGetter<TClass, TProperty>(PropertyInfo propertyInfo);
+        public abstract Func<object?, TProperty> CreateGetter<TClass, TProperty>(FieldInfo propertyInfo);
 
-        public abstract Action<object?, TProperty> CreatePropertySetter<TClass, TProperty>(PropertyInfo propertyInfo);
+        public abstract Action<object?, TProperty> CreateSetter<TClass, TProperty>(PropertyInfo propertyInfo);
+        public abstract Action<object?, TProperty> CreateSetter<TClass, TProperty>(FieldInfo propertyInfo);
     }
 }