Add source gen support + misc feedback

src/libraries/System.Text.Json/gen/JsonConstants.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.
+
+namespace System.Text.Json.SourceGeneration
+{
+    internal static class JsonConstants
+    {
+        public const string IJsonOnSerializedFullName = "System.Text.Json.Serialization.IJsonOnSerialized";
+        public const string IJsonOnSerializingFullName = "System.Text.Json.Serialization.IJsonOnSerializing";
+    }
+}

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -500,7 +500,13 @@ private string GenerateForObject(TypeGenerationSpec typeMetadata)
 
                 if (typeMetadata.GenerateSerializationLogic)
                 {
-                    serializeFuncSource = GenerateFastPathFuncForObject(typeCompilableName, serializeMethodName, typeMetadata.CanBeNull, properties);
+                    serializeFuncSource = GenerateFastPathFuncForObject(
+                        typeCompilableName,
+                        serializeMethodName,
+                        typeMetadata.CanBeNull,
+                        typeMetadata.ImplementsIJsonOnSerialized,
+                        typeMetadata.ImplementsIJsonOnSerializing,
+                        properties);
                     serializeFuncNamedArg = $@"serializeFunc: {serializeMethodName}";
                 }
                 else
@@ -635,6 +641,8 @@ private string GenerateFastPathFuncForObject(
                 string typeInfoTypeRef,
                 string serializeMethodName,
                 bool canBeNull,
+                bool implementsIJsonOnSerialized,
+                bool implementsIJsonOnSerializing,
                 List<PropertyGenerationSpec>? properties)
             {
                 JsonSourceGenerationOptionsAttribute options = _currentContext.GenerationOptions;
@@ -646,6 +654,12 @@ private string GenerateFastPathFuncForObject(
                 StringBuilder sb = new();
 
                 // Begin method definition
+                if (implementsIJsonOnSerializing)
+                {
+                    sb.Append($@"(({JsonConstants.IJsonOnSerializingFullName}){ValueVarName}).OnSerializing();");
+                    sb.Append($@"{Environment.NewLine}    ");
+                }
+
                 sb.Append($@"{WriterVarName}.WriteStartObject();");
 
                 if (properties != null)
@@ -733,6 +747,12 @@ private string GenerateFastPathFuncForObject(
 
         {WriterVarName}.WriteEndObject();");
 
+                if (implementsIJsonOnSerialized)
+                {
+                    sb.Append($@"{Environment.NewLine}    ");
+                    sb.Append($@"(({JsonConstants.IJsonOnSerializedFullName}){ValueVarName}).OnSerialized();");
+                };
+
                 return GenerateFastPathFuncForType(serializeMethodName, typeInfoTypeRef, sb.ToString(), canBeNull);
             }
 

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Parser.cs

@@ -494,6 +494,9 @@ private TypeGenerationSpec GetOrAddTypeGenerationSpec(Type type, JsonSourceGener
                 bool foundDesignTimeCustomConverter = false;
                 string? converterInstatiationLogic = null;
 
+                bool implementsIJsonOnSerialized = false;
+                bool implementsIJsonOnSerializing = false;
+
                 IList<CustomAttributeData> attributeDataList = CustomAttributeData.GetCustomAttributes(type);
                 foreach (CustomAttributeData attributeData in attributeDataList)
                 {
@@ -577,6 +580,11 @@ private TypeGenerationSpec GetOrAddTypeGenerationSpec(Type type, JsonSourceGener
                         constructionStrategy = ObjectConstructionStrategy.ParameterlessConstructor;
                     }
 
+                    // GetInterface() is currently not implemented, so we use GetInterfaces().
+                    IEnumerable<string> interfaces = type.GetInterfaces().Select(interfaceType => interfaceType.FullName);
+                    implementsIJsonOnSerialized = interfaces.FirstOrDefault(interfaceName => interfaceName == JsonConstants.IJsonOnSerializedFullName) != null;
+                    implementsIJsonOnSerializing = interfaces.FirstOrDefault(interfaceName => interfaceName == JsonConstants.IJsonOnSerializingFullName) != null;
+
                     for (Type? currentType = type; currentType != null; currentType = currentType.BaseType)
                     {
                         const BindingFlags bindingFlags =
@@ -627,7 +635,9 @@ private TypeGenerationSpec GetOrAddTypeGenerationSpec(Type type, JsonSourceGener
                     collectionValueTypeMetadata: collectionValueType != null ? GetOrAddTypeGenerationSpec(collectionValueType, generationMode) : null,
                     constructionStrategy,
                     nullableUnderlyingTypeMetadata: nullableUnderlyingType != null ? GetOrAddTypeGenerationSpec(nullableUnderlyingType, generationMode) : null,
-                    converterInstatiationLogic);
+                    converterInstatiationLogic,
+                    implementsIJsonOnSerialized,
+                    implementsIJsonOnSerializing);
 
                 return typeMetadata;
             }

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

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0</TargetFrameworks>
     <CLSCompliant>false</CLSCompliant>
@@ -35,6 +35,7 @@
     <Compile Include="..\Common\JsonSourceGenerationOptionsAttribute.cs" Link="Common\System\Text\Json\Serialization\JsonSourceGenerationOptionsAttribute.cs" />
     <Compile Include="ClassType.cs" />
     <Compile Include="CollectionType.cs" />
+    <Compile Include="JsonConstants.cs" />
     <Compile Include="JsonSourceGenerator.cs" />
     <Compile Include="JsonSourceGenerator.Emitter.cs" />
     <Compile Include="JsonSourceGenerator.Parser.cs" />

src/libraries/System.Text.Json/gen/TypeGenerationSpec.cs

@@ -33,6 +33,9 @@ internal class TypeGenerationSpec
 
         public ClassType ClassType { get; private set; }
 
+        public bool ImplementsIJsonOnSerialized { get; private set; }
+        public bool ImplementsIJsonOnSerializing { get; private set; }
+
         public bool IsValueType { get; private set; }
 
         public bool CanBeNull { get; private set; }
@@ -67,7 +70,9 @@ public void Initialize(
             TypeGenerationSpec? collectionValueTypeMetadata,
             ObjectConstructionStrategy constructionStrategy,
             TypeGenerationSpec? nullableUnderlyingTypeMetadata,
-            string? converterInstantiationLogic)
+            string? converterInstantiationLogic,
+            bool implementsIJsonOnSerialized,
+            bool implementsIJsonOnSerializing)
         {
             GenerationMode = generationMode;
             TypeRef = $"global::{typeRef}";
@@ -84,6 +89,8 @@ public void Initialize(
             ConstructionStrategy = constructionStrategy;
             NullableUnderlyingTypeMetadata = nullableUnderlyingTypeMetadata;
             ConverterInstantiationLogic = converterInstantiationLogic;
+            ImplementsIJsonOnSerialized = implementsIJsonOnSerialized;
+            ImplementsIJsonOnSerializing = implementsIJsonOnSerializing;
         }
 
         private bool FastPathIsSupported()

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

@@ -8,7 +8,7 @@ namespace System.Text.Json.Serialization
     /// </summary>
     /// <remarks>
     /// This behavior is only supported on types representing JSON objects.
-    /// Types that have a custom converter or represent collections or values do not support this behavior.
+    /// Types that have a custom converter or represent either collections or primitive values do not support this behavior.
     /// </remarks>
     public interface IJsonOnDeserialized
     {

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

@@ -8,7 +8,7 @@ namespace System.Text.Json.Serialization
     /// </summary>
     /// <remarks>
     /// This behavior is only supported on types representing JSON objects.
-    /// Types that have a custom converter or represent collections or values do not support this behavior.
+    /// Types that have a custom converter or represent either collections or primitive values do not support this behavior.
     /// </remarks>
     public interface IJsonOnDeserializing
     {

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

@@ -8,7 +8,7 @@ namespace System.Text.Json.Serialization
     /// </summary>
     /// <remarks>
     /// This behavior is only supported on types representing JSON objects.
-    /// Types that have a custom converter or represent collections or values do not support this behavior.
+    /// Types that have a custom converter or represent either collections or primitive values do not support this behavior.
     /// </remarks>
     public interface IJsonOnSerialized
     {

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

@@ -8,7 +8,7 @@ namespace System.Text.Json.Serialization
     /// </summary>
     /// <remarks>
     /// This behavior is only supported on types representing JSON objects.
-    /// Types that have a custom converter or represent collections or values do not support this behavior.
+    /// Types that have a custom converter or represent either collections or primitive values do not support this behavior.
     /// </remarks>
     public interface IJsonOnSerializing
     {

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/ContextClasses.cs

@@ -19,6 +19,7 @@ public interface ITestContext
         public JsonTypeInfo<HighLowTemps> HighLowTemps { get; }
         public JsonTypeInfo<MyType> MyType { get; }
         public JsonTypeInfo<MyType2> MyType2 { get; }
+        public JsonTypeInfo<MyTypeWithCallbacks> MyTypeWithCallbacks { get; }
         public JsonTypeInfo<MyIntermediateType> MyIntermediateType { get; }
         public JsonTypeInfo<HighLowTempsImmutable> HighLowTempsImmutable { get; }
         public JsonTypeInfo<RealWorldContextTests.MyNestedClass> MyNestedClass { get; }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MetadataAndSerializationContextTests.cs

@@ -17,6 +17,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(HighLowTemps))]
     [JsonSerializable(typeof(MyType))]
     [JsonSerializable(typeof(MyType2))]
+    [JsonSerializable(typeof(MyTypeWithCallbacks))]
     [JsonSerializable(typeof(MyIntermediateType))]
     [JsonSerializable(typeof(HighLowTempsImmutable))]
     [JsonSerializable(typeof(RealWorldContextTests.MyNestedClass))]
@@ -45,6 +46,7 @@ public override void EnsureFastPathGeneratedAsExpected()
             Assert.NotNull(MetadataAndSerializationContext.Default.HighLowTemps.Serialize);
             Assert.NotNull(MetadataAndSerializationContext.Default.MyType.Serialize);
             Assert.NotNull(MetadataAndSerializationContext.Default.MyType2.Serialize);
+            Assert.NotNull(MetadataAndSerializationContext.Default.MyTypeWithCallbacks.Serialize);
             Assert.NotNull(MetadataAndSerializationContext.Default.MyIntermediateType.Serialize);
             Assert.NotNull(MetadataAndSerializationContext.Default.HighLowTempsImmutable.Serialize);
             Assert.NotNull(MetadataAndSerializationContext.Default.MyNestedClass.Serialize);

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MetadataContextTests.cs

@@ -16,6 +16,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(HighLowTemps), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(MyType), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(MyType2), GenerationMode = JsonSourceGenerationMode.Metadata)]
+    [JsonSerializable(typeof(MyTypeWithCallbacks), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(MyIntermediateType), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(HighLowTempsImmutable), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(RealWorldContextTests.MyNestedClass), GenerationMode = JsonSourceGenerationMode.Metadata)]
@@ -93,6 +94,7 @@ public override void EnsureFastPathGeneratedAsExpected()
             Assert.Null(MetadataContext.Default.HighLowTemps.Serialize);
             Assert.Null(MetadataContext.Default.MyType.Serialize);
             Assert.Null(MetadataContext.Default.MyType2.Serialize);
+            Assert.Null(MetadataContext.Default.MyTypeWithCallbacks.Serialize);
             Assert.Null(MetadataContext.Default.MyIntermediateType.Serialize);
             Assert.Null(MetadataContext.Default.HighLowTempsImmutable.Serialize);
             Assert.Null(MetadataContext.Default.MyNestedClass.Serialize);

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MixedModeContextTests.cs

@@ -16,6 +16,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(HighLowTemps), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyType), GenerationMode = JsonSourceGenerationMode.Default)]
     [JsonSerializable(typeof(MyType2), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(MyTypeWithCallbacks), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyIntermediateType), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(HighLowTempsImmutable), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(RealWorldContextTests.MyNestedClass), GenerationMode = JsonSourceGenerationMode.Serialization)]
@@ -43,6 +44,7 @@ public override void EnsureFastPathGeneratedAsExpected()
             Assert.NotNull(MixedModeContext.Default.HighLowTemps.Serialize);
             Assert.NotNull(MixedModeContext.Default.MyType.Serialize);
             Assert.NotNull(MixedModeContext.Default.MyType2.Serialize);
+            Assert.NotNull(MixedModeContext.Default.MyTypeWithCallbacks.Serialize);
             Assert.NotNull(MixedModeContext.Default.MyIntermediateType.Serialize);
             Assert.Null(MixedModeContext.Default.HighLowTempsImmutable.Serialize);
             Assert.NotNull(MixedModeContext.Default.MyNestedClass.Serialize);
@@ -165,5 +167,24 @@ public override void SerializeObjectArray_WithCustomOptions()
             VerifyIndexViewModel(index, JsonSerializer.Deserialize(indexAsJsonElement.GetRawText(), metadataContext.IndexViewModel));
             VerifyCampaignSummaryViewModel(campaignSummary, JsonSerializer.Deserialize(campaignSummeryAsJsonElement.GetRawText(), metadataContext.CampaignSummaryViewModel));
         }
+
+        [Fact]
+        public void OnSerializeCallbacks_WithCustomOptions()
+        {
+            MyTypeWithCallbacks obj = new();
+            Assert.Null(obj.MyProperty);
+
+            ITestContext context = SerializationContextWithCamelCase.Default;
+            Assert.Same(JsonNamingPolicy.CamelCase, ((JsonSerializerContext)context).Options.PropertyNamingPolicy);
+
+            string json = JsonSerializer.Serialize(obj, context.MyTypeWithCallbacks);
+            Assert.Equal("{\"myProperty\":\"Before\"}", json);
+            Assert.Equal("After", obj.MyProperty);
+
+            context = new MetadataContext(new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase });
+            json = JsonSerializer.Serialize(obj, context.MyTypeWithCallbacks);
+            Assert.Equal("{\"myProperty\":\"Before\"}", json);
+            Assert.Equal("After", obj.MyProperty);
+        }
     }
 }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/SerializationContextTests.cs

@@ -38,6 +38,7 @@ internal partial class SerializationContext : JsonSerializerContext, ITestContex
     [JsonSerializable(typeof(HighLowTemps), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyType), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyType2), GenerationMode = JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(MyTypeWithCallbacks), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyIntermediateType), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(HighLowTempsImmutable), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(RealWorldContextTests.MyNestedClass), GenerationMode = JsonSourceGenerationMode.Serialization)]
@@ -60,6 +61,7 @@ internal partial class SerializationWithPerTypeAttributeContext : JsonSerializer
     [JsonSerializable(typeof(HighLowTemps), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyType), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyType2), GenerationMode = JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(MyTypeWithCallbacks), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyIntermediateType), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(HighLowTempsImmutable), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(RealWorldContextTests.MyNestedClass), GenerationMode = JsonSourceGenerationMode.Serialization)]
@@ -93,6 +95,7 @@ public override void EnsureFastPathGeneratedAsExpected()
             Assert.NotNull(SerializationContext.Default.HighLowTemps.Serialize);
             Assert.NotNull(SerializationContext.Default.MyType.Serialize);
             Assert.NotNull(SerializationContext.Default.MyType2.Serialize);
+            Assert.NotNull(SerializationContext.Default.MyTypeWithCallbacks.Serialize);
             Assert.NotNull(SerializationContext.Default.MyIntermediateType.Serialize);
             Assert.NotNull(SerializationContext.Default.HighLowTempsImmutable.Serialize);
             Assert.NotNull(SerializationContext.Default.MyNestedClass.Serialize);
@@ -307,6 +310,17 @@ public override void ParameterizedConstructor()
 
             JsonTestHelper.AssertThrows_PropMetadataInit(() => JsonSerializer.Deserialize(json, DefaultContext.HighLowTempsImmutable), typeof(HighLowTempsImmutable));
         }
+
+        [Fact]
+        public void OnSerializeCallbacks()
+        {
+            MyTypeWithCallbacks obj = new();
+            Assert.Null(obj.MyProperty);
+
+            string json = JsonSerializer.Serialize(obj, DefaultContext.MyTypeWithCallbacks);
+            Assert.Equal("{\"MyProperty\":\"Before\"}", json);
+            Assert.Equal("After", obj.MyProperty);
+        }
     }
 
     public sealed class SerializationWithPerTypeAttributeContextTests : SerializationContextTests

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/TestClasses.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
+using System.Text.Json.Serialization;
 
 namespace System.Text.Json.SourceGeneration.Tests.RepeatedTypes
 {
@@ -108,6 +109,14 @@ public class MyIntermediateType
         public MyType Type = new();
     }
 
+    public class MyTypeWithCallbacks : IJsonOnSerializing, IJsonOnSerialized
+    {
+        public string MyProperty { get; set; }
+
+        public void OnSerializing() => MyProperty = "Before";
+        void IJsonOnSerialized.OnSerialized() => MyProperty = "After";
+    }
+
     public class JsonMessage
     {
         public string Message { get; set; }

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/OnSerializeTests.cs

@@ -149,7 +149,6 @@ private class MyClassWithSmallConstructor :
         {
             public int MyInt { get; set; }
 
-            [JsonConstructor]
             public MyClassWithSmallConstructor(int myInt)
             {
                 MyInt = myInt;
@@ -229,7 +228,6 @@ private class MyClassWithLargeConstructor :
             public int MyInt4 { get; set; }
             public int MyInt5 { get; set; }
 
-            [JsonConstructor]
             public MyClassWithLargeConstructor(int myInt1, int myInt2, int myInt3, int myInt4, int myInt5)
             {
                 MyInt1 = myInt1;