Add serialization source generator

samples/PingPong/PingPong.csproj

@@ -9,10 +9,6 @@
     <ProjectReference Include="../../src/Models/Discord.Net.Models.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <ProjectReference Include="../../tools/SourceGenerators/Serialization/Discord.Net.SourceGenerators.Serialization.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Hosting" />
   </ItemGroup>

src/Models/Channel.cs

@@ -0,0 +1,241 @@
+using System;
+using Discord.Net.Serialization;
+
+namespace Discord.Net.Models
+{
+    /// <summary>
+    /// Represents a guild or DM channel within Discord.
+    /// </summary>
+    /// <remarks>
+    /// <see href="https://discord.com/developers/docs/resources/channel#channel-object-channel-structure"/>
+    /// </remarks>
+    /// <param name="Id">
+    /// The id of this channel.
+    /// </param>
+    /// <param name="Type">
+    /// The type of channel.
+    /// </param>
+    [DiscriminatedUnion(nameof(Channel.Type))]
+    [GenerateSerializer]
+    public record Channel(
+        ChannelType Type,
+        Snowflake Id);
+
+    /// <summary>
+    /// Represents a text channel within a server.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildText)]
+    [GenerateSerializer]
+    public record GuildTextChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        /*Overwrite[] PermissionOverwrites,*/
+        string Name,
+        string? Topic,
+        bool Nsfw,
+        Snowflake LastMessageId,
+        int RateLimitPerUser,
+        Snowflake? ParentId,
+        DateTimeOffset? LastPinTimestamp)
+        : Channel(
+            ChannelType.GuildText,
+            Id);
+
+    /*
+
+    /// <summary>
+    /// Represents a direct message between users.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.DM)]
+    [GenerateSerializer]
+    public record DMChannel(
+        Snowflake Id,
+        User[] Recipients)
+        : Channel(
+            ChannelType.DM,
+            Id);
+
+    /// <summary>
+    /// Represents a voice channel within a server.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildVoice)]
+    [GenerateSerializer]
+    public record GuildVoiceChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites,
+        string Name,
+        bool Nsfw,
+        int Bitrate,
+        int UserLimit,
+        Snowflake? ParentId,
+        string? RtcRegion,
+        int VideoQualityMode)
+        : Channel(
+            ChannelType.GuildVoice,
+            Id);
+
+    /// <summary>
+    /// Represents a direct message between multiple users.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GroupDM)]
+    [GenerateSerializer]
+    public record GroupDMChannel(
+        Snowflake Id,
+        string Name,
+        Snowflake LastMessageId,
+        User[] Recipients,
+        string? Icon,
+        Snowflake? OwnerId,
+        Snowflake? ApplicationId,
+        DateTimeOffset? LastPinTimestamp)
+        : Channel(
+            ChannelType.GroupDM,
+            Id);
+
+    /// <summary>
+    /// Represents an organizational category that contains up to 50 channels.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildCategory)]
+    [GenerateSerializer]
+    public record GuildCategoryChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites,
+        string Name)
+        : Channel(
+            ChannelType.GuildCategory,
+            Id);
+
+    /// <summary>
+    /// Represents a channel that users can follow and crosspost into their own
+    /// server.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildNews)]
+    [GenerateSerializer]
+    public record GuildNewsChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites,
+        string Name,
+        string? Topic,
+        bool Nsfw,
+        Snowflake? LastMessageId,
+        int RateLimitPerUser,
+        Snowflake? ParentId,
+        Snowflake? LastPinTimestamp)
+        : Channel(
+            ChannelType.GuildNews,
+            Id);
+
+    /// <summary>
+    /// Represents a channel in which game developers can sell their game on
+    /// Discord.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildStore)]
+    [GenerateSerializer]
+    public record GuildStoreChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites, // I guess???
+        string? Name,
+        Snowflake? ParentId)
+        : Channel(
+            ChannelType.GuildStore,
+            Id);
+
+    /// <summary>
+    /// Represents a temporary sub-channel within a
+    /// <see cref="GuildNewsChannel"/>.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildNewsThread)]
+    [GenerateSerializer]
+    public record GuildNewsThreadChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites, // I guess??
+        string Name,
+        Snowflake? LastMessageId,
+        Snowflake? ParentId,
+        Snowflake? LastPinTimestamp,
+        int MessageCount,
+        int MemberCount,
+        ThreadMetadata ThreadMetadata,
+        ThreadMember Member)
+        : Channel(
+            ChannelType.GuildNewsThread,
+            Id);
+
+    /// <summary>
+    /// Represents a temporary sub-channel within a
+    /// <see cref="GuildTextChannel"/>.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildPublicThread)]
+    [GenerateSerializer]
+    public record GuildPublicThreadChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites, // I guess??
+        string Name,
+        Snowflake? LastMessageId,
+        Snowflake? ParentId,
+        Snowflake? LastPinTimestamp,
+        int MessageCount,
+        int MemberCount,
+        ThreadMetadata ThreadMetadata,
+        ThreadMember Member)
+        : Channel(
+            ChannelType.GuildPublicThread,
+            Id);
+
+    /// <summary>
+    /// Represents a temporary sub-channel within a
+    /// <see cref="GuildTextChannel"/> that is only viewable by those invited
+    /// and those with the MANAGE_THREADS permission.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildPrivateThread)]
+    [GenerateSerializer]
+    public record GuildPrivateThreadChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites, // I guess???
+        string Name,
+        Snowflake? LastMessageId,
+        Snowflake? ParentId,
+        Snowflake? LastPinTimestamp,
+        int MessageCount,
+        int MemberCount,
+        ThreadMetadata ThreadMetadata,
+        ThreadMember Member)
+        : Channel(
+            ChannelType.GuildPrivateThread,
+            Id);
+
+    /// <summary>
+    /// Represents a voice channel for hosting events with an audience.
+    /// </summary>
+    [DiscriminatedUnionMember(ChannelType.GuildStageVoice)]
+    [GenerateSerializer]
+    public record GuildStageVoiceChannel(
+        Snowflake Id,
+        Snowflake GuildId,
+        int Position,
+        Overwrite[] PermissionOverwrites,
+        string Name,
+        int Bitrate,
+        int UserLimit,
+        string? RtcRegion)
+        : Channel(
+            ChannelType.GuildStageVoice,
+            Id);
+
+    */
+}

src/Models/ChannelType.cs

@@ -0,0 +1,68 @@
+namespace Discord.Net.Models
+{
+    /// <summary>
+    /// Declares an enum which represents the type of a <see cref="Channel"/>.
+    /// </summary>
+    /// <remarks>
+    /// <see href="https://discord.com/developers/docs/resources/channel#channel-object-channel-types"/>
+    /// </remarks>
+    public enum ChannelType
+    {
+        /// <summary>
+        /// A text channel within a server.
+        /// </summary>
+        GuildText = 0,
+
+        /// <summary>
+        /// A direct message between users.
+        /// </summary>
+        DM = 1,
+
+        /// <summary>
+        /// A voice channel within a server.
+        /// </summary>
+        GuildVoice = 2,
+
+        /// <summary>
+        /// A direct message between multiple users.
+        /// </summary>
+        GroupDM = 3,
+
+        /// <summary>
+        /// An organizational category that contains up to 50 channels.
+        /// </summary>
+        GuildCategory = 4,
+
+        /// <summary>
+        /// A channel that users can follow and crosspost into their own server.
+        /// </summary>
+        GuildNews = 5,
+
+        /// <summary>
+        /// A channel in which game developers can sell their game on Discord.
+        /// </summary>
+        GuildStore = 6,
+
+        /// <summary>
+        /// A temporary sub-channel within a <see cref="GuildNews"/> channel.
+        /// </summary>
+        GuildNewsThread = 10,
+
+        /// <summary>
+        /// A temporary sub-channel within a <see cref="GuildText"/> channel.
+        /// </summary>
+        GuildPublicThread = 11,
+
+        /// <summary>
+        /// A temporary sub-channel within a <see cref="GuildText"/> channel
+        /// that is only viewable by those invited and those with the
+        /// MANAGE_THREADS permission.
+        /// </summary>
+        GuildPrivateThread = 12,
+
+        /// <summary>
+        /// A voice channel for hosting events with an audience.
+        /// </summary>
+        GuildStageVoice = 13
+    }
+}

src/Models/Discord.Net.Models.csproj

@@ -7,12 +7,19 @@
       $(Description)
       Shared models between the Discord REST API and Gateway.
     </Description>
+
+    <DiscordNet_SerializationGenerator_OptionsTypeNamespace>Discord.Net.Serialization</DiscordNet_SerializationGenerator_OptionsTypeNamespace>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="System.Text.Json" />
   </ItemGroup>
 
+  <ItemGroup>
+    <CompilerVisibleProperty Include="DiscordNet_SerializationGenerator_OptionsTypeNamespace" />
+    <ProjectReference Include="../../tools/SourceGenerators/Serialization/Discord.Net.SourceGenerators.Serialization.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="../Serialization/Discord.Net.Serialization.csproj" />
   </ItemGroup>

src/Serialization/DiscriminatedUnionAttribute.cs

@@ -5,6 +5,9 @@ namespace Discord.Net.Serialization
     /// <summary>
     /// Defines an attribute used to mark discriminated unions.
     /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct,
+        AllowMultiple = false,
+        Inherited = false)]
     public class DiscriminatedUnionAttribute : Attribute
     {
         /// <summary>

src/Serialization/DiscriminatedUnionMemberAttribute.cs

@@ -5,12 +5,15 @@ namespace Discord.Net.Serialization
     /// <summary>
     /// Defines an attribute used to mark members of discriminated unions.
     /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct,
+        AllowMultiple = false,
+        Inherited = false)]
     public class DiscriminatedUnionMemberAttribute : Attribute
     {
         /// <summary>
         /// Gets the discriminator value used to identify this member type.
         /// </summary>
-        public string Discriminator { get; }
+        public object Discriminator { get; }
 
         /// <summary>
         /// Creates a new <see cref="DiscriminatedUnionMemberAttribute"/>
@@ -19,7 +22,7 @@ namespace Discord.Net.Serialization
         /// <param name="discriminator">
         /// The discriminator value used to identify this member type.
         /// </param>
-        public DiscriminatedUnionMemberAttribute(string discriminator)
+        public DiscriminatedUnionMemberAttribute(object discriminator)
         {
             Discriminator = discriminator;
         }

src/Serialization/GenerateSerializerAttribute.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace Discord.Net.Serialization
+{
+    /// <summary>
+    /// Defines an attribute which informs the serializer generator to generate
+    /// a serializer for this type.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct,
+        AllowMultiple = false,
+        Inherited = false)]
+    public class GenerateSerializerAttribute : Attribute
+    {
+
+    }
+}

tools/SourceGenerators/Directory.Build.props

@@ -21,6 +21,7 @@
   <PropertyGroup>
     <GenerateDocumentationFile>false</GenerateDocumentationFile>
     <NoPackageAnalysis>true</NoPackageAnalysis>
+    <IncludeBuildOutput>false</IncludeBuildOutput>
      <!-- Disable release tracking analyzers due to weird behaviour with OmniSharp -->
     <NoWarn>$(NoWarn);RS2000;RS2001;RS2002;RS2003;RS2004;RS2005;RS2006;RS2007;RS2008</NoWarn>
   </PropertyGroup>
@@ -33,4 +34,8 @@
     <None Include="$(OutputPath)$(AssemblyName).dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Compile Include="$(MSBuildThisFileDirectory)\IsExternalInit.cs" Link="IsExternalInit.cs" />
+  </ItemGroup>
+
 </Project>

tools/SourceGenerators/IsExternalInit.cs

@@ -0,0 +1,4 @@
+namespace System.Runtime.CompilerServices
+{
+    internal static class IsExternalInit { }
+}

tools/SourceGenerators/Serialization/Discord.Net.SourceGenerators.Serialization.csproj

@@ -4,4 +4,8 @@
     <TargetFramework>netstandard2.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Include="Discord.Net.SourceGenerators.Serialization.props" Pack="true" PackagePath="build" Visible="false" />
+  </ItemGroup>
+
 </Project>

tools/SourceGenerators/Serialization/Discord.Net.SourceGenerators.Serialization.props

@@ -0,0 +1,6 @@
+<Project>
+  <ItemGroup>
+    <CompilerVisibleProperty Include="DiscordNet_SerializationGenerator_OptionsTypeNamespace" />
+    <CompilerVisibleProperty Include="DiscordNet_SerializationGenerator_SearchThroughReferencedAssemblies" />
+  </ItemGroup>
+</Project>

tools/SourceGenerators/Serialization/SerializationSourceGenerator.ConverterSource.cs

@@ -1,37 +0,0 @@
-using Microsoft.CodeAnalysis;
-
-namespace Discord.Net.SourceGenerators.Serialization
-{
-    public partial class SerializationSourceGenerator
-    {
-        private static string GenerateConverter(INamedTypeSymbol @class)
-        {
-return $@"
-using System;
-using System.Text.Json;
-using System.Text.Json.Serialization;
-
-namespace Discord.Net.Serialization.Converters
-{{
-    public class {@class.Name}Converter : JsonConverter<{@class.ToDisplayString()}>
-    {{
-        public override {@class.ToDisplayString()} Read(
-            ref Utf8JsonReader reader,
-            Type typeToConvert,
-            JsonSerializerOptions options)
-        {{
-            return default;
-        }}
-
-        public override void Write(
-            Utf8JsonWriter writer,
-            {@class.ToDisplayString()} value,
-            JsonSerializerOptions options)
-        {{
-            writer.WriteNull();
-        }}
-    }}
-}}";
-        }
-    }
-}

tools/SourceGenerators/Serialization/SerializationSourceGenerator.OptionsSource.cs

@@ -5,20 +5,26 @@ namespace Discord.Net.SourceGenerators.Serialization
 {
     public partial class SerializationSourceGenerator
     {
-        private static string GenerateSerializerOptionsTemplateSourceCode()
+        private static string GenerateSerializerOptionsSourceCode(
+            string @namespace,
+            IEnumerable<SerializedType> converters)
         {
-return @"
-using System;
+            var snippets = string.Join("\n",
+                converters.Select(
+                    x => $"            options.Converters.Add(new {@namespace}.Internal.Converters.{x.ConverterTypeName}());"));
+
+return $@"using System;
 using System.Text.Json;
+using Discord.Net.Serialization.Converters;
 
-namespace Discord.Net.Serialization
-{
+namespace {@namespace}
+{{
     /// <summary>
     /// Defines extension methods for adding Discord.Net JSON converters to a
     /// <see cref=""JsonSerializerOptions""/> instance.
     /// </summary>
-    public static partial class JsonSerializerOptionsExtensions
-    {
+    public static class JsonSerializerOptionsExtensions
+    {{
         /// <summary>
         /// Adds Discord.Net JSON converters to the passed
         /// <see cref=""JsonSerializerOptions""/>.
@@ -30,33 +36,11 @@ namespace Discord.Net.Serialization
         /// The modified <see cref=""JsonSerializerOptions""/>, so this method
         /// can be chained.
         /// </returns>
-        public static partial JsonSerializerOptions WithDiscordNetConverters(
-            this JsonSerializerOptions options);
-    }
-}";
-        }
-
-        private static string GenerateSerializerOptionsSourceCode(
-            List<string> converters)
-        {
-            var snippets = string.Join("\n",
-                converters.Select(
-                    x => $"options.Converters.Add(new {x}());"));
-
-return $@"
-using System;
-using System.Text.Json;
-using Discord.Net.Serialization.Converters;
-
-namespace Discord.Net.Serialization
-{{
-    public static partial class JsonSerializerOptionsExtensions
-    {{
-        public static partial JsonSerializerOptions WithDiscordNetConverters(
+        public static JsonSerializerOptions WithDiscordNetConverters(
             this JsonSerializerOptions options)
         {{
             options.Converters.Add(new OptionalConverterFactory());
-            {snippets}
+{snippets}
 
             return options;
         }}

tools/SourceGenerators/Serialization/SerializationSourceGenerator.cs

@@ -3,7 +3,7 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
-using System.Reflection;
+using System.Threading;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 
@@ -14,94 +14,136 @@ namespace Discord.Net.SourceGenerators.Serialization
     {
         public void Execute(GeneratorExecutionContext context)
         {
+            if (!context.AnalyzerConfigOptions.GlobalOptions.TryGetValue(
+                "build_property.DiscordNet_SerializationGenerator_OptionsTypeNamespace",
+                out var serializerOptionsNamespace))
+                throw new InvalidOperationException(
+                    "Missing output namespace. Set DiscordNet_SerializationGenerator_OptionsTypeNamespace in your project file.");
+
+            bool searchThroughReferencedAssemblies =
+                context.AnalyzerConfigOptions.GlobalOptions.TryGetValue(
+                    "build_property.DiscordNet_SerializationGenerator_SearchThroughReferencedAssemblies",
+                    out var _);
+
+            var generateSerializerAttribute = context.Compilation
+                .GetTypeByMetadataName(
+                    "Discord.Net.Serialization.GenerateSerializerAttribute");
+            var discriminatedUnionSymbol = context.Compilation
+                .GetTypeByMetadataName(
+                    "Discord.Net.Serialization.DiscriminatedUnionAttribute");
+            var discriminatedUnionMemberSymbol = context.Compilation
+                .GetTypeByMetadataName(
+                    "Discord.Net.Serialization.DiscriminatedUnionMemberAttribute");
+
+            Debug.Assert(generateSerializerAttribute != null);
+            Debug.Assert(discriminatedUnionSymbol != null);
+            Debug.Assert(discriminatedUnionMemberSymbol != null);
+            Debug.Assert(context.SyntaxContextReceiver != null);
+
             var receiver = (SyntaxReceiver)context.SyntaxContextReceiver!;
-            var converters = new List<string>();
+            var symbolsToBuild = receiver.GetSerializedTypes(
+                context.Compilation);
 
-            foreach (var @class in receiver.Classes)
+            if (searchThroughReferencedAssemblies)
             {
-                var semanticModel = context.Compilation.GetSemanticModel(
-                    @class.SyntaxTree);
+                var visitor = new VisibleTypeVisitor(context.CancellationToken);
+                foreach (var module in context.Compilation.Assembly.Modules)
+                    foreach (var reference in module.ReferencedAssemblySymbols)
+                        visitor.Visit(reference);
 
-                if (semanticModel.GetDeclaredSymbol(@class) is
-                    not INamedTypeSymbol classSymbol)
-                    throw new InvalidOperationException(
-                        "Could not find named type symbol for " +
-                        $"{@class.Identifier}");
+                symbolsToBuild = symbolsToBuild
+                    .Concat(visitor.GetVisibleTypes());
+            }
 
-                context.AddSource(
-                    $"Converters.{classSymbol.Name}",
-                    GenerateConverter(classSymbol));
+            var types = SerializedTypeUtils.BuildTypeTrees(
+                generateSerializerAttribute: generateSerializerAttribute!,
+                discriminatedUnionSymbol: discriminatedUnionSymbol!,
+                discriminatedUnionMemberSymbol: discriminatedUnionMemberSymbol!,
+                symbolsToBuild: symbolsToBuild);
 
-                converters.Add($"{classSymbol.Name}Converter");
+            foreach (var type in types)
+            {
+                context.AddSource($"Converters.{type.ConverterTypeName}",
+                    type.GenerateSourceCode(serializerOptionsNamespace));
+
+                if (type is DiscriminatedUnionSerializedType duDeclaration)
+                    foreach (var member in duDeclaration.Members)
+                        context.AddSource(
+                            $"Converters.{type.ConverterTypeName}.{member.ConverterTypeName}",
+                            member.GenerateSourceCode(serializerOptionsNamespace));
             }
 
-            context.AddSource("SerializerOptions.Complete",
-                GenerateSerializerOptionsSourceCode(converters));
+            context.AddSource("SerializerOptions",
+                GenerateSerializerOptionsSourceCode(
+                    serializerOptionsNamespace, types));
         }
 
         public void Initialize(GeneratorInitializationContext context)
-        {
-            context.RegisterForPostInitialization(PostInitialize);
-            context.RegisterForSyntaxNotifications(() => new SyntaxReceiver());
-        }
-
-        public static void PostInitialize(
-            GeneratorPostInitializationContext context)
-            => context.AddSource("SerializerOptions.Template",
-                GenerateSerializerOptionsTemplateSourceCode());
+            => context.RegisterForSyntaxNotifications(
+                () => new SyntaxReceiver());
 
-        internal class SyntaxReceiver : ISyntaxContextReceiver
+        private class SyntaxReceiver : ISyntaxContextReceiver
         {
-            public List<ClassDeclarationSyntax> Classes { get; } = new();
-
-            private readonly Dictionary<string, INamedTypeSymbol> _interestingAttributes
-                = new();
+            private readonly List<SyntaxNode> _classes;
 
-            public void OnVisitSyntaxNode(GeneratorSyntaxContext context)
+            public SyntaxReceiver()
             {
-                _ = GetOrAddAttribute(_interestingAttributes,
-                    context.SemanticModel,
-                    "Discord.Net.Serialization.DiscriminatedUnionAttribute");
-                _ = GetOrAddAttribute(_interestingAttributes,
-                    context.SemanticModel,
-                    "Discord.Net.Serialization.DiscriminatedUnionMemberAttribute");
+                _classes = new();
+            }
 
-                if (context.Node is ClassDeclarationSyntax classDecl
-                    && classDecl.AttributeLists is
-                        SyntaxList<AttributeListSyntax> attrList
-                    && attrList.Any(
-                        list => list.Attributes
-                            .Any(a => IsInterestingAttribute(a,
-                                context.SemanticModel,
-                                _interestingAttributes.Values))))
+            public IEnumerable<INamedTypeSymbol> GetSerializedTypes(
+                Compilation compilation)
+            {
+                foreach (var @class in _classes)
                 {
-                    Classes.Add(classDecl);
+                    var semanticModel = compilation.GetSemanticModel(
+                        @class.SyntaxTree);
+
+                    if (semanticModel.GetDeclaredSymbol(@class) is
+                        INamedTypeSymbol classSymbol)
+                        yield return classSymbol;
                 }
             }
 
-            private static INamedTypeSymbol GetOrAddAttribute(
-                Dictionary<string, INamedTypeSymbol> cache,
-                SemanticModel model, string name)
+            private INamedTypeSymbol? _generateSerializerAttributeSymbol;
+
+            public void OnVisitSyntaxNode(GeneratorSyntaxContext context)
             {
-                if (!cache.TryGetValue(name, out var type))
+                _generateSerializerAttributeSymbol ??=
+                    context.SemanticModel.Compilation.GetTypeByMetadataName(
+                        "Discord.Net.Serialization.GenerateSerializerAttribute");
+
+                Debug.Assert(_generateSerializerAttributeSymbol != null);
+
+                if (context.Node is ClassDeclarationSyntax classDeclaration
+                    && classDeclaration.AttributeLists is
+                        SyntaxList<AttributeListSyntax> classAttributeLists
+                    && classAttributeLists.Any(
+                        list => list.Attributes.Any(
+                            n => IsAttribute(n, context.SemanticModel,
+                                _generateSerializerAttributeSymbol!))))
                 {
-                    type = model.Compilation.GetTypeByMetadataName(name);
-                    Debug.Assert(type != null);
-                    cache.Add(name, type!);
+                    _classes.Add(classDeclaration);
+                }
+                else if (context.Node is RecordDeclarationSyntax recordDeclaration
+                    && recordDeclaration.AttributeLists is
+                        SyntaxList<AttributeListSyntax> recordAttributeLists
+                    && recordAttributeLists.Any(
+                        list => list.Attributes.Any(
+                            n => IsAttribute(n, context.SemanticModel,
+                                _generateSerializerAttributeSymbol!))))
+                {
+                    _classes.Add(recordDeclaration);
                 }
 
-                return type!;
-            }
-
-            private static bool IsInterestingAttribute(
-                AttributeSyntax attribute, SemanticModel model,
-                IEnumerable<INamedTypeSymbol> interestingAttributes)
-            {
-                var typeInfo = model.GetTypeInfo(attribute.Name);
+                static bool IsAttribute(AttributeSyntax attribute,
+                    SemanticModel model, INamedTypeSymbol expected)
+                {
+                    var typeInfo = model.GetTypeInfo(attribute.Name);
 
-                return interestingAttributes.Any(
-                    x => SymbolEqualityComparer.Default
-                        .Equals(typeInfo.Type, x));
+                    return SymbolEqualityComparer.Default.Equals(
+                        typeInfo.Type, expected);
+                }
             }
         }
     }

tools/SourceGenerators/Serialization/Structure/SerializedType.cs

@@ -0,0 +1,253 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using static Discord.Net.SourceGenerators.Serialization.Utils;
+
+namespace Discord.Net.SourceGenerators.Serialization
+{
+    internal record SerializedType(
+        INamedTypeSymbol Declaration)
+    {
+        public virtual string ConverterTypeName
+            => $"{Declaration.Name}Converter";
+
+        protected virtual IEnumerable<IPropertySymbol> SymbolsToSerialize
+            => Declaration.GetProperties(includeInherited: true)
+                .Where(x => !x.IsReadOnly);
+
+        public virtual string GenerateSourceCode(string outputNamespace)
+        {
+            var deserializers = SymbolsToSerialize
+                .Select(GenerateFieldReader);
+
+            var bytes = string.Join("\n",
+                deserializers.Select(x => x.utf8));
+            var fields = string.Join("\n",
+                deserializers.Select(x => x.field));
+            var readers = string.Join("\n",
+                deserializers.Select(x => x.reader));
+
+            var fieldUnassigned = string.Join("\n                || ",
+                deserializers
+                    .Where(x => x.type.NullableAnnotation != NullableAnnotation.Annotated)
+                    .Select(
+                        x => $"{x.snakeCase}OrDefault is not {x.type} {x.snakeCase}"));
+
+            var constructorParams = string.Join(",\n",
+                deserializers
+                    .Select(x => $"                {x.name}: {x.snakeCase}{(x.type.NullableAnnotation == NullableAnnotation.Annotated ? "OrDefault" : "")}"));
+
+return $@"using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace {outputNamespace}.Converters
+{{
+    internal class {ConverterTypeName} : JsonConverter<{Declaration.ToDisplayString()}>
+    {{
+{bytes}
+
+        public override {Declaration.ToDisplayString()}? Read(
+            ref Utf8JsonReader reader,
+            Type typeToConvert,
+            JsonSerializerOptions options)
+        {{
+            if (reader.TokenType != JsonTokenType.StartObject)
+                throw new JsonException(""Expected StartObject"");
+
+{fields}
+
+            while (reader.Read())
+            {{
+                if (reader.TokenType == JsonTokenType.EndObject)
+                    break;
+
+                if (reader.TokenType != JsonTokenType.PropertyName)
+                    throw new JsonException(""Expected PropertyName"");
+
+{readers}
+                else if (!reader.Read())
+                    throw new JsonException();
+
+                if (reader.TokenType == JsonTokenType.StartArray
+                    || reader.TokenType == JsonTokenType.StartObject)
+                    reader.Skip();
+            }}
+
+            if ({fieldUnassigned})
+                throw new JsonException(""Missing field"");
+
+            return new {Declaration.ToDisplayString()}(
+{constructorParams}
+            );
+        }}
+
+        public override void Write(
+            Utf8JsonWriter writer,
+            {Declaration.ToDisplayString()} value,
+            JsonSerializerOptions options)
+        {{
+            writer.WriteNullValue();
+        }}
+    }}
+}}";
+
+            static (string name, ITypeSymbol type, string snakeCase, string utf8, string field, string reader)
+                GenerateFieldReader(IPropertySymbol member, int position)
+            {
+                var needsNullableAnnotation = false;
+                if (member.Type.IsValueType
+                    && member.Type.OriginalDefinition.SpecialType != SpecialType.System_Nullable_T)
+                    needsNullableAnnotation = true;
+
+                var snakeCase = ConvertToSnakeCase(member.Name);
+                return (member.Name, member.Type, snakeCase,
+$@"        private static ReadOnlySpan<byte> {member.Name}Bytes => new byte[]
+        {{
+            // {snakeCase}
+            {string.Join(", ", Encoding.UTF8.GetBytes(snakeCase))}
+        }};",
+$"            {member.Type.WithNullableAnnotation(NullableAnnotation.Annotated).ToDisplayString()}{(needsNullableAnnotation ? "?" : "")} {snakeCase}OrDefault = default;",
+$@"                {(position > 0 ? "else " : "")}if (reader.ValueTextEquals({member.Name}Bytes))
+                {{
+                    if (!reader.Read())
+                        throw new JsonException(""Expected value"");
+
+                    var cvt = options.GetConverter(
+                        typeof({member.Type.WithNullableAnnotation(NullableAnnotation.NotAnnotated).ToDisplayString()}));
+
+                    if (cvt is JsonConverter<{member.Type.WithNullableAnnotation(NullableAnnotation.NotAnnotated).ToDisplayString()}> converter)
+                        {snakeCase}OrDefault = converter.Read(ref reader,
+                            typeof({member.Type.WithNullableAnnotation(NullableAnnotation.NotAnnotated).ToDisplayString()}),
+                            options);
+                    else
+                        {snakeCase}OrDefault = JsonSerializer.Deserialize<{member.Type.ToDisplayString()}>(
+                            ref reader, options);
+                }}");
+            }
+        }
+    }
+
+    internal record DiscriminatedUnionSerializedType(
+        INamedTypeSymbol Declaration,
+        ISymbol Discriminator)
+        : SerializedType(Declaration)
+    {
+        public List<DiscriminatedUnionMemberSerializedType> Members { get; }
+            = new();
+
+        public override string GenerateSourceCode(string outputNamespace)
+        {
+            var discriminatorField = ConvertToSnakeCase(Discriminator.Name);
+
+            var discriminatorType = Discriminator switch
+            {
+                IPropertySymbol prop => prop.Type,
+                IFieldSymbol field => field.Type,
+                _ => throw new InvalidOperationException(
+                    "Unsupported discriminator member type")
+            };
+
+            var switchCaseMembers = string.Join(",\n",
+                Members.Select(
+                    x => $@"                {x.DiscriminatorValue.ToCSharpString()}
+                    => JsonSerializer.Deserialize(ref copy,
+                        typeof({x.Declaration.ToDisplayString()}), options)"));
+
+            return $@"using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace {outputNamespace}.Internal.Converters
+{{
+    internal class {ConverterTypeName} : JsonConverter<{Declaration.ToDisplayString()}>
+    {{
+        private static ReadOnlySpan<byte> DiscriminatorBytes => new byte[]
+        {{
+            // {discriminatorField}
+            {string.Join(", ", Encoding.UTF8.GetBytes(discriminatorField))}
+        }};
+
+        public override {Declaration.ToDisplayString()}? Read(
+            ref Utf8JsonReader reader,
+            Type typeToConvert,
+            JsonSerializerOptions options)
+        {{
+            var copy = reader;
+            if (reader.TokenType != JsonTokenType.StartObject)
+                throw new JsonException(""Expected StartObject"");
+
+            {discriminatorType.ToDisplayString()}? discriminator = null;
+
+            while (reader.Read())
+            {{
+                if (reader.TokenType == JsonTokenType.EndObject)
+                    break;
+
+                if (reader.TokenType != JsonTokenType.PropertyName)
+                    throw new JsonException(""Expected PropertyName"");
+
+                if (reader.ValueTextEquals(DiscriminatorBytes))
+                {{
+                    if (!reader.Read())
+                        throw new JsonException(""Expected value"");
+
+                    var cvt = options.GetConverter(
+                        typeof({discriminatorType.ToDisplayString()}));
+
+                    if (cvt is JsonConverter<{discriminatorType.ToDisplayString()}> converter)
+                        discriminator = converter.Read(ref reader,
+                            typeof({discriminatorType.ToDisplayString()}),
+                            options);
+                    else
+                        discriminator = JsonSerializer
+                            .Deserialize<{discriminatorType.ToDisplayString()}>(
+                                ref reader, options);
+                }}
+                else if (!reader.Read())
+                    throw new JsonException(""Expected value"");
+
+                if (reader.TokenType == JsonTokenType.StartArray
+                    || reader.TokenType == JsonTokenType.StartObject)
+                    reader.Skip();
+            }}
+
+            var result = discriminator switch
+            {{
+{switchCaseMembers},
+                _ => throw new JsonException(""Unknown discriminator value"")
+            }} as {Declaration.ToDisplayString()};
+
+            reader = copy;
+            return result;
+        }}
+
+        public override void Write(
+            Utf8JsonWriter writer,
+            {Declaration.ToDisplayString()} value,
+            JsonSerializerOptions options)
+        {{
+            writer.WriteNullValue();
+        }}
+    }}
+}}";
+        }
+    }
+
+    internal record DiscriminatedUnionMemberSerializedType(
+        INamedTypeSymbol Declaration,
+        TypedConstant DiscriminatorValue)
+        : SerializedType(Declaration)
+    {
+        public DiscriminatedUnionSerializedType? DiscriminatedUnionDeclaration
+            { get; init; }
+
+        protected override IEnumerable<IPropertySymbol> SymbolsToSerialize
+            => base.SymbolsToSerialize
+                .Where(x => !SymbolEqualityComparer.Default.Equals(x,
+                    DiscriminatedUnionDeclaration?.Discriminator));
+    }
+}

tools/SourceGenerators/Serialization/Structure/SerializedTypeUtils.cs

@@ -0,0 +1,119 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace Discord.Net.SourceGenerators.Serialization
+{
+    internal static class SerializedTypeUtils
+    {
+        public static List<SerializedType> BuildTypeTrees(
+            INamedTypeSymbol generateSerializerAttribute,
+            INamedTypeSymbol discriminatedUnionSymbol,
+            INamedTypeSymbol discriminatedUnionMemberSymbol,
+            IEnumerable<INamedTypeSymbol> symbolsToBuild)
+        {
+            var types = new List<SerializedType>();
+
+            FindAllSerializedTypes(types, generateSerializerAttribute,
+                discriminatedUnionSymbol, discriminatedUnionMemberSymbol,
+                symbolsToBuild);
+
+            // Now, move DU members into their relevant DU declaration.
+            int x = 0;
+            while (x < types.Count)
+            {
+                var type = types[x];
+                if (type is DiscriminatedUnionMemberSerializedType duMember)
+                {
+                    var declaration = types.FirstOrDefault(
+                        x => SymbolEqualityComparer.Default.Equals(
+                            x.Declaration, duMember.Declaration.BaseType));
+
+                    if (declaration is not DiscriminatedUnionSerializedType duDeclaration)
+                        throw new InvalidOperationException(
+                            "Could not find DU declaration for DU " +
+                            $"member {duMember.Declaration.ToDisplayString()}");
+
+                    duDeclaration.Members.Add(duMember with
+                    {
+                        DiscriminatedUnionDeclaration = duDeclaration
+                    });
+                    types.RemoveAt(x);
+                    continue;
+                }
+
+                x++;
+            }
+
+            return types;
+        }
+
+        private static void FindAllSerializedTypes(
+            List<SerializedType> types,
+            INamedTypeSymbol generateSerializerAttribute,
+            INamedTypeSymbol discriminatedUnionSymbol,
+            INamedTypeSymbol discriminatedUnionMemberSymbol,
+            IEnumerable<INamedTypeSymbol> symbolsToBuild)
+        {
+            foreach (var type in symbolsToBuild)
+            {
+                var generateSerializer = type.GetAttributes()
+                    .Any(x => SymbolEqualityComparer.Default
+                        .Equals(x.AttributeClass, generateSerializerAttribute));
+
+                if (!generateSerializer)
+                    continue;
+
+                var duDeclaration = type.GetAttributes()
+                    .FirstOrDefault(x => SymbolEqualityComparer.Default
+                        .Equals(x.AttributeClass, discriminatedUnionSymbol));
+
+                if (duDeclaration != null)
+                {
+                    if (duDeclaration
+                        .ConstructorArguments
+                        .FirstOrDefault()
+                        .Value is not string memberName)
+                        throw new InvalidOperationException(
+                            "Failed to get DU discriminator member name");
+
+                    var member = type.GetMembers(memberName)
+                        .FirstOrDefault(
+                            x => x is IPropertySymbol or IFieldSymbol);
+
+                    if (member is null)
+                        throw new InvalidOperationException(
+                            "Failed to get DU discriminator member symbol");
+
+                    types.Add(new DiscriminatedUnionSerializedType(
+                        type, member));
+
+                    continue;
+                }
+
+                var duMemberDeclaration = type
+                    .GetAttributes()
+                    .FirstOrDefault(x => SymbolEqualityComparer.Default
+                        .Equals(x.AttributeClass,
+                            discriminatedUnionMemberSymbol));
+
+                if (duMemberDeclaration != null)
+                {
+                    if (duMemberDeclaration.ConstructorArguments.Length == 0
+                        || duMemberDeclaration.ConstructorArguments[0].IsNull)
+                        throw new InvalidOperationException(
+                            "Failed to get DU discriminator value");
+
+                    types.Add(new DiscriminatedUnionMemberSerializedType(
+                        type, duMemberDeclaration.ConstructorArguments[0]));
+
+                    continue;
+                }
+
+                types.Add(new SerializedType(type));
+            }
+        }
+    }
+}

tools/SourceGenerators/Serialization/SymbolExtensions.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Diagnostics.SymbolStore;
+using Microsoft.CodeAnalysis;
+
+namespace Discord.Net.SourceGenerators.Serialization
+{
+    internal static class SymbolExtensions
+    {
+        public static IEnumerable<IPropertySymbol> GetProperties(
+            this INamedTypeSymbol symbol,
+            bool includeInherited)
+        {
+            var s = symbol;
+            do
+            {
+                foreach (var member in s.GetMembers())
+                    if (member is IPropertySymbol property)
+                        yield return property;
+
+                s = s.BaseType;
+            }
+            while (includeInherited && s != null);
+        }
+    }
+}

tools/SourceGenerators/Serialization/Utils.cs

@@ -0,0 +1,25 @@
+using System.Text;
+
+namespace Discord.Net.SourceGenerators.Serialization
+{
+    internal static class Utils
+    {
+        private static readonly StringBuilder CaseChangeBuffer = new();
+
+        public static string ConvertToSnakeCase(string value)
+        {
+            foreach (var c in value)
+            {
+                if (char.IsUpper(c) && CaseChangeBuffer.Length > 0)
+                    _ = CaseChangeBuffer.Append('_');
+
+                _ = CaseChangeBuffer.Append(char.ToLower(c));
+            }
+
+            var result = CaseChangeBuffer.ToString();
+            _ = CaseChangeBuffer.Clear();
+
+            return result;
+        }
+    }
+}

tools/SourceGenerators/Serialization/VisibleTypeVisitor.cs

@@ -0,0 +1,59 @@
+using System.Collections.Generic;
+using System.Threading;
+using Microsoft.CodeAnalysis;
+
+namespace Discord.Net.SourceGenerators.Serialization
+{
+    internal sealed class VisibleTypeVisitor
+        : SymbolVisitor
+    {
+        private readonly CancellationToken _cancellationToken;
+        private readonly HashSet<INamedTypeSymbol> _typeSymbols;
+
+        public VisibleTypeVisitor(CancellationToken cancellationToken)
+        {
+            _cancellationToken = cancellationToken;
+            _typeSymbols = new(SymbolEqualityComparer.Default);
+        }
+
+        public IEnumerable<INamedTypeSymbol> GetVisibleTypes()
+            => _typeSymbols;
+
+        public override void VisitAssembly(IAssemblySymbol symbol)
+        {
+            _cancellationToken.ThrowIfCancellationRequested();
+            symbol.GlobalNamespace.Accept(this);
+        }
+
+        public override void VisitNamespace(INamespaceSymbol symbol)
+        {
+            foreach (var member in symbol.GetMembers())
+            {
+                _cancellationToken.ThrowIfCancellationRequested();
+                member.Accept(this);
+            }
+        }
+
+        public override void VisitNamedType(INamedTypeSymbol symbol)
+        {
+            _cancellationToken.ThrowIfCancellationRequested();
+
+            var isVisible = symbol.DeclaredAccessibility switch
+            {
+                Accessibility.Protected => true,
+                Accessibility.ProtectedOrInternal => true,
+                Accessibility.Public => true,
+                _ => false,
+            };
+
+            if (!isVisible || !_typeSymbols.Add(symbol))
+                return;
+
+            foreach (var member in symbol.GetTypeMembers())
+            {
+                _cancellationToken.ThrowIfCancellationRequested();
+                member.Accept(this);
+            }
+        }
+    }
+}