Add Source Generator for AOT-compatible proxy generation #30

yang-xiaodong · 2026-01-06T13:01:00Z

Summary

This PR adds a new Multicaster.SourceGenerator package that generates static proxy implementations at compile time, enabling Native AOT compilation support for Multicaster.

Motivation

The current DynamicInMemoryProxyFactory and DynamicRemoteProxyFactory use System.Reflection.Emit to generate proxy classes at runtime. This approach is incompatible with:

.NET Native AOT publishing
iOS/Android with trimming enabled
Blazor WebAssembly with AOT
MagicOnion StreamingHub in AOT scenarios

New Package: Multicaster.SourceGenerator

A Roslyn source generator that analyzes [MulticasterProxyGeneration] attributes and generates:

InMemory Proxy Classes - Implement receiver interfaces and iterate over registered receivers
Remote Proxy Classes - Implement receiver interfaces and serialize method calls for remote invocation
Factory Implementation - Implements IInMemoryProxyFactory and IRemoteProxyFactory

Project Structure

src/Multicaster.SourceGenerator/
├── MulticasterSourceGenerator.cs      # Main generator entry point
├── CodeAnalysis/
│   └── ReceiverInterfaceCollector.cs  # Collects receiver interface metadata
├── CodeGen/
│   ├── InMemoryProxyGenerator.cs      # Generates InMemory proxy classes
│   ├── RemoteProxyGenerator.cs        # Generates Remote proxy classes
│   └── ProxyFactoryGenerator.cs       # Generates factory implementation
├── Helpers/
│   └── SourceBuilderExtensions.cs     # Code generation utilities
└── Internal/
    └── SourceBuilder.cs               # StringBuilder wrapper for code gen

Usage

1. Add the package

<PackageReference Include="Multicaster.SourceGenerator" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />

2. Define receiver interfaces

public interface IChatReceiver
{
    void OnMessage(string user, string message);
    void OnUserJoined(string user);
}

3. Create a proxy factory

[MulticasterProxyGeneration(typeof(IChatReceiver))]
public partial class MyProxyFactory { }

4. Use the generated factory

var factory = new MyProxyFactory();
var provider = new InMemoryGroupProvider(factory);

Features

✅ Generates IInMemoryProxyFactory implementation
✅ Generates IRemoteProxyFactory implementation
✅ Supports void methods
✅ Supports Task and Task<T> return types (client results)
✅ Supports methods with up to 15 parameters
✅ Supports CancellationToken parameters
✅ Handles params array in attribute constructor
✅ Proper namespace and using directive generation

Changes

New Files

src/Multicaster.SourceGenerator/ - Complete source generator implementation
src/Multicaster/MulticasterProxyGenerationAttribute.cs - Marker attribute for code generation
test/Multicaster.SourceGenerator.Tests/ - Unit tests for the generator
docs/aot-support.md - Documentation

Modified Files

Multicaster.sln - Added new projects
Directory.Packages.props - Added analyzer dependencies
.gitignore - Added **/generated/ for source generator output

Testing

dotnet test test/Multicaster.SourceGenerator.Tests

The tests verify:

Proxy generation for single and multiple receiver interfaces
Correct method signature generation
Factory method implementation
Handling of various method signatures (void, Task, Task)

Integration with MagicOnion

This source generator is designed to work with MagicOnion's AOT support:

[MulticasterProxyGeneration(typeof(IChatHubReceiver))]
public partial class MulticasterProxyFactory { }

// In MagicOnion configuration
builder.Services.AddMagicOnion()
    .UseStaticProxyFactory<MulticasterProxyFactory>();

Documentation

Added docs/aot-support.md with:

Installation instructions
Usage examples
Migration guide from dynamic proxies
Troubleshooting section
MagicOnion integration guide

Breaking Changes

None. This is an additive feature. Existing code using DynamicInMemoryProxyFactory and DynamicRemoteProxyFactory continues to work unchanged.

Checklist

- Add Multicaster.SourceGenerator project with source generator implementation - Implement MulticasterSourceGenerator to analyze receiver interfaces and generate proxy code - Add DiagnosticDescriptors for source generator diagnostics and error reporting - Add ReceiverInterfaceCollector to discover and validate receiver interface types - Add InMemoryProxyGenerator to generate in-memory proxy implementations - Add RemoteProxyGenerator to generate remote proxy implementations - Add ProxyFactoryGenerator to generate factory method implementations - Add helper utilities (RoslynExtensions, StringBuilderExtensions, FNV1A32) - Add MulticasterProxyGenerationAttribute for marking proxy factory classes - Add comprehensive source generator tests with SourceGeneratorTests project - Add AOT support documentation explaining usage and benefits - Update Directory.Packages.props with Microsoft.CodeAnalysis.CSharp and PolySharp dependencies - Update solution file to include new projects - Enables AOT compilation scenarios (Native AOT, trimming, Blazor WASM) by generating proxies at compile time instead of runtime

Updated Multicaster.SourceGenerator.csproj to: - Add required NuGet package references for source generation (Microsoft.CodeAnalysis.CSharp, Microsoft.CodeAnalysis.Analyzers, PolySharp) with PrivateAssets="all". - Include the built analyzer DLL in the NuGet package under analyzers/dotnet/cs. - Change file encoding (likely to UTF-8 with BOM). These changes improve packaging and dependency management for the source generator.

- Add generated/ directory to gitignore to exclude source generator output - Prevents accidental commits of auto-generated code files - Keeps repository clean by ignoring build artifacts from source generators

…uide - Add MagicOnion StreamingHub to list of supported AOT scenarios - Document project reference setup for source generator during development - Add comprehensive MagicOnion integration example with StreamingHub receiver - Include configuration example for static proxy factory with MagicOnion - Add reference to MagicOnion AOT Sample for complete implementation details - Improve documentation completeness for AOT adoption and integration patterns

Copilot

Pull request overview

This PR adds a new Multicaster.SourceGenerator package that enables AOT (Ahead-of-Time) compilation support for Multicaster by generating static proxy implementations at compile time, replacing runtime System.Reflection.Emit usage.

Key Changes:

New source generator that analyzes [MulticasterProxyGeneration] attributes and generates both InMemory and Remote proxy implementations
New marker attribute for triggering source generation at compile time
Comprehensive test suite covering proxy generation and invocation scenarios

Reviewed changes

Copilot reviewed 19 out of 20 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
`src/Multicaster/MulticasterProxyGenerationAttribute.cs`	Marker attribute for source generation, accepts params array of receiver interface types
`src/Multicaster.SourceGenerator/MulticasterSourceGenerator.cs`	Main incremental generator entry point using Roslyn's `ForAttributeWithMetadataName`
`src/Multicaster.SourceGenerator/CodeAnalysis/ReceiverInterfaceCollector.cs`	Collects interface metadata including methods, parameters, and return types
`src/Multicaster.SourceGenerator/CodeAnalysis/ReceiverInterfaceInfo.cs`	Data models representing receiver interfaces and their methods
`src/Multicaster.SourceGenerator/CodeAnalysis/DiagnosticDescriptors.cs`	Defines diagnostic errors and warnings for validation
`src/Multicaster.SourceGenerator/CodeGen/ProxyFactoryGenerator.cs`	Generates factory class implementing both IInMemoryProxyFactory and IRemoteProxyFactory
`src/Multicaster.SourceGenerator/CodeGen/InMemoryProxyGenerator.cs`	Generates in-memory proxy classes that iterate over receivers
`src/Multicaster.SourceGenerator/CodeGen/RemoteProxyGenerator.cs`	Generates remote proxy classes that serialize method calls
`src/Multicaster.SourceGenerator/Helpers/RoslynExtensions.cs`	Helper extensions for Roslyn symbol operations
`src/Multicaster.SourceGenerator/Helpers/StringBuilderExtensions.cs`	StringBuilder utilities for code generation
`src/Multicaster.SourceGenerator/Internal/FNV1A32.cs`	Hash function for generating method IDs
`test/Multicaster.SourceGenerator.Tests/GeneratedProxyFactory.cs`	Test factory annotated with `[MulticasterProxyGeneration]` attribute
`test/Multicaster.SourceGenerator.Tests/TestReceivers.cs`	Test interface definitions for chat, game, and async client results
`test/Multicaster.SourceGenerator.Tests/SourceGeneratorTests.cs`	Unit tests verifying proxy creation and invocation
`docs/aot-support.md`	Comprehensive documentation including usage, migration guide, and MagicOnion integration
`Multicaster.sln`	Added new source generator and test projects to solution
`Directory.Packages.props`	Added Roslyn analyzer dependencies

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

Copilot · 2026-01-06T13:09:20Z

src/Multicaster.SourceGenerator/CodeAnalysis/DiagnosticDescriptors.cs

+    public static readonly DiagnosticDescriptor NoReceiverInterfacesFound = new(
+        id: "MULT004",
+        title: "No receiver interfaces found",
+        messageFormat: "No receiver interfaces were specified or found for proxy generation",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Warning,
+        isEnabledByDefault: true
+    );
+
+    public static readonly DiagnosticDescriptor NoReceiverInterfacesSpecified = new(
+        id: "MULT006",
+        title: "No receiver interfaces specified",
+        messageFormat: "The [MulticasterProxyGeneration] attribute must specify at least one receiver interface type",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true
+    );
+
+    public static readonly DiagnosticDescriptor TooManyParameters = new(
+        id: "MULT005",
+        title: "Too many parameters",
+        messageFormat: "The method '{0}' has {1} parameters, but the maximum supported is 15",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true
+    );


The diagnostic descriptors TooManyParameters and NoReceiverInterfacesFound are defined but never used in the codebase. If they are intended for future use, consider removing them for now to reduce code clutter, or implement the validation logic that would use them. For TooManyParameters specifically, the documentation mentions a 15 parameter limit but no validation enforces this constraint.

Copilot · 2026-01-06T13:09:21Z

src/Multicaster.SourceGenerator/CodeAnalysis/DiagnosticDescriptors.cs

+    public static readonly DiagnosticDescriptor NoReceiverInterfacesSpecified = new(
+        id: "MULT006",
+        title: "No receiver interfaces specified",
+        messageFormat: "The [MulticasterProxyGeneration] attribute must specify at least one receiver interface type",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true
+    );
+
+    public static readonly DiagnosticDescriptor TooManyParameters = new(
+        id: "MULT005",
+        title: "Too many parameters",
+        messageFormat: "The method '{0}' has {1} parameters, but the maximum supported is 15",
+        category: Category,
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true
+    );


The diagnostic IDs are not in sequential order (MULT001, MULT002, MULT003, MULT004, MULT006, MULT005). Consider reordering MULT005 (TooManyParameters) to come before MULT006 (NoReceiverInterfacesSpecified) for better maintainability and consistency.

Copilot · 2026-01-06T13:09:21Z

src/Multicaster.SourceGenerator/Helpers/StringBuilderExtensions.cs

+    public static StringBuilder AppendLineWithFormat(this StringBuilder sb, [InterpolatedStringHandlerArgument(nameof(sb))] StringBuilderInterpolatedStringHandler s)
+    {
+        sb.AppendLine();
+        return sb;
+    }
+
+    [InterpolatedStringHandler]
+    public readonly ref struct StringBuilderInterpolatedStringHandler
+    {
+        readonly StringBuilder sb;
+
+        public StringBuilderInterpolatedStringHandler(int literalLength, int formattedCount, StringBuilder sb)
+        {
+            this.sb = sb;
+        }
+
+        public void AppendLiteral(string s)
+        {
+            sb.Append(s);
+        }
+
+        public void AppendFormatted<T>(T t)
+        {
+            sb.Append(t);
+        }
+    }


The AppendLineWithFormat method and its associated StringBuilderInterpolatedStringHandler are defined but never used in the codebase. Consider removing these to reduce unnecessary code, or use them in the code generation logic if they were intended to simplify string interpolation.

Suggested change

public static StringBuilder AppendLineWithFormat(this StringBuilder sb, [InterpolatedStringHandlerArgument(nameof(sb))] StringBuilderInterpolatedStringHandler s)

{

sb.AppendLine();

return sb;

}

[InterpolatedStringHandler]

public readonly ref struct StringBuilderInterpolatedStringHandler

{

readonly StringBuilder sb;

public StringBuilderInterpolatedStringHandler(int literalLength, int formattedCount, StringBuilder sb)

{

this.sb = sb;

}

public void AppendLiteral(string s)

{

sb.Append(s);

}

public void AppendFormatted<T>(T t)

{

sb.Append(t);

}

}

Copilot · 2026-01-06T13:09:22Z

src/Multicaster.SourceGenerator/CodeGen/InMemoryProxyGenerator.cs

+    static string GetSafeTypeName(string typeName)
+    {
+        return typeName.Replace(".", "_").Replace("<", "_").Replace(">", "_").Replace(",", "_");
+    }


The GetSafeTypeName method is duplicated across InMemoryProxyGenerator, RemoteProxyGenerator, and ProxyFactoryGenerator. Consider extracting this to a shared helper class to eliminate code duplication and ensure consistent behavior across all generators.

Copilot · 2026-01-06T13:09:22Z

src/Multicaster.SourceGenerator/Helpers/RoslynExtensions.cs

+    public static AttributeData? FindAttributeShortName(this IEnumerable<AttributeData> attributeDataList, string typeName)
+    {
+        return attributeDataList.FirstOrDefault(x => x.AttributeClass?.Name == typeName);
+    }
+
+    public static bool ApproximatelyEqual(this ITypeSymbol? left, ITypeSymbol? right)
+    {
+        if (left == null && right == null) return true;
+        if (left == null || right == null) return false;
+
+        if (left is IErrorTypeSymbol || right is IErrorTypeSymbol)
+        {
+            return left.ToDisplayString() == right.ToDisplayString();
+        }
+        else
+        {
+            return SymbolEqualityComparer.Default.Equals(left, right);
+        }
+    }
+


The extension methods FindAttributeShortName and ApproximatelyEqual are defined but never used in the codebase. Consider removing these unused methods to reduce code clutter, or use them if they were intended for specific logic.

Suggested change

public static AttributeData? FindAttributeShortName(this IEnumerable<AttributeData> attributeDataList, string typeName)

{

return attributeDataList.FirstOrDefault(x => x.AttributeClass?.Name == typeName);

}

public static bool ApproximatelyEqual(this ITypeSymbol? left, ITypeSymbol? right)

{

if (left == null && right == null) return true;

if (left == null || right == null) return false;

if (left is IErrorTypeSymbol || right is IErrorTypeSymbol)

{

return left.ToDisplayString() == right.ToDisplayString();

}

else

{

return SymbolEqualityComparer.Default.Equals(left, right);

}

}

Copilot · 2026-01-06T13:09:22Z

src/Multicaster.SourceGenerator/CodeAnalysis/ReceiverInterfaceCollector.cs

+    static IEnumerable<IMethodSymbol> GetAllInterfaceMethods(INamedTypeSymbol interfaceType)
+    {
+        foreach (var member in interfaceType.GetMembers())
+        {
+            if (member is IMethodSymbol method && method.MethodKind == MethodKind.Ordinary)
+            {
+                yield return method;
+            }
+        }
+
+        foreach (var baseInterface in interfaceType.AllInterfaces)
+        {
+            foreach (var member in baseInterface.GetMembers())
+            {
+                if (member is IMethodSymbol method && method.MethodKind == MethodKind.Ordinary)
+                {
+                    yield return method;
+                }
+            }
+        }
+    }


The method GetAllInterfaceMethods may return duplicate methods when an interface inherits from base interfaces. For example, if two base interfaces declare the same method, or if a method is redeclared in the derived interface, this will yield the same method multiple times, leading to duplicate method implementations in the generated proxy class. Consider deduplicating methods by their signature or using SymbolEqualityComparer to track already-seen methods.

Copilot · 2026-01-06T13:09:23Z

src/Multicaster.SourceGenerator/CodeAnalysis/ReceiverInterfaceCollector.cs

+        foreach (var member in interfaceType.GetMembers())
+        {
+            if (member is IMethodSymbol method && method.MethodKind == MethodKind.Ordinary)
+            {
+                yield return method;
+            }
+        }


This foreach loop implicitly filters its target sequence - consider filtering the sequence explicitly using '.Where(...)'.

Copilot · 2026-01-06T13:09:23Z

src/Multicaster.SourceGenerator/CodeAnalysis/ReceiverInterfaceCollector.cs

+            foreach (var member in baseInterface.GetMembers())
+            {
+                if (member is IMethodSymbol method && method.MethodKind == MethodKind.Ordinary)
+                {
+                    yield return method;
+                }
+            }


This foreach loop implicitly filters its target sequence - consider filtering the sequence explicitly using '.Where(...)'.

Copilot · 2026-01-06T13:09:23Z

src/Multicaster.SourceGenerator/MulticasterSourceGenerator.cs

+                foreach (var item in arg.Values)
+                {
+                    if (item.Value is INamedTypeSymbol typeSymbol)
+                    {
+                        types.Add(typeSymbol);
+                    }
+                }


This foreach loop implicitly filters its target sequence - consider filtering the sequence explicitly using '.Where(...)'.

Copilot · 2026-01-06T13:09:23Z

src/Multicaster.SourceGenerator/Helpers/RoslynExtensions.cs

+        if (left is IErrorTypeSymbol || right is IErrorTypeSymbol)
+        {
+            return left.ToDisplayString() == right.ToDisplayString();
+        }
+        else
+        {
+            return SymbolEqualityComparer.Default.Equals(left, right);
+        }


Both branches of this 'if' statement return - consider using '?' to express intent better.

yang-xiaodong and others added 4 commits January 5, 2026 22:45

chore(.gitignore): add source generator output directory

89ed816

- Add generated/ directory to gitignore to exclude source generator output - Prevents accidental commits of auto-generated code files - Keeps repository clean by ignoring build artifacts from source generators

Copilot AI review requested due to automatic review settings January 6, 2026 13:01

yang-xiaodong requested a review from mayuki as a code owner January 6, 2026 13:01

Copilot started reviewing on behalf of yang-xiaodong January 6, 2026 13:01 View session

Copilot AI reviewed Jan 6, 2026

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Add Source Generator for AOT-compatible proxy generation #30

Add Source Generator for AOT-compatible proxy generation #30

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yang-xiaodong commented Jan 6, 2026

Summary

Motivation

New Package: Multicaster.SourceGenerator

Project Structure

Usage

1. Add the package

2. Define receiver interfaces

3. Create a proxy factory

4. Use the generated factory

Features

Changes

New Files

Modified Files

Testing

Integration with MagicOnion

Documentation

Breaking Changes

Checklist

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