Lesson 16 of 40 Advanced C# Expert 60 min

Source Generators & Roslyn

Write Roslyn source generators to eliminate boilerplate at compile time — from simple attribute processors to full incremental generators.

Part 1: Incremental Source Generators

[Generator]
public class MyGenerator : IIncrementalGenerator
{
  public void Initialize(IncrementalGeneratorInitializationContext ctx)
  {
    var pipeline = ctx.SyntaxProvider
      .CreateSyntaxProvider(Predicate, Transform);
    ctx.RegisterSourceOutput(pipeline, Emit);
  }
}

Part 2: Debugging Source Generators

Add this to your generator project to attach VS debugger:

#if DEBUG
  System.Diagnostics.Debugger.Launch();
#endif

VS 2026 also supports attaching directly to the compiler host via Debug → Attach to Process → VBCSCompiler.

Part 3: Real-World Use Cases

Source generators power frameworks like:

System.Text.Json — context-based serialization without reflection
Entity Framework Core — compiled models
MediatR — request handler registration
MAUI — XAML to C# compilation

Part 4: Unit Testing Generators

var driver = CSharpGeneratorDriver.Create(new MyGenerator());
driver = driver.RunGenerators(compilation);
var result = driver.GetRunResult();
Assert.Single(result.GeneratedTrees);
// Verify generated code matches expected