How does source generation work in .NET?

Question

Accepted Answer

**Source generation** — compile-time code generation using Roslyn analyzers.

**Incremental source generator:**
```csharp
[Generator]
public class HelloGenerator : IIncrementalGenerator
{
    public void Initialize(IncrementalGeneratorInitializationContext ctx)
    {
        var classes = ctx.SyntaxProvider
            .CreateSyntaxProvider(
                predicate: static (node, _) => IsTargetClass(node),
                transform: static (ctx, _) => GetClassInfo(ctx))
            .Where(static info => info is not null);

ctx.RegisterSourceOutput(classes, static (spc, info) =>
        {
            var source = GenerateHelloMethod(info);
            spc.AddSource($"{info.Name}.g.cs", source);
        });
    }
}
```

**Built-in generators:**
- **System.Text.Json:** JSON serialization.
- **Regex:** [GeneratedRegex].
- **Logging:** [LoggerMessage].

**Benefits:**
- Faster startup (no reflection).
- Smaller publish size.
- AOT compatible.

C#: How does source generation work in .NET?