Source Generator not seeing classes in same project

Question

I have a Source Generator, it looks like this:

public class Generator : ISourceGenerator
{

    public Generator()
    {
        // Uncomment if you want to debug this
        Debugger.Launch();
    }
    public void Initialize(GeneratorInitializationContext context)
    {
        context.RegisterForSyntaxNotifications(() => new MySyntaxReceiver());
    }

    public void Execute(GeneratorExecutionContext context)
    {
        var syntaxReceiver = (MySyntaxReceiver)context.SyntaxReceiver;

        var responseMessageClasses = syntaxReceiver.ResponseMessageClasses;
        // do stuff to responseMessageClasses
    }
}

internal class MySyntaxReceiver : ISyntaxReceiver
{
    public List<ClassDeclarationSyntax> ResponseMessageClasses { get; private set; } = new List<ClassDeclarationSyntax>();

    public void OnVisitSyntaxNode(SyntaxNode syntaxNode)
    {
        if (syntaxNode is ClassDeclarationSyntax cds &&
            cds.Identifier.ValueText.EndsWith("ResponseMessage", StringComparison.OrdinalIgnoreCase))
        {
            ResponseMessageClasses.Add(cds);
        }
    }
}

In the same project, I have a folder of simple classes of which the name all ends with "ResponseMessage". These classes only have simple types like string, int and bool as properties. They are in a different namespace than the SourceGenerator.

There's a second console app project that references my source generator as an Analyzer. When I build the project I can succesfully break into the SourceGenerator code.

The problem: the simple ResponseMessage classes never get seen by the SyntaxReceiver class I have. The OnVisitSyntaxNode method only hits the Program.cs file. What is going on?

Answer 1

By design, it's not possible to use a source generator in the assembly where it was defined. According to the design spec:

Generator implementations are defined in external assemblies passed to the compiler using the same -analyzer: option used for diagnostic analyzers.

...

Since generators are loaded from external assemblies, a generator cannot be used to build the assembly in which it is defined.