Deepstaging — Roslyn code generation for LanguageExt effects

[trbngr]

I've been building a code generation toolkit on top of LanguageExt for the last year or so and it's at a point worth sharing.

The core idea is simple: everything fans out from a Runtime composed of EffectsModules.

[EffectsModule(typeof(IEmailService))]
public sealed partial class EmailModule;

[Runtime]
[Uses(typeof(ScribeStore))]
[Uses(typeof(EmailModule))]
[Uses(typeof(NotifyModule))]
public sealed partial class ScribeRuntime;

That's it. The generator sees your Runtime, sees what it [Uses], and generates the capability interfaces, the DI wiring, and OpenTelemetry instrumentation for every effect method. Your handlers work with Eff<ScribeRuntime, A> and the compiler enforces that you only touch capabilities you declared.

The testing story is where it gets interesting. Drop [TestRuntime] on a class and you get generated stubs, builders, and in-memory implementations for every capability. No mocking frameworks, no DI containers, no ceremony:

[TestRuntime<ScribeRuntime>]
public partial class TestScribeRuntime;

var runtime = TestScribeRuntime.Create()
    .WithStubEmailService(stub => stub
        .OnSendAsync(_ => unit));

var result = await ArticleCommands.Handle(cmd).Run(runtime);
await Assert.That(result).IsSucc();

Set INTEGRATION=true and the same tests run against real Postgres/Redis/whatever via Testcontainers. Same assertions, same test code — just a different runtime configuration.

There's a bunch of other stuff built on top: [DataStore] for persistence with generated CRUD effects, [DispatchModule] for typed CQRS where method overload resolution IS the dispatch (no runtime routing), [TypedId] for strongly-typed IDs, [ConfigProvider] for typed configuration with JSON Schema, [EventQueue] for Channel-backed async workflows. 50+ analyzers catch mistakes at compile time with one-click fixes.

Not open source yet but getting close. Docs site and NuGet packages attached below.

📎 deepstaging-site.zip
📎 deepstaging-packages.zip