Plugin registry

Source:examples/plugin-registry

Multi-binding, compiled: a health-check registry as a set port, two plugin modules that contribute to it without knowing of each other, and a composition root that collects and runs the lot — the plugin-registry guide's material as real code.

The set port and its contributors

export class HealthCheck extends Port.many("HealthCheck")<{
  readonly name: string;
  readonly run: () => AsyncResult<"healthy", HealthCheckFailed>;
}> {}

Each plugin module provides its own service and contributes one member — DatabaseModule a check over Database, CacheModule one over Cache:

export const DatabaseModule = Module("Database")({
  provides: [
    Provider(Database)({ value: { ping: () => OkAsync("healthy") } }),
    Provider.member(HealthCheck)([Database], {
      sync: (db) => ({ name: "database", run: db.ping }),
    }),
  ],
  exports: [Database, HealthCheck],
});

The cache's ping is wired to fail — deliberately, because a registry that only demonstrates the happy path would miss the design question below.

The composition root imports both and re-exports them whole:

export const AppModule = Module("App")({
  imports: [DatabaseModule, CacheModule],
  exports: [DatabaseModule, CacheModule],
});

The design question the example answers

What does "run them all" mean when one fails? That is the composition root's decision, not the library's — ctx.get(HealthCheck) hands back readonly Member[] and steps aside. This root folds: every check runs, and a failing one becomes an unhealthy row in the report rather than stopping the rest, with the errCases/defect split kept distinct to the end — an expected HealthCheckFailed carries its reason; an unexpected bug reads "unexpected failure".

What the spec proves

src/index.spec.ts builds AppModule and asserts:

• Both contributions land on one port. ctx.get(HealthCheck) yields the cache and database members — contributed by modules that never import each other.
• The fold works. The report holds database: healthy and cache: unhealthy with the failure's reason — collected, not aborted.
• Contribution is open. A third module adding a queue check joins the registry without either existing module changing — the list grows to ["cache", "database", "queue"].

Run it

pnpm --filter @btravstack/di-example-plugin-registry test