Why doesn't Fastify allow plugins to return a value as the promised value of fastify.register?

[Worldwidebrine]

FastifyPluginCallback and FastifyPluginAsync return void.
fastify.register(...) returns FastifyInstance<...> & PromiseLike<undefined>, so await fastify.register(...) is always undefined.

Why doesn't Fastify allow plugins to return a value and let it be the promised value of fastify.register?

const returnedValue = fastify.register((fastify, opts, done) => {
  setTimeout(() => done(undefined, "test"), 10);
  // or async return "test";
});
const promisedValue = await returnedValue;
console.log(returnedValue, promisedValue);

According to .d.ts files, the result should be [object Object] undefined, but actually [object Object] [object Object] both of them are objects.
Why shouldn't it be [object Object] test?

[metcoder95]

Indeed, it seems to be a mismatch between the Types and what Fastify actually does.
The promise resolves the fastify instance after fulfillment.
Though, not so sure why the Types do not match.

In any case, can you elaborate what is the value you expect by allowing plugins to return a specific value after the plugin is registered? Just want to understand what are you trying to achieve 🙂

[Worldwidebrine]

This was just the question that occurred to me when I found the mismatch. I was thinking about something that becomes available after the plugin is fully loaded but I don't need anything specifically.

[metcoder95]

Got it 👍
I'm not so sure about the intention the type mismatch was unintended or not. But feel free to open an issue to kick off a chat out of it