Initialization error in v3.0.0-rc.5

[rqbazan]

🐛 Bug Report

When I use an asynchronous factory function to create a Fastify instance, the return value from the promise is always undefined. Btw, this problem is not present in the v2.15.1

To Reproduce

I've created a repo (https://github.com/rqbazan/fastify-issue-async) to illustrate the issue, and compare it with v2

const fastify = require('fastify') // v3.0.0-rc.5

async function buildApp(opts) {
  const app = fastify(opts)

  // register plugins

  return app
}

async function main() {
  const app = await buildApp({ logger: true })

  console.log({ app: !!app }) // false

  try {
    await app.listen(3000)
  } catch (error) {
    console.log(error)
    process.exit(1)
  }
}

main()

Expected behavior

Start the server without initialization problems, like in the v2

Your Environment

• node version: 12.16.2
• fastify version: 3.0.0-rc.5
• os: Windows

[delvedor]

Hello! Thank you for reporting, I confirm it's a bug.

[delvedor]

If you return the app wrapped in an object from buildApp, the problem disappears.

async function buildApp(opts) {
  const app = fastify(opts)

  // register plugins

  return { app }
}

I think the reason is that app has a then method, which will be resolved to undefined by the async function.