Double server from CLI

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Pro
Binaries:
  Node: 16.15.1
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant packages:
  next: 12.2.1-canary.1
  eslint-config-next: 12.2.0
  react: 18.2.0
  react-dom: 18.2.0

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

CLI

Describe the Bug

I have app.js file in root folder.

const start = require('next/dist/cli/next-start')
start.nextStart()

It starts 2 servers at the same time. It starts dev server instead of production and overwrites contents of .next folder with files of dev server.

> node app.js
ready - started server on 0.0.0.0:3000, url: http://localhost:3000
ready - started server on 0.0.0.0:3000, url: http://localhost:3000

Accessing localhost:3000 returns error 404

Expected Behavior

Only start production server

Link to reproduction

https://github.com/Arctomachine/reproduction-double-server

To Reproduce

1. Run next build
2. Run node app.js

[QuiiBz]

I searched a bit and the issue first appeared in version 12.1.1-canary.5.

Importing next/dist/cli/next-start without calling nextStart() before this version does not start the server.

edit: It’s a regression from https://github.com/vercel/next.js/pull/34836:

When getProjectDir is called, it now also imports next/bin/next.ts, which is itself calling commands[command]().

This command should not be defined, but it fallbacks to defaultCommand, which is dev (that explains why the dev server is also started)

2nd edit: Opened a PR that fixes the issue: #38274

[Arctomachine]

require('next/dist/cli/next-start') alone already starts server and gives one output. If you try only this line, you will get fully working dev server. But in either case, with 2 outputs it starts malfunctioning dev server, while functioning production is expected.