Non-consistent basePath checking behaviour

[eolme]

Verify canary release

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

Provide environment information

    Operating System:
      Platform: darwin
      Arch: arm64
      Version: Darwin Kernel Version 21.5.0: Tue Apr 26 21:08:37 PDT 2022; root:xnu-8020.121.3~4/RELEASE_ARM64_T6000
    Binaries:
      Node: 16.15.0
      npm: 8.5.5
      Yarn: 3.2.1
      pnpm: N/A
    Relevant packages:
      next: 12.2.3
      eslint-config-next: N/A
      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)

No response

Describe the Bug

If basePath is an empty string, a warning is displayed:

warn  - Invalid next.config.js options detected: 
[
  {
    "instancePath": "/basePath",
    "schemaPath": "#/properties/basePath/minLength",
    "keyword": "minLength",
    "params": {
      "limit": 1
    },
    "message": "must NOT have fewer than 1 characters"
  }
] 
See more info here: https://nextjs.org/docs/messages/invalid-next-config

But if you set the basePath to / an error occurs:

Error: Specified basePath /. basePath has to be either an empty string or a path prefix"
    at assignDefaults (/node_modules/next/dist/server/config.js:266:19)
    at Object.loadConfig [as default] (/node_modules/next/dist/server/config.js:97:16)
    at async NextServer.prepare (/node_modules/next/dist/server/next.js:115:24)
    at async /node_modules/next/dist/cli/next-dev.js:147:9

Expected Behavior

Allow either an empty string or a slash as basePath

Link to reproduction

To Reproduce

[rikers]

probably related to issue #38967

[ijjk]

Hi, an empty string isn't a valid basePath and was previously normalized automatically since it's a falsy value so this warning is valid and the basePath value should be omitted for this case.

[eolme]

@ijjk but the error explicitly says that there may be an empty string 😕

[ijjk]

Hmm since we do mention the empty string is allowed and we normalize the value, it seems alright to avoid the warning here

[github-actions]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.