rsnext/packages/next/lib/get-project-dir.ts

import fs from 'fs'
import path from 'path'
import * as Log from '../build/output/log'

export function getProjectDir(dir?: string) {
  const resolvedDir = path.resolve(dir || '.')
  const realDir = fs.realpathSync.native(resolvedDir)

  if (
    resolvedDir !== realDir &&
    resolvedDir.toLowerCase() === realDir.toLowerCase()
  ) {
    Log.warn(
      `Invalid casing detected for project dir, received ${resolvedDir} actual path ${realDir}, see more info here https://nextjs.org/docs/messages/invalid-project-dir-casing`
    )
  }

  return realDir
}