config.ts

import { existsSync } from 'fs'
import { basename, extname, join, relative, isAbsolute, resolve } from 'path'
import { pathToFileURL } from 'url'
import { Agent as HttpAgent } from 'http'
import { Agent as HttpsAgent } from 'https'
import findUp from 'next/dist/compiled/find-up'
import chalk from '../lib/chalk'
import * as Log from '../build/output/log'
import { CONFIG_FILES, PHASE_DEVELOPMENT_SERVER } from '../shared/lib/constants'
import { execOnce } from '../shared/lib/utils'
import {
  defaultConfig,
  normalizeConfig,
  ExperimentalConfig,
  NextConfigComplete,
  validateConfig,
  NextConfig,
} from './config-shared'
import { loadWebpackHook } from './config-utils'
import {
  ImageConfig,
  imageConfigDefault,
  VALID_LOADERS,
} from '../shared/lib/image-config'
import { loadEnvConfig } from '@next/env'
import { gte as semverGte } from 'next/dist/compiled/semver'

export { DomainLocale, NextConfig, normalizeConfig } from './config-shared'

const NODE_16_VERSION = '16.8.0'
const NODE_18_VERSION = '18.0.0'
const isAboveNodejs16 = semverGte(process.version, NODE_16_VERSION)
const isAboveNodejs18 = semverGte(process.version, NODE_18_VERSION)

const experimentalWarning = execOnce(
  (configFileName: string, features: string[]) => {
    const s = features.length > 1 ? 's' : ''
    Log.warn(
      chalk.bold(
        `You have enabled experimental feature${s} (${features.join(
          ', '
        )}) in ${configFileName}.`
      )
    )
    Log.warn(
      `Experimental features are not covered by semver, and may cause unexpected or broken application behavior. ` +
        `Use at your own risk.`
    )
    if (features.includes('appDir')) {
      Log.info(
        `Thank you for testing \`appDir\` please leave your feedback at https://nextjs.link/app-feedback`
      )
    }

    console.warn()
  }
)

export function setHttpClientAndAgentOptions(config: {
  httpAgentOptions?: NextConfig['httpAgentOptions']
  experimental?: {
    enableUndici?: boolean
  }
}) {
  if (isAboveNodejs16) {
    // Node.js 18 has undici built-in.
    if (config.experimental?.enableUndici && !isAboveNodejs18) {
      // When appDir is enabled undici is the default because of Response.clone() issues in node-fetch
      ;(globalThis as any).__NEXT_USE_UNDICI = config.experimental?.enableUndici
    }
  } else if (config.experimental?.enableUndici) {
    Log.warn(
      `\`enableUndici\` option requires Node.js v${NODE_16_VERSION} or greater. Falling back to \`node-fetch\``
    )
  }
  if ((globalThis as any).__NEXT_HTTP_AGENT) {
    // We only need to assign once because we want
    // to reuse the same agent for all requests.
    return
  }

  if (!config) {
    throw new Error('Expected config.httpAgentOptions to be an object')
  }

  ;(globalThis as any).__NEXT_HTTP_AGENT_OPTIONS = config.httpAgentOptions
  ;(globalThis as any).__NEXT_HTTP_AGENT = new HttpAgent(
    config.httpAgentOptions
  )
  ;(globalThis as any).__NEXT_HTTPS_AGENT = new HttpsAgent(
    config.httpAgentOptions
  )
}

function setFontLoaderDefaults(config: NextConfigComplete) {
  try {
    // eslint-disable-next-line import/no-extraneous-dependencies
    require('@next/font/package.json')

    const googleFontLoader = {
      loader: '@next/font/google',
    }
    const localFontLoader = {
      loader: '@next/font/local',
    }
    if (!config.experimental) {
      config.experimental = {}
    }
    if (!config.experimental.fontLoaders) {
      config.experimental.fontLoaders = []
    }
    if (
      !config.experimental.fontLoaders.find(
        ({ loader }: any) => loader === googleFontLoader.loader
      )
    ) {
      config.experimental.fontLoaders.push(googleFontLoader)
    }
    if (
      !config.experimental.fontLoaders.find(
        ({ loader }: any) => loader === localFontLoader.loader
      )
    ) {
      config.experimental.fontLoaders.push(localFontLoader)
    }
  } catch {}
}

function assignDefaults(dir: string, userConfig: { [key: string]: any }) {
  const configFileName = userConfig.configFileName
  if (typeof userConfig.exportTrailingSlash !== 'undefined') {
    console.warn(
      chalk.yellow.bold('Warning: ') +
        `The "exportTrailingSlash" option has been renamed to "trailingSlash". Please update your ${configFileName}.`
    )
    if (typeof userConfig.trailingSlash === 'undefined') {
      userConfig.trailingSlash = userConfig.exportTrailingSlash
    }
    delete userConfig.exportTrailingSlash
  }

  const config = Object.keys(userConfig).reduce<{ [key: string]: any }>(
    (currentConfig, key) => {
      const value = userConfig[key]

      if (value === undefined || value === null) {
        return currentConfig
      }

      if (key === 'experimental' && typeof value === 'object') {
        const enabledExperiments: (keyof ExperimentalConfig)[] = []

        // defaultConfig.experimental is predefined and will never be undefined
        // This is only a type guard for the typescript
        if (defaultConfig.experimental) {
          for (const featureName of Object.keys(
            value
          ) as (keyof ExperimentalConfig)[]) {
            const featureValue = value[featureName]
            if (
              featureName === 'appDir' &&
              featureValue === true &&
              !isAboveNodejs16
            ) {
              throw new Error(
                `experimental.appDir requires Node v${NODE_16_VERSION} or later.`
              )
            }
            if (
              value[featureName] !== defaultConfig.experimental[featureName]
            ) {
              enabledExperiments.push(featureName)
            }
          }
        }

        if (enabledExperiments.length > 0) {
          experimentalWarning(configFileName, enabledExperiments)
        }
      }

      if (key === 'distDir') {
        if (typeof value !== 'string') {
          throw new Error(
            `Specified distDir is not a string, found type "${typeof value}"`
          )
        }
        const userDistDir = value.trim()

        // don't allow public as the distDir as this is a reserved folder for
        // public files
        if (userDistDir === 'public') {
          throw new Error(
            `The 'public' directory is reserved in Next.js and can not be set as the 'distDir'. https://nextjs.org/docs/messages/can-not-output-to-public`
          )
        }
        // make sure distDir isn't an empty string as it can result in the provided
        // directory being deleted in development mode
        if (userDistDir.length === 0) {
          throw new Error(
            `Invalid distDir provided, distDir can not be an empty string. Please remove this config or set it to undefined`
          )
        }
      }

      if (key === 'pageExtensions') {
        if (!Array.isArray(value)) {
          throw new Error(
            `Specified pageExtensions is not an array of strings, found "${value}". Please update this config or remove it.`
          )
        }

        if (!value.length) {
          throw new Error(
            `Specified pageExtensions is an empty array. Please update it with the relevant extensions or remove it.`
          )
        }

        value.forEach((ext) => {
          if (typeof ext !== 'string') {
            throw new Error(
              `Specified pageExtensions is not an array of strings, found "${ext}" of type "${typeof ext}". Please update this config or remove it.`
            )
          }
        })
      }

      if (!!value && value.constructor === Object) {
        currentConfig[key] = {
          ...defaultConfig[key],
          ...Object.keys(value).reduce<any>((c, k) => {
            const v = value[k]
            if (v !== undefined && v !== null) {
              c[k] = v
            }
            return c
          }, {}),
        }
      } else {
        currentConfig[key] = value
      }

      return currentConfig
    },
    {}
  )

  const result = { ...defaultConfig, ...config }

  if (typeof result.assetPrefix !== 'string') {
    throw new Error(
      `Specified assetPrefix is not a string, found type "${typeof result.assetPrefix}" https://nextjs.org/docs/messages/invalid-assetprefix`
    )
  }

  if (typeof result.basePath !== 'string') {
    throw new Error(
      `Specified basePath is not a string, found type "${typeof result.basePath}"`
    )
  }

  if (result.experimental?.appDir) {
    result.experimental.enableUndici = true
  }

  if (result.basePath !== '') {
    if (result.basePath === '/') {
      throw new Error(
        `Specified basePath /. basePath has to be either an empty string or a path prefix"`
      )
    }

    if (!result.basePath.startsWith('/')) {
      throw new Error(
        `Specified basePath has to start with a /, found "${result.basePath}"`
      )
    }

    if (result.basePath !== '/') {
      if (result.basePath.endsWith('/')) {
        throw new Error(
          `Specified basePath should not end with /, found "${result.basePath}"`
        )
      }

      if (result.assetPrefix === '') {
        result.assetPrefix = result.basePath
      }

      if (result.amp?.canonicalBase === '') {
        result.amp.canonicalBase = result.basePath
      }
    }
  }

  if (result?.images) {
    const images: ImageConfig = result.images

    if (typeof images !== 'object') {
      throw new Error(
        `Specified images should be an object received ${typeof images}.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
      )
    }

    if (images.domains) {
      if (!Array.isArray(images.domains)) {
        throw new Error(
          `Specified images.domains should be an Array received ${typeof images.domains}.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      // static images are automatically prefixed with assetPrefix
      // so we need to ensure _next/image allows downloading from
      // this resource
      if (config.assetPrefix?.startsWith('http')) {
        images.domains.push(new URL(config.assetPrefix).hostname)
      }

      if (images.domains.length > 50) {
        throw new Error(
          `Specified images.domains exceeds length of 50, received length (${images.domains.length}), please reduce the length of the array to continue.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      const invalid = images.domains.filter(
        (d: unknown) => typeof d !== 'string'
      )
      if (invalid.length > 0) {
        throw new Error(
          `Specified images.domains should be an Array of strings received invalid values (${invalid.join(
            ', '
          )}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }
    }

    const remotePatterns = result?.images?.remotePatterns
    if (remotePatterns) {
      if (!Array.isArray(remotePatterns)) {
        throw new Error(
          `Specified images.remotePatterns should be an Array received ${typeof remotePatterns}.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      if (remotePatterns.length > 50) {
        throw new Error(
          `Specified images.remotePatterns exceeds length of 50, received length (${remotePatterns.length}), please reduce the length of the array to continue.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      const validProps = new Set(['protocol', 'hostname', 'pathname', 'port'])
      const requiredProps = ['hostname']
      const invalidPatterns = remotePatterns.filter(
        (d: unknown) =>
          !d ||
          typeof d !== 'object' ||
          Object.entries(d).some(
            ([k, v]) => !validProps.has(k) || typeof v !== 'string'
          ) ||
          requiredProps.some((k) => !(k in d))
      )
      if (invalidPatterns.length > 0) {
        throw new Error(
          `Invalid images.remotePatterns values:\n${invalidPatterns
            .map((item) => JSON.stringify(item))
            .join(
              '\n'
            )}\n\nremotePatterns value must follow format { protocol: 'https', hostname: 'example.com', port: '', pathname: '/imgs/**' }.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }
    }

    if (images.deviceSizes) {
      const { deviceSizes } = images
      if (!Array.isArray(deviceSizes)) {
        throw new Error(
          `Specified images.deviceSizes should be an Array received ${typeof deviceSizes}.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      if (deviceSizes.length > 25) {
        throw new Error(
          `Specified images.deviceSizes exceeds length of 25, received length (${deviceSizes.length}), please reduce the length of the array to continue.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      const invalid = deviceSizes.filter((d: unknown) => {
        return typeof d !== 'number' || d < 1 || d > 10000
      })

      if (invalid.length > 0) {
        throw new Error(
          `Specified images.deviceSizes should be an Array of numbers that are between 1 and 10000, received invalid values (${invalid.join(
            ', '
          )}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }
    }
    if (images.imageSizes) {
      const { imageSizes } = images
      if (!Array.isArray(imageSizes)) {
        throw new Error(
          `Specified images.imageSizes should be an Array received ${typeof imageSizes}.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      if (imageSizes.length > 25) {
        throw new Error(
          `Specified images.imageSizes exceeds length of 25, received length (${imageSizes.length}), please reduce the length of the array to continue.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      const invalid = imageSizes.filter((d: unknown) => {
        return typeof d !== 'number' || d < 1 || d > 10000
      })

      if (invalid.length > 0) {
        throw new Error(
          `Specified images.imageSizes should be an Array of numbers that are between 1 and 10000, received invalid values (${invalid.join(
            ', '
          )}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }
    }

    if (!images.loader) {
      images.loader = 'default'
    }

    if (!VALID_LOADERS.includes(images.loader)) {
      throw new Error(
        `Specified images.loader should be one of (${VALID_LOADERS.join(
          ', '
        )}), received invalid value (${
          images.loader
        }).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
      )
    }

    if (
      images.loader !== 'default' &&
      images.loader !== 'custom' &&
      images.path === imageConfigDefault.path
    ) {
      throw new Error(
        `Specified images.loader property (${images.loader}) also requires images.path property to be assigned to a URL prefix.\nSee more info here: https://nextjs.org/docs/api-reference/next/legacy/image#loader-configuration`
      )
    }

    // Append trailing slash for non-default loaders and when trailingSlash is set
    if (images.path) {
      if (
        (images.loader !== 'default' &&
          images.path[images.path.length - 1] !== '/') ||
        result.trailingSlash
      ) {
        images.path += '/'
      }
    }

    if (images.path === imageConfigDefault.path && result.basePath) {
      images.path = `${result.basePath}${images.path}`
    }

    if (images.loaderFile) {
      if (images.loader !== 'default' && images.loader !== 'custom') {
        throw new Error(
          `Specified images.loader property (${images.loader}) cannot be used with images.loaderFile property. Please set images.loader to "custom".`
        )
      }
      const absolutePath = join(dir, images.loaderFile)
      if (!existsSync(absolutePath)) {
        throw new Error(
          `Specified images.loaderFile does not exist at "${absolutePath}".`
        )
      }
      images.loader = 'custom'
      images.loaderFile = absolutePath
    }

    if (
      images.minimumCacheTTL &&
      (!Number.isInteger(images.minimumCacheTTL) || images.minimumCacheTTL < 0)
    ) {
      throw new Error(
        `Specified images.minimumCacheTTL should be an integer 0 or more received (${images.minimumCacheTTL}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
      )
    }

    if (images.formats) {
      const { formats } = images
      if (!Array.isArray(formats)) {
        throw new Error(
          `Specified images.formats should be an Array received ${typeof formats}.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }
      if (formats.length < 1 || formats.length > 2) {
        throw new Error(
          `Specified images.formats must be length 1 or 2, received length (${formats.length}), please reduce the length of the array to continue.\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }

      const invalid = formats.filter((f) => {
        return f !== 'image/avif' && f !== 'image/webp'
      })

      if (invalid.length > 0) {
        throw new Error(
          `Specified images.formats should be an Array of mime type strings, received invalid values (${invalid.join(
            ', '
          )}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
        )
      }
    }

    if (
      typeof images.dangerouslyAllowSVG !== 'undefined' &&
      typeof images.dangerouslyAllowSVG !== 'boolean'
    ) {
      throw new Error(
        `Specified images.dangerouslyAllowSVG should be a boolean received (${images.dangerouslyAllowSVG}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
      )
    }

    if (
      typeof images.contentSecurityPolicy !== 'undefined' &&
      typeof images.contentSecurityPolicy !== 'string'
    ) {
      throw new Error(
        `Specified images.contentSecurityPolicy should be a string received (${images.contentSecurityPolicy}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
      )
    }

    const unoptimized = result?.images?.unoptimized
    if (
      typeof unoptimized !== 'undefined' &&
      typeof unoptimized !== 'boolean'
    ) {
      throw new Error(
        `Specified images.unoptimized should be a boolean, received (${unoptimized}).\nSee more info here: https://nextjs.org/docs/messages/invalid-images-config`
      )
    }
  }

  if (result.experimental && 'relay' in (result.experimental as any)) {
    Log.warn(
      `\`relay\` has been moved out of \`experimental\` and into \`compiler\`. Please update your ${configFileName} file accordingly.`
    )
    result.compiler = result.compiler || {}
    result.compiler.relay = (result.experimental as any).relay
  }

  if (
    result.experimental &&
    'styledComponents' in (result.experimental as any)
  ) {
    Log.warn(
      `\`styledComponents\` has been moved out of \`experimental\` and into \`compiler\`. Please update your ${configFileName} file accordingly.`
    )
    result.compiler = result.compiler || {}
    result.compiler.styledComponents = (
      result.experimental as any
    ).styledComponents
  }

  if (result.experimental && 'emotion' in (result.experimental as any)) {
    Log.warn(
      `\`emotion\` has been moved out of \`experimental\` and into \`compiler\`. Please update your ${configFileName} file accordingly.`
    )
    result.compiler = result.compiler || {}
    result.compiler.emotion = (result.experimental as any).emotion
  }

  if (
    result.experimental &&
    'reactRemoveProperties' in (result.experimental as any)
  ) {
    Log.warn(
      `\`reactRemoveProperties\` has been moved out of \`experimental\` and into \`compiler\`. Please update your ${configFileName} file accordingly.`
    )
    result.compiler = result.compiler || {}
    result.compiler.reactRemoveProperties = (
      result.experimental as any
    ).reactRemoveProperties
  }

  if (result.experimental && 'removeConsole' in (result.experimental as any)) {
    Log.warn(
      `\`removeConsole\` has been moved out of \`experimental\` and into \`compiler\`. Please update your ${configFileName} file accordingly.`
    )
    result.compiler = result.compiler || {}
    result.compiler.removeConsole = (result.experimental as any).removeConsole
  }

  if (result.experimental?.swcMinifyDebugOptions) {
    Log.warn(
      'SWC minify debug option specified. This option is for debugging minifier issues and will be removed once SWC minifier is stable.'
    )
  }

  if ((result.experimental as any).outputStandalone) {
    Log.warn(
      `experimental.outputStandalone has been renamed to "output: 'standalone'", please move the config.`
    )
    result.output = 'standalone'
  }

  if (
    result.experimental &&
    'transpilePackages' in (result.experimental as any)
  ) {
    Log.warn(
      `\`transpilePackages\` has been moved out of \`experimental\`. Please update your ${configFileName} file accordingly.`
    )
    result.transpilePackages = (result.experimental as any).transpilePackages
  }

  if (
    result.experimental?.outputFileTracingRoot &&
    !isAbsolute(result.experimental.outputFileTracingRoot)
  ) {
    result.experimental.outputFileTracingRoot = resolve(
      result.experimental.outputFileTracingRoot
    )
    Log.warn(
      `experimental.outputFileTracingRoot should be absolute, using: ${result.experimental.outputFileTracingRoot}`
    )
  }

  if (result.output === 'standalone' && !result.outputFileTracing) {
    Log.warn(
      `"output: 'standalone'" requires outputFileTracing not be disabled please enable it to leverage the standalone build`
    )
    result.output = undefined
  }

  setHttpClientAndAgentOptions(result || defaultConfig)

  if (result.i18n) {
    const { i18n } = result
    const i18nType = typeof i18n

    if (i18nType !== 'object') {
      throw new Error(
        `Specified i18n should be an object received ${i18nType}.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    if (!Array.isArray(i18n.locales)) {
      throw new Error(
        `Specified i18n.locales should be an Array received ${typeof i18n.locales}.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    if (i18n.locales.length > 100) {
      Log.warn(
        `Received ${i18n.locales.length} i18n.locales items which exceeds the recommended max of 100.\nSee more info here: https://nextjs.org/docs/advanced-features/i18n-routing#how-does-this-work-with-static-generation`
      )
    }

    const defaultLocaleType = typeof i18n.defaultLocale

    if (!i18n.defaultLocale || defaultLocaleType !== 'string') {
      throw new Error(
        `Specified i18n.defaultLocale should be a string.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    if (typeof i18n.domains !== 'undefined' && !Array.isArray(i18n.domains)) {
      throw new Error(
        `Specified i18n.domains must be an array of domain objects e.g. [ { domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] } ] received ${typeof i18n.domains}.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    if (i18n.domains) {
      const invalidDomainItems = i18n.domains.filter((item) => {
        if (!item || typeof item !== 'object') return true
        if (!item.defaultLocale) return true
        if (!item.domain || typeof item.domain !== 'string') return true

        const defaultLocaleDuplicate = i18n.domains?.find(
          (altItem) =>
            altItem.defaultLocale === item.defaultLocale &&
            altItem.domain !== item.domain
        )

        if (defaultLocaleDuplicate) {
          console.warn(
            `Both ${item.domain} and ${defaultLocaleDuplicate.domain} configured the defaultLocale ${item.defaultLocale} but only one can. Change one item's default locale to continue`
          )
          return true
        }

        let hasInvalidLocale = false

        if (Array.isArray(item.locales)) {
          for (const locale of item.locales) {
            if (typeof locale !== 'string') hasInvalidLocale = true

            for (const domainItem of i18n.domains || []) {
              if (domainItem === item) continue
              if (domainItem.locales && domainItem.locales.includes(locale)) {
                console.warn(
                  `Both ${item.domain} and ${domainItem.domain} configured the locale (${locale}) but only one can. Remove it from one i18n.domains config to continue`
                )
                hasInvalidLocale = true
                break
              }
            }
          }
        }

        return hasInvalidLocale
      })

      if (invalidDomainItems.length > 0) {
        throw new Error(
          `Invalid i18n.domains values:\n${invalidDomainItems
            .map((item: any) => JSON.stringify(item))
            .join(
              '\n'
            )}\n\ndomains value must follow format { domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] }.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
        )
      }
    }

    if (!Array.isArray(i18n.locales)) {
      throw new Error(
        `Specified i18n.locales must be an array of locale strings e.g. ["en-US", "nl-NL"] received ${typeof i18n.locales}.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    const invalidLocales = i18n.locales.filter(
      (locale: any) => typeof locale !== 'string'
    )

    if (invalidLocales.length > 0) {
      throw new Error(
        `Specified i18n.locales contains invalid values (${invalidLocales
          .map(String)
          .join(
            ', '
          )}), locales must be valid locale tags provided as strings e.g. "en-US".\n` +
          `See here for list of valid language sub-tags: http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry`
      )
    }

    if (!i18n.locales.includes(i18n.defaultLocale)) {
      throw new Error(
        `Specified i18n.defaultLocale should be included in i18n.locales.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    const normalizedLocales = new Set()
    const duplicateLocales = new Set()

    i18n.locales.forEach((locale) => {
      const localeLower = locale.toLowerCase()
      if (normalizedLocales.has(localeLower)) {
        duplicateLocales.add(locale)
      }
      normalizedLocales.add(localeLower)
    })

    if (duplicateLocales.size > 0) {
      throw new Error(
        `Specified i18n.locales contains the following duplicate locales:\n` +
          `${[...duplicateLocales].join(', ')}\n` +
          `Each locale should be listed only once.\n` +
          `See more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }

    // make sure default Locale is at the front
    i18n.locales = [
      i18n.defaultLocale,
      ...i18n.locales.filter((locale) => locale !== i18n.defaultLocale),
    ]

    const localeDetectionType = typeof i18n.localeDetection

    if (
      localeDetectionType !== 'boolean' &&
      localeDetectionType !== 'undefined'
    ) {
      throw new Error(
        `Specified i18n.localeDetection should be undefined or a boolean received ${localeDetectionType}.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
      )
    }
  }

  if (result.devIndicators?.buildActivityPosition) {
    const { buildActivityPosition } = result.devIndicators
    const allowedValues = [
      'top-left',
      'top-right',
      'bottom-left',
      'bottom-right',
    ]

    if (!allowedValues.includes(buildActivityPosition)) {
      throw new Error(
        `Invalid "devIndicator.buildActivityPosition" provided, expected one of ${allowedValues.join(
          ', '
        )}, received ${buildActivityPosition}`
      )
    }
  }

  return result
}

export default async function loadConfig(
  phase: string,
  dir: string,
  customConfig?: object | null,
  rawConfig?: boolean
): Promise<NextConfigComplete> {
  await loadEnvConfig(dir, phase === PHASE_DEVELOPMENT_SERVER, Log)
  loadWebpackHook()

  let configFileName = 'next.config.js'

  if (customConfig) {
    return assignDefaults(dir, {
      configOrigin: 'server',
      configFileName,
      ...customConfig,
    }) as NextConfigComplete
  }

  const path = await findUp(CONFIG_FILES, { cwd: dir })

  // If config file was found
  if (path?.length) {
    configFileName = basename(path)
    let userConfigModule: any

    try {
      // `import()` expects url-encoded strings, so the path must be properly
      // escaped and (especially on Windows) absolute paths must pe prefixed
      // with the `file://` protocol
      if (process.env.__NEXT_TEST_MODE === 'jest') {
        // dynamic import does not currently work inside of vm which
        // jest relies on so we fall back to require for this case
        // https://github.com/nodejs/node/issues/35889
        userConfigModule = require(path)
      } else {
        userConfigModule = await import(pathToFileURL(path).href)
      }

      if (rawConfig) {
        return userConfigModule
      }
    } catch (err) {
      Log.error(
        `Failed to load ${configFileName}, see more info here https://nextjs.org/docs/messages/next-config-error`
      )
      throw err
    }
    const userConfig = await normalizeConfig(
      phase,
      userConfigModule.default || userConfigModule
    )

    const validateResult = validateConfig(userConfig)

    if (validateResult.errors) {
      Log.warn(`Invalid next.config.js options detected: `)

      // Only load @segment/ajv-human-errors when invalid config is detected
      const { AggregateAjvError } =
        require('next/dist/compiled/@segment/ajv-human-errors') as typeof import('next/dist/compiled/@segment/ajv-human-errors')
      const aggregatedAjvErrors = new AggregateAjvError(validateResult.errors, {
        fieldLabels: 'js',
      })
      for (const error of aggregatedAjvErrors) {
        console.error(`  - ${error.message}`)
      }

      console.error(
        '\nSee more info here: https://nextjs.org/docs/messages/invalid-next-config'
      )
    }

    if (Object.keys(userConfig).length === 0) {
      Log.warn(
        `Detected ${configFileName}, no exported configuration found. https://nextjs.org/docs/messages/empty-configuration`
      )
    }

    if (userConfig.target && userConfig.target !== 'server') {
      throw new Error(
        `The "target" property is no longer supported in ${configFileName}.\n` +
          'See more info here https://nextjs.org/docs/messages/deprecated-target-config'
      )
    }

    if (userConfig.amp?.canonicalBase) {
      const { canonicalBase } = userConfig.amp || ({} as any)
      userConfig.amp = userConfig.amp || {}
      userConfig.amp.canonicalBase =
        (canonicalBase.endsWith('/')
          ? canonicalBase.slice(0, -1)
          : canonicalBase) || ''
    }

    const completeConfig = assignDefaults(dir, {
      configOrigin: relative(dir, path),
      configFile: path,
      configFileName,
      ...userConfig,
    }) as NextConfigComplete
    setFontLoaderDefaults(completeConfig)
    return completeConfig
  } else {
    const configBaseName = basename(CONFIG_FILES[0], extname(CONFIG_FILES[0]))
    const nonJsPath = findUp.sync(
      [
        `${configBaseName}.jsx`,
        `${configBaseName}.ts`,
        `${configBaseName}.tsx`,
        `${configBaseName}.json`,
      ],
      { cwd: dir }
    )
    if (nonJsPath?.length) {
      throw new Error(
        `Configuring Next.js via '${basename(
          nonJsPath
        )}' is not supported. Please replace the file with 'next.config.js' or 'next.config.mjs'.`
      )
    }
  }

  // always call assignDefaults to ensure settings like
  // reactRoot can be updated correctly even with no next.config.js
  const completeConfig = assignDefaults(
    dir,
    defaultConfig
  ) as NextConfigComplete
  completeConfig.configFileName = configFileName
  setHttpClientAndAgentOptions(completeConfig)
  setFontLoaderDefaults(completeConfig)
  return completeConfig
}