next.js/packages/next/src/build/babel/loader/get-config.ts

import { readFileSync } from 'fs'
import JSON5 from 'next/dist/compiled/json5'

import { createConfigItem, loadOptions } from 'next/dist/compiled/babel/core'
import loadConfig from 'next/dist/compiled/babel/core-lib-config'

import type { NextBabelLoaderOptions, NextJsLoaderContext } from './types'
import { consumeIterator } from './util'
import * as Log from '../../output/log'
import jsx from 'next/dist/compiled/babel/plugin-syntax-jsx'
import { isReactCompilerRequired } from '../../swc'

const nextDistPath =
  /(next[\\/]dist[\\/]shared[\\/]lib)|(next[\\/]dist[\\/]client)|(next[\\/]dist[\\/]pages)/

/**
 * The properties defined here are the conditions with which subsets of inputs
 * can be identified that are able to share a common Babel config.  For example,
 * in dev mode, different transforms must be applied to a source file depending
 * on whether you're compiling for the client or for the server - thus `isServer`
 * is germane.
 *
 * However, these characteristics need not protect against circumstances that
 * will not be encountered in Next.js.  For example, a source file may be
 * transformed differently depending on whether we're doing a production compile
 * or for HMR in dev mode.  However, those two circumstances will never be
 * encountered within the context of a single V8 context (and, thus, shared
 * cache).  Therefore, hasReactRefresh is _not_ germane to caching.
 *
 * NOTE: This approach does not support multiple `.babelrc` files in a
 * single project.  A per-cache-key config will be generated once and,
 * if `.babelrc` is present, that config will be used for any subsequent
 * transformations.
 */
interface CharacteristicsGermaneToCaching {
  isServer: boolean
  isPageFile: boolean
  isNextDist: boolean
  hasModuleExports: boolean
  fileNameOrExt: string
}

const fileExtensionRegex = /\.([a-z]+)$/
function getCacheCharacteristics(
  loaderOptions: NextBabelLoaderOptions,
  source: string,
  filename: string,
  transformMode: 'default' | 'standalone'
): CharacteristicsGermaneToCaching {
  const { isServer, pagesDir } = loaderOptions
  const isPageFile = filename.startsWith(pagesDir)
  const isNextDist = nextDistPath.test(filename)
  const hasModuleExports = source.indexOf('module.exports') !== -1
  const fileNameOrExt =
    transformMode === 'default'
      ? fileExtensionRegex.exec(filename)?.[1] || 'unknown'
      : filename

  return {
    isServer,
    isPageFile,
    isNextDist,
    hasModuleExports,
    fileNameOrExt,
  }
}

/**
 * Return an array of Babel plugins, conditioned upon loader options and
 * source file characteristics.
 */
function getPlugins(
  loaderOptions: NextBabelLoaderOptions,
  cacheCharacteristics: CharacteristicsGermaneToCaching
) {
  const { isServer, isPageFile, isNextDist, hasModuleExports } =
    cacheCharacteristics

  const { development } = loaderOptions
  const hasReactRefresh =
    loaderOptions.transformMode !== 'standalone'
      ? loaderOptions.hasReactRefresh
      : false

  const applyCommonJsItem = hasModuleExports
    ? createConfigItem(
        require('../plugins/commonjs') as typeof import('../plugins/commonjs'),
        { type: 'plugin' }
      )
    : null
  const reactRefreshItem = hasReactRefresh
    ? createConfigItem(
        [
          require('next/dist/compiled/react-refresh/babel') as typeof import('next/dist/compiled/react-refresh/babel'),
          { skipEnvCheck: true },
        ],
        { type: 'plugin' }
      )
    : null
  const pageConfigItem =
    !isServer && isPageFile
      ? createConfigItem(
          [
            require('../plugins/next-page-config') as typeof import('../plugins/next-page-config'),
          ],
          {
            type: 'plugin',
          }
        )
      : null
  const disallowExportAllItem =
    !isServer && isPageFile
      ? createConfigItem(
          [
            require('../plugins/next-page-disallow-re-export-all-exports') as typeof import('../plugins/next-page-disallow-re-export-all-exports'),
          ],
          { type: 'plugin' }
        )
      : null
  const transformDefineItem = createConfigItem(
    [
      require.resolve('next/dist/compiled/babel/plugin-transform-define'),
      {
        'process.env.NODE_ENV': development ? 'development' : 'production',
        'typeof window': isServer ? 'undefined' : 'object',
        'process.browser': isServer ? false : true,
      },
      'next-js-transform-define-instance',
    ],
    { type: 'plugin' }
  )
  const nextSsgItem =
    !isServer && isPageFile
      ? createConfigItem([require.resolve('../plugins/next-ssg-transform')], {
          type: 'plugin',
        })
      : null
  const commonJsItem = isNextDist
    ? createConfigItem(
        require('next/dist/compiled/babel/plugin-transform-modules-commonjs') as typeof import('next/dist/compiled/babel/plugin-transform-modules-commonjs'),
        { type: 'plugin' }
      )
    : null
  const nextFontUnsupported = createConfigItem(
    [
      require('../plugins/next-font-unsupported') as typeof import('../plugins/next-font-unsupported'),
    ],
    { type: 'plugin' }
  )

  return [
    reactRefreshItem,
    pageConfigItem,
    disallowExportAllItem,
    applyCommonJsItem,
    transformDefineItem,
    nextSsgItem,
    commonJsItem,
    nextFontUnsupported,
  ].filter(Boolean)
}

const isJsonFile = /\.(json|babelrc)$/
const isJsFile = /\.js$/

/**
 * While this function does block execution while reading from disk, it
 * should not introduce any issues.  The function is only invoked when
 * generating a fresh config, and only a small handful of configs should
 * be generated during compilation.
 */
function getCustomBabelConfig(configFilePath: string) {
  if (isJsonFile.exec(configFilePath)) {
    const babelConfigRaw = readFileSync(configFilePath, 'utf8')
    return JSON5.parse(babelConfigRaw)
  } else if (isJsFile.exec(configFilePath)) {
    return require(configFilePath)
  }
  throw new Error(
    'The Next.js Babel loader does not support .mjs or .cjs config files.'
  )
}

let babelConfigWarned = false
/**
 * Check if custom babel configuration from user only contains options that
 * can be migrated into latest Next.js features supported by SWC.
 *
 * This raises soft warning messages only, not making any errors yet.
 */
function checkCustomBabelConfigDeprecation(
  config: Record<string, any> | undefined
) {
  if (!config || Object.keys(config).length === 0) {
    return
  }

  const { plugins, presets, ...otherOptions } = config
  if (Object.keys(otherOptions ?? {}).length > 0) {
    return
  }

  if (babelConfigWarned) {
    return
  }

  babelConfigWarned = true

  const isPresetReadyToDeprecate =
    !presets ||
    presets.length === 0 ||
    (presets.length === 1 && presets[0] === 'next/babel')
  const pluginReasons = []
  const unsupportedPlugins = []

  if (Array.isArray(plugins)) {
    for (const plugin of plugins) {
      const pluginName = Array.isArray(plugin) ? plugin[0] : plugin

      // [NOTE]: We cannot detect if the user uses babel-plugin-macro based transform plugins,
      // such as `styled-components/macro` in here.
      switch (pluginName) {
        case 'styled-components':
        case 'babel-plugin-styled-components':
          pluginReasons.push(
            `\t- 'styled-components' can be enabled via 'compiler.styledComponents' in 'next.config.js'`
          )
          break
        case '@emotion/babel-plugin':
          pluginReasons.push(
            `\t- '@emotion/babel-plugin' can be enabled via 'compiler.emotion' in 'next.config.js'`
          )
          break
        case 'babel-plugin-relay':
          pluginReasons.push(
            `\t- 'babel-plugin-relay' can be enabled via 'compiler.relay' in 'next.config.js'`
          )
          break
        case 'react-remove-properties':
          pluginReasons.push(
            `\t- 'react-remove-properties' can be enabled via 'compiler.reactRemoveProperties' in 'next.config.js'`
          )
          break
        case 'transform-remove-console':
          pluginReasons.push(
            `\t- 'transform-remove-console' can be enabled via 'compiler.removeConsole' in 'next.config.js'`
          )
          break
        default:
          unsupportedPlugins.push(pluginName)
          break
      }
    }
  }

  if (isPresetReadyToDeprecate && unsupportedPlugins.length === 0) {
    Log.warn(
      `It looks like there is a custom Babel configuration that can be removed${
        pluginReasons.length > 0 ? ':' : '.'
      }`
    )

    if (pluginReasons.length > 0) {
      Log.warn(`Next.js supports the following features natively: `)
      Log.warn(pluginReasons.join(''))
      Log.warn(
        `For more details configuration options, please refer https://nextjs.org/docs/architecture/nextjs-compiler#supported-features`
      )
    }
  }
}

/**
 * Generate a new, flat Babel config, ready to be handed to Babel-traverse.
 * This config should have no unresolved overrides, presets, etc.
 */
async function getFreshConfig(
  this: NextJsLoaderContext,
  cacheCharacteristics: CharacteristicsGermaneToCaching,
  loaderOptions: NextBabelLoaderOptions,
  target: string,
  filename: string,
  inputSourceMap?: object | null
) {
  const hasReactCompiler = await (async () => {
    if (
      loaderOptions.reactCompilerPlugins &&
      loaderOptions.reactCompilerPlugins.length === 0
    ) {
      return false
    }

    if (/[/\\]node_modules[/\\]/.test(filename)) {
      return false
    }

    if (
      loaderOptions.reactCompilerExclude &&
      loaderOptions.reactCompilerExclude(filename)
    ) {
      return false
    }

    if (!(await isReactCompilerRequired(filename))) {
      return false
    }

    return true
  })()

  const reactCompilerPluginsIfEnabled = hasReactCompiler
    ? loaderOptions.reactCompilerPlugins ?? []
    : []

  let { isServer, pagesDir, srcDir, development } = loaderOptions

  let options = {
    babelrc: false,
    cloneInputAst: false,
    filename,
    inputSourceMap: inputSourceMap || undefined,

    // Ensure that Webpack will get a full absolute path in the sourcemap
    // so that it can properly map the module back to its internal cached
    // modules.
    sourceFileName: filename,
    sourceMaps: this.sourceMap,
  } as any

  const baseCaller = {
    name: 'next-babel-turbo-loader',
    supportsStaticESM: true,
    supportsDynamicImport: true,

    // Provide plugins with insight into webpack target.
    // https://github.com/babel/babel-loader/issues/787
    target: target,

    // Webpack 5 supports TLA behind a flag. We enable it by default
    // for Babel, and then webpack will throw an error if the experimental
    // flag isn't enabled.
    supportsTopLevelAwait: true,

    isServer,
    srcDir,
    pagesDir,
    isDev: development,

    ...loaderOptions.caller,
  }

  if (loaderOptions.transformMode === 'standalone') {
    if (!reactCompilerPluginsIfEnabled.length) {
      return null
    }

    options.plugins = [jsx, ...reactCompilerPluginsIfEnabled]
    options.presets = [
      [
        require('next/dist/compiled/babel/preset-typescript') as typeof import('next/dist/compiled/babel/preset-typescript'),
        { allowNamespaces: true },
      ],
    ]
    options.caller = baseCaller
  } else {
    let { configFile, hasJsxRuntime } = loaderOptions
    let customConfig: any = configFile
      ? getCustomBabelConfig(configFile)
      : undefined

    checkCustomBabelConfigDeprecation(customConfig)

    // Set the default sourcemap behavior based on Webpack's mapping flag,
    // but allow users to override if they want.
    options.sourceMaps =
      loaderOptions.sourceMaps === undefined
        ? this.sourceMap
        : loaderOptions.sourceMaps

    options.plugins = [
      ...getPlugins(loaderOptions, cacheCharacteristics),
      ...reactCompilerPluginsIfEnabled,
      ...(customConfig?.plugins || []),
    ]

    // target can be provided in babelrc
    options.target = isServer ? undefined : customConfig?.target

    // env can be provided in babelrc
    options.env = customConfig?.env

    options.presets = (() => {
      // If presets is defined the user will have next/babel in their babelrc
      if (customConfig?.presets) {
        return customConfig.presets
      }

      // If presets is not defined the user will likely have "env" in their babelrc
      if (customConfig) {
        return undefined
      }

      // If no custom config is provided the default is to use next/babel
      return ['next/babel']
    })()

    options.overrides = loaderOptions.overrides

    options.caller = {
      ...baseCaller,
      hasJsxRuntime,
    }
  }

  // Babel does strict checks on the config so undefined is not allowed
  if (typeof options.target === 'undefined') {
    delete options.target
  }

  Object.defineProperty(options.caller, 'onWarning', {
    enumerable: false,
    writable: false,
    value: (reason: any) => {
      if (!(reason instanceof Error)) {
        reason = new Error(reason)
      }
      this.emitWarning(reason)
    },
  })

  const loadedOptions = loadOptions(options)
  const config = consumeIterator(loadConfig(loadedOptions))

  return config
}

/**
 * Each key returned here corresponds with a Babel config that can be shared.
 * The conditions of permissible sharing between files is dependent on specific
 * file attributes and Next.js compiler states: `CharacteristicsGermaneToCaching`.
 */
function getCacheKey(cacheCharacteristics: CharacteristicsGermaneToCaching) {
  const { isServer, isPageFile, isNextDist, hasModuleExports, fileNameOrExt } =
    cacheCharacteristics

  const flags =
    0 |
    (isServer ? 0b0001 : 0) |
    (isPageFile ? 0b0010 : 0) |
    (isNextDist ? 0b0100 : 0) |
    (hasModuleExports ? 0b1000 : 0)

  return fileNameOrExt + flags
}

type BabelConfig = any
const configCache: Map<any, BabelConfig> = new Map()
const configFiles: Set<string> = new Set()

export default async function getConfig(
  this: NextJsLoaderContext,
  {
    source,
    target,
    loaderOptions,
    filename,
    inputSourceMap,
  }: {
    source: string
    loaderOptions: NextBabelLoaderOptions
    target: string
    filename: string
    inputSourceMap?: object | null
  }
): Promise<BabelConfig> {
  const cacheCharacteristics = getCacheCharacteristics(
    loaderOptions,
    source,
    filename,
    loaderOptions.transformMode
  )

  if (loaderOptions.transformMode === 'default' && loaderOptions.configFile) {
    // Ensures webpack invalidates the cache for this loader when the config file changes
    this.addDependency(loaderOptions.configFile)
  }

  const cacheKey = getCacheKey(cacheCharacteristics)
  if (configCache.has(cacheKey)) {
    const cachedConfig = configCache.get(cacheKey)
    if (!cachedConfig) {
      return null
    }

    return {
      ...cachedConfig,
      options: {
        ...cachedConfig.options,
        cwd: loaderOptions.cwd,
        root: loaderOptions.cwd,
        filename,
        sourceFileName: filename,
      },
    }
  }

  if (
    loaderOptions.transformMode === 'default' &&
    loaderOptions.configFile &&
    !configFiles.has(loaderOptions.configFile)
  ) {
    configFiles.add(loaderOptions.configFile)
    Log.info(
      `Using external babel configuration from ${loaderOptions.configFile}`
    )
  }

  const freshConfig = await getFreshConfig.call(
    this,
    cacheCharacteristics,
    loaderOptions,
    target,
    filename,
    inputSourceMap
  )

  configCache.set(cacheKey, freshConfig)

  return freshConfig
}