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 { NextBabelLoaderOptions, NextJsLoaderContext } from './types'
import { consumeIterator } from './util'
import * as Log from '../../output/log'

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
  fileExt: string
}

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

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

/**
 * 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 { hasReactRefresh, development } = loaderOptions

  const applyCommonJsItem = hasModuleExports
    ? createConfigItem(require('../plugins/commonjs'), { type: 'plugin' })
    : null
  const reactRefreshItem = hasReactRefresh
    ? createConfigItem(
        [
          require('next/dist/compiled/react-refresh/babel'),
          { skipEnvCheck: true },
        ],
        { type: 'plugin' }
      )
    : null
  const pageConfigItem =
    !isServer && isPageFile
      ? createConfigItem([require('../plugins/next-page-config')], {
          type: 'plugin',
        })
      : null
  const disallowExportAllItem =
    !isServer && isPageFile
      ? createConfigItem(
          [require('../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'),
        { type: 'plugin' }
      )
    : null

  return [
    reactRefreshItem,
    pageConfigItem,
    disallowExportAllItem,
    applyCommonJsItem,
    transformDefineItem,
    nextSsgItem,
    commonJsItem,
  ].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.'
  )
}

/**
 * Generate a new, flat Babel config, ready to be handed to Babel-traverse.
 * This config should have no unresolved overrides, presets, etc.
 */
function getFreshConfig(
  this: NextJsLoaderContext,
  cacheCharacteristics: CharacteristicsGermaneToCaching,
  loaderOptions: NextBabelLoaderOptions,
  target: string,
  filename: string,
  inputSourceMap?: object | null
) {
  let { isServer, pagesDir, development, hasJsxRuntime, configFile } =
    loaderOptions

  let customConfig: any = configFile
    ? getCustomBabelConfig(configFile)
    : undefined

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

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

    // 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,

    plugins: [
      ...getPlugins(loaderOptions, cacheCharacteristics),
      ...(customConfig?.plugins || []),
    ],

    // target can be provided in babelrc
    target: isServer ? undefined : customConfig?.target,
    // env can be provided in babelrc
    env: customConfig?.env,

    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']
    })(),

    overrides: loaderOptions.overrides,

    caller: {
      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,
      pagesDir,
      isDev: development,
      hasJsxRuntime,

      ...loaderOptions.caller,
    },
  } as any

  // 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, fileExt } =
    cacheCharacteristics

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

  return fileExt + flags
}

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

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

  if (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)

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

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

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

  configCache.set(cacheKey, freshConfig)

  return freshConfig
}