rsnext/packages/next/build/webpack/loaders/next-flight-client-loader.ts

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import * as acorn from 'acorn'

type ResolveContext = {
  conditions: Array<string>
  parentURL: string | void
}

type ResolveFunction = (
  specifier: string,
  context: ResolveContext,
  resolve: ResolveFunction
) => { url: string } | Promise<{ url: string }>

type TransformSourceFunction = (url: string, callback: () => void) => void

type Source = string | ArrayBuffer | Uint8Array

let stashedResolve: null | ResolveFunction = null

function addExportNames(names: string[], node: any) {
  switch (node.type) {
    case 'Identifier':
      names.push(node.name)
      return
    case 'ObjectPattern':
      for (let i = 0; i < node.properties.length; i++)
        addExportNames(names, node.properties[i])
      return
    case 'ArrayPattern':
      for (let i = 0; i < node.elements.length; i++) {
        const element = node.elements[i]
        if (element) addExportNames(names, element)
      }
      return
    case 'Property':
      addExportNames(names, node.value)
      return
    case 'AssignmentPattern':
      addExportNames(names, node.left)
      return
    case 'RestElement':
      addExportNames(names, node.argument)
      return
    case 'ParenthesizedExpression':
      addExportNames(names, node.expression)
      return
    default:
      return
  }
}

function resolveClientImport(
  specifier: string,
  parentURL: string
): { url: string } | Promise<{ url: string }> {
  // Resolve an import specifier as if it was loaded by the client. This doesn't use
  // the overrides that this loader does but instead reverts to the default.
  // This resolution algorithm will not necessarily have the same configuration
  // as the actual client loader. It should mostly work and if it doesn't you can
  // always convert to explicit exported names instead.
  const conditions = ['node', 'import']
  if (stashedResolve === null) {
    throw new Error(
      'Expected resolve to have been called before transformSource'
    )
  }
  return stashedResolve(specifier, { conditions, parentURL }, stashedResolve)
}

async function parseExportNamesInto(
  transformedSource: string,
  names: Array<string>,
  parentURL: string,
  loadModule: TransformSourceFunction
): Promise<void> {
  const { body } = acorn.parse(transformedSource, {
    ecmaVersion: 11,
    sourceType: 'module',
  }) as any
  for (let i = 0; i < body.length; i++) {
    const node = body[i]
    switch (node.type) {
      case 'ExportAllDeclaration':
        if (node.exported) {
          addExportNames(names, node.exported)
          continue
        } else {
          const { url } = await resolveClientImport(
            node.source.value,
            parentURL
          )
          const source = ''
          parseExportNamesInto(source, names, url, loadModule)
          continue
        }
      case 'ExportDefaultDeclaration':
        names.push('default')
        continue
      case 'ExportNamedDeclaration':
        if (node.declaration) {
          if (node.declaration.type === 'VariableDeclaration') {
            const declarations = node.declaration.declarations
            for (let j = 0; j < declarations.length; j++) {
              addExportNames(names, declarations[j].id)
            }
          } else {
            addExportNames(names, node.declaration.id)
          }
        }
        if (node.specificers) {
          const specificers = node.specificers
          for (let j = 0; j < specificers.length; j++) {
            addExportNames(names, specificers[j].exported)
          }
        }
        continue
      default:
        break
    }
  }
}

export default async function transformSource(
  this: any,
  source: Source
): Promise<Source> {
  const { resourcePath, resourceQuery } = this

  if (resourceQuery !== '?flight') return source

  let url = resourcePath
  const transformedSource = source
  if (typeof transformedSource !== 'string') {
    throw new Error('Expected source to have been transformed to a string.')
  }

  const names: string[] = []
  await parseExportNamesInto(
    transformedSource as string,
    names,
    url + resourceQuery,
    this.loadModule
  )

  // next.js/packages/next/<component>.js
  if (/[\\/]next[\\/](link|image)\.js$/.test(url)) {
    names.push('default')
  }

  let newSrc =
    "const MODULE_REFERENCE = Symbol.for('react.module.reference');\n"
  for (let i = 0; i < names.length; i++) {
    const name = names[i]
    if (name === 'default') {
      newSrc += 'export default '
    } else {
      newSrc += 'export const ' + name + ' = '
    }
    newSrc += '{ $$typeof: MODULE_REFERENCE, filepath: '
    newSrc += JSON.stringify(url)
    newSrc += ', name: '
    newSrc += JSON.stringify(name)
    newSrc += '};\n'
  }

  return newSrc
}