next.js/packages/next/src/build/webpack/loaders/next-flight-loader/index.ts

import type {
  javascript,
  LoaderContext,
  NormalModule,
  webpack,
} from 'next/dist/compiled/webpack/webpack'
import { RSC_MOD_REF_PROXY_ALIAS } from '../../../../lib/constants'
import {
  BARREL_OPTIMIZATION_PREFIX,
  RSC_MODULE_TYPES,
} from '../../../../shared/lib/constants'
import { warnOnce } from '../../../../shared/lib/utils/warn-once'
import { getRSCModuleInformation } from '../../../analysis/get-page-static-info'
import { formatBarrelOptimizedResource } from '../../utils'
import { getModuleBuildInfo } from '../get-module-build-info'
import { ModuleFilenameHelpers } from 'next/dist/compiled/webpack/webpack'

type SourceType = javascript.JavascriptParser['sourceType'] | 'commonjs'

const noopHeadPath = require.resolve('next/dist/client/components/noop-head')
// For edge runtime it will be aliased to esm version by webpack
const MODULE_PROXY_PATH =
  'next/dist/build/webpack/loaders/next-flight-loader/module-proxy'

export function getAssumedSourceType(
  mod: webpack.Module,
  sourceType: SourceType
): SourceType {
  const buildInfo = getModuleBuildInfo(mod)
  const detectedClientEntryType = buildInfo?.rsc?.clientEntryType
  const clientRefs = buildInfo?.rsc?.clientRefs || []

  // It's tricky to detect the type of a client boundary, but we should always
  // use the `module` type when we can, to support `export *` and `export from`
  // syntax in other modules that import this client boundary.

  if (sourceType === 'auto') {
    if (detectedClientEntryType === 'auto') {
      if (clientRefs.length === 0) {
        // If there's zero export detected in the client boundary, and it's the
        // `auto` type, we can safely assume it's a CJS module because it doesn't
        // have ESM exports.
        return 'commonjs'
      } else if (!clientRefs.includes('*')) {
        // Otherwise, we assume it's an ESM module.
        return 'module'
      }
    } else if (detectedClientEntryType === 'cjs') {
      return 'commonjs'
    }
  }

  return sourceType
}

export default function transformSource(
  this: LoaderContext<undefined>,
  source: string,
  sourceMap: any
) {
  // Avoid buffer to be consumed
  if (typeof source !== 'string') {
    throw new Error('Expected source to have been transformed to a string.')
  }
  const module = this._module!

  // Assign the RSC meta information to buildInfo.
  // Exclude next internal files which are not marked as client files
  const buildInfo = getModuleBuildInfo(module)
  buildInfo.rsc = getRSCModuleInformation(source, true)
  let prefix = ''
  if (process.env.BUILTIN_FLIGHT_CLIENT_ENTRY_PLUGIN) {
    const rscModuleInformationJson = JSON.stringify(buildInfo.rsc)
    prefix = `/* __rspack_internal_rsc_module_information_do_not_use__ ${rscModuleInformationJson} */\n`
    source = prefix + source
  }
  prefix += `// This file is generated by the Webpack next-flight-loader.\n`

  // Resource key is the unique identifier for the resource. When RSC renders
  // a client module, that key is used to identify that module across all compiler
  // layers.
  //
  // Usually it's the module's file path + the export name (e.g. `foo.js#bar`).
  // But with Barrel Optimizations, one file can be splitted into multiple modules,
  // so when you import `foo.js#bar` and `foo.js#baz`, they are actually different
  // "foo.js" being created by the Barrel Loader (one only exports `bar`, the other
  // only exports `baz`).
  //
  // Because of that, we must add another query param to the resource key to
  // differentiate them.
  let resourceKey: string = this.resourcePath
  if (module.matchResource?.startsWith(BARREL_OPTIMIZATION_PREFIX)) {
    resourceKey = formatBarrelOptimizedResource(
      resourceKey,
      module.matchResource
    )
  }

  // A client boundary.
  if (buildInfo.rsc?.type === RSC_MODULE_TYPES.client) {
    const assumedSourceType = getAssumedSourceType(
      module,
      sourceTypeFromModule(module)
    )

    const clientRefs = buildInfo.rsc.clientRefs!
    const stringifiedResourceKey = JSON.stringify(resourceKey)

    if (assumedSourceType === 'module') {
      if (clientRefs.length === 0) {
        return this.callback(null, 'export {}')
      }

      if (clientRefs.includes('*')) {
        this.callback(
          new Error(
            `It's currently unsupported to use "export *" in a client boundary. Please use named exports instead.`
          )
        )
        return
      }

      let esmSource =
        prefix +
        `\
import { registerClientReference } from "react-server-dom-webpack/server";
`
      for (const ref of clientRefs) {
        if (ref === 'default') {
          esmSource += `export default registerClientReference(
function() { throw new Error(${JSON.stringify(`Attempted to call the default \
export of ${stringifiedResourceKey} from the server, but it's on the client. \
It's not possible to invoke a client function from the server, it can only be \
rendered as a Component or passed to props of a Client Component.`)}); },
${stringifiedResourceKey},
"default",
);\n`
        } else {
          esmSource += `export const ${ref} = registerClientReference(
function() { throw new Error(${JSON.stringify(`Attempted to call ${ref}() from \
the server but ${ref} is on the client. It's not possible to invoke a client \
function from the server, it can only be rendered as a Component or passed to \
props of a Client Component.`)}); },
${stringifiedResourceKey},
${JSON.stringify(ref)},
);`
        }
      }

      const compilation = this._compilation!
      const originalSourceURL = ModuleFilenameHelpers.createFilename(
        module,
        {
          moduleFilenameTemplate:
            'webpack://[namespace]/[resource-path]/__nextjs-internal-proxy.mjs',
          namespace: '_N_E',
        },
        {
          requestShortener: compilation.requestShortener,
          chunkGraph: compilation.chunkGraph,
          hashFunction: compilation.outputOptions.hashFunction,
        }
      )

      return this.callback(null, esmSource, {
        version: 3,
        sources: [originalSourceURL],
        // minimal, parseable mappings
        mappings: 'AAAA',
        sourcesContent: [esmSource],
      })
    } else if (assumedSourceType === 'commonjs') {
      let cjsSource =
        prefix +
        `\
const { createProxy } = require("${MODULE_PROXY_PATH}")

module.exports = createProxy(${stringifiedResourceKey})
`

      const compilation = this._compilation!
      const originalSourceURL = ModuleFilenameHelpers.createFilename(
        module,
        {
          moduleFilenameTemplate:
            'webpack://[namespace]/[resource-path]/__nextjs-internal-proxy.cjs',
          namespace: '_N_E',
        },
        {
          requestShortener: compilation.requestShortener,
          chunkGraph: compilation.chunkGraph,
          hashFunction: compilation.outputOptions.hashFunction,
        }
      )

      return this.callback(null, cjsSource, {
        version: 3,
        sources: [originalSourceURL],
        // minimal, parseable mappings
        mappings: 'AAAA',
        sourcesContent: [cjsSource],
      })
    }
  }

  if (buildInfo.rsc?.type !== RSC_MODULE_TYPES.client) {
    if (noopHeadPath === this.resourcePath) {
      warnOnce(
        `Warning: You're using \`next/head\` inside the \`app\` directory, please migrate to the Metadata API. See https://nextjs.org/docs/app/building-your-application/upgrading/app-router-migration#step-3-migrating-nexthead for more details.`
      )
    }
  }

  const replacedSource = source.replace(
    RSC_MOD_REF_PROXY_ALIAS,
    MODULE_PROXY_PATH
  )
  this.callback(null, replacedSource, sourceMap)
}

function sourceTypeFromModule(module: NormalModule): SourceType {
  const moduleType = module.type
  switch (moduleType) {
    case 'javascript/auto':
      return 'auto'
    case 'javascript/dynamic':
      return 'script'
    case 'javascript/esm':
      return 'module'
    default:
      throw new Error('Unexpected module type ' + moduleType)
  }
}