rsnext/packages/next/build/webpack/plugins/build-manifest-plugin.ts

import devalue from 'next/dist/compiled/devalue'
import { webpack, sources } from 'next/dist/compiled/webpack/webpack'
import {
  BUILD_MANIFEST,
  CLIENT_STATIC_FILES_PATH,
  CLIENT_STATIC_FILES_RUNTIME_MAIN,
  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL,
  CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH,
  CLIENT_STATIC_FILES_RUNTIME_AMP,
} from '../../../shared/lib/constants'
import { BuildManifest } from '../../../server/get-page-files'
import getRouteFromEntrypoint from '../../../server/get-route-from-entrypoint'
import { ampFirstEntryNamesMap } from './next-drop-client-page-plugin'
import { Rewrite } from '../../../lib/load-custom-routes'
import { getSortedRoutes } from '../../../shared/lib/router/utils'
import { spans } from './profiling-plugin'
import { CustomRoutes } from '../../../lib/load-custom-routes'

type DeepMutable<T> = { -readonly [P in keyof T]: DeepMutable<T[P]> }

export type ClientBuildManifest = Record<string, string[]>

// This function takes the asset map generated in BuildManifestPlugin and creates a
// reduced version to send to the client.
function generateClientManifest(
  compiler: any,
  compilation: any,
  assetMap: BuildManifest,
  rewrites: CustomRoutes['rewrites']
): string {
  const compilationSpan = spans.get(compilation) || spans.get(compiler)
  const genClientManifestSpan = compilationSpan?.traceChild(
    'NextJsBuildManifest-generateClientManifest'
  )

  return genClientManifestSpan?.traceFn(() => {
    const clientManifest: ClientBuildManifest = {
      // TODO: update manifest type to include rewrites
      __rewrites: rewrites as any,
    }
    const appDependencies = new Set(assetMap.pages['/_app'])
    const sortedPageKeys = getSortedRoutes(Object.keys(assetMap.pages))

    sortedPageKeys.forEach((page) => {
      const dependencies = assetMap.pages[page]

      if (page === '/_app') return
      // Filter out dependencies in the _app entry, because those will have already
      // been loaded by the client prior to a navigation event
      const filteredDeps = dependencies.filter(
        (dep) => !appDependencies.has(dep)
      )

      // The manifest can omit the page if it has no requirements
      if (filteredDeps.length) {
        clientManifest[page] = filteredDeps
      }
    })
    // provide the sorted pages as an array so we don't rely on the object's keys
    // being in order and we don't slow down look-up time for page assets
    clientManifest.sortedPages = sortedPageKeys

    return devalue(clientManifest)
  })
}

function getEntrypointFiles(entrypoint: any): string[] {
  return (
    entrypoint
      ?.getFiles()
      .filter((file: string) => {
        // We don't want to include `.hot-update.js` files into the initial page
        return /(?<!\.hot-update)\.(js|css)($|\?)/.test(file)
      })
      .map((file: string) => file.replace(/\\/g, '/')) ?? []
  )
}

const processRoute = (r: Rewrite) => {
  const rewrite = { ...r }

  // omit external rewrite destinations since these aren't
  // handled client-side
  if (!rewrite.destination.startsWith('/')) {
    delete (rewrite as any).destination
  }
  return rewrite
}

// This plugin creates a build-manifest.json for all assets that are being output
// It has a mapping of "entry" filename to real filename. Because the real filename can be hashed in production
export default class BuildManifestPlugin {
  private buildId: string
  private rewrites: CustomRoutes['rewrites']
  private isDevFallback: boolean

  constructor(options: {
    buildId: string
    rewrites: CustomRoutes['rewrites']
    isDevFallback?: boolean
  }) {
    this.buildId = options.buildId
    this.isDevFallback = !!options.isDevFallback
    this.rewrites = {
      beforeFiles: [],
      afterFiles: [],
      fallback: [],
    }
    this.rewrites.beforeFiles = options.rewrites.beforeFiles.map(processRoute)
    this.rewrites.afterFiles = options.rewrites.afterFiles.map(processRoute)
    this.rewrites.fallback = options.rewrites.fallback.map(processRoute)
  }

  createAssets(compiler: any, compilation: any, assets: any) {
    const compilationSpan = spans.get(compilation) || spans.get(compiler)
    const createAssetsSpan = compilationSpan?.traceChild(
      'NextJsBuildManifest-createassets'
    )
    return createAssetsSpan?.traceFn(() => {
      const entrypoints: Map<string, any> = compilation.entrypoints
      const assetMap: DeepMutable<BuildManifest> = {
        polyfillFiles: [],
        devFiles: [],
        ampDevFiles: [],
        lowPriorityFiles: [],
        pages: { '/_app': [] },
        ampFirstPages: [],
      }

      const ampFirstEntryNames = ampFirstEntryNamesMap.get(compilation)
      if (ampFirstEntryNames) {
        for (const entryName of ampFirstEntryNames) {
          const pagePath = getRouteFromEntrypoint(entryName)
          if (!pagePath) {
            continue
          }

          assetMap.ampFirstPages.push(pagePath)
        }
      }

      const mainFiles = new Set(
        getEntrypointFiles(entrypoints.get(CLIENT_STATIC_FILES_RUNTIME_MAIN))
      )

      const compilationAssets: {
        name: string
        source: typeof sources.RawSource
        info: object
      }[] = compilation.getAssets()

      assetMap.polyfillFiles = compilationAssets
        .filter((p) => {
          // Ensure only .js files are passed through
          if (!p.name.endsWith('.js')) {
            return false
          }

          return (
            p.info && CLIENT_STATIC_FILES_RUNTIME_POLYFILLS_SYMBOL in p.info
          )
        })
        .map((v) => v.name)

      assetMap.devFiles = getEntrypointFiles(
        entrypoints.get(CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH)
      ).filter((file) => !mainFiles.has(file))

      assetMap.ampDevFiles = getEntrypointFiles(
        entrypoints.get(CLIENT_STATIC_FILES_RUNTIME_AMP)
      )

      const systemEntrypoints = new Set([
        CLIENT_STATIC_FILES_RUNTIME_MAIN,
        CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH,
        CLIENT_STATIC_FILES_RUNTIME_AMP,
      ])

      for (const entrypoint of compilation.entrypoints.values()) {
        if (systemEntrypoints.has(entrypoint.name)) continue
        const pagePath = getRouteFromEntrypoint(entrypoint.name)

        if (!pagePath) {
          continue
        }

        const filesForPage = getEntrypointFiles(entrypoint)

        assetMap.pages[pagePath] = [...new Set([...mainFiles, ...filesForPage])]
      }

      if (!this.isDevFallback) {
        // Add the runtime build manifest file (generated later in this file)
        // as a dependency for the app. If the flag is false, the file won't be
        // downloaded by the client.
        assetMap.lowPriorityFiles.push(
          `${CLIENT_STATIC_FILES_PATH}/${this.buildId}/_buildManifest.js`
        )
        // Add the runtime ssg manifest file as a lazy-loaded file dependency.
        // We also stub this file out for development mode (when it is not
        // generated).
        const srcEmptySsgManifest = `self.__SSG_MANIFEST=new Set;self.__SSG_MANIFEST_CB&&self.__SSG_MANIFEST_CB()`

        const ssgManifestPath = `${CLIENT_STATIC_FILES_PATH}/${this.buildId}/_ssgManifest.js`
        assetMap.lowPriorityFiles.push(ssgManifestPath)
        assets[ssgManifestPath] = new sources.RawSource(srcEmptySsgManifest)
      }

      assetMap.pages = Object.keys(assetMap.pages)
        .sort()
        // eslint-disable-next-line
        .reduce((a, c) => ((a[c] = assetMap.pages[c]), a), {} as any)

      let buildManifestName = BUILD_MANIFEST

      if (this.isDevFallback) {
        buildManifestName = `fallback-${BUILD_MANIFEST}`
      }

      assets[buildManifestName] = new sources.RawSource(
        JSON.stringify(assetMap, null, 2)
      )

      if (!this.isDevFallback) {
        const clientManifestPath = `${CLIENT_STATIC_FILES_PATH}/${this.buildId}/_buildManifest.js`

        assets[clientManifestPath] = new sources.RawSource(
          `self.__BUILD_MANIFEST = ${generateClientManifest(
            compiler,
            compilation,
            assetMap,
            this.rewrites
          )};self.__BUILD_MANIFEST_CB && self.__BUILD_MANIFEST_CB()`
        )
      }

      return assets
    })
  }

  apply(compiler: webpack.Compiler) {
    compiler.hooks.make.tap('NextJsBuildManifest', (compilation) => {
      // @ts-ignore TODO: Remove ignore when webpack 5 is stable
      compilation.hooks.processAssets.tap(
        {
          name: 'NextJsBuildManifest',
          // @ts-ignore TODO: Remove ignore when webpack 5 is stable
          stage: webpack.Compilation.PROCESS_ASSETS_STAGE_ADDITIONS,
        },
        (assets: any) => {
          this.createAssets(compiler, compilation, assets)
        }
      )
    })
    return
  }
}