build-manifest-plugin.ts

import devalue from 'next/dist/compiled/devalue'
import webpack, {
  isWebpack5,
  onWebpackInit,
} from 'next/dist/compiled/webpack/webpack'
// eslint-disable-next-line import/no-extraneous-dependencies
import type { Compiler, compilation as CompilationType } from 'webpack'
import sources from 'webpack-sources'
import {
  BUILD_MANIFEST,
  CLIENT_STATIC_FILES_PATH,
  CLIENT_STATIC_FILES_RUNTIME_MAIN,
  CLIENT_STATIC_FILES_RUNTIME_POLYFILLS,
  CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH,
  CLIENT_STATIC_FILES_RUNTIME_AMP,
} from '../../../next-server/lib/constants'
import { BuildManifest } from '../../../next-server/server/get-page-files'
import getRouteFromEntrypoint from '../../../next-server/server/get-route-from-entrypoint'
import { ampFirstEntryNamesMap } from './next-drop-client-page-plugin'
import { Rewrite } from '../../../lib/load-custom-routes'
import { getSortedRoutes } from '../../../next-server/lib/router/utils'
import { tracer, traceFn } from '../../tracer'

// @ts-ignore: TODO: remove ignore when webpack 5 is stable
let RawSource: typeof sources.RawSource
onWebpackInit(function () {
  ;({ RawSource } = (webpack as any).sources || sources)
})

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(
  assetMap: BuildManifest,
  rewrites: Rewrite[]
): string {
  const span = tracer.startSpan('NextJsBuildManifest-generateClientManifest')
  return traceFn(span, () => {
    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 isJsFile(file: string): boolean {
  // We don't want to include `.hot-update.js` files into the initial page
  return !file.endsWith('.hot-update.js') && file.endsWith('.js')
}

function getFilesArray(files: any) {
  if (!files) {
    return []
  }
  if (isWebpack5) {
    return Array.from(files)
  }

  return files
}

// 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: Rewrite[]

  constructor(options: { buildId: string; rewrites: Rewrite[] }) {
    this.buildId = options.buildId

    this.rewrites = options.rewrites.map((r) => {
      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
    })
  }

  createAssets(compilation: any, assets: any) {
    const span = tracer.startSpan('NextJsBuildManifest-createassets')
    return traceFn(span, () => {
      const namedChunks: Map<string, CompilationType.Chunk> =
        compilation.namedChunks
      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 mainJsChunk = namedChunks.get(CLIENT_STATIC_FILES_RUNTIME_MAIN)

      const mainJsFiles: string[] = getFilesArray(mainJsChunk?.files).filter(
        isJsFile
      )

      const polyfillChunk = namedChunks.get(
        CLIENT_STATIC_FILES_RUNTIME_POLYFILLS
      )

      // Create a separate entry  for polyfills
      assetMap.polyfillFiles = getFilesArray(polyfillChunk?.files).filter(
        isJsFile
      )

      const reactRefreshChunk = namedChunks.get(
        CLIENT_STATIC_FILES_RUNTIME_REACT_REFRESH
      )
      assetMap.devFiles = getFilesArray(reactRefreshChunk?.files).filter(
        isJsFile
      )

      for (const entrypoint of compilation.entrypoints.values()) {
        const isAmpRuntime = entrypoint.name === CLIENT_STATIC_FILES_RUNTIME_AMP

        if (isAmpRuntime) {
          for (const file of entrypoint.getFiles()) {
            if (!(isJsFile(file) || file.endsWith('.css'))) {
              continue
            }

            assetMap.ampDevFiles.push(file.replace(/\\/g, '/'))
          }
          continue
        }
        const pagePath = getRouteFromEntrypoint(entrypoint.name)

        if (!pagePath) {
          continue
        }

        const filesForEntry: string[] = []

        // getFiles() - helper function to read the files for an entrypoint from stats object
        for (const file of entrypoint.getFiles()) {
          if (!(isJsFile(file) || file.endsWith('.css'))) {
            continue
          }

          filesForEntry.push(file.replace(/\\/g, '/'))
        }

        assetMap.pages[pagePath] = [...mainJsFiles, ...filesForEntry]
      }

      // 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 RawSource(srcEmptySsgManifest)

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

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

      const clientManifestPath = `${CLIENT_STATIC_FILES_PATH}/${this.buildId}/_buildManifest.js`

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

      return assets
    })
  }

  apply(compiler: Compiler) {
    if (isWebpack5) {
      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(compilation, assets)
          }
        )
      })
      return
    }

    compiler.hooks.emit.tap('NextJsBuildManifest', (compilation: any) => {
      this.createAssets(compilation, compilation.assets)
    })
  }
}