index.ts

import {
  BuildOptions,
  Config,
  createLambda,
  debug,
  download,
  FileBlob,
  FileFsRef,
  Files,
  getLambdaOptionsFromFunction,
  getNodeVersion,
  getSpawnOptions,
  glob,
  Lambda,
  PackageJson,
  PrepareCacheOptions,
  Prerender,
  runNpmInstall,
  runPackageJsonScript,
} from '@now/build-utils';
import { Route } from '@now/routing-utils';
import {
  convertRedirects,
  convertRewrites,
} from '@now/routing-utils/dist/superstatic';
import nodeFileTrace, { NodeFileTraceReasons } from '@zeit/node-file-trace';
import { ChildProcess, fork } from 'child_process';
import {
  lstatSync,
  pathExists,
  readFile,
  unlink as unlinkFile,
  writeFile,
} from 'fs-extra';
import os from 'os';
import path from 'path';
import resolveFrom from 'resolve-from';
import semver from 'semver';
import createServerlessConfig from './create-serverless-config';
import nextLegacyVersions from './legacy-versions';
import {
  createLambdaFromPseudoLayers,
  createPseudoLayer,
  EnvConfig,
  excludeFiles,
  ExperimentalTraceVersion,
  getDynamicRoutes,
  getExportIntent,
  getExportStatus,
  getNextConfig,
  getPathsInside,
  getPrerenderManifest,
  getRoutes,
  getRoutesManifest,
  getSourceFilePathFromPage,
  isDynamicRoute,
  normalizePackageJson,
  normalizePage,
  PseudoLayer,
  stringMap,
  syncEnvVars,
  validateEntrypoint,
} from './utils';

interface BuildParamsMeta {
  isDev: boolean | undefined;
  env?: EnvConfig;
  buildEnv?: EnvConfig;
}

interface BuildParamsType extends BuildOptions {
  files: Files;
  entrypoint: string;
  workPath: string;
  meta: BuildParamsMeta;
}

export const version = 2;
const htmlContentType = 'text/html; charset=utf-8';
const nowDevChildProcesses = new Set<ChildProcess>();

['SIGINT', 'SIGTERM'].forEach(signal => {
  process.once(signal as NodeJS.Signals, () => {
    for (const child of nowDevChildProcesses) {
      debug(
        `Got ${signal}, killing dev server child process (pid=${child.pid})`
      );
      process.kill(child.pid, signal);
    }
    process.exit(0);
  });
});

/**
 * Read package.json from files
 */
async function readPackageJson(entryPath: string) {
  const packagePath = path.join(entryPath, 'package.json');

  try {
    return JSON.parse(await readFile(packagePath, 'utf8'));
  } catch (err) {
    debug('package.json not found in entry');
    return {};
  }
}

/**
 * Write package.json
 */
async function writePackageJson(workPath: string, packageJson: PackageJson) {
  await writeFile(
    path.join(workPath, 'package.json'),
    JSON.stringify(packageJson, null, 2)
  );
}

/**
 * Write .npmrc with npm auth token
 */
async function writeNpmRc(workPath: string, token: string) {
  await writeFile(
    path.join(workPath, '.npmrc'),
    `//registry.npmjs.org/:_authToken=${token}`
  );
}

function getNextVersion(packageJson: {
  dependencies?: { [key: string]: string };
  devDependencies?: { [key: string]: string };
}) {
  let nextVersion;
  if (packageJson.dependencies && packageJson.dependencies.next) {
    nextVersion = packageJson.dependencies.next;
  } else if (packageJson.devDependencies && packageJson.devDependencies.next) {
    nextVersion = packageJson.devDependencies.next;
  }
  return nextVersion;
}

function isLegacyNext(nextVersion: string) {
  // If version is using the dist-tag instead of a version range
  if (nextVersion === 'canary' || nextVersion === 'latest') {
    return false;
  }

  // If the version is an exact match with the legacy versions
  if (nextLegacyVersions.indexOf(nextVersion) !== -1) {
    return true;
  }

  const maxSatisfying = semver.maxSatisfying(nextLegacyVersions, nextVersion);
  // When the version can't be matched with legacy versions, so it must be a newer version
  if (maxSatisfying === null) {
    return false;
  }

  return true;
}

const name = '[@now/next]';
const urls: stringMap = {};

function startDevServer(entryPath: string, runtimeEnv: EnvConfig) {
  // `env` is omitted since that makes it default to `process.env`
  const forked = fork(path.join(__dirname, 'dev-server.js'), [], {
    cwd: entryPath,
    execArgv: [],
  });

  const getUrl = () =>
    new Promise<string>((resolve, reject) => {
      forked.once('message', resolve);
      forked.once('error', reject);
    });

  forked.send({ dir: entryPath, runtimeEnv });

  return { forked, getUrl };
}

export const build = async ({
  files,
  workPath,
  entrypoint,
  config = {} as Config,
  meta = {} as BuildParamsMeta,
}: BuildParamsType): Promise<{
  routes: Route[];
  output: Files;
  watch?: string[];
  childProcesses: ChildProcess[];
}> => {
  validateEntrypoint(entrypoint);

  const entryDirectory = path.dirname(entrypoint);
  const entryPath = path.join(workPath, entryDirectory);
  const dotNextStatic = path.join(entryPath, '.next/static');

  await download(files, workPath, meta);

  const pkg = await readPackageJson(entryPath);
  const nextVersion = getNextVersion(pkg);

  const nodeVersion = await getNodeVersion(entryPath, undefined, config);
  const spawnOpts = getSpawnOptions(meta, nodeVersion);

  if (!nextVersion) {
    throw new Error(
      'No Next.js version could be detected in "package.json". Make sure `"next"` is installed in "dependencies" or "devDependencies"'
    );
  }

  if (meta.isDev) {
    let childProcess: ChildProcess | undefined;

    // If this is the initial build, we want to start the server
    if (!urls[entrypoint]) {
      debug(`${name} Installing dependencies...`);
      await runNpmInstall(entryPath, ['--prefer-offline'], spawnOpts, meta);

      if (!process.env.NODE_ENV) {
        process.env.NODE_ENV = 'development';
      }

      // The runtime env vars consist of the base `process.env` vars, but with the
      // build env vars removed, and the runtime env vars mixed in afterwards
      const runtimeEnv: EnvConfig = Object.assign({}, process.env);
      syncEnvVars(runtimeEnv, meta.buildEnv || {}, meta.env || {});

      const { forked, getUrl } = startDevServer(entryPath, runtimeEnv);
      urls[entrypoint] = await getUrl();
      childProcess = forked;
      nowDevChildProcesses.add(forked);
      debug(
        `${name} Development server for ${entrypoint} running at ${urls[entrypoint]}`
      );
    }

    const pathsInside = getPathsInside(entryDirectory, files);

    return {
      output: {},
      routes: await getRoutes(
        entryPath,
        entryDirectory,
        pathsInside,
        files,
        urls[entrypoint]
      ),
      watch: pathsInside,
      childProcesses: childProcess ? [childProcess] : [],
    };
  }

  if (await pathExists(dotNextStatic)) {
    console.warn(
      'WARNING: You should not upload the `.next` directory. See https://zeit.co/docs/v2/deployments/official-builders/next-js-now-next/ for more details.'
    );
  }

  const isLegacy = isLegacyNext(nextVersion);
  let shouldRunScript = 'now-build';

  debug(`MODE: ${isLegacy ? 'legacy' : 'serverless'}`);

  if (isLegacy) {
    try {
      await unlinkFile(path.join(entryPath, 'yarn.lock'));
    } catch (err) {
      debug('no yarn.lock removed');
    }

    try {
      await unlinkFile(path.join(entryPath, 'package-lock.json'));
    } catch (err) {
      debug('no package-lock.json removed');
    }

    console.warn(
      "WARNING: your application is being deployed in @now/next's legacy mode. http://err.sh/zeit/now/now-next-legacy-mode"
    );

    debug('Normalizing package.json');
    const packageJson = normalizePackageJson(pkg);
    debug('Normalized package.json result: ', packageJson);
    await writePackageJson(entryPath, packageJson);
  } else if (pkg.scripts && pkg.scripts['now-build']) {
    debug('Found user `now-build` script');
    shouldRunScript = 'now-build';
  } else if (pkg.scripts && pkg.scripts['build']) {
    debug('Found user `build` script');
    shouldRunScript = 'build';
  } else if (!pkg.scripts || !pkg.scripts['now-build']) {
    debug(
      'Your application is being built using `next build`. ' +
        'If you need to define a different build step, please create a `now-build` script in your `package.json` ' +
        '(e.g. `{ "scripts": { "now-build": "npm run prepare && next build" } }`).'
    );
    pkg.scripts = {
      'now-build': 'next build',
      ...(pkg.scripts || {}),
    };
    shouldRunScript = 'now-build';
    await writePackageJson(entryPath, pkg);
  }

  if (process.env.NPM_AUTH_TOKEN) {
    debug('Found NPM_AUTH_TOKEN in environment, creating .npmrc');
    await writeNpmRc(entryPath, process.env.NPM_AUTH_TOKEN);
  }

  console.log('Installing dependencies...');
  await runNpmInstall(entryPath, ['--prefer-offline'], spawnOpts, meta);

  let realNextVersion: string | undefined;
  try {
    realNextVersion = require(resolveFrom(entryPath, 'next/package.json'))
      .version;

    debug(`Detected Next.js version: ${realNextVersion}`);
  } catch (_ignored) {
    debug(`Could not identify real Next.js version, that's OK!`);
  }

  if (!isLegacy) {
    await createServerlessConfig(workPath, entryPath, realNextVersion);
  }

  debug('Running user script...');
  const memoryToConsume = Math.floor(os.totalmem() / 1024 ** 2) - 128;
  const env: { [key: string]: string | undefined } = { ...spawnOpts.env };
  env.NODE_OPTIONS = `--max_old_space_size=${memoryToConsume}`;
  await runPackageJsonScript(entryPath, shouldRunScript, { ...spawnOpts, env });

  const routesManifest = await getRoutesManifest(entryPath, realNextVersion);
  const rewrites: Route[] = [];
  const redirects: Route[] = [];

  if (routesManifest) {
    switch (routesManifest.version) {
      case 1:
      case 2: {
        redirects.push(...convertRedirects(routesManifest.redirects));
        rewrites.push(...convertRewrites(routesManifest.rewrites));
        break;
      }
      default: {
        // update MIN_ROUTES_MANIFEST_VERSION in ./utils.ts
        throw new Error(
          'This version of `@now/next` does not support the version of Next.js you are trying to deploy.\n' +
            'Please upgrade your `@now/next` builder and try again. Contact support if this continues to happen.'
        );
      }
    }
  }

  const userExport = await getExportStatus(entryPath);

  if (userExport) {
    const exportIntent = await getExportIntent(entryPath);
    const { trailingSlash = false } = exportIntent || {};

    const resultingExport = await getExportStatus(entryPath);
    if (!resultingExport) {
      throw new Error(
        'Exporting Next.js app failed. Please check your build logs and contact us if this continues.'
      );
    }

    if (resultingExport.success !== true) {
      throw new Error(
        'Export of Next.js app failed. Please check your build logs.'
      );
    }

    const outDirectory = resultingExport.outDirectory;

    debug(`next export should use trailing slash: ${trailingSlash}`);

    // This handles pages, `public/`, and `static/`.
    const filesAfterBuild = await glob('**', outDirectory);

    const output: Files = { ...filesAfterBuild };

    // Strip `.html` extensions from build output
    Object.entries(output)
      .filter(([name]) => name.endsWith('.html'))
      .forEach(([name, value]) => {
        const cleanName = name.slice(0, -5);
        delete output[name];
        output[cleanName] = value;
        if (value.type === 'FileBlob' || value.type === 'FileFsRef') {
          value.contentType = value.contentType || 'text/html; charset=utf-8';
        }
      });

    return {
      output,
      routes: [
        // TODO: low priority: handle trailingSlash

        // redirects take the highest priority
        ...redirects,
        // Before we handle static files we need to set proper caching headers
        {
          // This ensures we only match known emitted-by-Next.js files and not
          // user-emitted files which may be missing a hash in their filename.
          src: path.join(
            '/',
            entryDirectory,
            '_next/static/(?:[^/]+/pages|chunks|runtime|css|media)/.+'
          ),
          // Next.js assets contain a hash or entropy in their filenames, so they
          // are guaranteed to be unique and cacheable indefinitely.
          headers: { 'cache-control': 'public,max-age=31536000,immutable' },
          continue: true,
        },
        {
          src: path.join('/', entryDirectory, '_next(?!/data(?:/|$))(?:/.*)?'),
        },
        // Next.js pages, `static/` folder, reserved assets, and `public/`
        // folder
        { handle: 'filesystem' },
        ...rewrites,

        // Dynamic routes
        // TODO: do we want to do this?: ...dynamicRoutes,
      ],
      watch: [],
      childProcesses: [],
    };
  }

  if (isLegacy) {
    debug('Running npm install --production...');
    await runNpmInstall(
      entryPath,
      ['--prefer-offline', '--production'],
      spawnOpts,
      meta
    );
  }

  if (process.env.NPM_AUTH_TOKEN) {
    await unlinkFile(path.join(entryPath, '.npmrc'));
  }

  const lambdas: { [key: string]: Lambda } = {};
  const prerenders: { [key: string]: Prerender | FileFsRef } = {};
  const staticPages: { [key: string]: FileFsRef } = {};
  const dynamicPages: string[] = [];
  const dynamicDataRoutes: Array<{ src: string; dest: string }> = [];

  const appMountPrefixNoTrailingSlash = path.posix
    .join('/', entryDirectory)
    .replace(/\/+$/, '');

  if (isLegacy) {
    const filesAfterBuild = await glob('**', entryPath);

    debug('Preparing serverless function files...');
    let buildId: string;
    try {
      buildId = await readFile(
        path.join(entryPath, '.next', 'BUILD_ID'),
        'utf8'
      );
    } catch (err) {
      console.error(
        'BUILD_ID not found in ".next". The "package.json" "build" script did not run "next build"'
      );
      throw new Error('Missing BUILD_ID');
    }
    const dotNextRootFiles = await glob('.next/*', entryPath);
    const dotNextServerRootFiles = await glob('.next/server/*', entryPath);
    const nodeModules = excludeFiles(
      await glob('node_modules/**', entryPath),
      file => file.startsWith('node_modules/.cache')
    );
    const launcherFiles = {
      'now__bridge.js': new FileFsRef({
        fsPath: path.join(__dirname, 'now__bridge.js'),
      }),
    };
    const nextFiles: { [key: string]: FileFsRef } = {
      ...nodeModules,
      ...dotNextRootFiles,
      ...dotNextServerRootFiles,
      ...launcherFiles,
    };
    if (filesAfterBuild['next.config.js']) {
      nextFiles['next.config.js'] = filesAfterBuild['next.config.js'];
    }
    const pagesDir = path.join(
      entryPath,
      '.next',
      'server',
      'static',
      buildId,
      'pages'
    );
    const pages = await glob('**/*.js', pagesDir);
    const launcherPath = path.join(__dirname, 'legacy-launcher.js');
    const launcherData = await readFile(launcherPath, 'utf8');

    await Promise.all(
      Object.keys(pages).map(async page => {
        // These default pages don't have to be handled as they'd always 404
        if (['_app.js', '_error.js', '_document.js'].includes(page)) {
          return;
        }

        const pathname = page.replace(/\.js$/, '');
        const launcher = launcherData.replace(
          'PATHNAME_PLACEHOLDER',
          `/${pathname.replace(/(^|\/)index$/, '')}`
        );

        const pageFiles = {
          [`.next/server/static/${buildId}/pages/_document.js`]: filesAfterBuild[
            `.next/server/static/${buildId}/pages/_document.js`
          ],
          [`.next/server/static/${buildId}/pages/_app.js`]: filesAfterBuild[
            `.next/server/static/${buildId}/pages/_app.js`
          ],
          [`.next/server/static/${buildId}/pages/_error.js`]: filesAfterBuild[
            `.next/server/static/${buildId}/pages/_error.js`
          ],
          [`.next/server/static/${buildId}/pages/${page}`]: filesAfterBuild[
            `.next/server/static/${buildId}/pages/${page}`
          ],
        };

        const lambdaOptions = await getLambdaOptionsFromFunction({
          sourceFile: await getSourceFilePathFromPage({ workPath, page }),
          config,
        });

        debug(`Creating serverless function for page: "${page}"...`);
        lambdas[path.join(entryDirectory, pathname)] = await createLambda({
          files: {
            ...nextFiles,
            ...pageFiles,
            'now__launcher.js': new FileBlob({ data: launcher }),
          },
          handler: 'now__launcher.launcher',
          runtime: nodeVersion.runtime,
          ...lambdaOptions,
        });
        debug(`Created serverless function for page: "${page}"`);
      })
    );
  } else {
    debug('Preparing serverless function files...');
    const pagesDir = path.join(entryPath, '.next', 'serverless', 'pages');

    const pages = await glob('**/*.js', pagesDir);
    const staticPageFiles = await glob('**/*.html', pagesDir);
    const prerenderManifest = await getPrerenderManifest(entryPath);

    Object.keys(staticPageFiles).forEach((page: string) => {
      const pathname = page.replace(/\.html$/, '');
      const routeName = normalizePage(pathname);

      // Prerendered routes emit a `.html` file but should not be treated as a
      // static page.
      // Lazily prerendered routes do not have a `.html` file so we don't need
      // to check/skip it here.
      if (
        Object.prototype.hasOwnProperty.call(
          prerenderManifest.routes,
          routeName
        )
      ) {
        return;
      }

      const staticRoute = path.join(entryDirectory, pathname);
      staticPages[staticRoute] = staticPageFiles[page];
      staticPages[staticRoute].contentType = htmlContentType;

      if (isDynamicRoute(pathname)) {
        dynamicPages.push(routeName);
        return;
      }
    });

    const pageKeys = Object.keys(pages);

    if (pageKeys.length === 0) {
      const nextConfig = await getNextConfig(workPath, entryPath);

      if (nextConfig != null) {
        console.info('Found next.config.js:');
        console.info(nextConfig);
        console.info();
      }

      throw new Error(
        'No serverless pages were built. https://err.sh/zeit/now/now-next-no-serverless-pages-built'
      );
    }

    // Assume tracing to be safe, bail if we know we don't need it.
    let requiresTracing = true;
    try {
      if (
        realNextVersion &&
        semver.lt(realNextVersion, ExperimentalTraceVersion)
      ) {
        debug(
          'Next.js version is too old for us to trace the required dependencies.\n' +
            'Assuming Next.js has handled it!'
        );
        requiresTracing = false;
      }
    } catch (err) {
      console.log(
        'Failed to check Next.js version for tracing compatibility: ' + err
      );
    }

    let assets:
      | undefined
      | {
          [filePath: string]: FileFsRef;
        };

    const pseudoLayers: PseudoLayer[] = [];
    const apiPseudoLayers: PseudoLayer[] = [];
    const isApiPage = (page: string) =>
      page.replace(/\\/g, '/').match(/serverless\/pages\/api/);

    const tracedFiles: {
      [filePath: string]: FileFsRef;
    } = {};
    const apiTracedFiles: {
      [filePath: string]: FileFsRef;
    } = {};

    if (requiresTracing) {
      const tracingLabel =
        'Traced Next.js serverless functions for external files in';
      console.time(tracingLabel);

      const apiPages: string[] = [];
      const nonApiPages: string[] = [];
      const allPagePaths = Object.keys(pages).map(page => pages[page].fsPath);

      for (const page of allPagePaths) {
        if (isApiPage(page)) {
          apiPages.push(page);
        } else {
          nonApiPages.push(page);
        }
      }

      const {
        fileList: apiFileList,
        reasons: apiReasons,
      } = await nodeFileTrace(apiPages, { base: workPath });

      const { fileList, reasons: nonApiReasons } = await nodeFileTrace(
        Object.keys(pages).map(page => pages[page].fsPath),
        { base: workPath }
      );

      debug(`node-file-trace result for pages: ${fileList}`);

      const collectTracedFiles = (
        reasons: NodeFileTraceReasons,
        files: { [filePath: string]: FileFsRef }
      ) => (file: string) => {
        const reason = reasons[file];
        if (reason && reason.type === 'initial') {
          // Initial files are manually added to the lambda later
          return;
        }
        const { mode } = lstatSync(path.join(workPath, file));

        files[file] = new FileFsRef({
          fsPath: path.join(workPath, file),
          mode,
        });
      };

      fileList.forEach(collectTracedFiles(nonApiReasons, tracedFiles));
      apiFileList.forEach(collectTracedFiles(apiReasons, apiTracedFiles));
      console.timeEnd(tracingLabel);

      const zippingLabel = 'Compressed shared serverless function files';
      console.time(zippingLabel);

      pseudoLayers.push(await createPseudoLayer(tracedFiles));
      apiPseudoLayers.push(await createPseudoLayer(apiTracedFiles));
      console.timeEnd(zippingLabel);
    } else {
      // An optional assets folder that is placed alongside every page
      // entrypoint.
      // This is a legacy feature that was needed before we began tracing
      // lambdas.
      assets = await glob(
        'assets/**',
        path.join(entryPath, '.next', 'serverless')
      );

      const assetKeys = Object.keys(assets);
      if (assetKeys.length > 0) {
        debug(
          'detected (legacy) assets to be bundled with serverless function:'
        );
        assetKeys.forEach(assetFile => debug(`\t${assetFile}`));
        debug(
          '\nPlease upgrade to Next.js 9.1 to leverage modern asset handling.'
        );
      }
    }

    const launcherPath = path.join(__dirname, 'templated-launcher.js');
    const launcherData = await readFile(launcherPath, 'utf8');
    const allLambdasLabel = `All serverless functions created in`;
    console.time(allLambdasLabel);

    await Promise.all(
      pageKeys.map(async page => {
        // These default pages don't have to be handled as they'd always 404
        if (['_app.js', '_document.js'].includes(page)) {
          return;
        }

        const pathname = page.replace(/\.js$/, '');

        if (isDynamicRoute(pathname)) {
          dynamicPages.push(normalizePage(pathname));
        }

        const pageFileName = path.normalize(
          path.relative(workPath, pages[page].fsPath)
        );
        const launcher = launcherData.replace(
          /__LAUNCHER_PAGE_PATH__/g,
          JSON.stringify(requiresTracing ? `./${pageFileName}` : './page')
        );
        const launcherFiles: { [name: string]: FileFsRef | FileBlob } = {
          'now__bridge.js': new FileFsRef({
            fsPath: path.join(__dirname, 'now__bridge.js'),
          }),
          'now__launcher.js': new FileBlob({ data: launcher }),
        };

        const lambdaOptions = await getLambdaOptionsFromFunction({
          sourceFile: await getSourceFilePathFromPage({ workPath, page }),
          config,
        });

        if (requiresTracing) {
          lambdas[
            path.join(entryDirectory, pathname)
          ] = await createLambdaFromPseudoLayers({
            files: {
              ...launcherFiles,
              [requiresTracing ? pageFileName : 'page.js']: pages[page],
            },
            layers: isApiPage(pageFileName) ? apiPseudoLayers : pseudoLayers,
            handler: 'now__launcher.launcher',
            runtime: nodeVersion.runtime,
            ...lambdaOptions,
          });
        } else {
          lambdas[path.join(entryDirectory, pathname)] = await createLambda({
            files: {
              ...launcherFiles,
              ...assets,
              ...tracedFiles,
              [requiresTracing ? pageFileName : 'page.js']: pages[page],
            },
            handler: 'now__launcher.launcher',
            runtime: nodeVersion.runtime,
            ...lambdaOptions,
          });
        }
      })
    );
    console.timeEnd(allLambdasLabel);

    let prerenderGroup = 1;
    const onPrerenderRoute = (routeKey: string, isLazy: boolean) => {
      // Get the route file as it'd be mounted in the builder output
      const routeFileNoExt = routeKey === '/' ? '/index' : routeKey;

      const htmlFsRef = isLazy
        ? null
        : new FileFsRef({
            fsPath: path.join(pagesDir, `${routeFileNoExt}.html`),
          });
      const jsonFsRef = isLazy
        ? null
        : new FileFsRef({
            fsPath: path.join(pagesDir, `${routeFileNoExt}.json`),
          });

      let initialRevalidate: false | number;
      let srcRoute: string | null;
      let dataRoute: string;

      if (isLazy) {
        const pr = prerenderManifest.lazyRoutes[routeKey];
        initialRevalidate = 1; // TODO: should Next.js provide this default?
        // @ts-ignore
        if (initialRevalidate === false) {
          // Lazy routes cannot be "snapshotted" in time.
          throw new Error('invariant isLazy: initialRevalidate !== false');
        }
        srcRoute = null;
        dataRoute = pr.dataRoute;
      } else {
        const pr = prerenderManifest.routes[routeKey];
        ({ initialRevalidate, srcRoute, dataRoute } = pr);
      }

      const outputPathPage = path.posix.join(entryDirectory, routeFileNoExt);
      const outputSrcPathPage =
        srcRoute == null
          ? outputPathPage
          : path.posix.join(
              entryDirectory,
              srcRoute === '/' ? '/index' : srcRoute
            );
      const outputPathData = path.posix.join(entryDirectory, dataRoute);

      if (initialRevalidate === false) {
        if (htmlFsRef == null || jsonFsRef == null) {
          throw new Error('invariant: htmlFsRef != null && jsonFsRef != null');
        }
        htmlFsRef.contentType = htmlContentType;
        prerenders[outputPathPage] = htmlFsRef;
        prerenders[outputPathData] = jsonFsRef;
      } else {
        const lambda = lambdas[outputSrcPathPage];
        if (lambda == null) {
          throw new Error(`Unable to find lambda for route: ${routeFileNoExt}`);
        }

        prerenders[outputPathPage] = new Prerender({
          expiration: initialRevalidate,
          lambda,
          fallback: htmlFsRef,
          group: prerenderGroup,
        });
        prerenders[outputPathData] = new Prerender({
          expiration: initialRevalidate,
          lambda,
          fallback: jsonFsRef,
          group: prerenderGroup,
        });

        ++prerenderGroup;
      }
    };

    Object.keys(prerenderManifest.routes).forEach(route =>
      onPrerenderRoute(route, false)
    );
    Object.keys(prerenderManifest.lazyRoutes).forEach(route =>
      onPrerenderRoute(route, true)
    );

    // Dynamic pages for lazy routes should be handled by the lambda flow.
    Object.keys(prerenderManifest.lazyRoutes).forEach(lazyRoute => {
      const { dataRouteRegex, dataRoute } = prerenderManifest.lazyRoutes[
        lazyRoute
      ];
      dynamicDataRoutes.push({
        // Next.js provided data route regex
        src: dataRouteRegex.replace(/^\^/, `^${appMountPrefixNoTrailingSlash}`),
        // Location of lambda in builder output
        dest: path.posix.join(entryDirectory, dataRoute),
      });
    });
  }

  const nextStaticFiles = await glob(
    '**',
    path.join(entryPath, '.next', 'static')
  );
  const staticFolderFiles = await glob('**', path.join(entryPath, 'static'));
  const publicFolderFiles = await glob('**', path.join(entryPath, 'public'));

  const staticFiles = Object.keys(nextStaticFiles).reduce(
    (mappedFiles, file) => ({
      ...mappedFiles,
      [path.join(entryDirectory, `_next/static/${file}`)]: nextStaticFiles[
        file
      ],
    }),
    {}
  );
  const staticDirectoryFiles = Object.keys(staticFolderFiles).reduce(
    (mappedFiles, file) => ({
      ...mappedFiles,
      [path.join(entryDirectory, 'static', file)]: staticFolderFiles[file],
    }),
    {}
  );
  const publicDirectoryFiles = Object.keys(publicFolderFiles).reduce(
    (mappedFiles, file) => ({
      ...mappedFiles,
      [path.join(
        entryDirectory,
        file.replace(/public[/\\]+/, '')
      )]: publicFolderFiles[file],
    }),
    {}
  );

  let dynamicPrefix = path.join('/', entryDirectory);
  dynamicPrefix = dynamicPrefix === '/' ? '' : dynamicPrefix;

  const dynamicRoutes = await getDynamicRoutes(
    entryPath,
    entryDirectory,
    dynamicPages,
    false,
    routesManifest
  ).then(arr =>
    arr.map(route => {
      route.src = route.src.replace('^', `^${dynamicPrefix}`);
      return route;
    })
  );

  return {
    output: {
      ...publicDirectoryFiles,
      ...lambdas,
      // Prerenders may override Lambdas -- this is an intentional behavior.
      ...prerenders,
      ...staticPages,
      ...staticFiles,
      ...staticDirectoryFiles,
    },
    routes: [
      // redirects take the highest priority
      ...redirects,
      // Before we handle static files we need to set proper caching headers
      {
        // This ensures we only match known emitted-by-Next.js files and not
        // user-emitted files which may be missing a hash in their filename.
        src: path.join(
          '/',
          entryDirectory,
          '_next/static/(?:[^/]+/pages|chunks|runtime|css|media)/.+'
        ),
        // Next.js assets contain a hash or entropy in their filenames, so they
        // are guaranteed to be unique and cacheable indefinitely.
        headers: { 'cache-control': 'public,max-age=31536000,immutable' },
        continue: true,
      },
      { src: path.join('/', entryDirectory, '_next(?!/data(?:/|$))(?:/.*)?') },
      // Next.js page lambdas, `static/` folder, reserved assets, and `public/`
      // folder
      { handle: 'filesystem' },
      ...rewrites,
      // Dynamic routes
      ...dynamicRoutes,
      ...dynamicDataRoutes,
      // Custom Next.js 404 page (TODO: do we want to remove this?)
      ...(isLegacy
        ? []
        : [
            {
              src: path.join('/', entryDirectory, '.*'),
              dest: path.join('/', entryDirectory, '_error'),
              status: 404,
            },
          ]),
    ],
    watch: [],
    childProcesses: [],
  };
};

export const prepareCache = async ({
  workPath,
  entrypoint,
}: PrepareCacheOptions): Promise<Files> => {
  debug('Preparing cache...');
  const entryDirectory = path.dirname(entrypoint);
  const entryPath = path.join(workPath, entryDirectory);

  const pkg = await readPackageJson(entryPath);
  const nextVersion = getNextVersion(pkg);
  if (!nextVersion) throw new Error('Could not parse Next.js version');
  const isLegacy = isLegacyNext(nextVersion);

  if (isLegacy) {
    // skip caching legacy mode (swapping deps between all and production can get bug-prone)
    return {};
  }

  debug('Producing cache file manifest...');
  const cacheEntrypoint = path.relative(workPath, entryPath);
  const cache = {
    ...(await glob(path.join(cacheEntrypoint, 'node_modules/**'), workPath)),
    ...(await glob(path.join(cacheEntrypoint, '.next/cache/**'), workPath)),
  };
  debug('Cache file manifest produced');
  return cache;
};