next.js/packages/next/src/build/webpack/loaders/next-app-loader/create-app-route-code.ts

import path from 'path'
import { stringify } from 'querystring'
import { WEBPACK_RESOURCE_QUERIES } from '../../../../lib/constants'
import {
  DEFAULT_METADATA_ROUTE_EXTENSIONS,
  isMetadataRouteFile,
} from '../../../../lib/metadata/is-metadata-route'
import type { NextConfig } from '../../../../server/config-shared'
import { AppBundlePathNormalizer } from '../../../../server/normalizers/built/app/app-bundle-path-normalizer'
import { AppPathnameNormalizer } from '../../../../server/normalizers/built/app/app-pathname-normalizer'
import { loadEntrypoint } from '../../../load-entrypoint'
import type { PageExtensions } from '../../../page-extensions-type'
import { getFilenameAndExtension } from '../next-metadata-route-loader'

export async function createAppRouteCode({
  appDir,
  name,
  page,
  pagePath,
  resolveAppRoute,
  pageExtensions,
  nextConfigOutput,
}: {
  appDir: string
  name: string
  page: string
  pagePath: string
  resolveAppRoute: (
    pathname: string
  ) => Promise<string | undefined> | string | undefined
  pageExtensions: PageExtensions
  nextConfigOutput: NextConfig['output']
}): Promise<string> {
  // routePath is the path to the route handler file,
  // but could be aliased e.g. private-next-app-dir/favicon.ico
  const routePath = pagePath.replace(/[\\/]/, '/')

  // This, when used with the resolver will give us the pathname to the built
  // route handler file.
  let resolvedPagePath = await resolveAppRoute(routePath)
  if (!resolvedPagePath) {
    throw new Error(
      `Invariant: could not resolve page path for ${name} at ${routePath}`
    )
  }

  // If this is a metadata route file, then we need to use the metadata-loader
  // for the route to ensure that the route is generated.
  const fileBaseName = path.parse(resolvedPagePath).name
  const appDirRelativePath = resolvedPagePath.slice(appDir.length)
  const isMetadataEntryFile = isMetadataRouteFile(
    appDirRelativePath,
    DEFAULT_METADATA_ROUTE_EXTENSIONS,
    true
  )
  if (isMetadataEntryFile) {
    const { ext } = getFilenameAndExtension(resolvedPagePath)
    const isDynamicRouteExtension = pageExtensions.includes(ext)

    resolvedPagePath = `next-metadata-route-loader?${stringify({
      filePath: resolvedPagePath,
      isDynamicRouteExtension: isDynamicRouteExtension ? '1' : '0',
    })}!?${WEBPACK_RESOURCE_QUERIES.metadataRoute}`
  }

  const pathname = new AppPathnameNormalizer().normalize(page)
  const bundlePath = new AppBundlePathNormalizer().normalize(page)

  return await loadEntrypoint(
    'app-route',
    {
      VAR_USERLAND: resolvedPagePath,
      VAR_DEFINITION_PAGE: page,
      VAR_DEFINITION_PATHNAME: pathname,
      VAR_DEFINITION_FILENAME: fileBaseName,
      VAR_DEFINITION_BUNDLE_PATH: bundlePath,
      VAR_RESOLVED_PAGE_PATH: resolvedPagePath,
    },
    {
      nextConfigOutput: JSON.stringify(nextConfigOutput),
    }
  )
}