[turbopack]: Serve _devMiddlewareManifest.json from router (#50241)

This change allows the Turbopack's node router to serve
`_next/static/development/_devMiddlewareManifest.json` file, which is
just the matchers for middleware routes. This is usually handled by the
node dev server anyways, but we were filtering out the route so that
Turbopack could handle it.

But, Turbopack doesn't implement the route matching logic at all, it's
all handled by our node router. So Turbopack can't know what the
middleware matchers are. Having the router just handle this like the
normal dev server is both easy and efficient (I don't want to spin up
_another_ node instance just to transform the matchers into the expected
format).

Fixes WEB-979

---------

Co-authored-by: JJ Kasper <jj@jjsweb.site>

packages/next-swc/crates/next-core/js/src/entry/router.ts

@@ -15,6 +15,10 @@ import 'next/dist/server/node-polyfill-fetch.js'
 import middlewareChunkGroup from 'MIDDLEWARE_CHUNK_GROUP'
 import middlewareConfig from 'MIDDLEWARE_CONFIG'
 
+type Resolver = Awaited<
+  ReturnType<typeof import('next/dist/server/lib/route-resolver').makeResolver>
+>
+
 type RouterRequest = {
   method: string
   pathname: string
@@ -51,16 +55,12 @@ type MiddlewareHeadersResponse = {
   headers: [string, string][]
 }
 
-let resolveRouteMemo: Promise<
-  (req: IncomingMessage, res: ServerResponse) => Promise<void>
->
+let resolveRouteMemo: Promise<Resolver>
 
 async function getResolveRoute(
   dir: string,
   serverInfo: ServerInfo
-): ReturnType<
-  typeof import('next/dist/server/lib/route-resolver').makeResolver
-> {
+): Promise<Resolver> {
   const nextConfig = await loadConfig(
     PHASE_DEVELOPMENT_SERVER,
     process.cwd(),

packages/next-swc/crates/next-core/js/src/internal/shims-client.ts

@@ -17,6 +17,3 @@ globalThis.__webpack_require__ = (name) => {
 
 // initialize() needs `__webpack_public_path__` to be defined.
 globalThis.__webpack_public_path__ = undefined
-
-// Avoids Next loading _next/static/[buildId]/_devMiddlewareManifest.json
-globalThis.__DEV_MIDDLEWARE_MATCHERS = []

packages/next-swc/crates/next-core/src/manifest.rs

@@ -174,7 +174,11 @@ impl ContentSource for DevManifestContentSource {
                 File::from(build_manifest.as_str()).with_content_type(APPLICATION_JAVASCRIPT_UTF_8)
             }
             "_next/static/development/_devMiddlewareManifest.json" => {
-                // empty middleware manifest
+                // If there is actual middleware, this request will have been handled by the
+                // node router in next-core/js/src/entry/router.ts and
+                // next/src/server/lib/route-resolver.ts.
+                // If we've reached this point, then there is no middleware and we need to
+                // respond with an empty `MiddlewareMatcher[]`.
                 File::from("[]").with_content_type(APPLICATION_JSON)
             }
             _ => return Ok(ContentSourceResultVc::not_found()),

packages/next/src/server/lib/route-resolver.ts

@@ -16,7 +16,7 @@ import { getMiddlewareMatchers } from '../../build/analysis/get-page-static-info
 import { getMiddlewareRouteMatcher } from '../../shared/lib/router/utils/middleware-route-matcher'
 import {
   CLIENT_STATIC_FILES_PATH,
-  DEV_CLIENT_PAGES_MANIFEST,
+  DEV_MIDDLEWARE_MANIFEST,
 } from '../../shared/lib/constants'
 import type { BaseNextRequest } from '../base-http'
 
@@ -193,20 +193,6 @@ export async function makeResolver(
   // @ts-expect-error protected
   const buildId = devServer.buildId
 
-  const pagesManifestRoute = routes.fsRoutes.find(
-    (r) =>
-      r.name ===
-      `_next/${CLIENT_STATIC_FILES_PATH}/${buildId}/${DEV_CLIENT_PAGES_MANIFEST}`
-  )
-  if (pagesManifestRoute) {
-    // make sure turbopack serves this
-    pagesManifestRoute.fn = () => {
-      return {
-        finished: true,
-      }
-    }
-  }
-
   const router = new Router({
     ...routes,
     catchAllMiddleware,
@@ -245,6 +231,8 @@ export async function makeResolver(
       route.type === 'header' ||
       route.name === 'catchall route' ||
       route.name === 'middleware catchall' ||
+      route.name ===
+        `_next/${CLIENT_STATIC_FILES_PATH}/${buildId}/${DEV_MIDDLEWARE_MANIFEST}` ||
       route.name?.includes('check')
     )
   })