Fixes serverless target in development (#7619)

packages/next-server/server/next-server.ts

@@ -326,7 +326,8 @@ export default class Server {
     return getPagePath(
       pathname,
       this.distDir,
-      this.nextConfig.target === 'serverless'
+      this.nextConfig.target === 'serverless',
+      this.renderOpts.dev
     )
   }
 

packages/next-server/server/require.ts

@@ -19,11 +19,12 @@ export function pageNotFoundError(page: string): Error {
 export function getPagePath(
   page: string,
   distDir: string,
-  serverless: boolean
+  serverless: boolean,
+  dev?: boolean
 ): string {
   const serverBuildPath = join(
     distDir,
-    serverless ? SERVERLESS_DIRECTORY : SERVER_DIRECTORY
+    serverless && !dev ? SERVERLESS_DIRECTORY : SERVER_DIRECTORY
   )
   const pagesManifest = require(join(serverBuildPath, PAGES_MANIFEST))
 

test/integration/api-support/next.config.js

+module.exports = {
+  target: 'serverless'
+}