fix(nextjs): Fix middleware detection logic

packages/nextjs/src/config/loaders/wrappingLoader.ts

@@ -41,8 +41,8 @@ const routeHandlerWrapperTemplatePath = path.resolve(__dirname, '..', 'templates
 const routeHandlerWrapperTemplateCode = fs.readFileSync(routeHandlerWrapperTemplatePath, { encoding: 'utf8' });
 
 export type WrappingLoaderOptions = {
-  pagesDir: string;
-  appDir: string;
+  pagesDir: string | undefined;
+  appDir: string | undefined;
   pageExtensionRegex: string;
   excludeServerRoutes: Array<RegExp | string>;
   wrappingTargetKind: 'page' | 'api-route' | 'middleware' | 'server-component' | 'sentry-init' | 'route-handler';
@@ -101,6 +101,11 @@ export default function wrappingLoader(
       return;
     }
   } else if (wrappingTargetKind === 'page' || wrappingTargetKind === 'api-route') {
+    if (pagesDir === undefined) {
+      this.callback(null, userCode, userModuleSourceMap);
+      return;
+    }
+
     // Get the parameterized route name from this page's filepath
     const parameterizedPagesRoute = path
       // Get the path of the file insde of the pages directory
@@ -137,6 +142,11 @@ export default function wrappingLoader(
     // Inject the route and the path to the file we're wrapping into the template
     templateCode = templateCode.replace(/__ROUTE__/g, parameterizedPagesRoute.replace(/\\/g, '\\\\'));
   } else if (wrappingTargetKind === 'server-component' || wrappingTargetKind === 'route-handler') {
+    if (appDir === undefined) {
+      this.callback(null, userCode, userModuleSourceMap);
+      return;
+    }
+
     // Get the parameterized route name from this page's filepath
     const parameterizedPagesRoute = path
       // Get the path of the file insde of the app directory

packages/nextjs/src/config/webpack.ts

@@ -98,26 +98,31 @@ export function constructWebpackConfigFunction(
       ],
     });
 
-    let pagesDirPath: string;
+    let pagesDirPath: string | undefined;
     const maybePagesDirPath = path.join(projectDir, 'pages');
+    const maybeSrcPagesDirPath = path.join(projectDir, 'src', 'pages');
     if (fs.existsSync(maybePagesDirPath) && fs.lstatSync(maybePagesDirPath).isDirectory()) {
-      pagesDirPath = path.join(projectDir, 'pages');
-    } else {
-      pagesDirPath = path.join(projectDir, 'src', 'pages');
+      pagesDirPath = maybePagesDirPath;
+    } else if (fs.existsSync(maybeSrcPagesDirPath) && fs.lstatSync(maybeSrcPagesDirPath).isDirectory()) {
+      pagesDirPath = maybeSrcPagesDirPath;
     }
 
-    let appDirPath: string;
+    let appDirPath: string | undefined;
     const maybeAppDirPath = path.join(projectDir, 'app');
+    const maybeSrcAppDirPath = path.join(projectDir, 'src', 'app');
     if (fs.existsSync(maybeAppDirPath) && fs.lstatSync(maybeAppDirPath).isDirectory()) {
-      appDirPath = path.join(projectDir, 'app');
-    } else {
-      appDirPath = path.join(projectDir, 'src', 'app');
+      appDirPath = maybeAppDirPath;
+    } else if (fs.existsSync(maybeSrcAppDirPath) && fs.lstatSync(maybeSrcAppDirPath).isDirectory()) {
+      appDirPath = maybeSrcAppDirPath;
     }
 
-    const apiRoutesPath = path.join(pagesDirPath, 'api');
+    const apiRoutesPath = pagesDirPath ? path.join(pagesDirPath, 'api') : undefined;
 
-    const middlewareJsPath = path.join(pagesDirPath, '..', 'middleware.js');
-    const middlewareTsPath = path.join(pagesDirPath, '..', 'middleware.ts');
+    const middlewareLocationFolder = pagesDirPath
+      ? path.join(pagesDirPath, '..')
+      : appDirPath
+      ? path.join(appDirPath, '..')
+      : projectDir;
 
     // Default page extensions per https://github.com/vercel/next.js/blob/f1dbc9260d48c7995f6c52f8fbcc65f08e627992/packages/next/server/config-shared.ts#L161
     const pageExtensions = userNextConfig.pageExtensions || ['tsx', 'ts', 'jsx', 'js'];
@@ -151,6 +156,7 @@ export function constructWebpackConfigFunction(
     const isPageResource = (resourcePath: string): boolean => {
       const normalizedAbsoluteResourcePath = normalizeLoaderResourcePath(resourcePath);
       return (
+        pagesDirPath !== undefined &&
         normalizedAbsoluteResourcePath.startsWith(pagesDirPath + path.sep) &&
         !normalizedAbsoluteResourcePath.startsWith(apiRoutesPath + path.sep) &&
         dotPrefixedPageExtensions.some(ext => normalizedAbsoluteResourcePath.endsWith(ext))
@@ -167,7 +173,10 @@ export function constructWebpackConfigFunction(
 
     const isMiddlewareResource = (resourcePath: string): boolean => {
       const normalizedAbsoluteResourcePath = normalizeLoaderResourcePath(resourcePath);
-      return normalizedAbsoluteResourcePath === middlewareJsPath || normalizedAbsoluteResourcePath === middlewareTsPath;
+      return (
+        normalizedAbsoluteResourcePath.startsWith(middlewareLocationFolder + path.sep) &&
+        !!normalizedAbsoluteResourcePath.match(/[\\/]middleware\.(js|jsx|ts|tsx)$/)
+      );
     };
 
     const isServerComponentResource = (resourcePath: string): boolean => {
@@ -176,6 +185,7 @@ export function constructWebpackConfigFunction(
       // ".js, .jsx, or .tsx file extensions can be used for Pages"
       // https://beta.nextjs.org/docs/routing/pages-and-layouts#pages:~:text=.js%2C%20.jsx%2C%20or%20.tsx%20file%20extensions%20can%20be%20used%20for%20Pages.
       return (
+        appDirPath !== undefined &&
         normalizedAbsoluteResourcePath.startsWith(appDirPath + path.sep) &&
         !!normalizedAbsoluteResourcePath.match(/[\\/](page|layout|loading|head|not-found)\.(js|jsx|tsx)$/)
       );
@@ -184,6 +194,7 @@ export function constructWebpackConfigFunction(
     const isRouteHandlerResource = (resourcePath: string): boolean => {
       const normalizedAbsoluteResourcePath = normalizeLoaderResourcePath(resourcePath);
       return (
+        appDirPath !== undefined &&
         normalizedAbsoluteResourcePath.startsWith(appDirPath + path.sep) &&
         !!normalizedAbsoluteResourcePath.match(/[\\/]route\.(js|jsx|ts|tsx)$/)
       );

packages/nextjs/test/config/loaders.test.ts

@@ -1,6 +1,8 @@
 // mock helper functions not tested directly in this file
 import './mocks';
 
+import * as fs from 'fs';
+
 import type { ModuleRuleUseProperty, WebpackModuleRule } from '../../src/config/types';
 import {
   clientBuildContext,
@@ -11,6 +13,9 @@ import {
 } from './fixtures';
 import { materializeFinalWebpackConfig } from './testUtils';
 
+const existsSyncSpy = jest.spyOn(fs, 'existsSync');
+const lstatSyncSpy = jest.spyOn(fs, 'lstatSync');
+
 type MatcherResult = { pass: boolean; message: () => string };
 
 expect.extend({
@@ -85,6 +90,7 @@ describe('webpack loaders', () => {
       });
     });
 
+    // For these tests we assume that we have an app and pages folder in {rootdir}/src
     it.each([
       {
         resourcePath: '/Users/Maisey/projects/squirrelChasingSimulator/src/pages/testPage.tsx',
@@ -139,8 +145,9 @@ describe('webpack loaders', () => {
         resourcePath: '/Users/Maisey/projects/squirrelChasingSimulator/src/middleware.ts',
         expectedWrappingTargetKind: 'middleware',
       },
+      // Since we assume we have a pages file in src middleware will only be included in the build if it is also in src
       {
-        resourcePath: '/Users/Maisey/projects/squirrelChasingSimulator/src/middleware.tsx',
+        resourcePath: '/Users/Maisey/projects/squirrelChasingSimulator/middleware.tsx',
         expectedWrappingTargetKind: undefined,
       },
       {
@@ -182,6 +189,22 @@ describe('webpack loaders', () => {
     ])(
       'should apply the right wrappingTargetKind with wrapping loader ($resourcePath)',
       async ({ resourcePath, expectedWrappingTargetKind }) => {
+        // We assume that we have an app and pages folder in {rootdir}/src
+        existsSyncSpy.mockImplementation(path => {
+          if (
+            path.toString().startsWith('/Users/Maisey/projects/squirrelChasingSimulator/app') ||
+            path.toString().startsWith('/Users/Maisey/projects/squirrelChasingSimulator/pages')
+          ) {
+            return false;
+          }
+          return true;
+        });
+
+        // @ts-expect-error Too lazy to mock the entire thing
+        lstatSyncSpy.mockImplementation(() => ({
+          isDirectory: () => true,
+        }));
+
         const finalWebpackConfig = await materializeFinalWebpackConfig({
           exportedNextConfig,
           incomingWebpackConfig: serverWebpackConfig,