Fix no-server-import-in-page eslint rule for subfolder middleware (ve…

…rcel#32139)

People have been reporting on vercel#30973 that the `no-server-import-in-page` eslint rule is reporting false positives for `_middleware` files inside sub-page folders.

Unlike `_document`, we can have multiple `_middleware` files.

Fixes vercel#32121

packages/eslint-plugin-next/lib/rules/no-server-import-in-page.js

@@ -21,8 +21,8 @@ module.exports = {
 
         if (
           !page ||
-          page.startsWith(`${path.sep}_middleware`) ||
-          page.startsWith(`${path.posix.sep}_middleware`)
+          page.includes(`${path.sep}_middleware`) ||
+          page.includes(`${path.posix.sep}_middleware`)
         ) {
           return
         }

test/unit/eslint-plugin-next/no-server-import-in-page.test.ts

@@ -78,6 +78,15 @@ ruleTester.run('no-server-import-in-page', rule, {
     `,
       filename: 'pagesapp/src/pages/_middleware.js',
     },
+    {
+      code: `import { NextFetchEvent, NextRequest } from "next/server"
+
+      export function middleware(req, ev) {
+        return new Response('Hello, world!')
+      }
+    `,
+      filename: 'src/pages/subFolder/_middleware.js',
+    },
   ],
   invalid: [
     {