fix(41456): check src/app folder too in getHasAppDir (#41458)

fixes #41456

When we check if app folder exists, check for src/app path too

## Bug

- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Co-authored-by: Jiachi Liu <inbox@huozhi.im>
Co-authored-by: JJ Kasper <jj@jjsweb.site>

packages/next/lib/find-pages-dir.ts

@@ -10,7 +10,7 @@ export const existsSync = (f: string): boolean => {
   }
 }
 
-function findDir(dir: string, name: 'pages' | 'app'): string | null {
+export function findDir(dir: string, name: 'pages' | 'app'): string | null {
   // prioritize ./${name} over ./src/${name}
   let curDir = path.join(dir, name)
   if (existsSync(curDir)) return curDir

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

@@ -305,7 +305,9 @@ export default class DevServer extends Server {
         ignored: (pathname: string) => {
           return (
             !files.some((file) => file.startsWith(pathname)) &&
-            !directories.some((dir) => pathname.startsWith(dir))
+            !directories.some(
+              (dir) => pathname.startsWith(dir) || dir.startsWith(pathname)
+            )
           )
         },
       }))

packages/next/server/next-server.ts

@@ -48,6 +48,7 @@ import {
   FONT_LOADER_MANIFEST,
 } from '../shared/lib/constants'
 import { recursiveReadDirSync } from './lib/recursive-readdir-sync'
+import { findDir } from '../lib/find-pages-dir'
 import { format as formatUrl, UrlWithParsedQuery } from 'url'
 import compression from 'next/dist/compiled/compression'
 import { getPathMatch } from '../shared/lib/router/utils/path-match'
@@ -474,15 +475,7 @@ export default class NextNodeServer extends BaseServer {
   }
 
   protected getHasAppDir(dev: boolean): boolean {
-    const appDirectory = dev
-      ? join(this.dir, 'app')
-      : join(this.serverDistDir, 'app')
-
-    try {
-      return fs.statSync(appDirectory).isDirectory()
-    } catch (err) {
-      return false
-    }
+    return Boolean(findDir(dev ? this.dir : this.serverDistDir, 'app'))
   }
 
   protected generateStaticRoutes(): Route[] {