[nextjs] Placing middleware.ts in src directory causes middleware to be ignored #8845

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/nextjs

SDK Version

7.64.0

Framework Version

7.64.0

Link to Sentry event

No response

SDK Setup

Sentry.init({
  dsn: "DSN",
  tracesSampleRate: 1,
  debug: false,
});

Steps to Reproduce

Basically, middleware gets bypassed/ignored when the middleware.(ts|js) file is placed in the src folder, something that is supported according to Next.js documentation.

1. npx create-next-app --example reproduction-template reproduction-app
2. cd reproduction-app
3. npx @sentry/wizard -i nextjs
4. mkdir src
5. mv app src/
6. touch src/middleware.ts
7. Middleware contents:

export function middleware(request) {
throw new Error("This never runs");
}

8. mkdir -p src/app/api/test
9. touch src/app/api/test/route.ts
10. src/app/api/test/route.ts contents:

import { NextResponse } from "next/server";

export function GET() {
  return NextResponse.json(
    {
      success: "middleware not called",
    },
    { status: 200 }
  );
}

11. yarn build && yarn start
12. curl http://localhost:3000/api/test

Expected Result

The curl request never reaches the src/api/test/route.ts route due to middleware throwing an error.
According to Next.js's documentation on middleware conventions the middleware.ts file should be able to be placed in both the root and in the src directory.

Actual Result

The curl request reaches the src/api/test/route.ts route.