Start: "Invalid lazy handler result" when srcDirectory is root

[djgrant]

Which project does this relate to?

Start

Describe the bug

When tsr.srcDirectory is set to . server routes and redirects trigger a nitro error "Invalid lazy handler result".

In browser:

{
  "error": true,
  "url": "http://[::]:3000/",
  "statusCode": 500,
  "statusMessage": "Server Error",
  "message": "Server Error"
}

In server logs:

[request error] [unhandled] [GET] https://5jd49m-3000.csb.app/
 TypeError: Invalid lazy handler result. It should be a function:
    at file:///project/workspace/.output/server/index.mjs:1473:17
    at async Object.handler (file:///project/workspace/.output/server/index.mjs:1557:19)
    at async Server.toNodeHandle (file:///project/workspace/.output/server/index.mjs:1828:7) {
  cause: TypeError: Invalid lazy handler result. It should be a function:
      at file:///project/workspace/.output/server/index.mjs:1473:17
      at async Object.handler (file:///project/workspace/.output/server/index.mjs:1557:19)
      at async Server.toNodeHandle (file:///project/workspace/.output/server/index.mjs:1828:7),
  statusCode: 500,
  fatal: false,
  unhandled: true,
  statusMessage: undefined,
  data: undefined
}

Note: this works ok in dev. It is only triggered by building and running a server (tested with node-server and aws-lambda targets).

Your Example Website or App

https://codesandbox.io/p/github/djgrant/repro-tanstack-start/invalid-lazy-handler

Steps to Reproduce the Bug or Issue

1. Open sandbox
2. Run npm run build
3. Run node .output/server/index.mjs
4. Open preview
5. Observe output

Expected behavior

Server routes should not trigger this error.

Screenshots or Videos

No response

Platform

Any

Additional context

No response

[djgrant]

I was able to work around this issue by adding this to nitro.config.ts:

export default defineNitroConfig({
  // prevent nitro picking up tanstack routes
  // https://github.com/TanStack/router/issues/4432
  apiDir: "non-existent-dir",
  routesDir: "non-existent-dir",
});

This prevents the nitro build from adding tanstack routes to its collection of event handlers.

@schiller-manuel I think this is indirectly caused by this setting https://github.com/TanStack/router/blob/main/packages/start-plugin-core/src/nitro-plugin/plugin.ts#L79. By default, nitro processes file routes in ${baseUrl}/routes, so if your tanstack srcDirectory is ., ./routes becomes a target for both tanstack and nitro.

It might be an idea to add some new defaults like:

{
  apiDir: "nitro/api",
  routesDir: "nitro/routes"
}