router.push() with rewrites for ISR experiment/feature flags

[matt-halliday]

Summary

We are rolling out variants across our site (Next 15, PageRouter, ISR, OpenNext). This involves a middleware decision using Optimizely, which then adds __variation/flag-a:variation-1 or similar to the end of the URL and returns a NextResponse.rewrite().

This is working well on catchAll routes and simple pages. On more complex interfaces like search, we use router.push to represent the managed state in the URL query. This is a problem and throws an error that routeInfo is undefined because the pathname on the router push is a page that exists... there is a caveat explaining this isn't possible with a shallow push.

Is there a way to handle this?

Additional information

Our directory structure looks like this:


pages
- search
-- index.tsx
-- __variation
--- [variant].tsx

The [variant].tsx page takes the request when there's an experiment running, and the router.push cannot succeed because we're pushing /search and a page for that route exists.

### Example

_No response_