This fixes our check for fallback pages during `next export` as we are currently erroring even when the erroneous pages are not included in the `exportPathMap`. This also adds additional tests to certify the expected behavior for the error.
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [x] Errors have helpful link attached, see `contributing.md`
Fixes: https://github.com/vercel/next.js/issues/29135
By popular request, this pull request adds support for returning `fallback: 'blocking'` from `getStaticPaths`.
This new mode will cause unknown paths to be rendered on-demand ("SSR") without the static (placeholder) fallback.
This feature is **currently experimental and should not be used in production yet**. It's currently flagged behind `unstable_`:
```
fallback: 'unstable_blocking'
```
TODO:
- [x] Next.js tests
- [ ] Add Vercel support
- [ ] Vercel tests
---
Fixes#15637
