Prefetching issues with middleware rewriting URL's with base path

[austintreneff]

Looking at the router code here: https://github.com/vercel/next.js/blob/6fd866bfd7d4377f5574aa1710eb89343ffad8bb/packages/next/src/shared/lib/router/router.ts#L2445 I am noticing some differences between my local next start versus what is happening when deployed to Vercel.

Background:

• I am running into some basePath URL rewrite issues that have led me to debugging this area of the router code.
• Locally (via next start), data.json has data (some local props)
• Once deployed (to Vercel), data.json is null
• This causes the getDataHref condition to run which is where things go wrong (my base path is included twice in the new href)

My question:
Why is this code checking for data.json to be truthy before setting the value to data.dataHref
data.dataHref can exist without data.json existing

Should this code instead look something like:

dataHref: data?.dataHref ??
    this.pageLoader.getDataHref({
      href: url,
      asPath: resolvedAs,
      locale: locale,
    }),

I am not sure why we would be checking for data.json when setting the dataHref variables instead of just checking for the data.dataHref and setting it if it exist, else fetch it.

[theodesp]

Hey @austintreneff maybe you could redirect this question to Vercel Devs. I don't think we will be able to shine much light here since this is next.js internals.

[austintreneff]

My apologies, I opened this issue in the wrong tab 🤦 This was meant to be a discussion in the Next.js repository.

Thanks for the quick response!