Summary

• Narrow the return type of the 2-arg rewrite(source, destination) overload from Rewrite | Route to Rewrite
• Narrow the return type of the 2-arg redirect(source, destination) overload from Redirect | Route to Redirect
• Fix the no-transforms code path that incorrectly returned a Route (with src/dest) instead of Rewrite/Redirect (with source/destination) when the destination contained env vars from deploymentEnv()

Bug

Since #15016 made Route.source optional (string | undefined), the union Rewrite | Route is no longer assignable to Rewrite[] in VercelConfig.rewrites, causing a type error on the documented usage pattern:

import { routes, type VercelConfig } from '@vercel/config/v1';

export const config: VercelConfig = {
  rewrites: [
    routes.rewrite('/about', '/about-our-company.html'), // TS2322
  ],
};

Type fix

The 2-arg overloads always produce Rewrite / Redirect at runtime, so the return type is narrowed to match. The callback and options overloads retain Rewrite | Route / Redirect | Route.

Runtime fix

When the destination contained env var references (e.g. deploymentEnv('API_HOST')), the no-transforms code path eagerly converted to Route format (regex src/dest). This meant the returned object had src/dest properties instead of the declared source/destination, which would break if passed to convertRewrites() downstream. Since both Rewrite and Redirect already have an env field, we now return the high-level type directly and let convertRewrites/convertRedirects handle regex conversion.