Remove deprecation for relative URL usage in middlewares

Author: Schniz

errors/middleware-relative-urls.md

@@ -2,11 +2,11 @@
 
 #### Why This Error Occurred
 
-You are using a Middleware function that uses `Response.redirect(url)`, `NextResponse.redirect(url)` or `NextResponse.rewrite(url)` where `url` is a relative or an invalid URL. Currently this will work, but building a request with `new Request(url)` or running `fetch(url)` when `url` is a relative URL will **not** work. For this reason and to bring consistency to Next.js Middleware, this behavior will be deprecated soon in favor of always using absolute URLs.
+You are using a Middleware function that uses `Response.redirect(url)`, `NextResponse.redirect(url)` or `NextResponse.rewrite(url)` where `url` is a relative or an invalid URL. Prior to Next.js 12.1, we allowed passing relative URLs. However, constructing a request with `new Request(url)` or running `fetch(url)` when `url` is a relative URL **does not** work. For this reason and to bring consistency to Next.js Middleware, this behavior has been deprecated and now removed.
 
 #### Possible Ways to Fix It
 
-To fix this warning you must always pass absolute URL for redirecting and rewriting. There are several ways to get the absolute URL but the recommended way is to clone `NextURL` and mutate it:
+To fix this error you must always pass absolute URL for redirecting and rewriting. There are several ways to get the absolute URL but the recommended way is to clone `NextURL` and mutate it:
 
 ```typescript
 import type { NextRequest } from 'next/server'

packages/next/server/web/utils.ts

@@ -149,18 +149,13 @@ export function splitCookiesString(cookiesString: string) {
 }
 
 /**
- * We will be soon deprecating the usage of relative URLs in Middleware introducing
- * URL validation. This helper puts the future code in place and prints a warning
- * for cases where it will break. Meanwhile we preserve the previous behavior.
+ * Validate the correctness of a user-provided URL.
  */
 export function validateURL(url: string | URL): string {
   try {
     return String(new URL(String(url)))
   } catch (error: any) {
-    console.log(
-      `warn  -`,
-      'using relative URLs for Middleware will be deprecated soon - https://nextjs.org/docs/messages/middleware-relative-urls'
-    )
-    return String(url)
+    error.message = `URLs is malformed. Please use only absolute URLs - https://nextjs.org/docs/messages/middleware-relative-urls\n${error.message}`
+    throw error
   }
 }