bug: allow scheme-relative url in links

packages/next/shared/lib/router/router.ts

@@ -315,7 +315,7 @@ export function resolveHref(
 
   // repeated slashes and backslashes in the URL are considered
   // invalid and will never match a Next.js page/file
-  const urlProtoMatch = urlAsString.match(/^[a-zA-Z]{1,}:\/\//)
+  const urlProtoMatch = urlAsString.match(/^(?:[a-zA-Z]+:)?\/\//)
   const urlAsStringNoProto = urlProtoMatch
     ? urlAsString.substr(urlProtoMatch[0].length)
     : urlAsString

test/e2e/relative-scheme-url.test.ts

@@ -0,0 +1,49 @@
+import { createNext } from 'e2e-utils'
+import { check } from 'next-test-utils'
+import webdriver from 'next-webdriver'
+import { NextInstance } from 'test/lib/next-modes/base'
+
+describe('should set-up next', () => {
+  let next: NextInstance
+
+  beforeAll(async () => {
+    next = await createNext({
+      files: {
+        'pages/index.js': `
+          import React from 'react'
+          import Link from 'next/link'
+
+          export default function Page() {
+            return (
+              <>
+                <Link href="//example.org">
+                  <a>&#47;&#47;example.org</a>
+                </Link>
+              </>
+            )
+          }
+        `,
+      },
+    })
+  })
+  afterAll(() => next.destroy())
+
+  it('scheme-relative urls should not have the starting // merged', async () => {
+    const browser = await webdriver(next.url, '/')
+
+    await check(
+      async () => {
+        const links = await browser.elementsByCss('a[href]')
+        const link = links[0]
+        const href = await link.getAttribute('href')
+
+        return href === '//example.org'
+      },
+      {
+        test(result) {
+          return result === true
+        },
+      }
+    )
+  })
+})