Fix canonical rel link generation (#9357)

packages/next/next-server/server/utils.ts

@@ -18,10 +18,10 @@ export function isBlockedPage(pathname: string): boolean {
 
 export function cleanAmpPath(pathname: string): string {
   if (pathname.match(/\?amp=(y|yes|true|1)/)) {
-    pathname = pathname.replace(/\?amp=(y|yes|true|1)/, '?')
+    pathname = pathname.replace(/\?amp=(y|yes|true|1)&?/, '?')
   }
   if (pathname.match(/&amp=(y|yes|true|1)/)) {
-    pathname = pathname.replace(/\?amp=(y|yes|true|1)/, '')
+    pathname = pathname.replace(/&amp=(y|yes|true|1)/, '')
   }
   pathname = pathname.replace(/\?$/, '')
   return pathname

test/unit/next-server-utils.test.js

+/* eslint-env jest */
+import { cleanAmpPath } from 'next/dist/next-server/server/utils'
+
+// convenince function so tests can be alligned neatly
+// and easy to eyeball
+const check = (input, expected) =>
+  expect(cleanAmpPath(input)).toBe(expected)
+
+describe('cleanAmpPath', () => {
+  it('should leave url unchanged when no apm parameter is present', () =>
+    check(
+      '/some/path?param=blah',
+      '/some/path?param=blah'
+    )
+  )
+
+  it('should handle amp as the only parameter', () =>
+    check(
+      '/some/path?amp=1',
+      '/some/path'
+    )
+  )
+
+  it('should handle amp as the first parameter', () =>
+    check(
+      '/some/path?amp=1&page=10',
+      '/some/path?page=10'
+    )
+  )
+
+  it('should handle amp as the middle parameter', () =>
+    check(
+      '/some/path?page=10&amp=1&last=here',
+      '/some/path?page=10&last=here'
+    )
+  )
+
+  it('should handle amp as the last parameter', () =>
+    check(
+      '/some/path?page=10&amp=1',
+      '/some/path?page=10'
+    )
+  )
+})