Avoid pulling extra code in the bundles for trailingSlash logic (#14696)

* avoid pulling code in the bundle for `trailingSlash` logic when it's not enabled
* avoid cloning the url an extra time if normalizing the path doesn't change it

packages/next/build/utils.ts

@@ -24,7 +24,7 @@ import { findPageFile } from '../server/lib/find-page-file'
 import { GetStaticPaths } from 'next/types'
 import { denormalizePagePath } from '../next-server/server/normalize-page-path'
 import { BuildManifest } from '../next-server/server/get-page-files'
-import { normalizeTrailingSlash } from '../next-server/lib/router/normalize-trailing-slash'
+import { removePathTrailingSlash } from '../client/normalize-trailing-slash'
 
 const fileGzipStats: { [k: string]: Promise<number> } = {}
 const fsStatGzip = (file: string) => {
@@ -574,7 +574,7 @@ export async function buildStaticPaths(
     // For a string-provided path, we must make sure it matches the dynamic
     // route.
     if (typeof entry === 'string') {
-      entry = normalizeTrailingSlash(entry)
+      entry = removePathTrailingSlash(entry)
       const result = _routeMatcher(entry)
       if (!result) {
         throw new Error(

packages/next/client/link.tsx

@@ -10,7 +10,7 @@ import {
 } from '../next-server/lib/utils'
 import Router from './router'
 import { addBasePath } from '../next-server/lib/router/router'
-import { normalizeTrailingSlash } from '../next-server/lib/router/normalize-trailing-slash'
+import { normalizeTrailingSlash } from './normalize-trailing-slash'
 
 function isLocal(href: string): boolean {
   const url = parse(href, false, true)
@@ -41,19 +41,11 @@ function memoizedFormatUrl(formatFunc: (href: Url, as?: Url) => FormatResult) {
   }
 }
 
-function formatTrailingSlash(url: UrlObject): UrlObject {
-  return Object.assign({}, url, {
-    pathname:
-      url.pathname &&
-      normalizeTrailingSlash(url.pathname, !!process.env.__NEXT_TRAILING_SLASH),
-  })
-}
-
 function formatUrl(url: Url): string {
   return (
     url &&
     formatWithValidation(
-      formatTrailingSlash(typeof url === 'object' ? url : parse(url))
+      normalizeTrailingSlash(typeof url === 'object' ? url : parse(url))
     )
   )
 }

packages/next/client/normalize-trailing-slash.ts

+import { UrlObject } from 'url'
+
+export function removePathTrailingSlash(path: string): string {
+  return path.endsWith('/') && path !== '/' ? path.slice(0, -1) : path
+}
+
+const normalizePathTrailingSlash = process.env.__NEXT_TRAILING_SLASH
+  ? (path: string): string => {
+      if (/\.[^/]+\/?$/.test(path)) {
+        return removePathTrailingSlash(path)
+      } else if (path.endsWith('/')) {
+        return path
+      } else {
+        return path + '/'
+      }
+    }
+  : removePathTrailingSlash
+
+export function normalizeTrailingSlash(url: UrlObject): UrlObject {
+  const normalizedPath =
+    url.pathname && normalizePathTrailingSlash(url.pathname)
+  return url.pathname === normalizedPath
+    ? url
+    : Object.assign({}, url, { pathname: normalizedPath })
+}

packages/next/next-server/lib/router/normalize-trailing-slash.ts

-export function normalizeTrailingSlash(
-  path: string,
-  requireSlash?: boolean
-): string {
-  if (requireSlash) {
-    if (!path.endsWith('/') && !/\.[^/]+$/.test(path)) {
-      return path + '/'
-    } else if (/\.[^/]+\/$/.test(path)) {
-      return path.slice(0, -1)
-    } else {
-      return path
-    }
-  } else {
-    if (path.endsWith('/') && path !== '/') {
-      return path.slice(0, -1)
-    } else {
-      return path
-    }
-  }
-}

packages/next/next-server/lib/router/router.ts

@@ -15,7 +15,10 @@ import {
 import { isDynamicRoute } from './utils/is-dynamic'
 import { getRouteMatcher } from './utils/route-matcher'
 import { getRouteRegex } from './utils/route-regex'
-import { normalizeTrailingSlash } from './normalize-trailing-slash'
+import {
+  normalizeTrailingSlash,
+  removePathTrailingSlash,
+} from '../../../client/normalize-trailing-slash'
 
 const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 
@@ -37,18 +40,10 @@ function prepareRoute(path: string) {
 
 type Url = UrlObject | string
 
-function formatTrailingSlash(url: UrlObject): UrlObject {
-  return Object.assign({}, url, {
-    pathname:
-      url.pathname &&
-      normalizeTrailingSlash(url.pathname, !!process.env.__NEXT_TRAILING_SLASH),
-  })
-}
-
 function formatUrl(url: Url): string {
   return url
     ? formatWithValidation(
-        formatTrailingSlash(typeof url === 'object' ? url : parse(url))
+        normalizeTrailingSlash(typeof url === 'object' ? url : parse(url))
       )
     : url
 }
@@ -427,7 +422,7 @@ export default class Router implements BaseRouter {
       // point by either next/link or router.push/replace so strip the
       // basePath from the pathname to match the pages dir 1-to-1
       pathname = pathname
-        ? normalizeTrailingSlash(delBasePath(pathname), false)
+        ? removePathTrailingSlash(delBasePath(pathname))
         : pathname
 
       if (!pathname || protocol) {

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

@@ -62,7 +62,7 @@ import { compile as compilePathToRegex } from 'next/dist/compiled/path-to-regexp
 import { loadEnvConfig } from '../../lib/load-env-config'
 import './node-polyfill-fetch'
 import { PagesManifest } from '../../build/webpack/plugins/pages-manifest-plugin'
-import { normalizeTrailingSlash } from '../lib/router/normalize-trailing-slash'
+import { removePathTrailingSlash } from '../../client/normalize-trailing-slash'
 import getRouteFromAssetPath from '../lib/router/utils/get-route-from-asset-path'
 
 const getCustomRouteMatcher = pathMatch(true)
@@ -586,7 +586,7 @@ export default class Server {
         }
 
         // next.js core assumes page path without trailing slash
-        pathname = normalizeTrailingSlash(pathname, false)
+        pathname = removePathTrailingSlash(pathname)
 
         if (params?.path?.[0] === 'api') {
           const handled = await this.handleApiRequest(