Handle defaultLocale on client router filter (#47180)

x-ref: [slack
thread](https://vercel.slack.com/archives/C03S8ED1DKM/p1678838567947919)

Follow-up to #46317. The issue is
that, if:

- `experimental.clientRouterFilter` is enabled
- `i18n` is enabled with `defaultLocale` set
- Next.js router navigates to a path that (1) is the same as
`defaultLocale` and (2) will be redirected,

then:

- **Expected:** Should hard-navigate to this path without any locale
prefix (and then redirect occurs)
- **Actual:** Hard-navigates to this path with `defaultLocale` prefix,
even though it's not needed (and then redirect occurrs)

### Solution

This PR fixes the above issue by adding `defaultLocale` to `addLocale`
which is passed to `handleHardNavigation`. [`addLocale` skips adding the
locale if `locale` is equal to
`defaultLocale`](https://github.com/vercel/next.js/blob/02125cf3b1dfba52b240fd6e0f959d896e4b6195/packages/next/src/shared/lib/router/utils/add-locale.ts#L17).

### Fixing a bug

- [x] Related issues linked using `fixes #number`
- [x] Tests added. See:
https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs

Co-authored-by: JJ Kasper <jj@jjsweb.site>

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

@@ -1096,7 +1096,9 @@ export default class Router implements BaseRouter {
             // a hard navigation
             if (matchesBflStatic || matchesBflDynamic) {
               handleHardNavigation({
-                url: addBasePath(addLocale(as, locale || this.locale)),
+                url: addBasePath(
+                  addLocale(as, locale || this.locale, this.defaultLocale)
+                ),
                 router: this,
               })
               return new Promise(() => {})

test/e2e/i18n-default-locale-redirect/app/next.config.js

@@ -0,0 +1,19 @@
+module.exports = {
+  i18n: {
+    locales: ['en', 'nl'],
+    defaultLocale: 'en',
+  },
+  experimental: {
+    clientRouterFilter: true,
+    clientRouterFilterRedirects: true,
+  },
+  redirects() {
+    return [
+      {
+        source: '/to-new',
+        destination: '/new',
+        permanent: false,
+      },
+    ]
+  },
+}

test/e2e/i18n-default-locale-redirect/app/pages/index.js

@@ -0,0 +1,18 @@
+import Link from 'next/link'
+
+export default function Home() {
+  return (
+    <div>
+      <div>
+        <Link href="/to-new" id="to-new">
+          To new (Default Locale)
+        </Link>
+      </div>
+      <div>
+        <Link href="/to-new" id="to-new-nl" locale="nl">
+          To new (NL)
+        </Link>
+      </div>
+    </div>
+  )
+}

test/e2e/i18n-default-locale-redirect/app/pages/new.js

@@ -0,0 +1,3 @@
+export default function New() {
+  return <div id="new">New</div>
+}

test/e2e/i18n-default-locale-redirect/i18n-default-locale-redirect.test.ts

@@ -0,0 +1,44 @@
+import { join } from 'path'
+import { createNextDescribe, FileRef } from 'e2e-utils'
+
+createNextDescribe(
+  'i18-default-locale-redirect',
+  {
+    files: {
+      pages: new FileRef(join(__dirname, './app/pages')),
+      'next.config.js': new FileRef(join(__dirname, './app/next.config.js')),
+    },
+  },
+  ({ next }) => {
+    it('should not request a path prefixed with default locale', async () => {
+      const browser = await next.browser('/')
+      let requestedDefaultLocalePath = false
+      browser.on('request', (request: any) => {
+        if (new URL(request.url(), 'http://n').pathname === '/en/to-new') {
+          requestedDefaultLocalePath = true
+        }
+      })
+
+      await browser.elementByCss('#to-new').click().waitForElementByCss('#new')
+      expect(await browser.elementByCss('#new').text()).toBe('New')
+      expect(requestedDefaultLocalePath).toBe(false)
+    })
+
+    it('should request a path prefixed with non-default locale', async () => {
+      const browser = await next.browser('/')
+      let requestedNonDefaultLocalePath = false
+      browser.on('request', (request: any) => {
+        if (new URL(request.url(), 'http://n').pathname === '/nl/to-new') {
+          requestedNonDefaultLocalePath = true
+        }
+      })
+
+      await browser
+        .elementByCss('#to-new-nl')
+        .click()
+        .waitForElementByCss('#new')
+      expect(await browser.elementByCss('#new').text()).toBe('New')
+      expect(requestedNonDefaultLocalePath).toBe(true)
+    })
+  }
+)

test/lib/browsers/playwright.ts

@@ -37,7 +37,7 @@ export class Playwright extends BrowserInterface {
     if (!this.eventCallbacks[event]) {
       throw new Error(
         `Invalid event passed to browser.on, received ${event}. Valid events are ${Object.keys(
-          event
+          this.eventCallbacks
         )}`
       )
     }