Fix resolving href with a rewrite (#16975)

This makes sure we properly resolve a rewrite when only the `href` value is used. This was causing a full-reload and was missed in the existing test since we weren't making sure a full navigation didn't occur which has been added in this PR. 

Fixes: https://github.com/vercel/next.js/issues/16974

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

@@ -609,7 +609,7 @@ export default class Router implements BaseRouter {
       method = 'replaceState'
     }
 
-    const route = removePathTrailingSlash(pathname)
+    let route = removePathTrailingSlash(pathname)
     const { shallow = false } = options
 
     // we need to resolve the as value using rewrites for dynamic SSG
@@ -625,6 +625,25 @@ export default class Router implements BaseRouter {
         query,
         (p: string) => this._resolveHref({ pathname: p }, pages).pathname!
       )
+
+      if (resolvedAs !== as) {
+        const potentialHref = removePathTrailingSlash(
+          this._resolveHref(
+            Object.assign({}, parsed, { pathname: resolvedAs }),
+            pages,
+            false
+          ).pathname!
+        )
+
+        // if this directly matches a page we need to update the href to
+        // allow the correct page chunk to be loaded
+        if (pages.includes(potentialHref)) {
+          route = potentialHref
+          pathname = potentialHref
+          parsed.pathname = pathname
+          url = formatWithValidation(parsed)
+        }
+      }
     }
     resolvedAs = delBasePath(resolvedAs)
 
@@ -980,10 +999,10 @@ export default class Router implements BaseRouter {
     return this.asPath !== asPath
   }
 
-  _resolveHref(parsedHref: UrlObject, pages: string[]) {
+  _resolveHref(parsedHref: UrlObject, pages: string[], applyBasePath = true) {
     const { pathname } = parsedHref
     const cleanPathname = removePathTrailingSlash(
-      denormalizePagePath(delBasePath(pathname!))
+      denormalizePagePath(applyBasePath ? delBasePath(pathname!) : pathname!)
     )
 
     if (cleanPathname === '/404' || cleanPathname === '/_error') {
@@ -998,7 +1017,7 @@ export default class Router implements BaseRouter {
           isDynamicRoute(page) &&
           getRouteRegex(page).re.test(cleanPathname!)
         ) {
-          parsedHref.pathname = addBasePath(page)
+          parsedHref.pathname = applyBasePath ? addBasePath(page) : page
           return true
         }
       })

packages/next/next-server/lib/router/utils/resolve-rewrites.ts

@@ -2,6 +2,7 @@ import { ParsedUrlQuery } from 'querystring'
 import pathMatch from './path-match'
 import prepareDestination from './prepare-destination'
 import { Rewrite } from '../../../../lib/load-custom-routes'
+import { removePathTrailingSlash } from '../../../../client/normalize-trailing-slash'
 
 const customRouteMatcher = pathMatch(true)
 
@@ -33,7 +34,7 @@ export default function resolveRewrites(
         asPath = destRes.parsedDestination.pathname!
         Object.assign(query, destRes.parsedDestination.query)
 
-        if (pages.includes(asPath)) {
+        if (pages.includes(removePathTrailingSlash(asPath))) {
           // check if we now match a page as this means we are done
           // resolving the rewrites
           break

test/integration/custom-routes/pages/auto-export/[slug].js

 import { useRouter } from 'next/router'
 
 export default function Page() {
-  return `auto-export ${useRouter().query.slug}`
+  return <p id="auto-export">auto-export {useRouter().query.slug}</p>
 }

test/integration/custom-routes/pages/nav.js

@@ -28,5 +28,9 @@ export default () => (
       <a id="to-params">to params</a>
     </Link>
     <br />
+    <Link href="/rewriting-to-auto-export">
+      <a id="to-rewritten-dynamic">to rewritten dynamic</a>
+    </Link>
+    <br />
   </>
 )

test/integration/custom-routes/test/index.test.js

@@ -316,11 +316,13 @@ const runTests = (isDev = false) => {
 
   it('should work with rewrite when manually specifying href/as', async () => {
     const browser = await webdriver(appPort, '/nav')
+    await browser.eval('window.beforeNav = 1')
     await browser
       .elementByCss('#to-params-manual')
       .click()
       .waitForElementByCss('#query')
 
+    expect(await browser.eval('window.beforeNav')).toBe(1)
     const query = JSON.parse(await browser.elementByCss('#query').text())
     expect(query).toEqual({
       something: '1',
@@ -330,11 +332,13 @@ const runTests = (isDev = false) => {
 
   it('should work with rewrite when only specifying href', async () => {
     const browser = await webdriver(appPort, '/nav')
+    await browser.eval('window.beforeNav = 1')
     await browser
       .elementByCss('#to-params')
       .click()
       .waitForElementByCss('#query')
 
+    expect(await browser.eval('window.beforeNav')).toBe(1)
     const query = JSON.parse(await browser.elementByCss('#query').text())
     expect(query).toEqual({
       something: '1',
@@ -342,6 +346,20 @@ const runTests = (isDev = false) => {
     })
   })
 
+  it('should work with rewrite when only specifying href and ends in dynamic route', async () => {
+    const browser = await webdriver(appPort, '/nav')
+    await browser.eval('window.beforeNav = 1')
+    await browser
+      .elementByCss('#to-rewritten-dynamic')
+      .click()
+      .waitForElementByCss('#auto-export')
+
+    expect(await browser.eval('window.beforeNav')).toBe(1)
+
+    const text = await browser.eval(() => document.documentElement.innerHTML)
+    expect(text).toContain('auto-export hello')
+  })
+
   it('should match a page after a rewrite', async () => {
     const html = await renderViaHTTP(appPort, '/to-hello')
     expect(html).toContain('Hello')