Marks app paths in dev as supporting dynamic html

packages/next/src/server/base-server.ts

@@ -1315,6 +1315,11 @@ export default abstract class Server<ServerOptions extends Options = Options> {
       opts.isBot = isBotRequest
     }
 
+    // In development, we always want to generate dynamic HTML.
+    if (opts.dev && opts.supportsDynamicHTML === false) {
+      opts.supportsDynamicHTML = true
+    }
+
     const defaultLocale = isSSG
       ? this.nextConfig.i18n?.defaultLocale
       : query.__nextDefaultLocale
@@ -1439,7 +1444,8 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     let isRevalidate = false
 
     const doRender: () => Promise<ResponseCacheEntry | null> = async () => {
-      const supportsDynamicHTML = !(isSSG || hasStaticPaths)
+      // In development, we always want to generate dynamic HTML.
+      const supportsDynamicHTML = opts.dev || !(isSSG || hasStaticPaths)
 
       const match =
         pathname !== '/_error' && !is404Page && !is500Page

test/e2e/app-dir/app-static/app-static.test.ts

@@ -724,6 +724,26 @@ createNextDescribe(
       }
     })
 
+    it('should allow dynamic routes to access cookies', async () => {
+      for (const slug of ['books', 'frameworks']) {
+        for (let i = 0; i < 2; i++) {
+          let $ = await next.render$(
+            `/force-dynamic-prerender/${slug}`,
+            {},
+            { headers: { cookie: 'session=value' } }
+          )
+
+          expect($('#slug').text()).toBe(slug)
+          expect($('#cookie-result').text()).toBe('has cookie')
+
+          $ = await next.render$(`/force-dynamic-prerender/${slug}`)
+
+          expect($('#slug').text()).toBe(slug)
+          expect($('#cookie-result').text()).toBe('no cookie')
+        }
+      }
+    })
+
     it('should not error with generateStaticParams and dynamic data', async () => {
       const res = await next.fetch('/gen-params-dynamic/one')
       const html = await res.text()

test/e2e/app-dir/app-static/app/force-dynamic-prerender/[slug]/page.js

@@ -0,0 +1,19 @@
+import { cookies } from 'next/headers'
+
+export const dynamic = 'force-dynamic'
+export const dynamicParams = true
+export const revalidate = 60
+
+export const generateStaticParams = async () => {
+  return [{ slug: 'frameworks' }]
+}
+
+export default function Page({ params }) {
+  const result = cookies().get('session')?.value ? 'has cookie' : 'no cookie'
+  return (
+    <div>
+      <div id="slug">{params.slug}</div>
+      <div id="cookie-result">{result}</div>
+    </div>
+  )
+}