Prevent storing page props cache when in SSG + preview mode

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

@@ -1511,7 +1511,7 @@ export default class Router implements BaseRouter {
               this.isSsr,
               false,
               __N_SSG ? this.sdc : this.sdr,
-              !!__N_SSG
+              !!__N_SSG && !this.isPreview
             )
           : this.getInitialProps(
               Component,

test/integration/prerender-preview/pages/index.js

@@ -1,24 +1,40 @@
+import { useState } from 'react'
 import { useRouter } from 'next/router'
 
 export function getStaticProps({ preview, previewData }) {
   return {
     props: {
       hasProps: true,
+      random: Math.random(),
       preview: !!preview,
       previewData: previewData || null,
     },
   }
 }
 
-export default function ({ hasProps, preview, previewData }) {
+export default function ({ hasProps, preview, previewData, random }) {
+  const router = useRouter()
+  const [reloaded, setReloaded] = useState(false)
+
   return (
     <>
       <pre id="props-pre">
         {hasProps
           ? JSON.stringify(preview) + ' and ' + JSON.stringify(previewData)
           : 'Has No Props'}
       </pre>
-      <p id="router">{JSON.stringify(useRouter())}</p>
+      <pre id="ssg-random">{random}</pre>
+      {reloaded ? <pre id="ssg-reloaded">Reloaded</pre> : null}
+      <button
+        id="reload-props"
+        onClick={async () => {
+          await router.replace(router.asPath)
+          setReloaded(true)
+        }}
+      >
+        Reload static props
+      </button>
+      <p id="router">{JSON.stringify(router)}</p>
     </>
   )
 }

test/integration/prerender-preview/test/index.test.js

@@ -321,6 +321,24 @@ describe('Prerender Preview Mode', () => {
       )
     })
 
+    it('should fetch live static props with preview active', async () => {
+      await browser.get(`http://localhost:${appPort}/`)
+
+      await browser.waitForElementByCss('#ssg-random')
+      const initialRandom = await browser.elementById('ssg-random').text()
+
+      // reload static props with router.replace
+      await browser.elementById('reload-props').click()
+
+      // wait for route change to complete and set updated state
+      await browser.waitForElementByCss('#ssg-reloaded')
+
+      // assert that the random number from static props has changed (thus, was re-evaluated)
+      expect(await browser.elementById('ssg-random').text()).not.toBe(
+        initialRandom
+      )
+    })
+
     afterAll(async () => {
       await browser.close()
       await killApp(app)