prevent revalidateTag/Path during render (#71093)

Makes `revalidatePath` and `revalidateTag` throw if called during
render. Revalidating is a side-effecting operation so it should not be
allowed there.

x-ref:
#70642 (comment)

packages/next/src/server/web/spec-extension/revalidate.ts

@@ -60,6 +60,11 @@ function revalidate(tag: string, expression: string) {
         `Route ${store.route} used "${expression}" inside a function cached with "unstable_cache(...)" which is unsupported. To ensure revalidation is performed consistently it must always happen outside of renders and cached functions. See more info here: https://nextjs.org/docs/app/building-your-application/rendering/static-and-dynamic#dynamic-rendering`
       )
     }
+    if (workUnitStore.phase === 'render') {
+      throw new Error(
+        `Route ${store.route} used "${expression}" during render which is unsupported. To ensure revalidation is performed consistently it must always happen outside of renders and cached functions. See more info here: https://nextjs.org/docs/app/building-your-application/rendering/static-and-dynamic#dynamic-rendering`
+      )
+    }
   }
 
   // a route that makes use of revalidation APIs should be considered dynamic

test/e2e/app-dir/revalidatetag-rsc/app/revalidate_via_page/page.tsx

@@ -0,0 +1,24 @@
+'use server'
+
+import Link from 'next/link'
+import { revalidateTag } from 'next/cache'
+
+const RevalidateViaPage = async ({
+  searchParams,
+}: {
+  searchParams: Promise<{ tag: string }>
+}) => {
+  const { tag } = await searchParams
+  revalidateTag(tag)
+
+  return (
+    <div className="flex flex-col items-center justify-center h-screen">
+      <pre>Tag [{tag}] has been revalidated</pre>
+      <Link href="/" id="home">
+        To Home
+      </Link>
+    </div>
+  )
+}
+
+export default RevalidateViaPage

test/e2e/app-dir/revalidatetag-rsc/revalidatetag-rsc.test.ts

@@ -1,8 +1,8 @@
 import { nextTestSetup } from 'e2e-utils'
-import { retry } from 'next-test-utils'
+import { getRedboxHeader, retry } from 'next-test-utils'
 
 describe('revalidateTag-rsc', () => {
-  const { next } = nextTestSetup({
+  const { next, isNextDev, isNextDeploy } = nextTestSetup({
     files: __dirname,
   })
 
@@ -20,4 +20,30 @@ describe('revalidateTag-rsc', () => {
       expect(randomNumber3).not.toEqual(randomNumber)
     })
   })
+
+  if (!isNextDeploy) {
+    // skipped in deploy because it uses `next.cliOutput`
+    it('should error if revalidateTag is called during render', async () => {
+      const browser = await next.browser('/')
+      await browser.elementByCss('#revalidate-via-page').click()
+
+      if (isNextDev) {
+        await retry(async () => {
+          expect(await getRedboxHeader(browser)).toContain(
+            'Route /revalidate_via_page used "revalidateTag data"'
+          )
+        })
+      } else {
+        await retry(async () => {
+          expect(
+            await browser.eval('document.documentElement.innerHTML')
+          ).toContain('Application error: a server-side exception has occurred')
+        })
+      }
+
+      expect(next.cliOutput).toContain(
+        'Route /revalidate_via_page used "revalidateTag data"'
+      )
+    })
+  }
 })