## <a id="prerendering"></a>31. What Gets Prerendered
### Test Evidence: Prerender Manifest
**Test Source**: `test/e2e/app-dir/use-cache/use-cache.test.ts` (lines 444-506)
```typescript
// With cacheComponents: true, the prerender-manifest.json includes:
const prerenderedRoutes = [
"/_not-found",
"/a123", // generateStaticParams entry
"/api", // Route handler with 'use cache'
"/b456", // generateStaticParams entry
"/cache-fetch", // Page with 'use cache'
"/cache-life", // Page with 'use cache' + cacheLife
"/cache-tag", // Page with 'use cache' + cacheTag
"/form", // Page with 'use cache'
// ... more routes
]
// Routes NOT prerendered:
// - Pages with cookies()/headers() and no 'use cache'
// - Pages with searchParams and no 'use cache'
// - Pages with dynamic params not in generateStaticParams
// - Pages with connection() calls
```
### Shell Completeness Test
```typescript
// Test checks if HTML ends with </html>
// COMPLETE SHELL (fully prerendered):
// .next/server/app/cache-life.html ends with "</html>"
// INCOMPLETE SHELL (partial prerender):
// .next/server/app/cache-life-with-dynamic.html does NOT end with "</html>"
// Contains: <div id="y">Loading...</div> (Suspense fallback)
```
---
## <a id="resume-data-cache"></a>32. Resume Data Cache (RDC)
### Test Pattern: What Goes in RDC
**Test Source**: `test/e2e/app-dir/use-cache/use-cache.test.ts` (lines 999-1028)
```typescript
// Test analyzes .next/server/app/rdc.meta file
async function outer(arg: string) {
'use cache'
cacheTag('outer-tag')
const middleValue = await middle(arg) // Inner cache
return middleValue
}
async function middle(arg: string) {
'use cache'
return await inner(arg) // Even more nested
}
async function inner(arg: string) {
'use cache'
return Math.random()
}
async function short(arg: { id: string }) {
'use cache'
cacheLife({ stale: 10, revalidate: 20, expire: 60 })
return Date.now()
}
export default async function Page() {
const outerValue = await outer('outer')
const innerValue = await inner('inner')
const shortValue = await short({ id: 'short' })
return <div>{outerValue} {innerValue} {shortValue}</div>
}
// TEST ASSERTION:
// Resume Data Cache includes:
// - 'outer' cache entry ✅ (called at page level)
// - 'inner' cache entry ✅ (called at page level)
// - 'middle' cache entry ❌ (only called inside 'outer')
// - 'short' cache entry ❌ (expire < 5min, omitted from prerender)
// Rule: Only caches called from prerender scope are in RDC
// Inner caches (only called from other caches) are NOT in RDC
```
---
## <a id="metadata-viewport"></a>34. generateMetadata and generateViewport
### Test Pattern: Cached Metadata
**Test Source**: `test/e2e/app-dir/use-cache/use-cache.test.ts` (lines 1049-1336)
```typescript
// Pattern 1: Shared cache between page and metadata
// lib/data.ts
async function getCachedData() {
'use cache'
return Math.random()
}
// page.tsx
import { getCachedData } from './lib/data'
export async function generateMetadata() {
const data = await getCachedData()
return {
title: String(data),
}
}
export default async function Page() {
const data = await getCachedData()
return <div id="page-data">{data}</div>
}
// TEST BEHAVIOR:
// - document.title === page-data value
// - Both use SAME cached value (cache is shared!)
// Pattern 2: Cached generateMetadata with params
export async function generateMetadata({
params
}: {
params: Promise<{ color: string }>
}) {
'use cache'
const { color } = await params
return {
title: color,
}
}
// TEST BEHAVIOR:
// - With JS disabled: <title> in <head> ✅
// - With JS enabled: document.title matches cached value ✅
// - Refresh: Same title (cached via RDC)
```
---
