label as Prefetch/Prefetchable depending on prefetch config (#85076)

Tweaks the environment label logic to only use label things as
`Prefetch` if there's a runtime prefetch config. If there's none, we
label it as `Prefetchable` instead.

---------

Co-authored-by: Josh Story <[email protected]>

Author: lubieowoce

packages/next/src/server/app-render/app-render.tsx

@@ -212,6 +212,7 @@ import { createPromiseWithResolvers } from '../../shared/lib/promise-with-resolv
 import { ImageConfigContext } from '../../shared/lib/image-config-context.shared-runtime'
 import { imageConfigDefault } from '../../shared/lib/image-config'
 import { RenderStage, StagedRenderingController } from './staged-rendering'
+import { anySegmentHasRuntimePrefetchEnabled } from './staged-validation'
 
 export type GetDynamicParamFromSegment = (
   // [slug] / [[slug]] / [...slug]
@@ -2767,7 +2768,16 @@ async function renderWithRestartOnCacheMissInDev(
   getPayload: (requestStore: RequestStore) => Promise<RSCPayload>,
   onError: (error: unknown) => void
 ) {
-  const { htmlRequestId, renderOpts, requestId } = ctx
+  const {
+    htmlRequestId,
+    renderOpts,
+    requestId,
+    componentMod: {
+      routeModule: {
+        userland: { loaderTree },
+      },
+    },
+  } = ctx
   const {
     clientReferenceManifest,
     ComponentMod,
@@ -2776,6 +2786,9 @@ async function renderWithRestartOnCacheMissInDev(
   } = renderOpts
   assertClientReferenceManifest(clientReferenceManifest)
 
+  const hasRuntimePrefetch =
+    await anySegmentHasRuntimePrefetchEnabled(loaderTree)
+
   // If the render is restarted, we'll recreate a fresh request store
   let requestStore: RequestStore = initialRequestStore
 
@@ -2785,8 +2798,7 @@ async function renderWithRestartOnCacheMissInDev(
       case RenderStage.Static:
         return 'Prerender'
       case RenderStage.Runtime:
-        // TODO: only label as "Prefetch" if the page has a `prefetch` config.
-        return 'Prefetch'
+        return hasRuntimePrefetch ? 'Prefetch' : 'Prefetchable'
       case RenderStage.Dynamic:
         return 'Server'
       default:

packages/next/src/server/app-render/staged-validation.tsx

@@ -0,0 +1,32 @@
+import { getLayoutOrPageModule } from '../lib/app-dir-module'
+import type { LoaderTree } from '../lib/app-dir-module'
+import { parseLoaderTree } from '../../shared/lib/router/utils/parse-loader-tree'
+import type { AppSegmentConfig } from '../../build/segment-config/app/app-segment-config'
+
+export async function anySegmentHasRuntimePrefetchEnabled(
+  tree: LoaderTree
+): Promise<boolean> {
+  const { mod: layoutOrPageMod } = await getLayoutOrPageModule(tree)
+
+  // TODO(restart-on-cache-miss): Does this work correctly for client page/layout modules?
+  const prefetchConfig = layoutOrPageMod
+    ? (layoutOrPageMod as AppSegmentConfig).unstable_prefetch
+    : undefined
+  /** Whether this segment should use a runtime prefetch instead of a static prefetch. */
+  const hasRuntimePrefetch = prefetchConfig?.mode === 'runtime'
+  if (hasRuntimePrefetch) {
+    return true
+  }
+
+  const { parallelRoutes } = parseLoaderTree(tree)
+  for (const parallelRouteKey in parallelRoutes) {
+    const parallelRoute = parallelRoutes[parallelRouteKey]
+    const hasChildRuntimePrefetch =
+      await anySegmentHasRuntimePrefetchEnabled(parallelRoute)
+    if (hasChildRuntimePrefetch) {
+      return true
+    }
+  }
+
+  return false
+}