fix: add activation guard for splitApiRoutes

Author: Skn0tt

packages/runtime/src/helpers/flags.ts

@@ -1,4 +1,6 @@
 import destr from 'destr'
+import { existsSync } from 'fs-extra'
+import { join } from 'pathe'
 
 /**
  * If this flag is enabled, we generate individual Lambda functions for API Routes.
@@ -11,7 +13,19 @@ import destr from 'destr'
  * If disabled, we bundle all API Routes into a single function.
  * This is can lead to large bundle sizes.
  *
+ * Relies on `next-server.js.nft.json`, which is only supported in Next.js 12+.
+ *
  * Disabled by default. Can be overriden using the NEXT_SPLIT_API_ROUTES env var.
  */
-export const splitApiRoutes = (featureFlags: Record<string, unknown>): boolean =>
-  destr(process.env.NEXT_SPLIT_API_ROUTES) ?? featureFlags.next_split_api_routes ?? false
+export const splitApiRoutes = (featureFlags: Record<string, unknown>, publish: string): boolean => {
+  const isEnabled = destr(process.env.NEXT_SPLIT_API_ROUTES) ?? featureFlags.next_split_api_routes ?? false
+
+  if (isEnabled && !existsSync(join(publish, 'next-server.js.nft.json'))) {
+    console.warn(
+      'Trace-based bundling not possible on this version of Next.js. Speed up your builds significantly by upgrading to Next.js v12.',
+    )
+    return false
+  }
+
+  return isEnabled
+}

packages/runtime/src/index.ts

@@ -166,7 +166,7 @@ const plugin: NetlifyPlugin = {
 
     const buildId = readFileSync(join(publish, 'BUILD_ID'), 'utf8').trim()
 
-    const apiLambdas: APILambda[] = splitApiRoutes(featureFlags)
+    const apiLambdas: APILambda[] = splitApiRoutes(featureFlags, publish)
       ? await getAPILambdas(publish, appDir, pageExtensions)
       : await getExtendedApiRouteConfigs(publish, appDir, pageExtensions).then((extendedRoutes) =>
           extendedRoutes.map(packSingleFunction),
@@ -180,7 +180,7 @@ const plugin: NetlifyPlugin = {
       ignore,
       publish: relative(process.cwd(), publish),
       apiLambdas,
-      splitApiRoutes: splitApiRoutes(featureFlags),
+      splitApiRoutes: splitApiRoutes(featureFlags, publish),
     })
 
     await movePublicFiles({ appDir, outdir, publish, basePath })