fix: guard split api routes behaviour by next version

packages/runtime/src/helpers/config.ts

@@ -8,7 +8,6 @@ import slash from 'slash'
 
 import { HANDLER_FUNCTION_NAME, IMAGE_FUNCTION_NAME, ODB_FUNCTION_NAME } from '../constants'
 
-import { splitApiRoutes } from './flags'
 import type { APILambda } from './functions'
 import type { RoutesManifest } from './types'
 import { escapeStringRegexp } from './utils'
@@ -102,13 +101,13 @@ export const configureHandlerFunctions = async ({
   publish,
   ignore = [],
   apiLambdas,
-  featureFlags,
+  splitApiRoutes,
 }: {
   netlifyConfig: NetlifyConfig
   publish: string
   ignore: Array<string>
   apiLambdas: APILambda[]
-  featureFlags: Record<string, unknown>
+  splitApiRoutes: boolean
 }) => {
   const config = await getRequiredServerFiles(publish)
   const files = config.files || []
@@ -168,7 +167,7 @@ export const configureHandlerFunctions = async ({
   configureFunction(HANDLER_FUNCTION_NAME)
   configureFunction(ODB_FUNCTION_NAME)
 
-  if (splitApiRoutes(featureFlags)) {
+  if (splitApiRoutes) {
     for (const apiLambda of apiLambdas) {
       const { functionName, includedFiles } = apiLambda
       netlifyConfig.functions[functionName] ||= { included_files: [] }

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 or newer.',
+    )
+    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,
-      featureFlags,
+      splitApiRoutes: splitApiRoutes(featureFlags, publish),
     })
 
     await movePublicFiles({ appDir, outdir, publish, basePath })

test/index.spec.ts

@@ -727,6 +727,16 @@ describe('onBuild()', () => {
     expect(existsSync(publicFile)).toBe(true)
     expect(await readJson(publicFile)).toMatchObject(expect.any(Array))
   })
+
+  it('does not split APIs when .nft.json files are unavailable', async () => {
+    await moveNextDist()
+
+    await unlink(path.join(process.cwd(), '.next', 'next-server.js.nft.json'))
+
+    await nextRuntime.onBuild(defaultArgs)
+
+    expect(netlifyConfig.functions['_api_*'].node_bundler).toEqual('nft')
+  })
 })
 
 describe('onPostBuild', () => {