Expose TS type for onRequestError

packages/next/src/server/instrumentation/types.ts

@@ -23,3 +23,7 @@ export type InstrumentationModule = {
   register?(): void
   onRequestError?: InstrumentationOnRequestError
 }
+
+export namespace Instrumentation {
+  export type onRequestError = InstrumentationOnRequestError
+}

packages/next/src/types.ts

@@ -38,6 +38,8 @@ export type {
   ResolvedViewport,
 } from './lib/metadata/types/metadata-interface'
 
+export type { Instrumentation } from './server/instrumentation/types'
+
 /**
  * Stub route type for typedRoutes before `next dev` or `next build` is run
  * @link https://nextjs.org/docs/app/building-your-application/configuring/typescript#statically-typed-links

test/e2e/on-request-error/basic/instrumentation.js → test/e2e/on-request-error/basic/instrumentation.ts

@@ -1,8 +1,14 @@
-export function onRequestError(err, request, context) {
+import { type Instrumentation } from 'next'
+
+export const onRequestError: Instrumentation.onRequestError = (
+  err,
+  request,
+  context
+) => {
   fetch(`http://localhost:${process.env.PORT}/write-log`, {
     method: 'POST',
     body: JSON.stringify({
-      message: err.message,
+      message: (err as Error).message,
       request,
       context,
     }),