False positive in "Could not find a Next.js instrumentation file" (when `pageExtensions` are used in Next)

[kachkaev]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/nextjs

SDK Version

9.5.0

Framework Version

next@15.2.2

Link to Sentry event

No response

Reproduction Example/SDK Setup

Sentry.init({
  dsn: process.env["SENTRY_DSN"] ?? "",
  enabled: Boolean(process.env["SENTRY_DSN"]),
});

Steps to Reproduce

1. Create a Next.js app

2. Open next.config.ts and configure pageExtensions (e.g. pageExtensions: ["page.tsx", "handler.ts"])

3. Create instrumentation.handler.ts or src/instrumentation.handler.ts (if .handler. suffix is specified, the file is ignored by Next.js)

4. Init and configure Sentry

5. Run pnpm dev --turbopack=false

Expected Result

No warnings (because Turbopack is off)

Actual Result

A false-positive warning:

[@sentry/nextjs] Could not find a Next.js instrumentation file. This indicates an incomplete configuration
of the Sentry SDK. An instrumentation file is required for the Sentry SDK to be initialized on the server:
https://docs.sentry.io/platforms/javascript/guides/nextjs/manual-setup/#create-initialization-config-files
(you can suppress this warning by setting SENTRY_SUPPRESS_INSTRUMENTATION_FILE_WARNING=1
as environment variable)

Additional context

The bug originates from #15488:

sentry-javascript/packages/nextjs/src/config/webpack.ts

Lines 452 to 499 in 48ed271

	function warnAboutMissingOnRequestErrorHandler(projectDir: string): void {
	const instrumentationPaths = [
	['src', 'instrumentation.ts'],
	['src', 'instrumentation.js'],
	['instrumentation.ts'],
	['instrumentation.js'],
	];
	const instrumentationFile = instrumentationPaths
	.map(pathSegments => path.resolve(projectDir, ...pathSegments))
	.find(function exists(filePath: string): string | null {
	try {
	fs.accessSync(filePath, fs.constants.F_OK);
	return filePath;
	} catch (error) {
	return null;
	}
	});
	function hasOnRequestErrorHandler(absolutePath: string): boolean {
	try {
	const content = fs.readFileSync(absolutePath, 'utf8');
	return content.includes('onRequestError');
	} catch (error) {
	return false;
	}
	}
	if (!instrumentationFile) {
	if (!process.env.SENTRY_SUPPRESS_INSTRUMENTATION_FILE_WARNING) {
	// eslint-disable-next-line no-console
	console.warn(
	chalk.yellow(
	'[@sentry/nextjs] Could not find a Next.js instrumentation file. This indicates an incomplete configuration of the Sentry SDK. An instrumentation file is required for the Sentry SDK to be initialized on the server: https://docs.sentry.io/platforms/javascript/guides/nextjs/manual-setup/#create-initialization-config-files (you can suppress this warning by setting SENTRY_SUPPRESS_INSTRUMENTATION_FILE_WARNING=1 as environment variable)',
	),
	);
	}
	return;
	}
	if (!hasOnRequestErrorHandler(instrumentationFile)) {
	// eslint-disable-next-line no-console
	console.warn(
	chalk.yellow(
	'[@sentry/nextjs] Could not find `onRequestError` hook in instrumentation file. This indicates outdated configuration of the Sentry SDK. Use `Sentry.captureRequestError` to instrument the `onRequestError` hook: https://docs.sentry.io/platforms/javascript/guides/nextjs/manual-setup/#errors-from-nested-react-server-components',
	),
	);
	}
	}

↑ The list of paths for instrumentation files is hard-coded so custom page extensions are not respected. It seems that the warning does not affect the actual runtime, but I’m not 100% about this.

Good news is that page extensions are already resolved in this file:

sentry-javascript/packages/nextjs/src/config/webpack.ts

Lines 113 to 115 in 48ed271

	// Default page extensions per https://github.com/vercel/next.js/blob/f1dbc9260d48c7995f6c52f8fbcc65f08e627992/packages/next/server/config-shared.ts#L161
	const pageExtensions = userNextConfig.pageExtensions || ['tsx', 'ts', 'jsx', 'js'];
	const dotPrefixedPageExtensions = pageExtensions.map(ext => `.${ext}`);

[andreiborza]

Hi @kachkaev, thanks for filing this.

I opened a PR for this, in the meantime, you can suppress this warning using SENTRY_SUPPRESS_INSTRUMENTATION_FILE_WARNING=1 .

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #15701, which was included in the 9.6.0 release.