fix(nextjs): Disable server instrumentation on Vercel (#4255)

On Vercel, the server instrumentation has no effect. Errors and transactions are captured through the [custom `_error.js` page](https://docs.sentry.io/platforms/javascript/guides/nextjs/manual-setup/#create-a-custom-_error-page) and the [`withSentry` handler](https://docs.sentry.io/platforms/javascript/guides/nextjs/#configure). Not instrumenting the server (to not import any modules from `next`) when an app is deployed on Vercel should fix the issue.

packages/nextjs/src/index.server.ts

@@ -6,7 +6,6 @@ import { escapeStringForRegex, logger } from '@sentry/utils';
 import * as domainModule from 'domain';
 import * as path from 'path';
 
-import { instrumentServer } from './utils/instrumentServer';
 import { MetadataBuilder } from './utils/metadataBuilder';
 import { NextjsOptions } from './utils/nextjsOptions';
 import { addIntegration } from './utils/userIntegrations';
@@ -20,6 +19,17 @@ export { ErrorBoundary, withErrorBoundary } from '@sentry/react';
 type GlobalWithDistDir = typeof global & { __rewriteFramesDistDir__: string };
 const domain = domainModule as typeof domainModule & { active: (domainModule.Domain & Carrier) | null };
 
+// During build, the main process is invoked by
+//   `node next build`
+// and child processes are invoked as
+//   `node <path>/node_modules/jest-worker/build/workers/processChild.js`,
+// whereas at runtime the process is invoked as
+//   `node next start`
+// or
+//   `node /var/runtime/index.js`.
+const isBuild = new RegExp('build').test(process.argv.toString());
+const isVercel = !!process.env.VERCEL;
+
 /** Inits the Sentry NextJS SDK on node. */
 export function init(options: NextjsOptions): void {
   if (options.debug) {
@@ -54,7 +64,7 @@ export function init(options: NextjsOptions): void {
 
   configureScope(scope => {
     scope.setTag('runtime', 'node');
-    if (process.env.VERCEL) {
+    if (isVercel) {
       scope.setTag('vercel', true);
     }
 
@@ -119,5 +129,24 @@ function filterTransactions(event: Event): Event | null {
 export { withSentryConfig } from './config';
 export { withSentry } from './utils/withSentry';
 
-// wrap various server methods to enable error monitoring and tracing
-instrumentServer();
+// Wrap various server methods to enable error monitoring and tracing. (Note: This only happens for non-Vercel
+// deployments, because the current method of doing the wrapping a) crashes Next 12 apps deployed to Vercel and
+// b) doesn't work on those apps anyway. We also don't do it during build, because there's no server running in that
+// phase.)
+if (!isVercel && !isBuild) {
+  // Dynamically require the file because even importing from it causes Next 12 to crash on Vercel.
+  // In environments where the JS file doesn't exist, such as testing, import the TS file.
+  try {
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
+    const { instrumentServer } = require('./utils/instrumentServer.js');
+    instrumentServer();
+  } catch {
+    try {
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
+      const { instrumentServer } = require('./utils/instrumentServer.ts');
+      instrumentServer();
+    } catch {
+      // Server not instrumented. Not adding logs to avoid noise.
+    }
+  }
+}

packages/nextjs/test/index.server.test.ts

@@ -24,6 +24,7 @@ describe('Server init()', () => {
   afterEach(() => {
     jest.clearAllMocks();
     global.__SENTRY__.hub = undefined;
+    delete process.env.VERCEL;
   });
 
   it('inits the Node SDK', () => {
@@ -66,18 +67,9 @@ describe('Server init()', () => {
     expect(currentScope._tags).toEqual({ runtime: 'node' });
   });
 
-  it('applies `vercel` tag when running on vercel', () => {
-    const currentScope = getCurrentHub().getScope();
-
-    process.env.VERCEL = '1';
-
-    init({});
-
-    // @ts-ignore need access to protected _tags attribute
-    expect(currentScope._tags.vercel).toEqual(true);
-
-    delete process.env.VERCEL;
-  });
+  // TODO: test `vercel` tag when running on Vercel
+  // Can't just add the test and set env variables, since the value in `index.server.ts`
+  // is resolved when importing.
 
   it('does not apply `vercel` tag when not running on vercel', () => {
     const currentScope = getCurrentHub().getScope();