feat(nextjs): Prepare for next 16 bundler default

dev-packages/e2e-tests/test-applications/nextjs-app-dir/package.json

@@ -4,12 +4,14 @@
   "private": true,
   "scripts": {
     "build": "next build > .tmp_build_stdout 2> .tmp_build_stderr || (cat .tmp_build_stdout && cat .tmp_build_stderr && exit 1)",
+    "build:webpack": "next build --webpack > .tmp_build_stdout 2> .tmp_build_stderr || (cat .tmp_build_stdout && cat .tmp_build_stderr && exit 1)",
     "clean": "npx rimraf node_modules pnpm-lock.yaml",
     "test:prod": "TEST_ENV=production playwright test",
     "test:dev": "TEST_ENV=development playwright test",
+    "test:dev-webpack": "TEST_ENV=development-webpack playwright test",
     "test:build": "pnpm install && pnpm build",
     "test:test-build": "pnpm ts-node --script-mode assert-build.ts",
-    "test:build-canary": "pnpm install && pnpm add next@canary && pnpm add react@beta && pnpm add react-dom@beta && pnpm build",
+    "test:build-canary": "pnpm install && pnpm add next@canary && pnpm add react@latest && pnpm add react-dom@latest && pnpm build:webpack",
     "test:build-latest": "pnpm install && pnpm add next@latest && pnpm build",
     "test:build-13": "pnpm install && pnpm add next@13.5.11 && pnpm build",
     "test:assert": "pnpm test:test-build && pnpm test:prod && pnpm test:dev"
@@ -43,7 +45,8 @@
     "optionalVariants": [
       {
         "build-command": "pnpm test:build-canary",
-        "label": "nextjs-app-dir (canary)"
+        "label": "nextjs-app-dir (canary, webpack opt-in)",
+        "assert-command": "pnpm test:prod"
       },
       {
         "build-command": "pnpm test:build-latest",

dev-packages/e2e-tests/test-applications/nextjs-app-dir/playwright.config.mjs

@@ -5,8 +5,16 @@ if (!testEnv) {
   throw new Error('No test env defined');
 }
 
+const getStartCommand = () => {
+  if (testEnv === 'development-webpack') {
+    return 'pnpm next dev -p 3030 --webpack';
+  }
+
+  return testEnv === 'development' ? 'pnpm next dev -p 3030' : 'pnpm next start -p 3030';
+};
+
 const config = getPlaywrightConfig({
-  startCommand: testEnv === 'development' ? 'pnpm next dev -p 3030' : 'pnpm next start -p 3030',
+  startCommand: getStartCommand(),
   port: 3030,
 });
 

dev-packages/e2e-tests/test-applications/nextjs-app-dir/tests/client-errors.test.ts

@@ -6,7 +6,7 @@ const packageJson = require('../package.json');
 test('Sends a client-side exception to Sentry', async ({ page }) => {
   const nextjsVersion = packageJson.dependencies.next;
   const nextjsMajor = Number(nextjsVersion.split('.')[0]);
-  const isDevMode = process.env.TEST_ENV === 'development';
+  const isDevMode = !!process.env.TEST_ENV && process.env.TEST_ENV.includes('development');
 
   await page.goto('/');
 

dev-packages/e2e-tests/test-applications/nextjs-app-dir/tests/devErrorSymbolification.test.ts

@@ -2,7 +2,8 @@ import { expect, test } from '@playwright/test';
 import { waitForError } from '@sentry-internal/test-utils';
 
 test('should have symbolicated dev errors', async ({ page }) => {
-  test.skip(process.env.TEST_ENV !== 'development', 'should be skipped for non-dev mode');
+  const isDevMode = !!process.env.TEST_ENV && process.env.TEST_ENV.includes('development');
+  test.skip(!isDevMode, 'should be skipped for non-dev mode');
 
   await page.goto('/');
 

dev-packages/e2e-tests/test-applications/nextjs-app-dir/tests/transactions.test.ts

@@ -6,7 +6,7 @@ const packageJson = require('../package.json');
 test('Sends a pageload transaction', async ({ page }) => {
   const nextjsVersion = packageJson.dependencies.next;
   const nextjsMajor = Number(nextjsVersion.split('.')[0]);
-  const isDevMode = process.env.TEST_ENV === 'development';
+  const isDevMode = !!process.env.TEST_ENV && process.env.TEST_ENV.includes('development');
 
   const pageloadTransactionEventPromise = waitForTransaction('nextjs-app-dir', transactionEvent => {
     return transactionEvent?.contexts?.trace?.op === 'pageload' && transactionEvent?.transaction === '/';
@@ -78,8 +78,9 @@ test('Should send a transaction for instrumented server actions', async ({ page
 test('Should send a wrapped server action as a child of a nextjs transaction', async ({ page }) => {
   const nextjsVersion = packageJson.dependencies.next;
   const nextjsMajor = Number(nextjsVersion.split('.')[0]);
+  const isDevMode = !!process.env.TEST_ENV && process.env.TEST_ENV.includes('development');
   test.skip(!isNaN(nextjsMajor) && nextjsMajor < 14, 'only applies to nextjs apps >= version 14');
-  test.skip(process.env.TEST_ENV === 'development', 'this magically only works in production');
+  test.skip(isDevMode, 'this magically only works in production');
 
   const nextjsPostTransactionPromise = waitForTransaction('nextjs-app-dir', async transactionEvent => {
     return (

dev-packages/e2e-tests/test-applications/nextjs-pages-dir/package.json

@@ -4,12 +4,14 @@
   "private": true,
   "scripts": {
     "build": "next build > .tmp_build_stdout 2> .tmp_build_stderr || (cat .tmp_build_stdout && cat .tmp_build_stderr && exit 1)",
+    "build:webpack": "next build --webpack > .tmp_build_stdout 2> .tmp_build_stderr || (cat .tmp_build_stdout && cat .tmp_build_stderr && exit 1)",
     "clean": "npx rimraf node_modules pnpm-lock.yaml",
     "test:prod": "TEST_ENV=production playwright test",
     "test:dev": "TEST_ENV=development playwright test",
+    "test:dev-webpack": "TEST_ENV=development-webpack playwright test",
     "test:build": "pnpm install && pnpm build",
     "test:test-build": "pnpm ts-node --script-mode assert-build.ts",
-    "test:build-canary": "pnpm install && pnpm add next@canary && pnpm add react@beta && pnpm add react-dom@beta && pnpm build",
+    "test:build-canary": "pnpm install && pnpm add next@canary && pnpm add react@latest && pnpm add react-dom@latest && pnpm build:webpack",
     "test:build-latest": "pnpm install && pnpm add next@latest && pnpm add react@latest && pnpm add react-dom@latest && pnpm build",
     "test:build-13": "pnpm install && pnpm add next@13.5.11 && pnpm build",
     "test:assert": "pnpm test:test-build && pnpm test:prod && pnpm test:dev"
@@ -43,7 +45,8 @@
     "optionalVariants": [
       {
         "build-command": "pnpm test:build-canary",
-        "label": "nextjs-pages-dir (canary)"
+        "label": "nextjs-pages-dir (canary, webpack opt-in)",
+        "assert-command": "pnpm test:prod"
       },
       {
         "build-command": "pnpm test:build-latest",

dev-packages/e2e-tests/test-applications/nextjs-pages-dir/playwright.config.mjs

@@ -5,8 +5,16 @@ if (!testEnv) {
   throw new Error('No test env defined');
 }
 
+const getStartCommand = () => {
+  if (testEnv === 'development-webpack') {
+    return 'pnpm next dev -p 3030 --webpack';
+  }
+
+  return testEnv === 'development' ? 'pnpm next dev -p 3030' : 'pnpm next start -p 3030';
+};
+
 const config = getPlaywrightConfig({
-  startCommand: testEnv === 'development' ? 'pnpm next dev -p 3030' : 'pnpm next start -p 3030',
+  startCommand: getStartCommand(),
   port: 3030,
 });
 

dev-packages/e2e-tests/test-applications/nextjs-pages-dir/tests/devErrorSymbolification.test.ts

@@ -2,7 +2,7 @@ import { expect, test } from '@playwright/test';
 import { waitForError } from '@sentry-internal/test-utils';
 
 test('should have symbolicated dev errors', async ({ page }) => {
-  test.skip(process.env.TEST_ENV !== 'development', 'should be skipped for non-dev mode');
+  test.skip(!process.env.TEST_ENV?.includes('development'), 'should be skipped for non-dev mode');
 
   await page.goto('/');
 

dev-packages/e2e-tests/test-applications/nextjs-pages-dir/tests/transactions.test.ts

@@ -1,12 +1,12 @@
 import { expect, test } from '@playwright/test';
-import { waitForError, waitForTransaction } from '@sentry-internal/test-utils';
+import { waitForTransaction } from '@sentry-internal/test-utils';
 
 const packageJson = require('../package.json');
 
 test('Sends a pageload transaction', async ({ page }) => {
   const nextjsVersion = packageJson.dependencies.next;
   const nextjsMajor = Number(nextjsVersion.split('.')[0]);
-  const isDevMode = process.env.TEST_ENV === 'development';
+  const isDevMode = process.env.TEST_ENV?.includes('development');
 
   const pageloadTransactionEventPromise = waitForTransaction('nextjs-pages-dir', transactionEvent => {
     return transactionEvent?.contexts?.trace?.op === 'pageload' && transactionEvent?.transaction === '/';

packages/nextjs/src/config/util.ts

@@ -65,3 +65,68 @@ export function supportsProductionCompileHook(version: string): boolean {
 
   return false;
 }
+
+/**
+ * Checks if the current Next.js version uses Turbopack as the default bundler.
+ * Starting from Next.js 15.6.0-canary.38, turbopack became the default for `next build`.
+ *
+ * @param version - Next.js version string to check.
+ * @returns true if the version uses Turbopack by default
+ */
+export function isTurbopackDefaultForVersion(version: string): boolean {
+  if (!version) {
+    return false;
+  }
+
+  const { major, minor, prerelease } = parseSemver(version);
+
+  if (major === undefined || minor === undefined) {
+    return false;
+  }
+
+  // Next.js 16+ uses turbopack by default
+  if (major >= 16) {
+    return true;
+  }
+
+  // For Next.js 15, only canary versions 15.6.0-canary.40+ use turbopack by default
+  // Stable 15.x releases still use webpack by default
+  if (major === 15 && minor >= 6 && prerelease && prerelease.startsWith('canary.')) {
+    if (minor >= 7) {
+      return true;
+    }
+    const canaryNumber = parseInt(prerelease.split('.')[1] || '0', 10);
+    if (canaryNumber >= 40) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+/**
+ * Determines which bundler is actually being used based on environment variables,
+ * CLI flags, and Next.js version.
+ *
+ * @param nextJsVersion - The Next.js version string
+ * @returns 'turbopack', 'webpack', or undefined if it cannot be determined
+ */
+export function detectActiveBundler(nextJsVersion: string | undefined): 'turbopack' | 'webpack' | undefined {
+  if (process.env.TURBOPACK || process.argv.includes('--turbo')) {
+    return 'turbopack';
+  }
+
+  // Explicit opt-in to webpack via --webpack flag
+  if (process.argv.includes('--webpack')) {
+    return 'webpack';
+  }
+
+  // Fallback to version-based default behavior
+  if (nextJsVersion) {
+    const turbopackIsDefault = isTurbopackDefaultForVersion(nextJsVersion);
+    return turbopackIsDefault ? 'turbopack' : 'webpack';
+  }
+
+  // Unlikely but at this point, we just assume webpack for older behavior
+  return 'webpack';
+}

packages/nextjs/src/config/withSentryConfig.ts

@@ -15,7 +15,7 @@ import type {
   NextConfigObject,
   SentryBuildOptions,
 } from './types';
-import { getNextjsVersion, supportsProductionCompileHook } from './util';
+import { detectActiveBundler, getNextjsVersion, supportsProductionCompileHook } from './util';
 import { constructWebpackConfigFunction } from './webpack';
 
 let showedExportModeTunnelWarning = false;
@@ -258,28 +258,24 @@ function getFinalConfigObject(
     nextMajor = major;
   }
 
-  const isTurbopack = process.env.TURBOPACK;
+  const activeBundler = detectActiveBundler(nextJsVersion);
+  const isTurbopack = activeBundler === 'turbopack';
+  const isWebpack = activeBundler === 'webpack';
   const isTurbopackSupported = supportsProductionCompileHook(nextJsVersion ?? '');
 
+  // Warn if using turbopack with an unsupported Next.js version
   if (!isTurbopackSupported && isTurbopack) {
-    if (process.env.NODE_ENV === 'development') {
-      // eslint-disable-next-line no-console
-      console.warn(
-        `[@sentry/nextjs] WARNING: You are using the Sentry SDK with Turbopack (\`next dev --turbopack\`). The Sentry SDK is compatible with Turbopack on Next.js version 15.4.1 or later. You are currently on ${nextJsVersion}. Please upgrade to a newer Next.js version to use the Sentry SDK with Turbopack.`,
-      );
-    } else if (process.env.NODE_ENV === 'production') {
-      // eslint-disable-next-line no-console
-      console.warn(
-        `[@sentry/nextjs] WARNING: You are using the Sentry SDK with Turbopack (\`next build --turbopack\`). The Sentry SDK is compatible with Turbopack on Next.js version 15.4.1 or later. You are currently on ${nextJsVersion}. Please upgrade to a newer Next.js version to use the Sentry SDK with Turbopack.`,
-      );
-    }
+    // eslint-disable-next-line no-console
+    console.warn(
+      `[@sentry/nextjs] WARNING: You are using the Sentry SDK with Turbopack. The Sentry SDK is compatible with Turbopack on Next.js version 15.4.1 or later. You are currently on ${nextJsVersion}. Please upgrade to a newer Next.js version to use the Sentry SDK with Turbopack.`,
+    );
   }
 
-  // webpack case
+  // Webpack case - warn if trying to use runAfterProductionCompile hook with unsupported Next.js version
   if (
     userSentryOptions.useRunAfterProductionCompileHook &&
     !supportsProductionCompileHook(nextJsVersion ?? '') &&
-    !isTurbopack
+    isWebpack
   ) {
     // eslint-disable-next-line no-console
     console.warn(
@@ -367,17 +363,18 @@ function getFinalConfigObject(
             ],
           },
         }),
-    webpack:
-      isTurbopack || userSentryOptions.disableSentryWebpackConfig
-        ? incomingUserNextConfigObject.webpack // just return the original webpack config
-        : constructWebpackConfigFunction({
+    ...(isWebpack && !userSentryOptions.disableSentryWebpackConfig
+      ? {
+          webpack: constructWebpackConfigFunction({
             userNextConfig: incomingUserNextConfigObject,
             userSentryOptions,
             releaseName,
             routeManifest,
             nextJsVersion,
             useRunAfterProductionCompileHook: shouldUseRunAfterProductionCompileHook,
           }),
+        }
+      : {}),
     ...(isTurbopackSupported && isTurbopack
       ? {
           turbopack: constructTurbopackConfig({