feat(nextjs)!: Respect user-provided source map generation settings (#14956)

- Enables `deleteSourceMapsAfterUpload` by default if unset
- Modifies the webpack sourcemap config if no explicit value is set

closes #14905

---------

Co-authored-by: Luca Forstner <luca.forstner@sentry.io>

Author: chargome

docs/migration/v8-to-v9.md

@@ -100,6 +100,10 @@ In v9, an `undefined` value will be treated the same as if the value is not defi
 
   This behavior was changed because the Next.js Build ID is non-deterministic and the release name is injected into client bundles, causing build artifacts to be non-deterministic. This caused issues for some users. Additionally, because it is uncertain whether it will be possible to rely on a Build ID when Turbopack becomes stable, we decided to pull the plug now instead of introducing confusing behavior in the future.
 
+- Source maps are now automatically enabled for both client and server builds unless explicitly disabled via `sourcemaps.disable`. Client builds use `hidden-source-map` while server builds use `source-map` as their webpack `devtool` setting unless any other value than `false` or `undefined` has been assigned already.
+
+- By default, source maps will now be automatically deleted after being uploaded to Sentry for client-side builds. You can opt out of this behavior by explicitly setting `sourcemaps.deleteSourcemapsAfterUpload` to `false` in your Sentry config.
+
 ### All Meta-Framework SDKs (`@sentry/astro`, `@sentry/nuxt`)
 
 - Updated source map generation to respect the user-provided value of your build config, such as `vite.build.sourcemap`:

packages/nextjs/src/config/webpack.ts

@@ -336,23 +336,36 @@ export function constructWebpackConfigFunction(
 
       if (sentryWebpackPlugin) {
         if (!userSentryOptions.sourcemaps?.disable) {
-          // TODO(v9): Remove this warning and print warning in case source map deletion is auto configured
-          if (!isServer && !userSentryOptions.sourcemaps?.deleteSourcemapsAfterUpload) {
-            // eslint-disable-next-line no-console
-            console.warn(
-              "[@sentry/nextjs] The Sentry SDK has enabled source map generation for your Next.js app. If you don't want to serve Source Maps to your users, either set the `sourcemaps.deleteSourcemapsAfterUpload` option to true, or manually delete the source maps after the build. In future Sentry SDK versions `sourcemaps.deleteSourcemapsAfterUpload` will default to `true`. If you do not want to generate and upload sourcemaps, set the `sourcemaps.disable` option in `withSentryConfig()`.",
-            );
+          // Source maps can be configured in 3 ways:
+          // 1. (next config): productionBrowserSourceMaps
+          // 2. (next config): experimental.serverSourceMaps
+          // 3. custom webpack configuration
+          //
+          // We only update this if no explicit value is set
+          // (Next.js defaults to `false`: https://github.com/vercel/next.js/blob/5f4f96c133bd6b10954812cc2fef6af085b82aa5/packages/next/src/build/webpack/config/blocks/base.ts#L61)
+          if (!newConfig.devtool) {
+            logger.info(`[@sentry/nextjs] Automatically enabling source map generation for ${runtime} build.`);
+            // `hidden-source-map` produces the same sourcemaps as `source-map`, but doesn't include the `sourceMappingURL`
+            // comment at the bottom. For folks who aren't publicly hosting their sourcemaps, this is helpful because then
+            // the browser won't look for them and throw errors into the console when it can't find them. Because this is a
+            // front-end-only problem, and because `sentry-cli` handles sourcemaps more reliably with the comment than
+            // without, the option to use `hidden-source-map` only applies to the client-side build.
+            if (isServer) {
+              newConfig.devtool = 'source-map';
+            } else {
+              newConfig.devtool = 'hidden-source-map';
+            }
           }
 
-          // `hidden-source-map` produces the same sourcemaps as `source-map`, but doesn't include the `sourceMappingURL`
-          // comment at the bottom. For folks who aren't publicly hosting their sourcemaps, this is helpful because then
-          // the browser won't look for them and throw errors into the console when it can't find them. Because this is a
-          // front-end-only problem, and because `sentry-cli` handles sourcemaps more reliably with the comment than
-          // without, the option to use `hidden-source-map` only applies to the client-side build.
-          if (isServer || userNextConfig.productionBrowserSourceMaps) {
-            newConfig.devtool = 'source-map';
-          } else {
-            newConfig.devtool = 'hidden-source-map';
+          // enable source map deletion if not explicitly disabled
+          if (!isServer && userSentryOptions.sourcemaps?.deleteSourcemapsAfterUpload === undefined) {
+            logger.warn(
+              '[@sentry/nextjs] Source maps will be automatically deleted after being uploaded to Sentry. If you want to keep the source maps, set the `sourcemaps.deleteSourcemapsAfterUpload` option to false in `withSentryConfig()`. If you do not want to generate and upload sourcemaps at all, set the `sourcemaps.disable` option to true.',
+            );
+            userSentryOptions.sourcemaps = {
+              ...userSentryOptions.sourcemaps,
+              deleteSourcemapsAfterUpload: true,
+            };
           }
         }
 

packages/nextjs/test/config/webpack/constructWebpackConfig.test.ts

@@ -1,6 +1,7 @@
 // mock helper functions not tested directly in this file
 import '../mocks';
 
+import * as getWebpackPluginOptionsModule from '../../../src/config/webpackPluginOptions';
 import {
   CLIENT_SDK_CONFIG_FILE,
   clientBuildContext,
@@ -29,6 +30,48 @@ describe('constructWebpackConfigFunction()', () => {
     );
   });
 
+  it('preserves existing devtool setting', async () => {
+    const customDevtool = 'eval-source-map';
+    const finalWebpackConfig = await materializeFinalWebpackConfig({
+      exportedNextConfig,
+      incomingWebpackConfig: {
+        ...serverWebpackConfig,
+        devtool: customDevtool,
+      },
+      incomingWebpackBuildContext: serverBuildContext,
+      sentryBuildTimeOptions: {},
+    });
+
+    expect(finalWebpackConfig.devtool).toEqual(customDevtool);
+  });
+
+  it('automatically enables deleteSourcemapsAfterUpload for client builds when not explicitly set', async () => {
+    const getWebpackPluginOptionsSpy = jest.spyOn(getWebpackPluginOptionsModule, 'getWebpackPluginOptions');
+
+    await materializeFinalWebpackConfig({
+      exportedNextConfig,
+      incomingWebpackConfig: clientWebpackConfig,
+      incomingWebpackBuildContext: clientBuildContext,
+      sentryBuildTimeOptions: {
+        sourcemaps: {},
+      },
+    });
+
+    expect(getWebpackPluginOptionsSpy).toHaveBeenCalledWith(
+      expect.objectContaining({
+        isServer: false,
+      }),
+      expect.objectContaining({
+        sourcemaps: {
+          deleteSourcemapsAfterUpload: true,
+        },
+      }),
+      undefined,
+    );
+
+    getWebpackPluginOptionsSpy.mockRestore();
+  });
+
   it('preserves unrelated webpack config options', async () => {
     const finalWebpackConfig = await materializeFinalWebpackConfig({
       exportedNextConfig,