ref(nextjs): Stop setting redundant productionBrowserSourceMaps in config (#3765)

Before this change, `withSentryConfig` both set `productionBrowserSourceMaps` to `true` in the main `nextjs` config and set `devtool` to `source-map` in the webpack config. 

It turns out, though, that the only thing the former change does is cause nextjs to make the latter change itself. [1] (All other references to `productionBrowserSourceMaps` in the nextjs code are merely type annotations or instances of passing the value from one function to another. [2] The linked code is the only place that value is actually used.) Therefore, since we're making the `devtool` config change ourselves, the `productionBrowserSourceMaps` config change was redundant, and could be removed.

(Of the two config changes, we wanted to remove this one and not the `devtool` one, since we want sourcemaps for both server and client builds. `devtool` affects both, whereas `productionBrowserSourceMaps` (as the name implies) only affects the client build.)

[1] https://github.com/vercel/next.js/blob/fa138358e1df7ca6d1bab7da57e18031d5abbf27/packages/next/build/webpack/config/blocks/base.ts#L39-L43

[2] https://github.com/vercel/next.js/search?q=productionBrowserSourceMaps

Author: lobsterkatie

packages/nextjs/src/config/index.ts

@@ -12,21 +12,17 @@ export function withSentryConfig(
   userNextConfig: ExportedNextConfig = {},
   userSentryWebpackPluginOptions: Partial<SentryWebpackPluginOptions> = {},
 ): NextConfigFunction | NextConfigObject {
-  const partialConfig = {
-    // TODO When we add a way to disable the webpack plugin, doing so should turn this off, too
-    productionBrowserSourceMaps: true,
-    webpack: constructWebpackConfigFunction(userNextConfig, userSentryWebpackPluginOptions),
-  };
+  const newWebpackConfig = constructWebpackConfigFunction(userNextConfig, userSentryWebpackPluginOptions);
 
   // If the user has passed us a function, we need to return a function, so that we have access to `phase` and
   // `defaults` in order to pass them along to the user's function
   if (typeof userNextConfig === 'function') {
     return (phase: string, defaults: { defaultConfig: { [key: string]: unknown } }): NextConfigObject => ({
       ...userNextConfig(phase, defaults),
-      ...partialConfig,
+      webpack: newWebpackConfig,
     });
   }
 
   // Otherwise, we can just merge their config with ours and return an object.
-  return { ...userNextConfig, ...partialConfig };
+  return { ...userNextConfig, webpack: newWebpackConfig };
 }

packages/nextjs/test/config.test.ts

@@ -115,7 +115,6 @@ describe('withSentryConfig', () => {
 
     expect(finalConfig).toEqual(
       expect.objectContaining({
-        productionBrowserSourceMaps: true,
         webpack: expect.any(Function), // `webpack` is tested specifically elsewhere
       }),
     );
@@ -133,7 +132,6 @@ describe('withSentryConfig', () => {
     expect(finalConfig).toEqual(
       expect.objectContaining({
         ...userNextConfig,
-        productionBrowserSourceMaps: true,
         webpack: expect.any(Function), // `webpack` is tested specifically elsewhere
       }),
     );
@@ -147,7 +145,6 @@ describe('withSentryConfig', () => {
     expect(finalConfig).toEqual(
       expect.objectContaining({
         ...userNextConfigFunction(),
-        productionBrowserSourceMaps: true,
         webpack: expect.any(Function), // `webpack` is tested specifically elsewhere
       }),
     );