ref(nextjs): Simplify NextConfigObject type (#5514)

This simplifies the `NextConfigObject` type in the nextjs SDK, to enable future work. Key changes:
- Removed index signature.
- Added missing `basePath` and `publicRuntimeConfig` properties.
- Made all properties optional. (This allowed for removal of the `Partial` annotation everywhere the type was used.)
- Clarified variable names in `config/index.ts` to better reflect their types.

packages/nextjs/src/config/index.ts

@@ -1,33 +1,33 @@
-import { ExportedNextConfig, NextConfigFunction, NextConfigObject, SentryWebpackPluginOptions } from './types';
+import type { ExportedNextConfig, NextConfigFunction, NextConfigObject, SentryWebpackPluginOptions } from './types';
 import { constructWebpackConfigFunction } from './webpack';
 
 /**
  * Add Sentry options to the config to be exported from the user's `next.config.js` file.
  *
- * @param userNextConfig The existing config to be exported prior to adding Sentry
+ * @param exportedUserNextConfig The existing config to be exported prior to adding Sentry
  * @param userSentryWebpackPluginOptions Configuration for SentryWebpackPlugin
  * @returns The modified config to be exported
  */
 export function withSentryConfig(
-  userNextConfig: ExportedNextConfig = {},
+  exportedUserNextConfig: ExportedNextConfig = {},
   userSentryWebpackPluginOptions: Partial<SentryWebpackPluginOptions> = {},
-): NextConfigFunction | Partial<NextConfigObject> {
+): NextConfigFunction | NextConfigObject {
   // 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 function (phase: string, defaults: { defaultConfig: NextConfigObject }): Partial<NextConfigObject> {
-      const materializedUserNextConfig = userNextConfig(phase, defaults);
+  if (typeof exportedUserNextConfig === 'function') {
+    return function (phase: string, defaults: { defaultConfig: NextConfigObject }): NextConfigObject {
+      const userNextConfigObject = exportedUserNextConfig(phase, defaults);
 
       // Next 12.2.3+ warns about non-canonical properties on `userNextConfig`, so grab and then remove the `sentry`
       // property there. Where we actually need it is in the webpack config function we're going to create, so pass it
       // to `constructWebpackConfigFunction` so that it will be in the created function's closure.
-      const { sentry: userSentryOptions } = materializedUserNextConfig;
-      delete materializedUserNextConfig.sentry;
+      const { sentry: userSentryOptions } = userNextConfigObject;
+      delete userNextConfigObject.sentry;
 
       return {
-        ...materializedUserNextConfig,
+        ...userNextConfigObject,
         webpack: constructWebpackConfigFunction(
-          materializedUserNextConfig,
+          userNextConfigObject,
           userSentryWebpackPluginOptions,
           userSentryOptions,
         ),
@@ -39,11 +39,11 @@ export function withSentryConfig(
 
   // Prevent nextjs from getting mad about having a non-standard config property in `userNextConfig`. (See note above
   // for a more thorough explanation of what we're doing here.)
-  const { sentry: userSentryOptions } = userNextConfig;
-  delete userNextConfig.sentry;
+  const { sentry: userSentryOptions } = exportedUserNextConfig;
+  delete exportedUserNextConfig.sentry;
 
   return {
-    ...userNextConfig,
-    webpack: constructWebpackConfigFunction(userNextConfig, userSentryWebpackPluginOptions, userSentryOptions),
+    ...exportedUserNextConfig,
+    webpack: constructWebpackConfigFunction(exportedUserNextConfig, userSentryWebpackPluginOptions, userSentryOptions),
   };
 }

packages/nextjs/src/config/types.ts

@@ -8,19 +8,20 @@ export type SentryWebpackPlugin = WebpackPluginInstance & { options: SentryWebpa
  * Overall Nextjs config
  */
 
-export type ExportedNextConfig = Partial<NextConfigObject> | NextConfigFunction;
+export type ExportedNextConfig = NextConfigObject | NextConfigFunction;
 
 export type NextConfigObject = {
   // custom webpack options
-  webpack: WebpackConfigFunction;
+  webpack?: WebpackConfigFunction;
   // whether to build serverless functions for all pages, not just API routes
-  target: 'server' | 'experimental-serverless-trace';
+  target?: 'server' | 'experimental-serverless-trace';
   // the output directory for the built app (defaults to ".next")
-  distDir: string;
+  distDir?: string;
+  // the root at which the nextjs app will be served (defaults to "/")
+  basePath?: string;
+  // config which will be available at runtime
+  publicRuntimeConfig?: { [key: string]: unknown };
   sentry?: UserSentryOptions;
-} & {
-  // other `next.config.js` options
-  [key: string]: unknown;
 };
 
 export type UserSentryOptions = {
@@ -40,10 +41,7 @@ export type UserSentryOptions = {
   widenClientFileUpload?: boolean;
 };
 
-export type NextConfigFunction = (
-  phase: string,
-  defaults: { defaultConfig: NextConfigObject },
-) => Partial<NextConfigObject>;
+export type NextConfigFunction = (phase: string, defaults: { defaultConfig: NextConfigObject }) => NextConfigObject;
 
 /**
  * Webpack config

packages/nextjs/src/config/webpack.ts

@@ -36,7 +36,7 @@ export { SentryWebpackPlugin };
  * @returns The function to set as the nextjs config's `webpack` value
  */
 export function constructWebpackConfigFunction(
-  userNextConfig: Partial<NextConfigObject> = {},
+  userNextConfig: NextConfigObject = {},
   userSentryWebpackPluginOptions: Partial<SentryWebpackPluginOptions> = {},
   userSentryOptions: UserSentryOptions = {},
 ): WebpackConfigFunction {

packages/nextjs/test/config.test.ts

@@ -64,7 +64,7 @@ afterEach(() => {
 });
 
 /** Mocks of the arguments passed to `withSentryConfig` */
-const userNextConfig: Partial<NextConfigObject> = {
+const userNextConfig: NextConfigObject = {
   publicRuntimeConfig: { location: 'dogpark', activities: ['fetch', 'chasing', 'digging'] },
   webpack: (config: WebpackConfigObject, _options: BuildContext) => ({
     ...config,
@@ -124,7 +124,7 @@ const clientWebpackConfig = {
 // dynamically.
 function getBuildContext(
   buildTarget: 'server' | 'client',
-  userNextConfig: Partial<NextConfigObject>,
+  userNextConfig: NextConfigObject,
   webpackVersion: string = '5.4.15',
 ): BuildContext {
   return {