Remove missingSuspenseWithCSRBailout config (#65688)

### What

Remove `missingSuspenseWithCSRBailout` and always treate the conditions
where it was used as `true`.


### Why

This was an intended behavior introduced in 14.1, which requires users
to always add suspense boundaries if it's using any hook that could bail
out to client rendering. `missingSuspenseWithCSRBailout` as `true` was
the default behavior and you could disable it with
`missingSuspenseWithCSRBailout: false` in next config. Now after the
removal you will not be able to opt-out it.

errors/missing-suspense-with-csr-bailout.mdx

@@ -58,6 +58,8 @@ This will ensure the page does not de-opt to client-side rendering.
 
 #### Disabling
 
+> Note: This is only available with Next.js version 14.x. If you're in versions above 15 please fix it with the approach above.
+
 We don't recommend disabling this rule. However, if you need to, you can disable it by setting the `missingSuspenseWithCSRBailout` option to `false` in your `next.config.js`:
 
 ```js filename="next.config.js"

packages/next/src/export/index.ts

@@ -420,8 +420,6 @@ export async function exportAppImpl(
     deploymentId: nextConfig.deploymentId,
     experimental: {
       isAppPPREnabled: checkIsAppPPREnabled(nextConfig.experimental.ppr),
-      missingSuspenseWithCSRBailout:
-        nextConfig.experimental.missingSuspenseWithCSRBailout === true,
       swrDelta: nextConfig.experimental.swrDelta,
     },
   }

packages/next/src/export/routes/app-page.ts

@@ -169,12 +169,9 @@ export async function exportAppPage(
       throw err
     }
 
-    // If enabled, we should fail rendering if a client side rendering bailout
+    // We should fail rendering if a client side rendering bailout
     // occurred at the page level.
-    if (
-      renderOpts.experimental.missingSuspenseWithCSRBailout &&
-      isBailoutToCSRError(err)
-    ) {
+    if (isBailoutToCSRError(err)) {
       throw err
     }
 

packages/next/src/server/app-render/app-render.tsx

@@ -1222,17 +1222,11 @@ async function renderToHTMLOrFlightImpl(
         const shouldBailoutToCSR = isBailoutToCSRError(err)
         if (shouldBailoutToCSR) {
           const stack = getStackWithoutErrorMessage(err)
-          if (renderOpts.experimental.missingSuspenseWithCSRBailout) {
-            error(
-              `${err.reason} should be wrapped in a suspense boundary at page "${pagePath}". Read more: https://nextjs.org/docs/messages/missing-suspense-with-csr-bailout\n${stack}`
-            )
-
-            throw err
-          }
-
-          warn(
-            `Entire page "${pagePath}" deopted into client-side rendering due to "${err.reason}". Read more: https://nextjs.org/docs/messages/deopted-into-client-rendering\n${stack}`
+          error(
+            `${err.reason} should be wrapped in a suspense boundary at page "${pagePath}". Read more: https://nextjs.org/docs/messages/missing-suspense-with-csr-bailout\n${stack}`
           )
+
+          throw err
         }
 
         if (isNotFoundError(err)) {

packages/next/src/server/app-render/types.ts

@@ -169,7 +169,6 @@ export interface RenderOptsPartial {
      * prerendering.
      */
     isRoutePPREnabled?: boolean
-    missingSuspenseWithCSRBailout: boolean
     swrDelta: SwrDelta | undefined
   }
   postponed?: string

packages/next/src/server/base-server.ts

@@ -555,8 +555,6 @@ export default abstract class Server<
       isExperimentalCompile: this.nextConfig.experimental.isExperimentalCompile,
       experimental: {
         isAppPPREnabled,
-        missingSuspenseWithCSRBailout:
-          this.nextConfig.experimental.missingSuspenseWithCSRBailout === true,
         swrDelta: this.nextConfig.experimental.swrDelta,
       },
     }

packages/next/src/server/config-schema.ts

@@ -417,7 +417,6 @@ export const configSchema: zod.ZodType<NextConfig> = z.lazy(() =>
         staticWorkerRequestDeduping: z.boolean().optional(),
         useWasmBinary: z.boolean().optional(),
         useLightningcss: z.boolean().optional(),
-        missingSuspenseWithCSRBailout: z.boolean().optional(),
         useEarlyImport: z.boolean().optional(),
         testProxy: z.boolean().optional(),
         defaultTestRunner: z.enum(SUPPORTED_TEST_RUNNERS_LIST).optional(),

packages/next/src/server/config-shared.ts

@@ -418,17 +418,6 @@ export interface ExperimentalConfig {
    */
   useLightningcss?: boolean
 
-  /**
-   * Certain methods calls like `useSearchParams()` can bail out of server-side rendering of **entire** pages to client-side rendering,
-   * if they are not wrapped in a suspense boundary.
-   *
-   * When this flag is set to `true`, Next.js will break the build instead of warning, to force the developer to add a suspense boundary above the method call.
-   *
-   * @note This flag will be removed in Next.js 15.
-   * @default true
-   */
-  missingSuspenseWithCSRBailout?: boolean
-
   /**
    * Enables early import feature for app router modules
    */
@@ -943,7 +932,6 @@ export const defaultConfig: NextConfig = {
         process.env.__NEXT_EXPERIMENTAL_PPR === 'true'
       ),
     webpackBuildWorker: undefined,
-    missingSuspenseWithCSRBailout: true,
     optimizeServerReact: true,
     useEarlyImport: false,
     staleTimes: {

test/e2e/app-dir/missing-suspense-with-csr-bailout/missing-suspense-with-csr-bailout.test.ts

@@ -42,26 +42,6 @@ describe('missing-suspense-with-csr-bailout', () => {
       await next.renameFile('app/layout.js', 'app/layout-suspense.js')
       await next.renameFile('app/layout-no-suspense.js', 'app/layout.js')
     })
-
-    it('should pass build if missingSuspenseWithCSRBailout os set to false', async () => {
-      let _content
-      await next.patchFile('next.config.js', (content) => {
-        _content = content
-        return content.replace(
-          '{}',
-          '{ experimental: { missingSuspenseWithCSRBailout: false } }'
-        )
-      })
-
-      const result = await next.build()
-      expect(result.exitCode).toBe(0)
-      expect(result.cliOutput).toMatch(
-        '⚠ Entire page "/" deopted into client-side rendering due to "useSearchParams()". Read more: https://nextjs.org/docs/messages/deopted-into-client-rendering'
-      )
-      expect(result.cliOutput).toMatch(/app\/page\.js:\d+:\d+/)
-
-      await next.patchFile('next.config.js', _content)
-    })
   })
 
   describe('next/dynamic', () => {