Next.js Invalid left-hand side in assignment when using compile + generate build commands

[m-sanders]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/nextjs

SDK Version

9.22.0

Framework Version

15.3.2

Link to Sentry event

No response

Reproduction Example/SDK Setup

https://github.com/m-sanders/nextjs-sentry-asset-prefix

Steps to Reproduce

1. Create a new Next.js app
2. Use the Sentry Wizard.
3. Add assetPrefix to next.config.js
4. npm run build -- --experimental-build-mode compile
5. npm run build -- --experimental-build-mode generate

Further information about the experimental mode can be found here and here

Expected Result

A successful build (like with 14.2.2x).

The latest Next.js version that works with these steps is 15.2.5. 15.3.0-canary-0 is the last good working release.

Actual Result

> next build --experimental-build-mode generate

   ▲ Next.js 15.3.2
   - Experiments (use with caution):
     · clientTraceMetadata

   Creating an optimized production build ...
 ✓ Collecting page data
   Inlining static env ...
Error occurred prerendering page "/_not-found". Read more: https://nextjs.org/docs/messages/prerender-error
/Users/me/code/nextjs-sentry-asset-prefix/.next/server/chunks/575.js:172413
    "/assets/" = userNextConfig.assetPrefix;
    ^^^^^^^^^^

SyntaxError: Invalid left-hand side in assignment
    at wrapSafe (node:internal/modules/cjs/loader:1486:18)
    at Module._compile (node:internal/modules/cjs/loader:1528:20)
    at Object..js (node:internal/modules/cjs/loader:1706:10)
    at Module.load (node:internal/modules/cjs/loader:1289:32)
    at Function._load (node:internal/modules/cjs/loader:1108:12)
    at TracingChannel.traceSync (node:diagnostics_channel:322:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:220:24)
    at Module.<anonymous> (node:internal/modules/cjs/loader:1311:12)
    at mod.require (/Users/me/code/nextjs-sentry-asset-prefix/node_modules/next/dist/server/require-hook.js:65:28)
    at require (node:internal/modules/helpers:136:16)
Export encountered an error on /_not-found/page: /_not-found, exiting the build.
 ⨯ Next.js build worker exited with code: 1 and signal: null

15.3.0-canary-1 introduced this change vercel/next.js#76990

[chargome]

Hey @m-sanders thanks for writing in! We're already looking into it 👍

[m-sanders]

Hello @RulaKhaled, why was this closed as completed? Is there a fix?

[RulaKhaled]

Hello @m-sanders, I've submitted this PR: #16410. When this is released, It should prevent the conflict during the generate phase, and your build should function as expected. This issue stems from both Sentry's handling of two-step phases and Next.js's variable replacement. Please note that this quick fix does not imply full Sentry support for this experimental build feature; issues may still arise until Next.js stabilizes and documents it.

[m-sanders]

That's fantastic, thank you!