Regression: class static block no longer transpiled in Next.js 15.4.7 (works in 15.3.4)

[zo-ly]

Summary

In Next.js 15.3.4, class static initialization blocks (static {}) are correctly transpiled and work in both next dev and next build.
After upgrading to 15.4.7, the same code throws a SyntaxError in next dev when visiting a page, although next build && next start still works fine.

This looks like a regression in how SWC handles class static blocks between 15.3.4 and 15.4.7.

Current Behavior：

In Next.js 15.4.7 (dev mode):

SyntaxError: Unexpected token '{'

Expected Behavior：

The class static block should be transpiled (as in 15.3.4), and next dev should run without syntax errors.

Example

No response

[icyJoseph]

Hi,

Have you tried with 15.5.0? There was one more SWC bump done from 15.4 to 15.5 and I know some bugs had been fixed upstream.

[zo-ly]

Thanks for your suggestion!

I tried 15.5.0 and this issue still exists. I found this issue started appearing from 15.4.1.

I switched to turbopack, and it works correctly. Since turbopack is already stable, I'll just use turbopack directly.

[dserdiuk3c]

It's happening again with the turbopack with version 16.0.10.

[icyJoseph]

Got a quick example I could try to repro?