styled-jsx is always included in client bundle (even when unused)

What version of Next.js are you using?

12.0.0

What version of Node.js are you using?

16.6.2

What browser are you using?

N/A

What operating system are you using?

macOS

How are you deploying your application?

N/A

Describe the Bug

Starting with nextjs 12.0.0 styled-jsx is included in the client bundle even when it’s not used anywhere in the project. e.g. in a fresh create-next-app:

This wasn’t the case with Next.js 11.

Expected Behavior

styled-jsx should only be included in the bundle if it’s used in the project.

To Reproduce

Here’s a reproduction based on the latest create-next-app (with the typescript preset):

https://github.com/GrantASL19/nextjs-12-unusued-styled-jsx-in-bundle

It’s stock code with WebpackBundleAnalyzer set to run in the next.config.js webpack config.

[timneutkens]

Going to re-open this to investigate if it might be optimized 👍 Thanks for bringing this to our attention @GrantASL19 👍

[GrantASL19]

Could you please try next@12.0.8-canary.13 to see if it resolves your issue? Thanks 🙏

next@12.0.8-canary.13 resolves the issue, thanks! 🙏

I’m still seeing a ~4kb bundle size increase vs. 11.1.2, but that’s described by #32417. I’ll try to make a reproduction for it in January.