🐛 BUG: [REGRESSION] Scoped CSS wrongly generated since `astro@5.15.6`

[mr-wildcard]

What version of @astrojs/compiler are you using?

2.12.3

What package manager are you using?

pnpm

What operating system are you using?

Mac

Describe the Bug

Hello,

I have a website using Astro 5.15.5 and I'm unable to upgrade it to 5.15.9 because the CSS generated in the production build contains invalid selectors.
I believe that this issue is in Astro since version 5.15.6, the one who comes with the @astrojs/compiler bump to 2.12.3.

Working version ✅ astro@5.15.5	Broken version 💥 astro@5.15.9
Link	Link

The working version is using a correct CSS selector:

div[data-astro-cid-daii5eay] .curve:last-of-type {
    transform: scaleY(-1)
}

But the broken version uses an invalid selector:

div[data-astro-cid-daii5eay] .curve[data-astro-cid-daii5eay]:last-of-type {
    transform: scaleY(-1)
}

How to reproduce:

$ git clone git@github.com:mr-wildcard/team-ux.com.git
$ corepack use
$ pnpm i
$ pnpm why @astrojs/compiler // should output 2.12.3
$ pnpm build && pnpm preview 

and open http://localhost:4322/nos-deux-profils : you should see the working version ✅

To reproduce the bug, bump astro to 5.15.6:

$ pnpm i astro@5.15.6
$ pnpm build && pnpm preview 

and open http://localhost:4322/nos-deux-profils : you should see the broken version ❌

Now to fix it while keeping astro@5.15.6 we need @astrojs/compiler version to remain at 2.12.2:

Create pnpm-workspace.yaml file at the root of the project with the following content:

overrides:
  "@astrojs/compiler": "2.12.2"

Then run:

$ git checkout pnpm-lock.yaml // reset dependencies resolution
$ rm -rf node_modules
$ pnpm i
$ pnpm build && pnpm preview 

and open http://localhost:4322/nos-deux-profils : you should see the working version again ✅

I'm no Golang expert but reading the latest release changelog, it seems that the following change might be the root cause? 🤷

Patch Changes
1264286: Fixes a CSS scoping issue when a selector contains only pseudo selectors.

Link to Minimal Reproducible Example

https://7e2a0fae.team-ux-com.pages.dev/nos-deux-profils/