svelte: 3.55.1
svelte-preprocess: 5.0.1

Having the same issue:

<style lang="scss" global>
.highlight {
    background: yellow;
}

div:has(input.highlight) {
    span {
        color: red;
    }
}

.test {
    input {
        @extend .highlight;
    }
}
</style>

Output

/src/routes/+page.svelte:320:0 :global(...) must contain a single selector

/src/routes/+page.svelte:320:0

318 |  }
 319 |  
 320 |  :global(div:has(input.highlight), :global(.test) :global(input)) :global(span) {
        ^
 321 |    color: red;
 322 |  }

A workaround would be to wrap the problematic part in :global(), but this is not feasible when the problematic part is in an external scss file that we are just extending inside the global style tag.

<style lang="scss" global>
@use 'node_modules/.../highlight.scss';

.test {
    input {
        @extend .highlight;
    }
}
</style>

A potential fix would be to set the combinatorPattern to the following:

/(?<!\\)(?:\\\\)*([ >+~,]\s*)(?![^(]*\))(?![^[]+\]|\d)/g

It excludes the content of the parentheses.

This bit me hard when migrating from Tailwind v2 to v3. The symptom was that dark mode in my app stopped being dark, it was stuck in light mode. They changed how class-based dark mode works, and it took me way too long to realize that the breakage was being caused by svelte-preprocess.

Selectors that should look like this:
:is(.dark .dark\:bg-black)

are instead emitted like this:
:is(.dark) :global(.dark\:bg-black)

when one brings in tailwind like this:

<style global lang="postcss">
	@tailwind base;
	@tailwind components;
	@tailwind utilities;
</style>

Quite the bummer. Now I'll have to find some workaround based on patching/forking svelte-preprocess or by doing string replacements on the resulting CSS bundle, and I'm not sure which approach I'm least looking forward to 😅

This bit me hard when migrating from Tailwind v2 to v3. The symptom was that dark mode in my app stopped being dark, it was stuck in light mode. They changed how class-based dark mode works, and it took me way too long to realize that the breakage was being caused by svelte-preprocess.

Selectors that should look like this: :is(.dark .dark\:bg-black)

are instead emitted like this: :is(.dark) :global(.dark\:bg-black)

when one brings in tailwind like this:

<style global lang="postcss">
	@tailwind base;
	@tailwind components;
	@tailwind utilities;
</style>

Quite the bummer. Now I'll have to find some workaround based on patching/forking svelte-preprocess or by doing string replacements on the resulting CSS bundle, and I'm not sure which approach I'm least looking forward to 😅

I'm having this exact issue right now. Any temp fixes so far?

@alvissraghnall I'm sorry I'm some months late but it turns out I wasn't subscribed to this issue and only saw your message when checking if this issue was fixed. The "fix" I've found is to use patch-package to modify combinatorPattern. The patch looks like this:

diff --git a/node_modules/svelte-preprocess/dist/modules/globalifySelector.js b/node_modules/svelte-preprocess/dist/modules/globalifySelector.js
index fff3bd6..e1c72a9 100644
--- a/node_modules/svelte-preprocess/dist/modules/globalifySelector.js
+++ b/node_modules/svelte-preprocess/dist/modules/globalifySelector.js
@@ -9,7 +9,7 @@ exports.globalifySelector = void 0;
  * escaped combinators like `\~`.
  */
 // TODO: maybe replace this ugly pattern with an actual selector parser? (https://github.com/leaverou/parsel, 2kb)
-const combinatorPattern = /(?<!\\)(?:\\\\)*([ >+~,]\s*)(?![^[]+\]|\d)/g;
+const combinatorPattern = /(?<!\\)(?:\\\\)*([ >+~,]\s*)(?![^(]*\))(?![^[]+\]|\d)/g;
 function globalifySelector(selector) {
     const parts = selector.trim().split(combinatorPattern);
     const newSelector = [];

Is this a fix someone would want to upstream so we don't have to use patch-package suggested by @gbl08ma?

+1, this has been left open for longer than it should !

Has anyone found a condition where that modified regular expression fails? I am going to submit a PR so hopefully this can get fixed. Right now it's preventing me from using either tailwind (and daisy ui) with my svelte project.

Ok, I opened a PR as I didn't see any existing PR for this change.

Thanks for the fix ! 👌