fix: allow for nesting selector in pseudoclasses (#13209)

Fixes #13203

The problem is that we were checking for NestingSelectors only in the selectors of the immediate child of the selectors. Since Nesting could be in selectors like :is or :where or :has that can also be nested i think we need to walk the selectors to find if there's a selector or not.

.changeset/tough-snails-chew.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow for nesting selector in pseudoclasses

packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js

@@ -73,9 +73,23 @@ const visitors = {
 		const inner = selectors[selectors.length - 1];
 
 		if (node.metadata.rule?.metadata.parent_rule && selectors.length > 0) {
-			const has_explicit_nesting_selector = selectors.some((selector) =>
-				selector.selectors.some((s) => s.type === 'NestingSelector')
-			);
+			let has_explicit_nesting_selector = false;
+
+			// nesting could be inside pseudo classes like :is, :has or :where
+			for (let selector of selectors) {
+				walk(
+					selector,
+					{},
+					{
+						// @ts-ignore
+						NestingSelector() {
+							has_explicit_nesting_selector = true;
+						}
+					}
+				);
+				// if we found one we can break from the others
+				if (has_explicit_nesting_selector) break;
+			}
 
 			if (!has_explicit_nesting_selector) {
 				selectors[0] = {

packages/svelte/tests/css/samples/nested-in-pseudo/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: []
+});

packages/svelte/tests/css/samples/nested-in-pseudo/expected.css

@@ -0,0 +1,6 @@
+
+nav.svelte-xyz{
+	header:where(.svelte-xyz):has(&){
+		color: red;
+	}
+}	

packages/svelte/tests/css/samples/nested-in-pseudo/expected.html

@@ -0,0 +1 @@
+<header class="svelte-xyz"><nav class="svelte-xyz"></nav></header>

packages/svelte/tests/css/samples/nested-in-pseudo/input.svelte

@@ -0,0 +1,11 @@
+<header>
+	<nav></nav>		
+</header>
+
+<style>
+nav{
+	header:has(&){
+		color: red;
+	}
+}	
+</style>