fix: enhance class selector matching to include ClassDirective attributes

.changeset/metal-insects-flow.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: restore ClassDirective check for compound class selectors in CSS pruning

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

@@ -532,7 +532,12 @@ function relative_selector_might_apply_to_node(relative_selector, rule, element,
 			}
 
 			case 'ClassSelector': {
-				if (!attribute_matches(element, 'class', name, '~=', false)) {
+				if (
+					!attribute_matches(element, 'class', name, '~=', false) &&
+					!element.attributes.some(
+						(attribute) => attribute.type === 'ClassDirective' && attribute.name === name
+					)
+				) {
 					return false;
 				}
 

packages/svelte/tests/css/samples/class-directive-compound-selectors/_config.js

@@ -0,0 +1,20 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector ".unused"\nhttps://svelte.dev/e/css_unused_selector',
+			start: {
+				line: 18,
+				column: 1,
+				character: 231
+			},
+			end: {
+				line: 18,
+				column: 8,
+				character: 238
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/class-directive-compound-selectors/expected.css

@@ -0,0 +1,11 @@
+.sidebar.collapsed.svelte-xyz {
+		width: 60px;
+	}
+
+	.collapsed.svelte-xyz .content:where(.svelte-xyz) {
+		opacity: 0;
+	}
+
+	/* (unused) .unused {
+		color: red;
+	}*/

packages/svelte/tests/css/samples/class-directive-compound-selectors/input.svelte

@@ -0,0 +1,21 @@
+<script>
+	let collapsed = false;
+</script>
+
+<div class="sidebar" class:collapsed={collapsed}>
+	<div class="content">Content</div>
+</div>
+
+<style>
+	.sidebar.collapsed {
+		width: 60px;
+	}
+
+	.collapsed .content {
+		opacity: 0;
+	}
+
+	.unused {
+		color: red;
+	}
+</style>