fix: disregard TypeScript nodes when pruning CSS

.changeset/plenty-hairs-kneel.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: disregard TypeScript nodes when pruning CSS

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

@@ -7,6 +7,13 @@ const UNKNOWN = {};
  * @param {Set<any>} set
  */
 function gather_possible_values(node, set) {
+	// @ts-expect-error
+	if (node.type === 'TSAsExpression') {
+		// @ts-expect-error
+		gather_possible_values(node.expression, set);
+		return;
+	}
+
 	if (node.type === 'Literal') {
 		set.add(String(node.value));
 	} else if (node.type === 'ConditionalExpression') {

packages/svelte/tests/css/samples/unused-ts-as-expression/_config.js

@@ -0,0 +1,20 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'css_unused_selector',
+			end: {
+				character: 127,
+				column: 28,
+				line: 10
+			},
+			message: 'Unused CSS selector "[data-active=\'true\'] > span"',
+			start: {
+				character: 100,
+				column: 1,
+				line: 10
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/unused-ts-as-expression/expected.css

@@ -0,0 +1,4 @@
+
+	/* (unused) [data-active='true'] > span {
+		background-color: red;
+	}*/

packages/svelte/tests/css/samples/unused-ts-as-expression/input.svelte

@@ -0,0 +1,13 @@
+<script lang="ts">
+	//
+</script>
+
+<div data-active={false as true}>
+	<span></span>
+</div>
+
+<style>
+	[data-active='true'] > span {
+		background-color: red;
+	}
+</style>