chore: improve condition and add comment

Author: dominikg

packages/vite-plugin-svelte/src/utils/compile.js

@@ -133,29 +133,30 @@ export function createCompileSvelte() {
 		let compiled;
 		try {
 			compiled = svelte.compile(finalCode, { ...finalCompileOptions, filename });
-			if (compiled.css) {
-				if (finalCode.includes(':global') && compiled.ast.css) {
-					walk(
-						compiled.ast.css,
-						{},
-						{
-							Selector(node, { stop }) {
-								if (
-									node.children?.[0].type === 'PseudoClassSelector' &&
-									node.children[0].name === 'global'
-								) {
-									Object.defineProperty(compiled.css, '__meta', {
-										value: { hasUnscopedGlobalCss: true },
-										writable: false,
-										enumerable: false,
-										configurable: false
-									});
-									stop();
-								}
+
+			// check if css has unscoped :global.
+			// This is later used to decide if css output can be scoped to the js module for treeshaking
+			if (compiled.css && compiled.ast.css && finalCode.includes(':global')) {
+				walk(
+					compiled.ast.css,
+					{},
+					{
+						Selector(node, { stop }) {
+							if (
+								node.children?.[0].type === 'PseudoClassSelector' &&
+								node.children[0].name === 'global'
+							) {
+								Object.defineProperty(compiled.css, '__meta', {
+									value: { hasUnscopedGlobalCss: true },
+									writable: false,
+									enumerable: false,
+									configurable: false
+								});
+								stop();
 							}
 						}
-					);
-				}
+					}
+				);
 			}
 
 			// patch output with partial accept until svelte does it