fix: support async PostCSS plugins in postcss-if-function (#137)

* fix: async error

* Create six-monkeys-draw.md

Author: mfranzke

.changeset/six-monkeys-draw.md

@@ -0,0 +1,5 @@
+---
+"postcss-if-function": patch
+---
+
+fix: support `async` PostCSS plugins in `postcss-if-function`

packages/postcss-if-function/src/index.js

@@ -59,7 +59,7 @@ function postcssIfFunction(options = {}) {
 
 	return {
 		postcssPlugin: PLUGIN_NAME,
-		Once(root, { result }) {
+		async Once(root, { result }) {
 			// Collect all CSS text first
 			const cssText = root.toString();
 
@@ -85,13 +85,14 @@ function postcssIfFunction(options = {}) {
 			// double parsing overhead identified by static analysis tools.
 
 			try {
-				const transformedRoot = result.processor.process(
+				const processed = await result.processor.process(
 					transformed.nativeCSS,
 					{
 						from: undefined,
 						parser: result.processor.parser
 					}
-				).root;
+				);
+				const transformedRoot = processed.root;
 
 				// Clone nodes to preserve original formatting and avoid reference issues
 				transformedRoot.each((node) => {