fix(no-ununsed-class-name): not reporting errors on invalid lang

Author: marekdedic

src/rules/no-unused-class-name.ts

@@ -28,6 +28,7 @@ export default createRule("no-unused-class-name", {
   },
   create(context) {
     const classesUsedInTemplate: Record<string, SourceLocation> = {}
+    let hasStyleNode = false
 
     return {
       SvelteElement(node) {
@@ -39,12 +40,16 @@ export default createRule("no-unused-class-name", {
           classesUsedInTemplate[className] = node.startTag.loc
         }
       },
+      SvelteStyleElement() {
+        hasStyleNode = true
+      },
       "Program:exit"() {
         const styleAst = context.parserServices.getStyleSourceAst()
-        if (styleAst === null) {
+        if (hasStyleNode && styleAst === null) {
           return
         }
-        const classesUsedInStyle = findClassesInPostCSSNode(styleAst)
+        const classesUsedInStyle =
+          styleAst != null ? findClassesInPostCSSNode(styleAst) : []
         for (const className in classesUsedInTemplate) {
           if (!classesUsedInStyle.includes(className)) {
             context.report({