Fix crash when formatting svelte files that have "let:class". (#24)

* Add tests for svelte's let directive.

* Avoid formatting svelte's let directive.

Author: chrsep

src/index.js

@@ -379,7 +379,7 @@ export const parsers = {
 
 function transformSvelte(ast, { env, changes }) {
   for (let attr of ast.attributes ?? []) {
-    if (attr.name === 'class') {
+    if (attr.name === 'class' && attr.type === 'Attribute') {
       for (let i = 0; i < attr.value.length; i++) {
         let value = attr.value[i]
         if (value.type === 'Text') {

tests/test.js

@@ -156,6 +156,7 @@ let tests = {
     t`<div class={\`${yes} \${'${yes}' + \`${yes}\`} ${yes}\`} />`,
     t`<div class={\`${no}\${someVar}${no}\`} />`,
     t`<div class="${yes} {\`${yes}\`}" />`,
+    t`<div let:class={clazz} class="${yes} {clazz}" />`,
     [
       `<div class="sm:block uppercase flex{someVar}" />`,
       `<div class="uppercase sm:block flex{someVar}" />`,