Fix: rewrite filterUsercss

background/storage.js

@@ -372,8 +372,15 @@ function filterStylesInternal({
 // Parse the source and find the duplication
 // {id: int, style: object, source: string, checkDup: boolean}
 function filterUsercss(req) {
-  return Promise.resolve().then(() => {
   let style;
+  let pendingBuild;
+  return buildMeta()
+    .then(buildSection)
+    .then(decide)
+    .catch(err => ({status: 'error', error: err.message}));
+
+  function buildMeta() {
+    return new Promise(resolve => {
       if (req.source) {
         style = usercss.buildMeta(req.source);
       } else {
@@ -382,18 +389,26 @@ function filterUsercss(req) {
       if (!style.id && req.id) {
         style.id = req.id;
       }
-    let pending;
-    if (!style.sections || !style.sections.length) {
-      pending = usercss.buildCode(style);
-    } else {
-      pending = Promise.resolve(style);
+      resolve();
+    });
   }
+
+  function buildSection() {
+    if (!style.sections || !style.sections.length) {
+      pendingBuild = usercss.buildCode(style);
+    } else {
+      pendingBuild = Promise.resolve(style);
+    }
+  }
+
+  function decide() {
+    // decide result
     if (!style.id && req.checkDup) {
-      return Promise.all([pending, findDupUsercss(style)])
+      return Promise.all([pendingBuild, findDupUsercss(style)])
         .then(([, dup]) => ({status: 'success', style, dup}));
     }
-    return pending.then(() => ({status: 'success', style}));
-  }).catch(err => ({status: 'error', error: String(err)}));
+    return pendingBuild.then(() => ({status: 'success', style}));
+  }
 }
 
 function saveUsercss(style) {