Fix: use promise API

background/usercss-helper.js

@@ -40,14 +40,13 @@
     if (style.usercssData) {
       return Promise.resolve(style);
     }
-    try {
-      const {sourceCode} = style;
-      // allow sourceCode to be normalized
-      delete style.sourceCode;
-      return Promise.resolve(Object.assign(usercss.buildMeta(sourceCode), style));
-    } catch (e) {
-      return Promise.reject(e);
-    }
+
+    // allow sourceCode to be normalized
+    const {sourceCode} = style;
+    delete style.sourceCode;
+
+    return usercss.buildMeta(sourceCode)
+      .then(newStyle => Object.assign(newStyle, style));
   }
 
   function assignVars(style) {
@@ -59,7 +58,8 @@
       style.id = dup.id;
       if (style.reason !== 'config') {
         // preserve style.vars during update
-        usercss.assignVars(style, dup);
+        return usercss.assignVars(style, dup)
+          .then(() => style);
       }
     }
     return style;