Async rendering of tags within a post

lib/hexo/post.js

@@ -29,6 +29,21 @@ const isNonWhiteSpaceChar = char => char !== '\r'
   && char !== '\v'
   && char !== ' ';
 
+function replaceAsync(string, searchValue, replacer) {
+  // An alternative to string.replace, but with an async replacer.
+  // Reference: https://github.com/dsblv/string-replace-async
+  var values = [];
+  String.prototype.replace.call(string, searchValue, function () {
+    values.push(replacer.apply(undefined, arguments));
+    return "";
+  });
+  return Promise.all(values).then(function (resolvedValues) {
+    return String.prototype.replace.call(string, searchValue, function () {
+      return resolvedValues.shift();
+    });
+  });
+}
+
 class PostRenderEscape {
   constructor() {
     this.stored = [];
@@ -47,11 +62,6 @@ class PostRenderEscape {
     };
   }
 
-  restoreAllSwigTags(str) {
-    const restored = str.replace(rSwigPlaceHolder, PostRenderEscape.restoreContent(this.stored));
-    return restored;
-  }
-
   restoreCodeBlocks(str) {
     return str.replace(rCodeBlockPlaceHolder, PostRenderEscape.restoreContent(this.stored));
   }
@@ -415,17 +425,17 @@ class Post {
         path: source,
         engine: data.engine,
         toString: true,
-        onRenderEnd(content) {
-          // Replace cache data with real contents
-          data.content = cacheObj.restoreAllSwigTags(content);
-
-          // Return content after replace the placeholders
-          if (disableNunjucks) return data.content;
+      }, options);
+    }).then(content => {
+        // Use replaceAsync so that tags within a post can render concurrently
+        return replaceAsync(content, rSwigPlaceHolder, async(match, name) => {
+          // Replace swig placeholder produced by `escapeAllSwigTags` with real contents stored previously
+          let ret = PostRenderEscape.restoreContent(cacheObj.stored)(match, name);
+          if (disableNunjucks) return ret;
 
           // Render with Nunjucks
-          return tag.render(data.content, data);
-        }
-      }, options);
+          return await tag.render(ret, data);
+        });
     }).then(content => {
       data.content = cacheObj.restoreCodeBlocks(content);