Feature Request: Allow templates to get assets referenced in a post and their order

Environment Info

Hexo version 3.2.2

Plugin version(npm ls --depth 0)

+-- hexo@3.2.2
+-- hexo-deployer-git@0.2.0
+-- hexo-generator-archive@0.1.4
+-- hexo-generator-category@0.1.3
+-- hexo-generator-feed@1.2.0
+-- hexo-generator-index@0.2.0
+-- hexo-generator-tag@0.2.0
+-- hexo-renderer-ejs@0.2.0
+-- hexo-renderer-marked@0.2.11
+-- hexo-renderer-stylus@0.3.1
+-- hexo-server@0.2.0

Feature Request

Allow templates to get assets referenced in a post and their order

Use Case

Right now templates don't know what assets are used in posts (e.g. those referenced by asset_img). It would be nice if we can keep a record of asset reference calls and their order. That way, a template can auto generate the thumbnail for a post from the first referenced image asset, for example.

Note this might be against the design since it would require tag plugins to have side effects. An alternative may be is to let template code to trigger tag plugin code in post front-matter, e.g.:

thumbnail: <% asset_img blah.png %>

Template code:

var link = post.thumbnail;
if (hasTagPlugin(link)) {
  link = Tag.eval(link);
}  // link = '/url/to/post/blah.png'

hexojs / hexo