Tags within context data in helper

I'm trying to solve for a scenario where data can contain tags that refers to other data. So if my dust file looked like this:

Document.title: {Document.title}
cfg.title: {cfg.title}
output: {#ctx key="{cfg.title}" /}

and my context looks like this:

{
  cfg: {
    title: '{Document.title}'
  }
  , Document: {
    title: 'Here is my title'
  }
  , ctx: function(chunk, context, bodies, params){
    return context.resolve(params.key);
  }
}

I'm getting the following output:

Document.title: This is the title
cfg.title: {Document.title}
output:

What does my "ctx" helper function need to look like to get it to output "Here is my title"? (note: I know it would be easier to just point to Document.title, but 'cfg' and 'Document' are being generated from different places and are merged at render time)

Solution

At some point, you have to compile (or otherwise parse) the minitemplate that forms your config. Here is one possible approach, where I use dust.compile to build the config in advance:

{
  cfg: {
    title: dust.compile('{Document.title}')
  }, Document: {
    title: 'Here is my title'
  }, ctx: function(chunk, context, bodies, params){
    eval(params.key)(chunk, context);
  }
}

With the template:

{#ctx key=cfg.title /}

Note that you are passing cfg.title directly here instead of stringifying it first-- this is important so that you don't have to use context.resolve to do a double-lookup.

This approach does not generate a template-readable cfg.title, so if that is important to you, you can move the dust.compile step to inside the ctx function.