Themes/modules cannot alter entity render arrays before ds layouts are rendered

Revamped issue summary.

I spoke with swentel on IRC this morning about this and he gave me a couple of good suggestions:

1. the field_group module
2. hook_entity_view_alter

The first suggestion works well but only for the limited case of grouping fields together - super powerful, but limited. The second suggestion gets envoked too early to alter the render array after ds has made its changes. I stil content that ds should alter that render array in such a way that other themes/modules can alter it further if desired.

I made one proposal in the original post that I still feel is valid, but here is an alternative (better?) approach: instead of using hook_theme_registry_alter to add a preprocess function to all entities, why doesn't ds use hook_entitiy_view_alter to rejigger the render array according to the appropriate layout. This would allow other modules/themes to use hook_entity_view_alter() to modify that array even further and I think this would be cleaner to maintain in general.

This would not require any new hooks and I think it would be more inline with render_api in d7...

I'd be willing to put in some time on a patch as long as I knew there was some support from the maintainers (and no gotchas that I havent thought of)

Thoughts?

A few points:

I dont think there would have to be an API change given my proposal in #2, as ds could still render the render_arrays in a preprocess function. They would simply be built in hook_entity_view_alter(). You're concern about waiting until preprocess for the sake of other modules (like field_group) may make this suggestion moot however.

As for your proposal in #3... if we added a drupal_alter around line 596, it would stil be (just barely) too early. To illustrate this suggestion, here is some pseudo code:

   drupal_alter('ds_prerender', array($content, $layout, ...));

   // Create region variables based on the layout settings.
    foreach ($layout['regions'] as $region_name => $region) {

      // Create the region content.
      $vars[$region_name] = ds_render_region($vars[$render_container], $region_name, $layout);
       ...
    }

With the drupal_alter in that position I still could not alter $vars['left'] for example. This means that I could not modify a render array of left to add new item of #type->markup in the correct position within the left region.

Now, lets say that ds_render_region returned a render array instead of markup, the drupal_alter was called and then drupal_render was called. Something like this (more pseudo-code):

   // Create region variables based on the layout settings.
    foreach ($layout['regions'] as $region_name => $region) {
      $layout_render_array = array();

      // Create the region content.
      $layout_render_array[$region_name] = ds_render_region($vars[$render_container], $region_name, $layout);
       ...
    }
    drupal_alter('ds_prerender', array($content, $layout, ...));
    foreach($layout_render_array as $reg=>$content) {
        $vars[$reg] = drupal_render($content);
    }

Thoughts?

(PS ... I'm enjoying this, thanks for taking the time to talk it out with me)

swentel: any chance you can post the patch you're working with?

swentel ... writing this from your DC London session just before it starts :)

Are you still considering the patch in #7?

Havent had a chance to test this properly, but in perusing the code the patch in #17 looks great :)