Panopoly Magic live preview does not render field collections

Thanks for the bug report, with really great steps to reproduce! Unfortunately, I still haven't had a chance to dig into this. However, I suspect that the patch in this issue will have an affect (could be positive or negative) on field collections in the live preview:

#2398347: Panopoly Magic abuses FPP revisions

If you have the time, could you try using that patch and seeing if it helps?

The above patch does not help. I'm using Panopoly version 7.x-1.28 and am experiencing this bug.

I've tracked the fieldable_panel_pane entity object around panopoly_magic.module and found a function call that takes the object as an argument (with all fields containing their proper values) and then returns the object except with my Field Collection field set to an empty array. This is the source of the problem as the object no longer contains any values for the Field Collection field but is then used to render the preview. The call is to field_attach_submit() on line 371 inside panopoly_magic_form_alter().

After this point things are a little too deep for me to grasp. I know field_attach_submit is a part of the core Field module but I don't quite understand what it does. Does this mean this issue is outside of Panopoly's control? If so, how does the Field Collection module not run into this issue elsewhere?

I can confirm what @maskedjellybean says - the field_attach_submit() is removing the field values from the entity. However, removing that doesn't automatically fix things.

The problem is that the field formatter is unable to get the field_collection_item entity in order to view it. It's field_collection_field_get_entity() that's responsible for getting it from the field item, and it first tries to pull the entity off of $item['entity'].

So, I think if we could somehow detect that a field collection is in use, and then makes sure the field items contain the fully built out field_collection_item entities, we should be able to get this to work. We will need to prevent field_attach_submit() from clearing out the values, though.

I validated that setting the $item['entity'] value would work by hacking up panopoly_magic with some code specific to the field I was testing. Making that more generic and having it run for any fields we detected were using field_collection is an option, but it'll be tricky because we can't conditionally remove the field_attach_submit() - that runs for all fields on the entity at once.

So, I dug more and found where field_collection is going wrong in the first place. In field_collection_field_widget_embed_validate() it's got a conditional block at the end:

  // Only if the form is being submitted, finish the collection entity and
  // prepare it for saving.
  if ($form_state['submitted'] && !form_get_errors()) {
    field_attach_submit('field_collection_item', $field_collection_item, $element, $form_state);

    // Load initial form values into $item, so any other form values below the
    // same parents are kept.
    $item = drupal_array_get_nested_value($form_state['values'], $element['#parents']);

    // Set the _weight if it is a multiple field.
    if (isset($element['_weight']) && ($field['cardinality'] > 1 || $field['cardinality'] == FIELD_CARDINALITY_UNLIMITED)) {
      $item['_weight'] = $element['_weight']['#value'];
    }

    // Put the field collection item in $item['entity'], so it is saved with
    // the host entity via hook_field_presave() / field API if it is not empty.
    // @see field_collection_field_presave()
    $item['entity'] = $field_collection_item;
    form_set_value($element, $item, $form_state);
  }

This gets the field's items into the right format - the problem is that $form_state['submitted'] isn't TRUE when generating the preview, I think because we're using the AJAX system. I'm not sure if there is an earlier place we can force it to be TRUE? Or if we're going to have to come up with a way to repeat this logic in panopoly_magic?

I forgot that we are using our own custom AJAX page callback! So, we can set $form_state['submitted'] = TRUE before the element validation runs.

I've attached super simple patch that almost works.

However, it has the following problems:

1. It saves the fields on the field collection when the preview updates. So, if you make a change, but don't click "Save" and only close the dialog, and reload the page, then your temporary changes persist
2. It acts kind of strange on new FPPs - the preview doesn't appear until you add a 2nd item, at least in my testing, which might be a little specific because I'm using an image field and have lots of required fields

So, we probably don't want to run the submit stuff and just temporarily setup the field items just before they are viewed?

Here's a patch without the weaknesses of the previous patch! It doesn't save on preview, and it works as expected with new FPPs. Unfortunately, it requires direct support for field_collection, but we have a history for putting specific support for contrib modules in panopoly_magic.

Here's a tiny change to this patch. I was experiencing a problem where we couldn't access the host entity when the preview was rendering the field collection items (which we could access during normal rendering). This fixes that in my minimal testing!

This has been in use on a client site for a while without major incident. It's also very clearly looking for field_collection fields specifically, so it shouldn't have negative effects on sites that don't use it, and they are already experiencing problems with field_collections, so... I'm going to run this through our test suite and if it passes, I'm going to merge it!

Here's the Travis build: https://travis-ci.org/panopoly/panopoly/builds/188951458

Committed!