move field_view_field() to _field_invoke() single-field mode

I think I can help with this too, with some help please. The relevant function in field.module is field_view_field() and this is how I think this change can be done:

1. Check that $object->$field['field_name'] is set
2. call _field_invoke('sanitize)
3. call _field_invoke('view') to get $view
4. assign $view[$field['field_name']] to $output

But I couldn't find any calls to the function anywhere so I really won't be able to test that my code works as expected.

@dakala: Your approach sounds correct. I don't think you need step 1 b/c _field_invoke does that.

It looks like you are right that there is no test for this function, and none of the function's normal callers (e.g. Views) exist for D7 yet. Therefore, as yched says, the function needs a test. So, this is a great opportunity for you to learn how to write D7 tests!

Look in field.test for examples. FieldAttachOtherTestCase has some tests for field_attach_view(). This isn't quite the same, as that function returns renderable content instead of rendered content, but it will still show you how to write a test that creates a field, instance, and entity, renders the entity, and verifies that it contains the right thing.

@bjaspan: Thanks for the tips.

Here's what I've come up with. Now working on the test but can't figure out what to assert yet.

function field_view_field($obj_type, $object, $build_mode = 'full') {
  $output = '';
  if (isset($object->$field['field_name'])) {
    $null = NULL;
    $options = array('field_name' => $object->$field['field_name']);

    _field_invoke('sanitize', $obj_type, $object, $null, $null, $options);

    $output = _field_invoke('view', $obj_type, $object, $build_mode, $null, $options);
  }

  return $output;
}