Missing subfields on edit mapping form

Problem/Motivation

I have a field handler that adds subfields to certain migration classes. These subfields are not shown on the migration edit form, but they are shown on the migration view page. This is because the migration variable is not being passed to the fields method in the edit form.

Migration view page

Line 852: $destination_fields = $destination->fields($migration);

Migration edit form

Line 971: $dest_fields = $migration->getDestination()->fields();

Proposed resolution

The migration variable should be passed to the fields method in the edit form.

Remaining tasks

1. Patch is ready for review.