This has been moved into the official Chef docs:

https://docs.chef.io/custom_resources_notes.html

12.5 style custom resources

This is by far the most recommended way of writing resources for all users. There are two gotchas which we're working through:

1. For helper functions that you used to write in your provider code or used to mixin to your provider code, you have to use an action_class do ... end block.