Actions were inspired by Python and Python does not implicitly default
any field when an action is given. From a Builder API perspective, this
seemed fine because we tend to focus the Builder API on giving the user
all information so they can make their own decisions. When working on
the Derive API, this became a problem because users were going to have
to migrate from an implied default to an explicit default when a common
default is good enough most of the time. This shouldn't interfere with
Builder users getting more details when needed.
This also highlighted two problems
- We set the index for defaults
- We don't debug_assert when applying conditional requirements with a
default present
This round out the new style actions and allow us to start deprecating
occurrences.
As part of an effort to unify code paths, this does change flag parsing
to do splits. This will only be a problem if the user enables splits
but we'll at least not crash. Once we also address #3776, we'll be able
to have envs all work the same.
