1 AbstractRule Per Partial, vs 1 AbstractRule returning a tuple of Differentials (one per partial)

[oxinabox]

From the ML call:
why do rrules in chainrules return 1 pullback (Rule) per partial.
Rather than 1 pullback that returns a tuple of partials? (what Zygote does) (edited)
This seems better, since it make is possible to share work between the partials.
and if you don’t want to do the work of the partials that you don’t need, you just wrap them in thunks.

[oxinabox]

Spoke to Will, and Nick on this.
We are going to change it.