New feature: Detect the type of a function and arrange so that it is available for outward type hinting.
For reference, a small amount of discussion from Jan 2016 in the #cljs-dev Slack:
mfikes: Curious if "outward" ^boolean propagation has been debated / rejected. Example: If simple analysis detects that ^boolean can be applied as in for functions like (defn f [x] (not x)). Perhaps automatically propagating type hints in this direction would be unwelcome by users?
dnolen: @mfikes: we have already have outward propagation for numerics which broke because of changes for code motion
dnolen: absolutely nothing against that