julia

f71b8398 - lattice: Allow external lattice to have a say in how to widen (#47307)

lattice: Allow external lattice to have a say in how to widen (#47307) Currently, when e.g. a PartialStruct is not of interest to the lattice code, it just calls `widenconst` on it to pass it to the next lattice layer. This might be insufficient if an intermediate lattice layer has some other representation that is wider that the `PartialStruct`, but narrower than the corresponding `widenconst`. This adds `widenconst(::AbstractLatice, ::Any)` to allow the lattices to insert custom widening code. By default, it ends up calling `widenconst`, so there's no functional change in base, but custom lattices can make use of the extra hook. I'm not entirely sure that this is what we want the final interface to look like (I think it probably does too many type checks), but it works reasonably well and I think is good enough to experiment with.