Why3 is incompatible with OCaml ≥ 4.09
Compiler plugins have been removed from the OCaml compiler starting from version 4.09 .
This leads to a build failure in why3 on the recent OCaml 4.09 beta due to the Debug_util
plugin.
Surprisingly, this plugin seems to implement a parsetree transformation that could be implemented as a ppx. So it seems that compatibility could be restored either by disabling this plugin at configuration time for Ocaml versions outside of the [4.05, 4.08] interval or by translating this plugin to a ppx.