Module `Ppx_mina.Expires_after`

This is a ppx to flag code that will expire after a certain date

Motivation: RFC 0012 indicates that RPC versions should eventually expire, in order to encourage nodes to upgrade their software

Usage: %%expires_after "20201231"

There will be a compile-time error if

val name : string

val expand : 
  loc:Ppxlib.location ->
  path:'a ->
  Core_kernel__.Import.string Ppxlib.loc ->
  Ppxlib.structure_item

val ext : Ppxlib.Extension.t