I’m not sure if this the right place to ask this question, but ppx_deriving_yojson issues seemed a little too “specialist” so I figured I’d ask here too: https://github.com/ocaml-ppx/ppx_deriving_yojson/issues/119
Manifest types allow @@deriving rewriters to generate code for (e.g. generative) types already declared elsewhere. But there’s no equivalent that I can see for extensible variants. The issue has the details (so I won’t reproduce them here).
Am I missing something, or is there a gap in the syntax? [It seems … straightforward to use attributes to fill the gap, but I figured I ought to at least ask the question before proceeding.]
 OK, not a gap, since it’s not necessary for anything in the type system, and the way that @@deriving uses manifest types is … a happy coincidence. So maybe better described as “an unfortunate lack of verbosity that makes writing macro-processors a little more cumbersome”.