$MDX delimiters in ocaml cut off any code on the same line

[ceastlund]

If I write code like this:

(* $MDX part-begin=something *)
type t =
  | Foo
  | Bar (* $MDX part-end *)

Then what shows up in the MDX is:

type t =
  | Foo

This cuts off | Bar. Granted, a solution is to always put the comment on a separate line. But ocamlformat doesn't know this, for example. It would be better if mdx always preserved all the code between delimiters.

[NathanReb]

Out of curiosity, does ocamlformat still format it this way if you had an empty line between | Bar and the comment?

I understand this is annoying but I'm wondering if from a user perspective, you really want inline part delimiters. If there's no way to get ocamlformat and MDX to agree on how this, we'll of course fix it in MDX but I'm wondering whether this is the formatting you actually want or if you'd also rather have it on a separate line.

[Leonidas-from-XIV]

@ceastlund Thanks for the report and the example. I'm currently trying to implement a reasonable solution to this problem. Could you specify a configuration where OCamlformat formats the comment on the end of the line? I'm playing around with source code like this:

(* $MDX part-begin=something *)
type t =
  | Foo
  | Bar
  | Baz
  | Quuz
  | Fnuug
  | Gbaz of { foo : int; bar : int; baz : int; bat : int }
  | Hoog
(* $MDX part-end *)

to get ocamlformat 0.21 to put the part-end on the same line as Hoog but with both the conventional and janestreet profiles it leaves it on its own line (the conventional profile puts types with less variants on one line but the part-end stays on a separate line. Unfortunately, there's a ton of flags so it would be good to have a reproducible case that we can reach out to the OCamlformat maintainers to find a solution that is both readable and doesn't drop lines silently.

[ceastlund]

I believe the case I've run into is when there's an [@@deriving] clause on a new line after the comment, and the comment is aligned with the "|" on the previous line, it gets moved up to after "Hoog". And if it's after "Hoog", it stays there.