Get access to the path in content merge function

[clecat]

Fast question:
Could we have access to the current path of the objects to be merged inside the merge function of the store's content.

Long description:
I am currently using Irmin for a project and want to handle merges properly.
From what I have understood, I need to redefine the merge function inside the module I use as content for the store functor:

module Content_string = struct
  include Irmin.Contents.String

  let merge =
    let dt = Irmin.Type.(option string) in
    let equal = Irmin.Type.(unstage (equal dt)) in
    let default = Irmin.Merge.default dt in
    let f ~old x y =
      (* do my own stuff instead of the default idempotent behavior *)
      if equal x y then Irmin.Merge.ok x else Irmin.Merge.f default ~old x y
    in
    Irmin.Merge.v dt f
end

In this bit of code, I would have to replace the content of f copy-pasted from Merge.idempotent with my own custom function.
However, it appeared that I have not access to the current path of the objects that I want to merge.

Indeed, I do not always have the same objects inside the different trees of my store and I will want to have a specific merge for each type of them.

Therefore would it be possible for the signature of the merge function to be something like:
val merge: ~old:t -> ~key:Key.t -> t -> t -> t
Instead of
val merge: ~old:t -> t -> t -> t
It would allow a more specific and refined merge behavior

[samoht]

That's a great idea and something I wanted to do for a very long time but that API is hard to define properly. as Key.t is (currently) generic and opaque. I am hoping that now that we have introduced schemas, this could be somehow be passed to the user-defined merge function.

[clecat]

Cool, thanks a lot, I will waiting for that :D