Upgrade all opam files in the folder to opam2

upgrade_opam_files.ml

(* requires opam-format and opam-state *)

let opam_files =
    Sys.readdir "."
    |> Array.to_list
    |> List.filter (fun l -> match String.split_on_char '.' l with | _ :: ["opam"] -> true | _ -> false)
;;

let make_opam_file fname =
    fname |> OpamFilename.of_string |> OpamFile.make
;;

let real_opam_files =
    opam_files
    |> List.map (make_opam_file)
    |> List.map (OpamFile.OPAM.read)
;;

let upgraded_real_opam_files =
    real_opam_files
    |> List.map OpamFormatUpgrade.opam_file_from_1_2_to_2_0
;;

let () = 
    upgraded_real_opam_files
    |> List.combine opam_files
    |> List.iter (fun (fname, content) ->
        let opamfile = make_opam_file fname in
        OpamFile.OPAM.write opamfile content
    )
;;