Fix configurator on older versions

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

.github/workflows/workflow.yml

@@ -84,3 +84,7 @@ jobs:
       - name: test source is well formatted
         run: opam exec -- make fmt
         if: env.OCAML_VERSION == '4.10.0' && env.OS == 'ubuntu-latest'
+
+      - name: build configurator
+        run: opam install ./dune-configurator.opam
+        if: env.CONFIGURATOR == 'true'

otherlibs/configurator/src/import.ml

@@ -100,7 +100,20 @@ module Bool = struct
 end
 
 module Map (S : Map.OrderedType) = struct
-  include MoreLabels.Map.Make (S)
+  module M = MoreLabels.Map.Make (S)
+  include M
+
+  let update (type a) (t : a t) (key : M.key) ~(f : a option -> a option) : a t
+      =
+    let v =
+      match find key t with
+      | exception Not_found -> None
+      | v -> Some v
+    in
+    match (f v, v) with
+    | None, None -> t
+    | None, Some _ -> remove key t
+    | Some data, _ -> add ~key ~data t
 
   let find m k =
     match find k m with

otherlibs/configurator/src/v1.ml

@@ -529,7 +529,7 @@ const char *s%i = "BEGIN-%i-false-END";
     let values =
       Io.with_lexbuf_from_file obj_file ~f:(Extract_obj.extract [])
       |> List.fold_left ~init:Int.Map.empty ~f:(fun acc (key, v) ->
-             Int.Map.update acc ~key ~f:(function
+             Int.Map.update acc key ~f:(function
                | None -> Some [ v ]
                | Some vs -> Some (v :: vs)))
     in