Pass ocamlc explicitly to configurator using DUNE_CONFIGURATOR

src/configurator/v1.ml

@@ -419,13 +419,14 @@ module Pkg_config = struct
 end
 
 let main ?(args=[]) ~name f =
-  let ocamlc  = ref None  in
+  let ocamlc  = ref (Sys.getenv_opt "DUNE_CONFIGURATOR") in
   let verbose = ref false in
   let dest_dir = ref None in
   let args =
     Arg.align
       ([ "-ocamlc", Arg.String (fun s -> ocamlc := Some s),
-         "PATH ocamlc command to use"
+         "PATH ocamlc command to use. \
+          This value is set automatically when configurator is invoked by dune."
        ; "-verbose", Arg.Set verbose,
          " be verbose"
        ; "-dest-dir", Arg.String (fun s -> dest_dir := Some s),

src/context.ml

@@ -303,6 +303,7 @@ let create ~(kind : Kind.t) ~path ~env ~name ~merlin ~targets () =
                "lib")
         ; extend_var "MANPATH"
             (Config.local_install_man_dir ~context:name)
+        ; "DUNE_CONFIGURATOR", (Path.to_string ocamlc)
         ]
       in
       Env.extend env ~vars:(Env.Map.of_list_exn vars)

test/blackbox-tests/test-cases/configurator/config/run.ml

@@ -1,6 +1,10 @@
 module Configurator = Configurator.V1
 
 let () =
+  begin match Sys.getenv_opt "DUNE_CONFIGURATOR" with
+  | None -> failwith "DUNE_CONFIGURATOR is not passed"
+  | Some _ -> print_endline "DUNE_CONFIGURATOR is present"
+  end;
   Configurator.main ~name:"config" (fun t ->
     match Configurator.ocaml_config_var t "version" with
     | None -> failwith "version is absent"

test/blackbox-tests/test-cases/configurator/run.t

@@ -1,5 +1,6 @@
 Show that config values are present
   $ jbuilder exec config/run.exe
+  DUNE_CONFIGURATOR is present
   version is present
 
 We're able to compile C program sucessfully