Address @rgrinberg's review comments

bin/toplevel_init_file.ml

@@ -18,20 +18,21 @@ let man =
 let info = Term.info "toplevel-init-file" ~doc ~man
 
 let link_deps link ~lib_config =
-  List.map link ~f:(fun t ->
+  List.concat_map link ~f:(fun t ->
       Dune.Lib.link_deps t Dune.Link_mode.Byte lib_config)
-  |> List.flatten
 
 let term =
   let+ common = Common.term
-  and+ dir = Arg.(value & pos 0 string "" & Arg.info [] ~docv:"DIR") in
+  and+ dir = Arg.(value & pos 0 string "" & Arg.info [] ~docv:"DIR")
+  and+ ctx_name =
+    Common.context_arg ~doc:{|Select context where to build/run utop.|}
+  in
   Common.set_common common ~targets:[];
   Scheduler.go ~common (fun () ->
       let open Fiber.O in
       let* setup = Import.Main.setup common in
       let sctx =
-        Dune.Context_name.Map.find setup.scontexts Dune.Context_name.default
-        |> Option.value_exn
+        Dune.Context_name.Map.find setup.scontexts ctx_name |> Option.value_exn
       in
       let dir =
         Path.Build.relative
@@ -48,11 +49,8 @@ let term =
       let* () = do_build (List.map files ~f:(fun f -> Target.File f)) in
       let files_to_load =
         List.filter files ~f:(fun p ->
-            match Path.extension p with
-            | ".cma"
-            | ".cmo" ->
-              true
-            | _ -> false)
+            let ext = Path.extension p in
+            ext = Dune.Mode.compiled_lib_ext Byte || ext = Dune.Cm_kind.ext Cmo)
       in
       Dune.Toplevel.print_toplevel_init_file ~include_paths ~files_to_load;
       Fiber.return ())

src/dune/utop.mli

@@ -8,7 +8,6 @@ val utop_exe : string
 
 val is_utop_dir : Path.Build.t -> bool
 
-val libs_under_dir :
-  Super_context.t -> db:Lib.DB.t -> dir:Import.Path.t -> Lib.L.t
+val libs_under_dir : Super_context.t -> db:Lib.DB.t -> dir:Path.t -> Lib.L.t
 
 val setup : Super_context.t -> dir:Path.Build.t -> unit