fix: allow to override partially the setup config (ocaml#10229)

Signed-off-by: Alpha DIALLO <moyodiallo@gmail.com>

bin/install_uninstall.ml

@@ -41,7 +41,11 @@ let get_dirs context ~prefix_from_command_line ~from_command_line =
     | Some prefix ->
       Roots.opam_from_prefix prefix ~relative:Path.relative
       |> Roots.map ~f:(fun s -> Some s)
-      |> Fiber.return
+      |> (fun opam_roots ->
+           Memo.map
+             ~f:(fun context_roots -> Roots.first_has_priority context_roots opam_roots)
+             (Context.roots ~only_setup:true context))
+      |> Memo.run
   in
   let roots = Roots.first_has_priority from_command_line roots in
   let must_be_defined name v =

src/dune_rules/context.ml

@@ -700,7 +700,7 @@ let map_exe (context : t) =
        | _ -> exe)
 ;;
 
-let roots t =
+let roots ?(only_setup = false) t =
   let module Roots = Install.Roots in
   let+ prefix_roots =
     let+ env = t.builder.env in
@@ -714,6 +714,6 @@ let roots t =
   match t.kind with
   | Lock _ | Default ->
     let setup_roots = Roots.map ~f:(Option.map ~f:Path.of_string) Setup.roots in
-    Roots.first_has_priority setup_roots prefix_roots
+    if only_setup then setup_roots else Roots.first_has_priority setup_roots prefix_roots
   | Opam _ -> prefix_roots
 ;;

src/dune_rules/context.mli

@@ -98,7 +98,7 @@ val map_exe : t -> Path.t -> Path.t
 
 (** Query where build artifacts should be installed if the user doesn't specify
     an explicit installation directory. *)
-val roots : t -> Path.t option Install.Roots.t Memo.t
+val roots : ?only_setup:bool -> t -> Path.t option Install.Roots.t Memo.t
 
 val host : t -> t Memo.t