Pass obj_dir explicitely to Exe.build_and_link and don't return it

The only place where we used the default value was gen_rules

src/exe.ml

@@ -112,7 +112,7 @@ let link_exe
     SC.add_rules sctx (List.map rules ~f:(fun r -> libs_and_cm_and_flags >>> r))
 
 let build_and_link_many
-      ?obj_dir ~dir ~programs ~modules
+      ~dir ~obj_dir ~programs ~modules
       ~scope
       ~linkages
       ?(requires=Build.return [])
@@ -122,14 +122,6 @@ let build_and_link_many
       ?(js_of_ocaml=Jbuild.Js_of_ocaml.default)
       sctx
   =
-  let item = (List.hd programs).Program.name in
- let obj_dir =
-    match obj_dir with
-    (* Use "eobjs" rather than "objs" to avoid a potential conflict with a
-       library of the same name *)
-    | None -> Path.relative dir ("." ^ item ^ ".eobjs")
-    | Some d -> d
-  in
   let modules =
     String_map.map modules ~f:(Module.set_obj_name ~wrapper:None)
   in
@@ -162,9 +154,7 @@ let build_and_link_many
         ~top_sorted_modules
         ~js_of_ocaml
         ~flags
-        ?link_flags));
+        ?link_flags))
 
-  obj_dir
-
-let build_and_link ?obj_dir ~dir ~program =
-  build_and_link_many ?obj_dir ~dir ~programs:[program]
+let build_and_link ~dir ~obj_dir ~program =
+  build_and_link_many ~dir ~obj_dir ~programs:[program]

src/exe.mli

@@ -34,11 +34,11 @@ end
 
 (** {1 High-level functions} *)
 
-(** Build and link one or more executables. Return the object directory. *)
+(** Build and link one or more executables *)
 
 val build_and_link
-  :  ?obj_dir:Path.t
-  -> dir:Path.t
+  :  dir:Path.t
+  -> obj_dir:Path.t
   -> program:Program.t
   -> modules:Module.t String_map.t
   -> scope:Scope.t
@@ -49,11 +49,11 @@ val build_and_link
   -> ?link_flags:(unit, string list) Build.t
   -> ?js_of_ocaml:Jbuild.Js_of_ocaml.t
   -> Super_context.t
-  -> Path.t
+  -> unit
 
 val build_and_link_many
-  :  ?obj_dir:Path.t
-  -> dir:Path.t
+  :  dir:Path.t
+  -> obj_dir:Path.t
   -> programs:Program.t list
   -> modules:Module.t String_map.t
   -> scope:Scope.t
@@ -64,7 +64,7 @@ val build_and_link_many
   -> ?link_flags:(unit, string list) Build.t
   -> ?js_of_ocaml:Jbuild.Js_of_ocaml.t
   -> Super_context.t
-  -> Path.t
+  -> unit
 
 (** {1 Low-level functions} *)
 

src/gen_rules.ml

@@ -813,19 +813,23 @@ module Gen(P : Params) = struct
         compile_info
     in
 
+    (* Use "eobjs" rather than "objs" to avoid a potential conflict
+       with a library of the same name *)
     let obj_dir =
-      Exe.build_and_link_many sctx
-        ~dir
-        ~programs
-        ~modules
-        ~already_used
-        ~scope
-        ~linkages
-        ~requires
-        ~flags
-        ~link_flags
-        ~js_of_ocaml:exes.buildable.js_of_ocaml
+      Path.relative dir ("." ^ (List.hd programs).name ^ ".eobjs")
     in
+    Exe.build_and_link_many sctx
+      ~dir
+      ~obj_dir
+      ~programs
+      ~modules
+      ~already_used
+      ~scope
+      ~linkages
+      ~requires
+      ~flags
+      ~link_flags
+      ~js_of_ocaml:exes.buildable.js_of_ocaml;
 
     { Merlin.
       requires    = real_requires

src/utop.ml

@@ -68,16 +68,14 @@ let setup sctx ~dir ~(libs : Library.t list) ~scope =
       |> Lib.Compile.make
       |> Super_context.Libs.requires sctx ~dir ~has_dot_merlin:false
     in
-    let (_obj_dir : Path.t) =
-      Exe.build_and_link sctx
-        ~dir:utop_exe_dir
-        ~obj_dir:utop_exe_dir
-        ~program:{ name = exe_name ; main_module_name }
-        ~modules
-        ~scope
-        ~linkages:[Exe.Linkage.custom]
-        ~requires
-        ~flags:(Ocaml_flags.append_common (Ocaml_flags.default ()) ["-w"; "-24"])
-        ~link_flags:(Build.return ["-linkall"; "-warn-error"; "-31"])
-    in
+    Exe.build_and_link sctx
+      ~dir:utop_exe_dir
+      ~obj_dir:utop_exe_dir
+      ~program:{ name = exe_name ; main_module_name }
+      ~modules
+      ~scope
+      ~linkages:[Exe.Linkage.custom]
+      ~requires
+      ~flags:(Ocaml_flags.append_common (Ocaml_flags.default ()) ["-w"; "-24"])
+      ~link_flags:(Build.return ["-linkall"; "-warn-error"; "-31"]);
     add_module_rules sctx ~dir:utop_exe_dir requires