Avoid generating .bc rule twice, also apply to .cmo.js rules

src/dune_file.mli

@@ -271,6 +271,7 @@ module Executables : sig
     val object_       : t
     val shared_object : t
     val byte          : t
+    val byte_js       : t
     val native        : t
 
     val compare : t -> t -> Ordering.t

src/exe.ml

@@ -32,12 +32,6 @@ module Linkage = struct
     ; flags = []
     }
 
-  let js =
-    { mode = Byte
-    ; ext  = ".bc.js"
-    ; flags = []
-    }
-
   let custom =
     { mode  = Byte
     ; ext   = ".exe"
@@ -131,15 +125,9 @@ let link_exe
       ~top_sorted_modules
       ~arg_spec_for_requires
       ?(link_flags=Build.arr (fun _ -> []))
-      ?(js_of_ocaml=Dune_file.Js_of_ocaml.default)
+      ?js_of_ocaml
       cctx
   =
-  let linkage, js =
-    if linkage.ext = ".bc.js" then
-      {linkage with ext = ".bc"}, true
-    else
-      linkage, false
-  in
   let sctx     = CC.super_context cctx in
   let ctx      = SC.context       sctx in
   let dir      = CC.dir           cctx in
@@ -149,9 +137,6 @@ let link_exe
   let exe = exe_path_from_name cctx ~name ~linkage in
   let compiler = Option.value_exn (Context.compiler ctx mode) in
   let kind = Mode.cm_kind mode in
-  let explicit_js_mode =
-    Dune_project.explicit_js_mode (Scope.project (CC.scope cctx))
-  in
   let artifacts ~ext modules =
     List.map modules ~f:(Module.obj_file ~mode ~ext)
   in
@@ -192,32 +177,38 @@ let link_exe
        ; Dyn (fun (cm_files, _, _) -> Deps cm_files)
        ]);
   if linkage.ext = ".bc" then
-    let rules =
-      if not explicit_js_mode || js then
-        Js_of_ocaml_rules.build_exe cctx ~js_of_ocaml ~src:exe
-      else
-        []
-    in
-    let cm_and_flags =
-      Build.fanout
-        (modules_and_cm_files >>^ snd)
-        (Expander.expand_and_eval_set expander
-           js_of_ocaml.flags
-           ~standard:(Build.return (Js_of_ocaml_rules.standard sctx)))
-    in
-    SC.add_rules ~dir sctx (List.map rules ~f:(fun r -> cm_and_flags >>> r))
+    Option.iter ~f:(fun js_of_ocaml ->
+      let rules = Js_of_ocaml_rules.build_exe cctx ~js_of_ocaml ~src:exe in
+      let cm_and_flags =
+        Build.fanout
+          (modules_and_cm_files >>^ snd)
+          (Expander.expand_and_eval_set expander
+             js_of_ocaml.flags
+             ~standard:(Build.return (Js_of_ocaml_rules.standard sctx)))
+      in
+      SC.add_rules ~dir sctx (List.map rules ~f:(fun r -> cm_and_flags >>> r))
+    ) js_of_ocaml
 
 let build_and_link_many
       ~programs
       ~linkages
       ?link_flags
-      ?(js_of_ocaml=Dune_file.Js_of_ocaml.default)
+      ?js_of_ocaml
       cctx
   =
   let dep_graphs = Ocamldep.rules cctx in
 
+  let explicit_js_mode =
+    Dune_project.explicit_js_mode (Scope.project (CC.scope cctx))
+  in
+  let js_of_ocaml =
+    match explicit_js_mode, js_of_ocaml with
+    | false, None -> Some Dune_file.Js_of_ocaml.default
+    | _ -> js_of_ocaml
+  in
+
   (* CR-someday jdimino: this should probably say [~dynlink:false] *)
-  Module_compilation.build_modules cctx ~js_of_ocaml ~dep_graphs;
+  Module_compilation.build_modules cctx ?js_of_ocaml ~dep_graphs;
 
   List.iter programs ~f:(fun { Program.name; main_module_name ; loc } ->
     let top_sorted_modules =
@@ -237,7 +228,7 @@ let build_and_link_many
         ~name
         ~linkage
         ~top_sorted_modules
-        ~js_of_ocaml
+        ?js_of_ocaml
         ~arg_spec_for_requires
         ?link_flags))
 

src/exe.mli

@@ -21,9 +21,6 @@ module Linkage : sig
   (** Byte compilation, link with [-custom], extension [.exe] *)
   val custom : t
 
-  (** Javascript compilation, extension [.bc.js] *)
-  val js : t
-
   (** [native] if supported, [custom] if not *)
   val native_or_custom : Context.t -> t
 

src/exe_rules.ml

@@ -47,12 +47,20 @@ let executables_rules ~sctx ~dir ~dir_kind ~expander
                   Module.Name.pp mod_name)
   in
 
+  let has_js = Dune_file.Executables.Link_mode.(Set.mem exes.modes byte_js) in
+
   let linkages =
     let module L = Dune_file.Executables.Link_mode in
     let ctx = SC.context sctx in
+    let modes =
+      if has_js then
+        L.Set.remove (L.Set.add exes.modes L.byte) L.byte_js
+      else
+        exes.modes
+    in
     let l =
       let has_native = Option.is_some ctx.ocamlopt in
-      List.filter_map (L.Set.to_list exes.modes) ~f:(fun (mode : L.t) ->
+      List.filter_map (L.Set.to_list modes) ~f:(fun (mode : L.t) ->
         match has_native, mode.mode with
         | false, Native ->
           None
@@ -97,12 +105,19 @@ let executables_rules ~sctx ~dir ~dir_kind ~expander
   in
 
   let requires_compile = Compilation_context.requires_compile cctx in
+  let explicit_js_mode = Dune_project.explicit_js_mode (Scope.project scope) in
+  let js_of_ocaml =
+    if not explicit_js_mode || has_js then
+      Some exes.buildable.js_of_ocaml
+    else
+      None
+  in
 
   Exe.build_and_link_many cctx
     ~programs
     ~linkages
     ~link_flags
-    ~js_of_ocaml:exes.buildable.js_of_ocaml;
+    ?js_of_ocaml;
 
   (cctx,
    Merlin.make ()