fix(melange): run melc ppx with merlin

src/dune_rules/merlin.ml

@@ -33,6 +33,7 @@ module Processed = struct
     ; src_dirs : Path.Set.t
     ; flags : string list
     ; extensions : string Ml_kind.Dict.t list
+    ; mode : [ `Ocaml | `Melange ]
     }
 
   (* ...but modules can have different preprocessing specifications*)
@@ -68,7 +69,7 @@ module Processed = struct
 
   let serialize_path = Path.to_absolute_filename
 
-  let to_sexp ~pp { stdlib_dir; obj_dirs; src_dirs; flags; extensions } =
+  let to_sexp ~pp { stdlib_dir; obj_dirs; src_dirs; flags; extensions; mode } =
     let make_directive tag value = Sexp.List [ Atom tag; value ] in
     let make_directive_of_path tag path =
       make_directive tag (Sexp.Atom (serialize_path path))
@@ -94,11 +95,20 @@ module Processed = struct
               (Sexp.List (List.map ~f:(fun s -> Sexp.Atom s) flags))
           ]
       in
-      match pp with
-      | None -> flags
-      | Some { flag; args } ->
+      let flags =
+        match pp with
+        | None -> flags
+        | Some { flag; args } ->
+          make_directive "FLG"
+            (Sexp.List [ Atom (Pp_kind.to_flag flag); Atom args ])
+          :: flags
+      in
+      match mode with
+      | `Ocaml -> flags
+      | `Melange ->
         make_directive "FLG"
-          (Sexp.List [ Atom (Pp_kind.to_flag flag); Atom args ])
+          (Sexp.List
+             [ Atom (Pp_kind.to_flag Ppx); Atom "melc -as-ppx -bs-jsx 3" ])
         :: flags
     in
     let suffixes =
@@ -120,7 +130,8 @@ module Processed = struct
     in
     if String.need_quoting s then Filename.quote s else s
 
-  let to_dot_merlin stdlib_dir pp_configs flags obj_dirs src_dirs extensions =
+  let to_dot_merlin stdlib_dir pp_configs flags obj_dirs src_dirs extensions
+      (* TODO print melange flag *) _mode =
     let b = Buffer.create 256 in
     let printf = Printf.bprintf b in
     let print = Buffer.add_string b in
@@ -183,32 +194,42 @@ module Processed = struct
     | Error msg -> Printf.eprintf "%s\n" msg
     | Ok [] -> Printf.eprintf "No merlin configuration found.\n"
     | Ok (init :: tl) ->
-      let pp_configs, obj_dirs, src_dirs, flags, extensions =
+      let pp_configs, obj_dirs, src_dirs, flags, extensions, mode =
         (* We merge what is easy to merge and ignore the rest *)
         List.fold_left tl
           ~init:
             ( [ init.pp_config ]
             , init.config.obj_dirs
             , init.config.src_dirs
             , [ init.config.flags ]
-            , init.config.extensions )
+            , init.config.extensions
+            , init.config.mode )
           ~f:(fun
-               (acc_pp, acc_obj, acc_src, acc_flags, acc_ext)
+               (acc_pp, acc_obj, acc_src, acc_flags, acc_ext, acc_mode)
                { modules = _
                ; pp_config
                ; config =
-                   { stdlib_dir = _; obj_dirs; src_dirs; flags; extensions }
+                   { stdlib_dir = _
+                   ; obj_dirs
+                   ; src_dirs
+                   ; flags
+                   ; extensions
+                   ; mode
+                   }
                }
              ->
             ( pp_config :: acc_pp
             , Path.Set.union acc_obj obj_dirs
             , Path.Set.union acc_src src_dirs
             , flags :: acc_flags
-            , extensions @ acc_ext ))
+            , extensions @ acc_ext
+            , match acc_mode with
+              | `Melange -> `Melange
+              | `Ocaml -> mode ))
       in
       Printf.printf "%s\n"
         (to_dot_merlin init.config.stdlib_dir pp_configs flags obj_dirs src_dirs
-           extensions)
+           extensions mode)
 end
 
 let obj_dir_of_lib kind mode obj_dir =
@@ -418,7 +439,7 @@ module Unprocessed = struct
         Path.Set.union src_dirs
           (Path.Set.of_list_map ~f:Path.source more_src_dirs)
       in
-      { Processed.stdlib_dir; src_dirs; obj_dirs; flags; extensions }
+      { Processed.stdlib_dir; src_dirs; obj_dirs; flags; extensions; mode }
     and+ pp_config = pp_config t sctx ~expander in
     let modules =
       (* And copy for each module the resulting pp flags *)

test/blackbox-tests/test-cases/melange/merlin.t

@@ -10,6 +10,7 @@
   > (library
   >  (name $lib)
   >  (private_modules bar)
+  >  (flags :standard -bs-jsx 3)
   >  (modes melange))
   > EOF
 
@@ -25,6 +26,13 @@
     $TESTCASE_ROOT/_build/default/.foo.objs/melange)
      Foo__
 
+All 3 entries (Foo, Foo__ and Bar) contain a ppx directive
+
+  $ dune ocaml-merlin --dump-config="$(pwd)" | grep -i "ppx"
+   (FLG (-ppx "melc -as-ppx -bs-jsx 3"))
+   (FLG (-ppx "melc -as-ppx -bs-jsx 3"))
+   (FLG (-ppx "melc -as-ppx -bs-jsx 3"))
+
   $ target=output
   $ cat >dune <<EOF
   > (melange.emit
@@ -37,3 +45,8 @@
   $ dune build @check
   $ dune ocaml-merlin --dump-config="$PWD" | grep -i "$target"
     $TESTCASE_ROOT/_build/default/.output.mobjs/melange)
+
+The melange.emit entry contains a ppx directive
+
+  $ dune ocaml-merlin --dump-config="$(pwd)" | grep -i "ppx"
+   (FLG (-ppx "melc -as-ppx -bs-jsx 3"))