diff --git a/doc/changes/8567.md b/doc/changes/8567.md
new file mode 100644
index 00000000000..64cd6d2ca9d
--- /dev/null
+++ b/doc/changes/8567.md
@@ -0,0 +1,3 @@
+- merlin: add optional `(merlin_reader CMD)` construct to `(dialect)` stanza to
+  configure a merlin reader (#8567, @andreypopp)
+
diff --git a/src/dune_rules/dialect.ml b/src/dune_rules/dialect.ml
index e5f556f3fc8..56a876fadb2 100644
--- a/src/dune_rules/dialect.ml
+++ b/src/dune_rules/dialect.ml
@@ -11,9 +11,10 @@ module File_kind = struct
     ; preprocess : (Loc.t * Action.t) option
     ; format : (Loc.t * Action.t * string list) option
     ; print_ast : (Loc.t * Action.t) option
+    ; merlin_reader : (Loc.t * string list) option
     }
 
-  let encode { kind; extension; preprocess; format; print_ast } =
+  let encode { kind; extension; preprocess; format; print_ast; merlin_reader } =
     let open Dune_lang.Encoder in
     let kind =
       string
@@ -33,10 +34,11 @@ module File_kind = struct
                 "print_ast"
                 Action.encode
                 (Option.map ~f:(fun (_, x) -> x) print_ast)
+            ; field_o "merlin_reader" (list string) (Option.map ~f:snd merlin_reader)
             ])
   ;;
 
-  let to_dyn { kind; extension; preprocess; format; print_ast } =
+  let to_dyn { kind; extension; preprocess; format; print_ast; merlin_reader } =
     let open Dyn in
     record
       [ "kind", Ml_kind.to_dyn kind
@@ -44,6 +46,7 @@ module File_kind = struct
       ; "preprocess", option (fun (_, x) -> Action.to_dyn x) preprocess
       ; "format", option (fun (_, x, y) -> pair Action.to_dyn (list string) (x, y)) format
       ; "print_ast", option (fun (_, x) -> Action.to_dyn x) print_ast
+      ; "merlin_reader", option (fun (_, x) -> list string x) merlin_reader
       ]
   ;;
 end
@@ -85,13 +88,17 @@ let decode =
         "format"
         (map ~f:(fun (loc, x) -> loc, x, []) (located Action.decode_dune_file))
     and+ print_ast = field_o "print_ast" (located Action.decode_dune_file)
+    and+ merlin_reader =
+      field_o
+        "merlin_reader"
+        (Dune_lang.Syntax.since Stanza.syntax (3, 16) >>> located (repeat1 string))
     and+ syntax_ver = Syntax.get_exn Stanza.syntax in
     let ver = 3, 9 in
     if syntax_ver < ver && Option.is_some (String.index_from extension 1 '.')
     then (
       let what = "the possibility of defining extensions containing periods" in
       Syntax.Error.since loc Stanza.syntax ver ~what);
-    { File_kind.kind; extension; preprocess; format; print_ast }
+    { File_kind.kind; extension; preprocess; format; print_ast; merlin_reader }
   in
   fields
     (let+ name = field "name" string
@@ -143,6 +150,13 @@ let print_ast { file_kinds; _ } ml_kind =
   x.print_ast
 ;;
 
+let merlin_reader { file_kinds; _ } ml_kind =
+  let open Option.O in
+  let* dialect = Ml_kind.Dict.get file_kinds ml_kind in
+  let+ _, merlin_reader = dialect.merlin_reader in
+  merlin_reader
+;;
+
 let ocaml =
   let format kind =
     let flag_of_kind = function
@@ -180,6 +194,7 @@ let ocaml =
           , format kind
           , [ ".ocamlformat"; ".ocamlformat-ignore"; ".ocamlformat-enable" ] )
     ; print_ast = Some (Loc.none, print_ast kind)
+    ; merlin_reader = None
     }
   in
   let intf = Some (file_kind Ml_kind.Intf ".mli") in
@@ -222,6 +237,7 @@ let reason =
     ; preprocess = Some (Loc.none, preprocess)
     ; format = Some (Loc.none, format, [])
     ; print_ast = Some (Loc.none, print_ast)
+    ; merlin_reader = None
     }
   in
   let intf = Some (file_kind Ml_kind.Intf ".rei") in
@@ -251,6 +267,7 @@ let rescript =
     ; preprocess = Some (Loc.none, preprocess)
     ; format = Some (Loc.none, format, [])
     ; print_ast = None
+    ; merlin_reader = None
     }
   in
   let intf = Some (file_kind Ml_kind.Intf ".resi") in
@@ -271,7 +288,12 @@ module DB = struct
   type t =
     { by_name : dialect String.Map.t
     ; by_extension : dialect Filename.Extension.Map.t
-    ; mutable extensions_for_merlin : string option Ml_kind.Dict.t list option
+    ; for_merlin : for_merlin Lazy.t
+    }
+
+  and for_merlin =
+    { extensions : Filename.Extension.t option Ml_kind.Dict.t list
+    ; readers : Filename.Extension.t list String.Map.t
     }
 
   let fold { by_name; _ } = String.Map.fold by_name
@@ -279,35 +301,49 @@ module DB = struct
   let empty =
     { by_name = String.Map.empty
     ; by_extension = Filename.Extension.Map.empty
-    ; extensions_for_merlin = None
+    ; for_merlin = lazy { extensions = []; readers = String.Map.empty }
     }
   ;;
 
-  let set_extensions_for_merlin t =
-    let v =
-      fold t ~init:[] ~f:(fun d s ->
-        let impl = extension d Ml_kind.Impl in
-        let intf = extension d Ml_kind.Intf in
-        if (* Only include dialects with no preprocessing and skip default file
-              extensions *)
-           preprocess d Ml_kind.Impl <> None
-           || preprocess d Ml_kind.Intf <> None
-           || (impl = extension ocaml Ml_kind.Impl && intf = extension ocaml Ml_kind.Intf)
-        then s
-        else { Ml_kind.Dict.impl; intf } :: s)
-      |> List.sort ~compare:(Ml_kind.Dict.compare (Option.compare String.compare))
+  let compute_for_merlin =
+    let handle_ml_kind ~dialect kind readers =
+      let ext = extension dialect kind in
+      if ext = extension ocaml kind
+      then (* this is standard dialect, exclude *) None, readers
+      else (
+        match ext, merlin_reader dialect kind with
+        | Some ext, Some reader -> Some ext, String.Map.add_exn readers ext reader
+        | _ ->
+          if preprocess dialect kind <> None
+          then (* we have preprocessor defined *) None, readers
+          else ext, readers)
     in
-    t.extensions_for_merlin <- Some v;
-    v
+    fun by_name ->
+      let extensions, readers =
+        String.Map.fold
+          by_name
+          ~init:([], String.Map.empty)
+          ~f:(fun dialect (extensions, readers) ->
+            let impl, readers = handle_ml_kind ~dialect Ml_kind.Impl readers in
+            let intf, readers = handle_ml_kind ~dialect Ml_kind.Intf readers in
+            let extensions =
+              match impl, intf with
+              | None, None -> extensions
+              | _ -> { Ml_kind.Dict.impl; intf } :: extensions
+            in
+            extensions, readers)
+      in
+      let extensions =
+        List.sort
+          ~compare:(Ml_kind.Dict.compare (Option.compare String.compare))
+          extensions
+      in
+      { extensions; readers }
   ;;
 
-  let extensions_for_merlin t =
-    match t.extensions_for_merlin with
-    | Some s -> s
-    | None -> set_extensions_for_merlin t
-  ;;
+  let for_merlin t = Lazy.force t.for_merlin
 
-  let add { by_name; by_extension; extensions_for_merlin = _ } ~loc dialect =
+  let add { by_name; by_extension; for_merlin = _ } ~loc dialect =
     let by_name =
       match String.Map.add by_name dialect.name dialect with
       | Ok by_name -> by_name
@@ -331,7 +367,7 @@ module DB = struct
     let by_extension =
       add_ext (add_ext by_extension dialect.file_kinds.intf) dialect.file_kinds.impl
     in
-    { by_name; by_extension; extensions_for_merlin = None }
+    { by_name; by_extension; for_merlin = lazy (compute_for_merlin by_name) }
   ;;
 
   let of_list dialects = List.fold_left ~f:(add ~loc:Loc.none) ~init:empty dialects
diff --git a/src/dune_rules/dialect.mli b/src/dune_rules/dialect.mli
index 6cb8b7a1680..7cd9b9b0ee8 100644
--- a/src/dune_rules/dialect.mli
+++ b/src/dune_rules/dialect.mli
@@ -43,8 +43,14 @@ module DB : sig
   val find_by_name : t -> string -> dialect option
   val find_by_extension : t -> Filename.Extension.t -> (dialect * Ml_kind.t) option
   val fold : t -> init:'a -> f:(dialect -> 'a -> 'a) -> 'a
-  val extensions_for_merlin : t -> Filename.Extension.t option Ml_kind.Dict.t list
   val to_dyn : t -> Dyn.t
   val builtin : t
   val is_default : t -> bool
+
+  type for_merlin =
+    { extensions : string option Ml_kind.Dict.t list
+    ; readers : Filename.Extension.t list String.Map.t
+    }
+
+  val for_merlin : t -> for_merlin
 end
diff --git a/src/dune_rules/merlin/merlin.ml b/src/dune_rules/merlin/merlin.ml
index 89781b27cda..fa70393ae8e 100644
--- a/src/dune_rules/merlin/merlin.ml
+++ b/src/dune_rules/merlin/merlin.ml
@@ -68,25 +68,30 @@ module Processed = struct
   type module_config =
     { opens : Module_name.t list
     ; module_ : Module.t
+    ; reader : string list option
     }
 
-  let dyn_of_module_config { opens; module_ } =
+  let dyn_of_module_config { opens; module_; reader } =
     let open Dyn in
-    record [ "opens", list Module_name.to_dyn opens; "module_", Module.to_dyn module_ ]
+    record
+      [ "opens", list Module_name.to_dyn opens
+      ; "module_", Module.to_dyn module_
+      ; "reader", option (list string) reader
+      ]
   ;;
 
   (* ...but modules can have different preprocessing specifications*)
   type t =
     { config : config
-    ; per_module_config : module_config Path.Build.Map.t
+    ; per_file_config : module_config Path.Build.Map.t
     ; pp_config : pp_flag option Module_name.Per_item.t
     }
 
-  let to_dyn { config; per_module_config; pp_config } =
+  let to_dyn { config; per_file_config; pp_config } =
     let open Dyn in
     record
       [ "config", dyn_of_config config
-      ; "per_module_config", Path.Build.Map.to_dyn dyn_of_module_config per_module_config
+      ; "per_file_config", Path.Build.Map.to_dyn dyn_of_module_config per_file_config
       ; "pp_config", Module_name.Per_item.to_dyn (option dyn_of_pp_flag) pp_config
       ]
   ;;
@@ -106,7 +111,7 @@ module Processed = struct
           ; flags = [ "-x" ]
           ; extensions = [ { Ml_kind.Dict.intf = None; impl = Some "ext" } ]
           }
-      ; per_module_config = Path.Build.Map.empty
+      ; per_file_config = Path.Build.Map.empty
       ; pp_config =
           (match
              Module_name.Per_item.of_mapping
@@ -144,7 +149,7 @@ module Processed = struct
     | None, None -> None
   ;;
 
-  let to_sexp ~opens ~pp { stdlib_dir; obj_dirs; src_dirs; flags; extensions } =
+  let to_sexp ~opens ~pp ~reader { stdlib_dir; obj_dirs; src_dirs; flags; extensions } =
     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))
@@ -185,8 +190,16 @@ module Processed = struct
         let+ impl, intf = get_ext x in
         make_directive "SUFFIX" (Sexp.Atom (Printf.sprintf "%s %s" impl intf)))
     in
+    let reader =
+      match reader with
+      | Some reader ->
+        [ make_directive "READER" (Sexp.List (List.map ~f:(fun r -> Sexp.Atom r) reader))
+        ]
+      | None -> []
+    in
     Sexp.List
-      (List.concat [ stdlib_dir; exclude_query_dir; obj_dirs; src_dirs; flags; suffixes ])
+      (List.concat
+         [ stdlib_dir; exclude_query_dir; obj_dirs; src_dirs; flags; suffixes; reader ])
   ;;
 
   let quote_for_dot_merlin s =
@@ -231,39 +244,46 @@ module Processed = struct
     Buffer.contents b
   ;;
 
-  let get { per_module_config; pp_config; config } ~file =
-    (* We only match the first part of the filename : foo.ml -> foo foo.cppo.ml
-       -> foo *)
+  let get { per_file_config; pp_config; config } ~file =
     let open Option.O in
-    let+ { module_; opens } =
-      let find file =
-        let file_without_ext = remove_extension file in
-        Path.Build.Map.find per_module_config file_without_ext
-      in
+    let+ { module_; opens; reader } =
+      let find file = Path.Build.Map.find per_file_config file in
       match find file with
       | Some _ as s -> s
-      | None -> Copy_line_directive.DB.follow_while file ~f:find
+      | None ->
+        (match Copy_line_directive.DB.follow_while file ~f:find with
+         | Some _ as s -> s
+         | None ->
+           (* Fallback to handle preprocessed files (where the preprocessor has
+              the file extensison changed).
+
+              We choose to fallback by a lookup by filename without extension.
+
+              This is too rough but, really, preprocessors should emit copy
+              line directives instead and then Dune should have the database
+              similar to Copy_line_directive to handle this. *)
+           Path.Build.Map.find per_file_config (remove_extension file))
     in
     let pp = Module_name.Per_item.get pp_config (Module.name module_) in
-    to_sexp ~opens ~pp config
+    to_sexp ~opens ~pp ~reader config
   ;;
 
   let print_file path =
     match load_file path with
     | Error msg -> Printf.eprintf "%s\n" msg
-    | Ok { per_module_config; pp_config; config } ->
-      let pp_one (source, { module_; opens }) =
+    | Ok { per_file_config; pp_config; config } ->
+      let pp_one (source, { module_; opens; reader }) =
         let open Pp.O in
         let name = Module.name module_ in
         let pp = Module_name.Per_item.get pp_config name in
-        let sexp = to_sexp ~opens ~pp config in
+        let sexp = to_sexp ~reader ~opens ~pp config in
         Pp.hvbox
           (Pp.textf "%s: %s" (Module_name.to_string name) (Path.Build.to_string source))
         ++ Pp.newline
         ++ Pp.vbox (Sexp.pp sexp)
       in
       let pp =
-        Path.Build.Map.to_list per_module_config
+        Path.Build.Map.to_list per_file_config
         |> Pp.concat_map ~sep:Pp.cut ~f:pp_one
         |> Pp.vbox
       in
@@ -288,7 +308,7 @@ module Processed = struct
           ~f:
             (fun
               (acc_pp, acc_obj, acc_src, acc_flags, acc_ext)
-              { per_module_config = _
+              { per_file_config = _
               ; pp_config
               ; config = { stdlib_dir = _; obj_dirs; src_dirs; flags; extensions }
               }
@@ -335,6 +355,7 @@ module Unprocessed = struct
     ; source_dirs : Path.Source.Set.t
     ; objs_dirs : Path.Set.t
     ; extensions : string option Ml_kind.Dict.t list
+    ; readers : string list String.Map.t
     ; mode : Lib_mode.t
     }
 
@@ -373,7 +394,7 @@ module Unprocessed = struct
       Path.Set.singleton @@ obj_dir_of_lib `Private mode (Obj_dir.of_local obj_dir)
     in
     let flags = Ocaml_flags.get flags mode in
-    let extensions = Dialect.DB.extensions_for_merlin dialects in
+    let { Dialect.DB.extensions; readers } = Dialect.DB.for_merlin dialects in
     let config =
       { stdlib_dir
       ; mode
@@ -384,6 +405,7 @@ module Unprocessed = struct
       ; source_dirs
       ; objs_dirs
       ; extensions
+      ; readers
       }
     in
     { ident; config; modules }
@@ -488,6 +510,7 @@ module Unprocessed = struct
      ; config =
          { stdlib_dir
          ; extensions
+         ; readers
          ; flags
          ; objs_dirs
          ; source_dirs
@@ -562,24 +585,27 @@ module Unprocessed = struct
       in
       { Processed.stdlib_dir; src_dirs; obj_dirs; flags; extensions }
     and+ pp_config = pp_config t (Super_context.context sctx) ~expander in
-    let per_module_config =
+    let per_file_config =
       (* And copy for each module the resulting pp flags *)
       modules
       |> Modules.With_vlib.drop_vlib
       |> Modules.fold ~init:[] ~f:(fun m init ->
-        Module.sources m
-        |> Path.Build.Set.of_list_map ~f:(fun src ->
-          Path.as_in_build_dir_exn src |> remove_extension)
+        Module.sources_without_pp m
+        |> Path.Build.Set.of_list_map ~f:(fun src -> Path.as_in_build_dir_exn src)
         |> Path.Build.Set.fold ~init ~f:(fun src acc ->
           let config =
             { Processed.module_ = Module.set_pp m None
             ; opens = Modules.With_vlib.local_open modules m
+            ; reader = String.Map.find readers (Path.Build.extension src)
             }
           in
-          (src, config) :: acc))
-      |> Path.Build.Map.of_list_exn
+          (* we add the config with and without the extension, the latter is
+             needed for a fallback in this file's [get] function. *)
+          let src_without_extension = remove_extension src in
+          (src, config) :: (src_without_extension, config) :: acc))
+      |> Path.Build.Map.of_list_reduce ~f:(fun existing _ -> existing)
     in
-    { Processed.pp_config; config; per_module_config }
+    { Processed.pp_config; config; per_file_config }
   ;;
 end
 
diff --git a/src/dune_rules/module.ml b/src/dune_rules/module.ml
index 21d5053f86b..6ea97e25ad9 100644
--- a/src/dune_rules/module.ml
+++ b/src/dune_rules/module.ml
@@ -3,6 +3,9 @@ open Import
 module File = struct
   type t =
     { path : Path.t
+    ; original_path : Path.t
+        (* while path can be changed for a module (when it is being pp'ed), the
+           original_path stays the same and points to an original source file *)
     ; dialect : Dialect.t
     }
 
@@ -11,16 +14,17 @@ module File = struct
     fields
     @@ let+ path = field "path" (Dune_lang.Path.Local.decode ~dir) in
        (* TODO do not just assume the dialect is OCaml *)
-       { path; dialect = Dialect.ocaml }
+       { path; original_path = path; dialect = Dialect.ocaml }
   ;;
 
-  let encode { path; dialect = _ } ~dir =
+  let encode { path; original_path = _; dialect = _ } ~dir =
     let open Dune_lang.Encoder in
     record_fields [ field "path" (Dune_lang.Path.Local.encode ~dir) path ]
   ;;
 
   let dialect t = t.dialect
   let path t = t.path
+  let original_path t = t.original_path
 
   let version_installed t ~src_root ~install_dir =
     let path =
@@ -32,11 +36,15 @@ module File = struct
     { t with path }
   ;;
 
-  let make dialect path = { dialect; path }
+  let make dialect path = { dialect; path; original_path = path }
 
-  let to_dyn { path; dialect } =
+  let to_dyn { path; original_path; dialect } =
     let open Dyn in
-    record [ "path", Path.to_dyn path; "dialect", Dyn.string @@ Dialect.name dialect ]
+    record
+      [ "path", Path.to_dyn path
+      ; "original_path", Path.to_dyn original_path
+      ; "dialect", Dyn.string @@ Dialect.name dialect
+      ]
   ;;
 end
 
@@ -305,17 +313,17 @@ let wrapped_compat t =
   assert (t.visibility = Public);
   let source =
     let impl =
-      Some
-        { File.dialect = Dialect.ocaml
-        ; path =
-            (* Option.value_exn cannot fail because we disallow wrapped
-               compatibility mode for virtual libraries. That means none of the
-               modules are implementing a virtual module, and therefore all have
-               a source dir *)
-            Path.L.relative
-              (src_dir t)
-              [ ".wrapped_compat"; Module_name.Path.to_string t.source.path ^ ml_gen ]
-        }
+      let path =
+        (* TODO(andreypopp): is this comment still relevant? *)
+        (* Option.value_exn cannot fail because we disallow wrapped
+           compatibility mode for virtual libraries. That means none of the
+           modules are implementing a virtual module, and therefore all have
+           a source dir *)
+        Path.L.relative
+          (src_dir t)
+          [ ".wrapped_compat"; Module_name.Path.to_string t.source.path ^ ml_gen ]
+      in
+      Some { File.dialect = Dialect.ocaml; path; original_path = path }
     in
     { t.source with files = { intf = None; impl } }
   in
@@ -330,6 +338,12 @@ let sources t =
     ~f:(Option.map ~f:(fun (x : File.t) -> x.path))
 ;;
 
+let sources_without_pp t =
+  List.filter_map
+    [ t.source.files.intf; t.source.files.impl ]
+    ~f:(Option.map ~f:(fun (x : File.t) -> x.original_path))
+;;
+
 module Obj_map = struct
   include Map.Make (struct
       type nonrec t = t
@@ -387,7 +401,7 @@ let ml_source =
     | None -> f
     | Some suffix ->
       let path = Path.extend_basename f.path ~suffix in
-      File.make Dialect.ocaml path)
+      { f with dialect = Dialect.ocaml; path })
 ;;
 
 let version_installed t ~src_root ~install_dir =
diff --git a/src/dune_rules/module.mli b/src/dune_rules/module.mli
index 7788038b68d..4e54bd91461 100644
--- a/src/dune_rules/module.mli
+++ b/src/dune_rules/module.mli
@@ -7,6 +7,7 @@ module File : sig
 
   val dialect : t -> Dialect.t
   val path : t -> Path.t
+  val original_path : t -> Path.t
   val make : Dialect.t -> Path.t -> t
 end
 
@@ -61,7 +62,6 @@ val set_obj_name : t -> Module_name.Unique.t -> t
 val set_path : t -> Module_name.Path.t -> t
 val add_file : t -> Ml_kind.t -> File.t -> t
 val set_source : t -> Ml_kind.t -> File.t option -> t
-val map_files : t -> f:(Ml_kind.t -> File.t -> File.t) -> t
 
 (** Set preprocessing flags *)
 val set_pp : t -> (string list Action_builder.t * Sandbox_config.t) option -> t
@@ -88,6 +88,7 @@ module Obj_map : sig
 end
 
 val sources : t -> Path.t list
+val sources_without_pp : t -> Path.t list
 val visibility : t -> Visibility.t
 val encode : t -> src_dir:Path.t -> Dune_lang.t list
 val decode : src_dir:Path.t -> t Dune_lang.Decoder.t
diff --git a/test/blackbox-tests/test-cases/github2206.t/run.t b/test/blackbox-tests/test-cases/github2206.t/run.t
index 2d0989b9469..976772d7dc0 100644
--- a/test/blackbox-tests/test-cases/github2206.t/run.t
+++ b/test/blackbox-tests/test-cases/github2206.t/run.t
@@ -5,3 +5,7 @@ copy_files would break the generation of the preprocessing flags
    (FLG
     (-pp
      $TESTCASE_ROOT/_build/default/pp.exe))
+  --
+   (FLG
+    (-pp
+     $TESTCASE_ROOT/_build/default/pp.exe))
diff --git a/test/blackbox-tests/test-cases/melange/merlin-compile-flags.t b/test/blackbox-tests/test-cases/melange/merlin-compile-flags.t
index d6dc06619c2..3bd56c798ff 100644
--- a/test/blackbox-tests/test-cases/melange/merlin-compile-flags.t
+++ b/test/blackbox-tests/test-cases/melange/merlin-compile-flags.t
@@ -21,6 +21,9 @@ Show that the merlin config knows about melange.compile_flags
      +42)))
      +42)))
      +42)))
+     +42)))
+     +42)))
+     +42)))
 
   $ cat >dune <<EOF
   > (melange.emit
@@ -35,4 +38,7 @@ Show that the merlin config knows about melange.compile_flags
      +42)))
      +42)))
      +42)))
+     +42)))
+     +42)))
+     +42)))
 
diff --git a/test/blackbox-tests/test-cases/melange/merlin.t b/test/blackbox-tests/test-cases/melange/merlin.t
index 7002f53a1a6..8a4d7e6a873 100644
--- a/test/blackbox-tests/test-cases/melange/merlin.t
+++ b/test/blackbox-tests/test-cases/melange/merlin.t
@@ -25,11 +25,18 @@
   $ dune ocaml merlin dump-config "$PWD" | grep -i "$lib"
     $TESTCASE_ROOT/_build/default/.foo.objs/melange)
    (FLG (-open Foo__))
+    $TESTCASE_ROOT/_build/default/.foo.objs/melange)
+   (FLG (-open Foo__))
   Foo: _build/default/foo
     $TESTCASE_ROOT/_build/default/.foo.objs/melange)
    (FLG (-open Foo__))
+  Foo: _build/default/foo.ml
+    $TESTCASE_ROOT/_build/default/.foo.objs/melange)
+   (FLG (-open Foo__))
   Foo__: _build/default/foo__
     $TESTCASE_ROOT/_build/default/.foo.objs/melange)
+  Foo__: _build/default/foo__.ml-gen
+    $TESTCASE_ROOT/_build/default/.foo.objs/melange)
 
 Paths to Melange stdlib appear in B and S entries without melange.emit stanza
 
@@ -54,6 +61,7 @@ Paths to Melange stdlib appear in B and S entries without melange.emit stanza
   $ dune build @check
   $ dune ocaml merlin dump-config $PWD | grep -i "$target"
     $TESTCASE_ROOT/_build/default/.output.mobjs/melange)
+    $TESTCASE_ROOT/_build/default/.output.mobjs/melange)
 
 Dump-dot-merlin includes the melange flags
 
@@ -103,6 +111,28 @@ User ppx flags should appear in merlin config
 
   $ dune ocaml merlin dump-config $PWD | grep -v "(B "  | grep -v "(S "
   Bar: _build/default/bar
+  ((STDLIB /MELC_STDLIB/melange)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/melange)
+   (S
+    $TESTCASE_ROOT)
+   (FLG (-open Foo))
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/4128e43a9cfb141a37f547484cc9bf46/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="foo"'"))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Bar: _build/default/bar.ml
   ((STDLIB /MELC_STDLIB/melange)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -125,6 +155,27 @@ User ppx flags should appear in merlin config
      -keep-locs
      -g)))
   Foo: _build/default/foo
+  ((STDLIB /MELC_STDLIB/melange)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/melange)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/4128e43a9cfb141a37f547484cc9bf46/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="foo"'"))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Foo: _build/default/foo.ml-gen
   ((STDLIB /MELC_STDLIB/melange)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -160,3 +211,18 @@ User ppx flags should appear in merlin config
      -short-paths
      -keep-locs
      -g)))
+  Fooppx: _build/default/fooppx.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.fooppx.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/default-based-context.t/run.t b/test/blackbox-tests/test-cases/merlin/default-based-context.t/run.t
index d29e5ee4eee..bab44db75f2 100644
--- a/test/blackbox-tests/test-cases/merlin/default-based-context.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/default-based-context.t/run.t
@@ -37,6 +37,21 @@ If Merlin field is absent, default context is chosen
      -short-paths
      -keep-locs
      -g)))
+  Foo: _build/default/foo.ml
+  ((STDLIB OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
 
 If Merlin field is present, this context is chosen
 
@@ -75,3 +90,18 @@ If Merlin field is present, this context is chosen
      -short-paths
      -keep-locs
      -g)))
+  Foo: _build/cross/foo.ml
+  ((STDLIB OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/cross/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/dune-project b/test/blackbox-tests/test-cases/merlin/dialect.t/dune-project
new file mode 100644
index 00000000000..1bf4647c9b4
--- /dev/null
+++ b/test/blackbox-tests/test-cases/merlin/dialect.t/dune-project
@@ -0,0 +1,10 @@
+(lang dune 3.16)
+
+(using melange 0.1)
+
+(dialect
+ (name mlx)
+ (implementation
+  (extension mlx)
+  (preprocess (run cat %{input-file}))
+  (merlin_reader mlx)))
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/exe/dune b/test/blackbox-tests/test-cases/merlin/dialect.t/exe/dune
new file mode 100644
index 00000000000..efd40e79e08
--- /dev/null
+++ b/test/blackbox-tests/test-cases/merlin/dialect.t/exe/dune
@@ -0,0 +1,2 @@
+(executable
+ (name x))
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/exe/x.mlx b/test/blackbox-tests/test-cases/merlin/dialect.t/exe/x.mlx
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/lib/dune b/test/blackbox-tests/test-cases/merlin/dialect.t/lib/dune
new file mode 100644
index 00000000000..caefbf89753
--- /dev/null
+++ b/test/blackbox-tests/test-cases/merlin/dialect.t/lib/dune
@@ -0,0 +1,2 @@
+(library
+ (name x))
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/lib/x.mlx b/test/blackbox-tests/test-cases/merlin/dialect.t/lib/x.mlx
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/melange/dune b/test/blackbox-tests/test-cases/merlin/dialect.t/melange/dune
new file mode 100644
index 00000000000..e7804c2555b
--- /dev/null
+++ b/test/blackbox-tests/test-cases/merlin/dialect.t/melange/dune
@@ -0,0 +1,3 @@
+(library
+ (modes melange)
+ (name x_mel))
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/melange/x_mel.mlx b/test/blackbox-tests/test-cases/merlin/dialect.t/melange/x_mel.mlx
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/test/blackbox-tests/test-cases/merlin/dialect.t/run.t b/test/blackbox-tests/test-cases/merlin/dialect.t/run.t
new file mode 100644
index 00000000000..62106c4a9af
--- /dev/null
+++ b/test/blackbox-tests/test-cases/merlin/dialect.t/run.t
@@ -0,0 +1,94 @@
+  $ ocamlc_where="$(ocamlc -where)"
+  $ export BUILD_PATH_PREFIX_MAP="/OCAMLC_WHERE=$ocamlc_where:$BUILD_PATH_PREFIX_MAP"
+  $ ocamlfind_libs="$(ocamlfind printconf path | while read line; do printf lib=${line}:; done)"
+  $ export BUILD_PATH_PREFIX_MAP="$ocamlfind_libs:$BUILD_PATH_PREFIX_MAP"
+  $ melc_compiler="$(which melc)"
+  $ export BUILD_PATH_PREFIX_MAP="/MELC_COMPILER=$melc_compiler:$BUILD_PATH_PREFIX_MAP"
+
+CRAM sanitization
+  $ dune build ./exe/.merlin-conf/exe-x --profile release
+  $ dune ocaml merlin dump-config $PWD/exe
+  X: _build/default/exe/x
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/exe/.x.eobjs/byte)
+   (S
+    $TESTCASE_ROOT/exe)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx"))
+  X: _build/default/exe/x.mlx
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/exe/.x.eobjs/byte)
+   (S
+    $TESTCASE_ROOT/exe)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx")
+   (READER (mlx)))
+  X: _build/default/exe/x.mlx.mli
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/exe/.x.eobjs/byte)
+   (S
+    $TESTCASE_ROOT/exe)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx"))
+
+CRAM sanitization
+  $ dune build ./lib/.merlin-conf/lib-x --profile release
+  $ dune ocaml merlin dump-config $PWD/lib
+  X: _build/default/lib/x
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.x.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx")
+   (READER (mlx)))
+  X: _build/default/lib/x.mlx
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.x.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx")
+   (READER (mlx)))
+
+CRAM sanitization
+  $ dune build ./melange/.merlin-conf/lib-x_mel --profile release
+  $ dune ocaml merlin dump-config $PWD/melange
+  X_mel: _build/default/melange/x_mel
+  ((STDLIB lib/melange/melange)
+   (EXCLUDE_QUERY_DIR)
+   (B lib/melange/js/melange)
+   (B lib/melange/melange)
+   (B
+    $TESTCASE_ROOT/_build/default/melange/.x_mel.objs/melange)
+   (S lib/melange)
+   (S lib/melange/js)
+   (S
+    $TESTCASE_ROOT/melange)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx")
+   (READER (mlx)))
+  X_mel: _build/default/melange/x_mel.mlx
+  ((STDLIB lib/melange/melange)
+   (EXCLUDE_QUERY_DIR)
+   (B lib/melange/js/melange)
+   (B lib/melange/melange)
+   (B
+    $TESTCASE_ROOT/_build/default/melange/.x_mel.objs/melange)
+   (S lib/melange)
+   (S lib/melange/js)
+   (S
+    $TESTCASE_ROOT/melange)
+   (FLG (-w -40 -g))
+   (SUFFIX ".mlx .mlx")
+   (READER (mlx)))
diff --git a/test/blackbox-tests/test-cases/merlin/future-syntax.t b/test/blackbox-tests/test-cases/merlin/future-syntax.t
index c9aa4119907..c70ccca2e6f 100644
--- a/test/blackbox-tests/test-cases/merlin/future-syntax.t
+++ b/test/blackbox-tests/test-cases/merlin/future-syntax.t
@@ -25,3 +25,19 @@
    (S
     $TESTCASE_ROOT)
    (FLG (-w -40 -g)))
+  Pp_future_syntax: _build/default/pp_future_syntax.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.pp_future_syntax.eobjs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG (-w -40 -g)))
+  Pp_future_syntax: _build/default/pp_future_syntax.mli
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.pp_future_syntax.eobjs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG (-w -40 -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/github1946.t/run.t b/test/blackbox-tests/test-cases/merlin/github1946.t/run.t
index 248f27088e9..ffa28575f75 100644
--- a/test/blackbox-tests/test-cases/merlin/github1946.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/github1946.t/run.t
@@ -7,6 +7,20 @@ in the same dune file, but require different ppx specifications
   $ dune build @all --profile release
   $ dune ocaml merlin dump-config $PWD
   Usesppx1: _build/default/usesppx1
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.usesppx1.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/c152d6ca3c7e1d83471ffdf48bf729ae/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="usesppx1"'"))
+   (FLG (-w -40 -g)))
+  Usesppx1: _build/default/usesppx1.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -34,3 +48,17 @@ in the same dune file, but require different ppx specifications
      --cookie
      'library-name="usesppx2"'"))
    (FLG (-w -40 -g)))
+  Usesppx2: _build/default/usesppx2.ml-gen
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.usesppx2.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/d7394c27c5e0f7ad7ab1110d6b092c05/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="usesppx2"'"))
+   (FLG (-w -40 -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/github4125.t/run.t b/test/blackbox-tests/test-cases/merlin/github4125.t/run.t
index 05645739523..39b8b2fd915 100644
--- a/test/blackbox-tests/test-cases/merlin/github4125.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/github4125.t/run.t
@@ -37,3 +37,18 @@ We call `$(opam switch show)` so that this test always uses an existing switch
      -short-paths
      -keep-locs
      -g)))
+  Foo: _build/cross/foo.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/cross/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/github759.t/run.t b/test/blackbox-tests/test-cases/merlin/github759.t/run.t
index d9c548a4a03..286f4180c8b 100644
--- a/test/blackbox-tests/test-cases/merlin/github759.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/github759.t/run.t
@@ -4,6 +4,14 @@
   $ dune build foo.cma --profile release
   $ dune ocaml merlin dump-config $PWD
   Foo: _build/default/foo
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG (-w -40 -g)))
+  Foo: _build/default/foo.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -16,6 +24,14 @@
   $ dune build foo.cma --profile release
   $ dune ocaml merlin dump-config $PWD
   Foo: _build/default/foo
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG (-w -40 -g)))
+  Foo: _build/default/foo.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -35,3 +51,11 @@
    (S
     $TESTCASE_ROOT)
    (FLG (-w -40 -g)))
+  Foo: _build/default/foo.ml-gen
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG (-w -40 -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/granularity.t b/test/blackbox-tests/test-cases/merlin/granularity.t
new file mode 100644
index 00000000000..ec8bdb63cd1
--- /dev/null
+++ b/test/blackbox-tests/test-cases/merlin/granularity.t
@@ -0,0 +1,213 @@
+  $ ocamlc_where="$(ocamlc -where)"
+  $ export BUILD_PATH_PREFIX_MAP="/OCAMLC_WHERE=$ocamlc_where:$BUILD_PATH_PREFIX_MAP"
+
+A utility to query merlin configuration for a file:
+  $ cat >merlin_conf.sh <<EOF
+  > #!/bin/sh
+  > FILE=\$1
+  > printf "(4:File%d:%s)" \${#FILE} \$FILE | dune ocaml-merlin \
+  >   | sed -E "s/[[:digit:]]+:/\?:/g" | sed -E "s/\)(\(+)/\n\1/g"
+  > EOF
+
+  $ chmod a+x merlin_conf.sh
+
+Project sources
+
+  $ cat >dune-project <<EOF
+  > (lang dune 3.16)
+  > (using melange 0.1)
+  > 
+  > (dialect
+  >  (name mlx)
+  >  (implementation
+  >   (extension mlx)
+  >   (preprocess (run cat %{input-file}))
+  >   (merlin_reader mlx)))
+  > EOF
+
+  $ cat >pp.sh <<EOF
+  > #!/bin/sh
+  > sed 's/%INT%/42/g' \$1
+  > EOF
+
+  $ chmod a+x pp.sh
+
+  $ cat >dune <<EOF
+  > (executable
+  >  (name test)
+  >  (flags :standard -no-strict-formats)
+  >  (preprocess
+  >   (per_module
+  >    ((action (run ./pp.sh %{input-file})) pped))))
+  > 
+  > (rule
+  >  (action  (copy cppomod.cppo.ml cppomod.ml)))
+  > 
+  > (rule
+  >  (action  (copy wrongext.cppo.cml wrongext.ml)))
+  > 
+  > (rule
+  >  (target generatedx.mlx)
+  >  (mode promote)
+  >  (action  (with-stdout-to %{target} (echo "let x = \"Generatedx!\""))))
+  > 
+  > (rule
+  >  (target generated.ml)
+  >  (mode promote)
+  >  (action  (with-stdout-to %{target} (echo "let x = \"Generated!\""))))
+  > EOF
+
+  $ cat >test.ml <<EOF
+  > print_endline Pped.x_42;;
+  > print_endline Mel.x;;
+  > print_endline Cppomod.x;;
+  > print_endline Wrongext.x;;
+  > print_endline Generated.x;;
+  > EOF
+
+Both Pped's ml and mli files will be preprocessed
+  $ cat >pped.mli <<EOF
+  > val x_%INT% : string
+  > EOF
+
+  $ cat >pped.ml <<EOF
+  > let x_42 = "%INT%"
+  > EOF
+
+Melange module signature
+  $ cat >mel.mli <<EOF
+  > val x : string
+  > EOF
+
+Melange module implementation in Melange syntax
+  $ cat >mel.mlx <<EOF
+  > let x = "43"
+  > EOF
+
+A pped file with unconventionnal filename
+  $ cat >cppomod.cppo.ml <<EOF
+  > let x = "44"
+  > EOF
+
+  $ cat >wrongext.cppo.cml <<EOF
+  > let x = "45"
+  > EOF
+
+  $ dune build @check
+  $ dune exec ./test.exe
+  42
+  43
+  44
+  45
+  Generated!
+
+We now query Merlin configuration for the various source files:
+
+Some configuration fields are common to all the modules of a same stanza. This
+is the case for the stdlib, build and sources directories, flags and suffixes.
+
+Some configuration can be specific to a module like preprocessing.
+
+Dialects are specified by extensions so are specific to a file. This means a
+different reader might be used for the signature and the implementation.
+
+Note that Merlin should always be told about dialect-provided suffixes, to make `MerlinLocate` work correctly.
+
+Preprocessing:
+
+Is it expected that the suffix for implementation and interface is the same ?
+  $ ./merlin_conf.sh pped.ml | tee pped.out
+  ((?:STDLIB?:/OCAMLC_WHERE
+  (?:EXCLUDE_QUERY_DIR
+  (?:B?:$TESTCASE_ROOT/_build/default/.test.eobjs/byte
+  (?:S?:$TESTCASE_ROOT
+  (?:FLG(?:-open?:Dune__exe)
+  (?:FLG(?:-pp?:$TESTCASE_ROOT/_build/default/pp.sh)
+  (?:FLG(?:-w?:@1..3@5..28@31..39@43@46..47@49..57@61..62@67@69-?:-strict-sequence?:-strict-formats?:-short-paths?:-keep-locs?:-no-strict-formats?:-g)
+  (?:SUFFIX?:.mlx .mlx))
+
+  $ ./merlin_conf.sh pped.mli | diff pped.out -
+
+Melange:
+
+As expected, the reader is not communicated for the standard mli
+  $ ./merlin_conf.sh mel.mli | tee mel.out
+  ((?:STDLIB?:/OCAMLC_WHERE
+  (?:EXCLUDE_QUERY_DIR
+  (?:B?:$TESTCASE_ROOT/_build/default/.test.eobjs/byte
+  (?:S?:$TESTCASE_ROOT
+  (?:FLG(?:-open?:Dune__exe)
+  (?:FLG(?:-w?:@1..3@5..28@31..39@43@46..47@49..57@61..62@67@69-?:-strict-sequence?:-strict-formats?:-short-paths?:-keep-locs?:-no-strict-formats?:-g)
+  (?:SUFFIX?:.mlx .mlx))
+
+The reader is set for the mlx file
+  $ ./merlin_conf.sh mel.mlx | diff mel.out -
+  7c7,8
+  < (?:SUFFIX?:.mlx .mlx))
+  \ No newline at end of file
+  ---
+  > (?:SUFFIX?:.mlx .mlx
+  > (?:READER(?:mlx)))
+  \ No newline at end of file
+  [1]
+
+Unconventional file names:
+
+Users might have preprocessing steps that start with a non-conventional
+filename like `mymodule.cppo.ml`. 
+
+While Dune first tries to match by the exact filename requested, if nothing is
+found, then it'll make a guess that the file was preprocessed into a file with
+.ml extension:
+
+  $ ./merlin_conf.sh cppomod.cppo.ml | tee cppomod.out
+  ((?:STDLIB?:/OCAMLC_WHERE
+  (?:EXCLUDE_QUERY_DIR
+  (?:B?:$TESTCASE_ROOT/_build/default/.test.eobjs/byte
+  (?:S?:$TESTCASE_ROOT
+  (?:FLG(?:-open?:Dune__exe)
+  (?:FLG(?:-w?:@1..3@5..28@31..39@43@46..47@49..57@61..62@67@69-?:-strict-sequence?:-strict-formats?:-short-paths?:-keep-locs?:-no-strict-formats?:-g)
+  (?:SUFFIX?:.mlx .mlx))
+
+  $ ./merlin_conf.sh cppomod.ml | diff cppomod.out -
+
+Note that this means unrelated files might be given the same configuration:
+
+  $ ./merlin_conf.sh cppomod.tralala.ml | diff cppomod.out -
+
+And with unconventional extension: 
+(note that without appropriate suffix configuration Merlin will never jump to
+such files) 
+We could expect dune to get the wrongext module configuration
+  $ ./merlin_conf.sh wrongext.cppo.cml | tee wrongext.out
+  ((?:STDLIB?:/OCAMLC_WHERE
+  (?:EXCLUDE_QUERY_DIR
+  (?:B?:$TESTCASE_ROOT/_build/default/.test.eobjs/byte
+  (?:S?:$TESTCASE_ROOT
+  (?:FLG(?:-open?:Dune__exe)
+  (?:FLG(?:-w?:@1..3@5..28@31..39@43@46..47@49..57@61..62@67@69-?:-strict-sequence?:-strict-formats?:-short-paths?:-keep-locs?:-no-strict-formats?:-g)
+  (?:SUFFIX?:.mlx .mlx))
+
+We also have generated.ml and generatedx.mlx promoted:
+  $ ls -1 . | grep generated
+  generated.ml
+  generatedx.mlx
+
+It should be possible to get its merlin configuration as well:
+  $ ./merlin_conf.sh generated.ml
+  ((?:STDLIB?:/OCAMLC_WHERE
+  (?:EXCLUDE_QUERY_DIR
+  (?:B?:$TESTCASE_ROOT/_build/default/.test.eobjs/byte
+  (?:S?:$TESTCASE_ROOT
+  (?:FLG(?:-open?:Dune__exe)
+  (?:FLG(?:-w?:@1..3@5..28@31..39@43@46..47@49..57@61..62@67@69-?:-strict-sequence?:-strict-formats?:-short-paths?:-keep-locs?:-no-strict-formats?:-g)
+  (?:SUFFIX?:.mlx .mlx))
+  $ ./merlin_conf.sh generatedx.mlx
+  ((?:STDLIB?:/OCAMLC_WHERE
+  (?:EXCLUDE_QUERY_DIR
+  (?:B?:$TESTCASE_ROOT/_build/default/.test.eobjs/byte
+  (?:S?:$TESTCASE_ROOT
+  (?:FLG(?:-open?:Dune__exe)
+  (?:FLG(?:-w?:@1..3@5..28@31..39@43@46..47@49..57@61..62@67@69-?:-strict-sequence?:-strict-formats?:-short-paths?:-keep-locs?:-no-strict-formats?:-g)
+  (?:SUFFIX?:.mlx .mlx
+  (?:READER(?:mlx)))
diff --git a/test/blackbox-tests/test-cases/merlin/include-subdirs-qualified.t b/test/blackbox-tests/test-cases/merlin/include-subdirs-qualified.t
index 9a1847ad0ac..834f28c3694 100644
--- a/test/blackbox-tests/test-cases/merlin/include-subdirs-qualified.t
+++ b/test/blackbox-tests/test-cases/merlin/include-subdirs-qualified.t
@@ -22,6 +22,25 @@
   $ dune build .merlin-conf/lib-foo
   $ dune ocaml merlin dump-config .
   Foo: _build/default/foo
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Foo: _build/default/foo.ml-gen
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -41,6 +60,25 @@
      -keep-locs
      -g)))
   Foo__Groupintf__: _build/default/foo__Groupintf__
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Foo__Groupintf__: _build/default/foo__Groupintf__.ml-gen
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -60,6 +98,25 @@
      -keep-locs
      -g)))
   Utils: _build/default/foo__Utils
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Utils: _build/default/foo__Utils.ml-gen
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -79,6 +136,26 @@
      -keep-locs
      -g)))
   Calc: _build/default/groupintf/calc
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG (-open Foo__Groupintf__ -open Foo))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Calc: _build/default/groupintf/calc.ml
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -99,6 +176,26 @@
      -keep-locs
      -g)))
   Groupintf: _build/default/groupintf/groupintf
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG (-open Foo__Groupintf__ -open Foo))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Groupintf: _build/default/groupintf/groupintf.ml
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -119,6 +216,26 @@
      -keep-locs
      -g)))
   Main: _build/default/main
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG (-open Foo))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Main: _build/default/main.ml
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -139,6 +256,26 @@
      -keep-locs
      -g)))
   Calc: _build/default/utils/calc
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/groupintf)
+   (S
+    $TESTCASE_ROOT/utils)
+   (FLG (-open Foo__Utils -open Foo))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62@67@69-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Calc: _build/default/utils/calc.ml
   ((STDLIB /OPAM_PREFIX)
    (EXCLUDE_QUERY_DIR)
    (B
diff --git a/test/blackbox-tests/test-cases/merlin/instrumentation.t/run.t b/test/blackbox-tests/test-cases/merlin/instrumentation.t/run.t
index 7a94d814404..2fea5f64a9f 100644
--- a/test/blackbox-tests/test-cases/merlin/instrumentation.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/instrumentation.t/run.t
@@ -9,6 +9,20 @@ up a project with instrumentation and testing checking the merlin config.
   $ dune build --instrument-with hello ./lib/.merlin-conf/lib-foo ./lib/.merlin-conf/lib-bar --profile release
   $ dune ocaml merlin dump-config $PWD/lib
   Bar: _build/default/lib/bar
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.bar.objs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/ppx/.hello.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (S
+    $TESTCASE_ROOT/ppx)
+   (FLG (-w -40 -g)))
+  Bar: _build/default/lib/bar.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -23,6 +37,21 @@ up a project with instrumentation and testing checking the merlin config.
     $TESTCASE_ROOT/ppx)
    (FLG (-w -40 -g)))
   File: _build/default/lib/subdir/file
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.bar.objs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/ppx/.hello.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (S
+    $TESTCASE_ROOT/ppx)
+   (FLG (-open Bar))
+   (FLG (-w -40 -g)))
+  File: _build/default/lib/subdir/file.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -38,6 +67,20 @@ up a project with instrumentation and testing checking the merlin config.
    (FLG (-open Bar))
    (FLG (-w -40 -g)))
   Foo: _build/default/lib/foo
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.foo.objs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/ppx/.hello.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (S
+    $TESTCASE_ROOT/ppx)
+   (FLG (-w -40 -g)))
+  Foo: _build/default/lib/foo.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -66,3 +109,18 @@ up a project with instrumentation and testing checking the merlin config.
     $TESTCASE_ROOT/ppx)
    (FLG (-open Foo))
    (FLG (-w -40 -g)))
+  Privmod: _build/default/lib/privmod.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.foo.objs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/ppx/.hello.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (S
+    $TESTCASE_ROOT/ppx)
+   (FLG (-open Foo))
+   (FLG (-w -40 -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/merlin-from-subdir.t/run.t b/test/blackbox-tests/test-cases/merlin/merlin-from-subdir.t/run.t
index b3aab326d86..3895364d430 100644
--- a/test/blackbox-tests/test-cases/merlin/merlin-from-subdir.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/merlin-from-subdir.t/run.t
@@ -8,6 +8,25 @@ We build the project
 Verify that merlin configuration was generated...
   $ dune ocaml merlin dump-config $PWD
   Test: _build/default/test
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/.test.eobjs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/411)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Test: _build/default/test.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -43,6 +62,23 @@ Verify that merlin configuration was generated...
      -short-paths
      -keep-locs
      -g)))
+  Foo: _build/default/foo.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/411)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
 
 ...but not in the sub-folder whose content was copied
   $ dune ocaml merlin dump-config $PWD/411
diff --git a/test/blackbox-tests/test-cases/merlin/merlin-tests.t/run.t b/test/blackbox-tests/test-cases/merlin/merlin-tests.t/run.t
index ed506bb77df..c164517d918 100644
--- a/test/blackbox-tests/test-cases/merlin/merlin-tests.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/merlin-tests.t/run.t
@@ -14,6 +14,25 @@ CRAM sanitization
   $ dune build ./exe/.merlin-conf/exe-x --profile release
   $ dune ocaml merlin dump-config $PWD/exe
   X: _build/default/exe/x
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_findlib/publicfoo)
+   (B
+    $TESTCASE_ROOT/_build/default/exe/.x.eobjs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.foo.objs/public_cmi)
+   (S
+    $TESTCASE_ROOT/_findlib/publicfoo)
+   (S
+    $TESTCASE_ROOT/exe)
+   (S
+    $TESTCASE_ROOT/lib)
+   (FLG
+    (-pp
+     $TESTCASE_ROOT/_build/default/pp/pp.exe))
+   (FLG (-w -40 -g)))
+  X: _build/default/exe/x.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -36,6 +55,22 @@ CRAM sanitization
   $ dune build ./lib/.merlin-conf/lib-foo ./lib/.merlin-conf/lib-bar --profile release
   $ dune ocaml merlin dump-config $PWD/lib
   Bar: _build/default/lib/bar
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.bar.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/4128e43a9cfb141a37f547484cc9bf46/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="bar"'"))
+   (FLG (-w -40 -g)))
+  Bar: _build/default/lib/bar.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -52,6 +87,23 @@ CRAM sanitization
      'library-name="bar"'"))
    (FLG (-w -40 -g)))
   File: _build/default/lib/subdir/file
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.bar.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (FLG (-open Bar))
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/4128e43a9cfb141a37f547484cc9bf46/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="bar"'"))
+   (FLG (-w -40 -g)))
+  File: _build/default/lib/subdir/file.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -69,6 +121,26 @@ CRAM sanitization
      'library-name="bar"'"))
    (FLG (-w -40 -g)))
   Foo: _build/default/lib/foo
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_findlib/publicfoo)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT/_findlib/publicfoo)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/4128e43a9cfb141a37f547484cc9bf46/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="foo"'"))
+   (FLG (-w -40 -g)))
+  Foo: _build/default/lib/foo.ml-gen
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -109,6 +181,27 @@ CRAM sanitization
      --cookie
      'library-name="foo"'"))
    (FLG (-w -40 -g)))
+  Privmod: _build/default/lib/privmod.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_findlib/publicfoo)
+   (B
+    $TESTCASE_ROOT/_build/default/lib/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT/_findlib/publicfoo)
+   (S
+    $TESTCASE_ROOT/lib)
+   (S
+    $TESTCASE_ROOT/lib/subdir)
+   (FLG (-open Foo))
+   (FLG
+    (-ppx
+     "$TESTCASE_ROOT/_build/default/.ppx/4128e43a9cfb141a37f547484cc9bf46/ppx.exe
+     --as-ppx
+     --cookie
+     'library-name="foo"'"))
+   (FLG (-w -40 -g)))
 
 Make sure a ppx directive is generated (if not, the [grep ppx] step fails)
   $ dune ocaml merlin dump-config $PWD/lib | grep ppx > /dev/null
@@ -129,11 +222,38 @@ Make sure pp flag is correct and variables are expanded
      "$TESTCASE_ROOT/_build/default/pp/pp.exe
      -nothing"))
    (FLG (-w -40 -g)))
+  Foobar: _build/default/pp-with-expand/foobar.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/pp-with-expand/.foobar.eobjs/byte)
+   (S
+    $TESTCASE_ROOT/pp-with-expand)
+   (FLG
+    (-pp
+     "$TESTCASE_ROOT/_build/default/pp/pp.exe
+     -nothing"))
+   (FLG (-w -40 -g)))
 
 Check hash of executables names if more than one
   $ dune build ./exes/.merlin-conf/exe-x-6562915302827c6dce0630390bfa68b7
   $ dune ocaml merlin dump-config $PWD/exes
   X: _build/default/exes/x
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/exes/.x.eobjs/byte)
+   (S
+    $TESTCASE_ROOT/exes)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  X: _build/default/exes/x.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -163,3 +283,18 @@ Check hash of executables names if more than one
      -short-paths
      -keep-locs
      -g)))
+  Y: _build/default/exes/y.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/exes/.x.eobjs/byte)
+   (S
+    $TESTCASE_ROOT/exes)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/per-module-pp.t/run.t b/test/blackbox-tests/test-cases/merlin/per-module-pp.t/run.t
index bc757674273..532a2f258a7 100644
--- a/test/blackbox-tests/test-cases/merlin/per-module-pp.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/per-module-pp.t/run.t
@@ -8,6 +8,21 @@ should appear only once since only Foo is using it.
 
   $ dune ocaml merlin dump-config $PWD
   Bar: _build/default/bar
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Bar: _build/default/bar.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -40,3 +55,21 @@ should appear only once since only Foo is using it.
      -short-paths
      -keep-locs
      -g)))
+  Foo: _build/default/foo.ml
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (FLG
+    (-pp
+     $TESTCASE_ROOT/_build/default/pp/pp.exe))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/src-dirs-of-deps.t b/test/blackbox-tests/test-cases/merlin/src-dirs-of-deps.t
index 9b5eb4152a5..178fccc1c7b 100644
--- a/test/blackbox-tests/test-cases/merlin/src-dirs-of-deps.t
+++ b/test/blackbox-tests/test-cases/merlin/src-dirs-of-deps.t
@@ -43,3 +43,24 @@ library also has more than one src dir.
      -short-paths
      -keep-locs
      -g)))
+  Lib2: _build/default/lib2/lib2.ml-gen
+  ((STDLIB /OPAM_PREFIX)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/lib1/.lib1.objs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/lib2/.lib2.objs/byte)
+   (S
+    $TESTCASE_ROOT/lib1)
+   (S
+    $TESTCASE_ROOT/lib1/sub)
+   (S
+    $TESTCASE_ROOT/lib2)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
diff --git a/test/blackbox-tests/test-cases/merlin/suffix.t/run.t b/test/blackbox-tests/test-cases/merlin/suffix.t/run.t
index 159ba87fd27..9e3e0002406 100644
--- a/test/blackbox-tests/test-cases/merlin/suffix.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/suffix.t/run.t
@@ -3,3 +3,5 @@
   $ dune ocaml merlin dump-config $PWD | grep SUFFIX
    (SUFFIX ".aml .amli")
    (SUFFIX ".baml .bamli"))
+   (SUFFIX ".aml .amli")
+   (SUFFIX ".baml .bamli"))
diff --git a/test/blackbox-tests/test-cases/merlin/unit-names-merlin-gh1233.t/run.t b/test/blackbox-tests/test-cases/merlin/unit-names-merlin-gh1233.t/run.t
index 80e7b75a08b..0a181e434b2 100644
--- a/test/blackbox-tests/test-cases/merlin/unit-names-merlin-gh1233.t/run.t
+++ b/test/blackbox-tests/test-cases/merlin/unit-names-merlin-gh1233.t/run.t
@@ -6,6 +6,25 @@
 
   $ dune ocaml merlin dump-config $PWD
   Foo: _build/default/foo
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/.foo.eobjs/byte)
+   (B
+    $TESTCASE_ROOT/_build/default/foo/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT)
+   (S
+    $TESTCASE_ROOT/foo)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Foo: _build/default/foo.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -27,6 +46,22 @@
 
   $ dune ocaml merlin dump-config $PWD/foo
   Bar: _build/default/foo/bar
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/foo/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT/foo)
+   (FLG (-open Foo))
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
+  Bar: _build/default/foo/bar.ml
   ((STDLIB /OCAMLC_WHERE)
    (EXCLUDE_QUERY_DIR)
    (B
@@ -57,6 +92,21 @@
      -short-paths
      -keep-locs
      -g)))
+  Foo: _build/default/foo/foo.ml-gen
+  ((STDLIB /OCAMLC_WHERE)
+   (EXCLUDE_QUERY_DIR)
+   (B
+    $TESTCASE_ROOT/_build/default/foo/.foo.objs/byte)
+   (S
+    $TESTCASE_ROOT/foo)
+   (FLG
+    (-w
+     @1..3@5..28@30..39@43@46..47@49..57@61..62-40
+     -strict-sequence
+     -strict-formats
+     -short-paths
+     -keep-locs
+     -g)))
 
 FIXME : module Foo is not unbound
 This test is disabled because it depends on root detection and is not reproducible.