diff --git a/jscomp/outcome_printer/reason_syntax_util.ml b/jscomp/outcome_printer/reason_syntax_util.ml
index 6273d7f55c..2023ae185a 100644
--- a/jscomp/outcome_printer/reason_syntax_util.ml
+++ b/jscomp/outcome_printer/reason_syntax_util.ml
@@ -324,8 +324,6 @@ let processLineEndingsAndStarts str =
   |> String.concat "\n"
   |> String.trim
 
-module StringMap = Map.Make (String)
-
 (** Generate a suitable extension node for Merlin's consumption,
     for the purposes of reporting a syntax error - only used
     in recovery mode.
@@ -347,12 +345,6 @@ let syntax_error_extension_node loc message =
  in
  (str, payload)
 
-let swap_txt map txt =
-  if StringMap.mem txt map then
-    StringMap.find txt map
-  else
-    txt
-
 (** identifier_mapper maps all identifiers in an AST with a mapping function f
   this is used by swap_operator_mapper right below, to traverse the whole AST
   and swapping the symbols listed above.
diff --git a/jscomp/outcome_printer/reason_syntax_util.mli b/jscomp/outcome_printer/reason_syntax_util.mli
new file mode 100644
index 0000000000..0f22827b54
--- /dev/null
+++ b/jscomp/outcome_printer/reason_syntax_util.mli
@@ -0,0 +1,105 @@
+(* Hello! Welcome to the Reason syntax util logic.
+
+  This file's shared between the Reason repo and the BuckleScript repo. In
+  Reason, it's in src/reason-parser. In BuckleScript, it's in
+  jscomp/outcome_printer. We periodically copy this file from Reason (the source
+  of truth) to BuckleScript, then uncomment the #if #else #end cppo macros you
+  see in the file. That's because BuckleScript's on OCaml 4.02 while Reason's on
+  4.04; so the #if macros surround the pieces of code that are different between
+  the two compilers.
+
+  When you modify this file, please make sure you're not dragging in too many
+  things. You don't necessarily have to test the file on both Reason and
+  BuckleScript; ping @chenglou and a few others and we'll keep them synced up by
+  patching the right parts, through the power of types(tm)
+*)
+
+val ml_to_reason_swap : string -> string
+
+val escape_string : string -> string
+
+(* Everything below is used by reason repo but not the BuckleScript repo *)
+
+#if defined BS_NO_COMPILER_PATCH then
+
+module TrailingCommaMarker : sig val char : char val string : string end
+
+val pick_while : ('a -> bool) -> 'a list -> 'a list * 'a list
+
+val split_by : ?keep_empty:bool -> (char -> bool) -> string -> string list
+
+val processLineEndingsAndStarts : string -> string
+
+val syntax_error_extension_node :
+  Ast_404.Location.t ->
+  string -> string Ast_404.Location.loc * Ast_404.Parsetree.payload
+
+val escape_stars_slashes_mapper :
+  Ast_404.Ast_mapper.mapper -> Ast_404.Ast_mapper.mapper
+
+val reason_to_ml_swap_operator_mapper :
+  Ast_404.Ast_mapper.mapper -> Ast_404.Ast_mapper.mapper
+
+val ml_to_reason_swap_operator_mapper :
+  Ast_404.Ast_mapper.mapper -> Ast_404.Ast_mapper.mapper
+
+val attribute_exists : 'a -> ('a Ast_404.Asttypes.loc * 'b) list -> bool
+
+val attributes_conflicted :
+  'a -> 'a -> ('a Ast_404.Asttypes.loc * 'b) list -> bool
+
+val normalized_attributes :
+  'a ->
+  ('a Ast_404.Asttypes.loc * 'b) list -> ('a Ast_404.Asttypes.loc * 'b) list
+
+val apply_mapper_to_structure :
+  Ast_404.Parsetree.structure ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.structure
+
+val apply_mapper_to_signature :
+  Ast_404.Parsetree.signature ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.signature
+
+val apply_mapper_to_type :
+  Ast_404.Parsetree.core_type ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.core_type
+
+val apply_mapper_to_expr :
+  Ast_404.Parsetree.expression ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.expression
+
+val apply_mapper_to_pattern :
+  Ast_404.Parsetree.pattern ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.pattern
+
+val apply_mapper_to_toplevel_phrase :
+  Ast_404.Parsetree.toplevel_phrase ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.toplevel_phrase
+
+val apply_mapper_to_use_file :
+  Ast_404.Parsetree.toplevel_phrase list ->
+  Ast_404.Ast_mapper.mapper -> Ast_404.Parsetree.toplevel_phrase list
+
+type error = Syntax_error of string
+
+exception Error of Ast_404.Location.t * error
+
+val map_first : ('a -> 'a) -> 'a list -> 'a list
+
+val map_last : ('a -> 'a) -> 'a list -> 'a list
+
+type menhirMessagesError = { msg : string; loc : Ast_404.Location.t; }
+
+type menhirError =
+    NoMenhirMessagesError
+  | MenhirMessagesError of menhirMessagesError
+
+val findMenhirErrorMessage : Ast_404.Location.t -> menhirError
+
+val add_error_message : menhirMessagesError -> unit
+
+val location_is_before : Ast_404.Location.t -> Ast_404.Location.t -> bool
+
+val location_contains : Ast_404.Location.t -> Ast_404.Location.t -> bool
+
+#end