refactor: move j.ml{,i} (#844)

* refactor: move `j.ml{,i}`

* refactor: make it clear we're parsing an interface

jscomp/core/dune

@@ -2,7 +2,7 @@
  (name melangelib)
  (flags
   (:standard -open Melange_compiler_libs))
- (modules_without_implementation js_op)
+ (modules_without_implementation js_op j)
  (libraries ext melange_compiler_libs melange_ffi ppxlib.ast dune-build-info))
 
 (rule
@@ -37,23 +37,23 @@
 
 (rule
  (targets js_record_iter.ml)
- (deps j.ml)
+ (deps j.mli)
  (action
   (with-stdout-to
    %{targets}
    (run ./gen/gen_traversal.exe --input %{deps} --mode record-iter))))
 
 (rule
  (targets js_record_map.ml)
- (deps j.ml)
+ (deps j.mli)
  (action
   (with-stdout-to
    %{targets}
    (run ./gen/gen_traversal.exe --input %{deps} --mode record-map))))
 
 (rule
  (targets js_record_fold.ml)
- (deps j.ml)
+ (deps j.mli)
  (action
   (with-stdout-to
    %{targets}

jscomp/core/gen/gen_traversal.ml

@@ -11,7 +11,7 @@ let parse fname =
   end in
   In_ch.with_file fname ~f:(fun ch ->
       let lexbuf = Lexing.from_channel ch in
-      let ast = Parse.implementation lexbuf in
+      let ast = Parse.interface lexbuf in
       ast)
 
 let write_ast oc ~input_name ast =

jscomp/core/gen/node_types.ml

@@ -50,12 +50,12 @@ let isSupported (def : Longident.t) names =
       else `no
   | _ -> `no
 
-let get_type_defs (ast : Parsetree.structure) =
+let get_type_defs (ast : Parsetree.signature) =
   let types_with_deriving_definitions, deriving_attrs =
     List.filter_map
-      ~f:(fun { Parsetree.pstr_desc; _ } ->
-        match pstr_desc with
-        | Pstr_type (_, tdcls) -> (
+      ~f:(fun { Parsetree.psig_desc; _ } ->
+        match psig_desc with
+        | Psig_type (_, tdcls) -> (
             match List.rev tdcls with
             | [] -> None
             | { ptype_attributes = []; _ } :: _ -> None