clarify Obj.magic

ocamlmerlin_mlx/ocamlmerlin_mlx.ml

@@ -1,21 +1,35 @@
 open Merlin_extend
 open Merlin_extend.Extend_protocol.Reader
-open Ocaml_parsing
+open Mlx_ocaml_parsing
 open Mlx_kernel
 
-module Conv = Ppxlib_ast.Convert(Ppxlib_ast__Versions.OCaml_501)(Ppxlib_ast.Compiler_version)
-
-let conv_signature intf =
-  let intf: Astlib.Ast_501.Parsetree.signature = Obj.magic intf in
-  let intf = Conv.copy_signature intf in
-  let intf: Ocaml_parsing.Parsetree.signature = Obj.magic intf in
-  intf
-
-let conv_structure impl =
-  let impl: Astlib.Ast_501.Parsetree.structure = Obj.magic impl in
-  let impl = Conv.copy_structure impl in
-  let impl: Ocaml_parsing.Parsetree.structure = Obj.magic impl in
-  impl
+(* Some notes on usage of Obj.magic here...
+   - we copy parsetree.ml from merlin' 501 branch which copies AST from OCaml's
+     5.1.x branch. TODO: instead we should inject ppxlib's Ast_501 module there
+   - then finally the currently installed merlin-extend should have the same
+     AST as the one used by compiled. TODO: figure out why compiler doesn't see
+     that...
+*)
+module Conv = struct
+  module Conv =
+    Ppxlib_ast.Convert
+      (Ppxlib_ast__Versions.OCaml_501)
+      (Ppxlib_ast.Compiler_version)
+
+  let conv_signature (intf : Mlx_ocaml_parsing.Parsetree.signature) :
+      Ocaml_parsing.Parsetree.signature =
+    let intf : Astlib.Ast_501.Parsetree.signature = Obj.magic intf in
+    let intf = Conv.copy_signature intf in
+    let intf : Ocaml_parsing.Parsetree.signature = Obj.magic intf in
+    intf
+
+  let conv_structure (impl : Mlx_ocaml_parsing.Parsetree.structure) :
+      Ocaml_parsing.Parsetree.structure =
+    let impl : Astlib.Ast_501.Parsetree.structure = Obj.magic impl in
+    let impl = Conv.copy_structure impl in
+    let impl : Ocaml_parsing.Parsetree.structure = Obj.magic impl in
+    impl
+end
 
 let parse_string filename str =
   let src = Msource.make str in
@@ -81,17 +95,18 @@ module Mlx_reader = struct
       List.filter_map to_extension_node res.lexer_errors
     in
     match res.parsetree with
-    | `Interface intf -> Signature (conv_signature intf)
+    | `Interface intf -> Signature (Conv.conv_signature intf)
     | `Implementation impl ->
-        Structure (conv_structure impl @ parser_errors @ lexer_errors)
+        Structure
+          (Conv.conv_structure (impl @ parser_errors @ lexer_errors))
 
   let for_completion t _pos = { complete_labels = true }, parse t
 
   let parse_line _ _ text =
     let res = parse_string "*buffer*" text in
     match res.parsetree with
-    | `Interface intf -> Signature (conv_signature intf)
-    | `Implementation impl -> Structure (conv_structure impl)
+    | `Interface intf -> Signature (Conv.conv_signature intf)
+    | `Implementation impl -> Structure (Conv.conv_structure impl)
 
   let ident_at _ _ = []
   let pretty_print _ppf _ = ()