fix offset

Author: hhugo

compiler/lib/link_js.ml

@@ -324,11 +324,12 @@ let link ~output ~linkall ~mklib ~toplevel ~files ~resolve_sourcemap_url ~source
       let sm_for_file = ref None in
       let ic = Line_reader.open_ file in
       let skip ic = Line_reader.drop ic in
+      let line_offset = Line_writer.lnum oc in
       let reloc = ref [] in
       let copy ic oc =
         let line = Line_reader.next ic in
         Line_writer.write ~source:ic oc line;
-        reloc := (Line_reader.lnum ic, Line_writer.lnum oc) :: !reloc
+        reloc := (Line_reader.lnum ic, Line_writer.lnum oc - line_offset) :: !reloc
       in
       let rec read () =
         match Line_reader.peek ic with
@@ -432,7 +433,7 @@ let link ~output ~linkall ~mklib ~toplevel ~files ~resolve_sourcemap_url ~source
           Line_writer.write_lines oc content);
       (match !sm_for_file with
       | None -> ()
-      | Some x -> sm := (x, !reloc) :: !sm);
+      | Some x -> sm := (x, !reloc, line_offset) :: !sm);
       match !build_info, build_info_for_file with
       | None, None -> ()
       | Some _, None -> ()
@@ -446,10 +447,10 @@ let link ~output ~linkall ~mklib ~toplevel ~files ~resolve_sourcemap_url ~source
   | None -> ()
   | Some (file, init_sm) ->
       let sections =
-        List.rev_map !sm ~f:(fun (sm, reloc) ->
+        List.rev_map !sm ~f:(fun (sm, reloc, offset) ->
             let tbl = Hashtbl.create 17 in
             List.iter reloc ~f:(fun (a, b) -> Hashtbl.add tbl a b);
-            ( { Source_map.Index.gen_line = 0; gen_column = 0 }
+            ( { Source_map.Index.gen_line = offset; gen_column = 0 }
             , `Map (Source_map.Standard.filter_map sm ~f:(Hashtbl.find_opt tbl)) ))
       in
       let sm =