CR

compiler/lib/link_js.ml

@@ -471,23 +471,37 @@ let link ~output ~linkall ~mklib ~toplevel ~files ~resolve_sourcemap_url ~source
                       , gen_column
                       , sm ))
             in
-            List.concat_map reloc ~f:(function
-                | `Drop _ -> []
-                | `Copy (src, dst, len) ->
-                    List.filter_map sm ~f:(fun (first, last, gen_line, gen_column, sm) ->
-                        if first > src + len || last < src
-                        then None
-                        else (
-                          assert (src <= first && last <= src + len);
-                          Some (gen_line + dst - src, gen_column, sm)))))
+            (* select sourcemaps that cover copied section *)
+            let maps =
+              List.concat_map reloc ~f:(function
+                  | `Drop _ -> []
+                  | `Copy (src, dst, len) ->
+                      List.filter_map
+                        sm
+                        ~f:(fun (first, last, gen_line, gen_column, sm) ->
+                          if first > src + len || last < src
+                          then None
+                          else (
+                            (* We don't want to deal with overlapping but not included
+                               sourcemap, but we could in theory filter out part of it. *)
+                            assert (src <= first && last <= src + len);
+                            Some (first, last, gen_line + dst - src, gen_column, sm))))
+            in
+            (* Make sure dropped sections are not overlapping selected sourcemap. *)
+            List.iter reloc ~f:(function
+                | `Copy _ -> ()
+                | `Drop (src, len) ->
+                    List.iter maps ~f:(fun (first, last, _, _, _) ->
+                        if first > src + len || last < src then () else assert false));
+            maps)
       in
       let sections = List.concat sections in
       let sm =
         { Source_map.Index.version = init_sm.Source_map.Standard.version
         ; file = init_sm.file
         ; sections =
             (* preserve some info from [init_sm] *)
-            List.map sections ~f:(fun (gen_line, gen_column, sm) ->
+            List.map sections ~f:(fun (_, _, gen_line, gen_column, sm) ->
                 ( { Source_map.Index.gen_line; gen_column }
                 , `Map { sm with sourceroot = init_sm.sourceroot } ))
         }