simplify backtrack log, and add reviewer

Changes

@@ -752,7 +752,7 @@ OCaml 4.13.0 (24 September 2021)
   Completes #10474 by making row_field abstract too.
   An immutable view row_field_view is provided, and one converts between it
   and row_field via inj_row_field and row_field_repr.
-  (Jacques Garrigue and Takafumi Saikawa)
+  (Jacques Garrigue and Takafumi Saikawa, review by Florian Angeletti)
 
 - #10358: Use a hash table for the load path.
   (Leo White, review by Gabriel Scherer)

typing/types.ml

@@ -487,7 +487,7 @@ type change =
   | Cscope of type_expr * int
   | Cname of
       (Path.t * type_expr list) option ref * (Path.t * type_expr list) option
-  | Crow of [`none|`some] typed_row_field ref * [`none|`some] typed_row_field
+  | Crow of [`none|`some] typed_row_field ref
   | Ckind of field_kind option ref * field_kind option
   | Ccommu of commutable ref * commutable
   | Cuniv of type_expr option ref * type_expr option
@@ -704,7 +704,7 @@ let undo_change = function
   | Clevel (ty, level) -> Transient_expr.set_level ty level
   | Cscope (ty, scope) -> Transient_expr.set_scope ty scope
   | Cname  (r, v) -> r := v
-  | Crow   (r, v) -> r := v
+  | Crow   r      -> r := RFnone
   | Ckind  (r, v) -> r := v
   | Ccommu (r, v) -> r := v
   | Cuniv  (r, v) -> r := v
@@ -766,7 +766,7 @@ let rec link_row_field_ext ~(inside : row_field) (v : row_field) =
   match inside with
   | RFeither {ext = {contents = RFnone} as e} ->
       let RFeither _ | RFpresent _ | RFabsent as v = v in
-      log_change (Crow (e, !e)); e := v
+      log_change (Crow e); e := v
   | RFeither {ext = {contents = RFeither _ | RFpresent _ | RFabsent as rf}} ->
       link_row_field_ext ~inside:rf v
   | _ -> invalid_arg "Types.link_row_field_ext"