Using ssreflect fancy `rewrite` `r_pattern` conflicts with Ltac (found on #coq)

bugLtacSsreflect.v

(* Based on example from
https://coq.github.io/doc/V8.10.0/refman/proof-engine/ssreflect-proof-language.html#contextual-patterns-in-rewrite *)

(* Find `Fail` to see the error *)
From Coq Require Import ssreflect.
Notation "n .+1" := (Datatypes.S n) (at level 2, left associativity,
                     format "n .+1") : nat_scope.
Axiom addSn : forall m n, m.+1 + n = (m + n).+1.
(* addSn is declared *)
Axiom addn0 : forall m, m + 0 = m.
(* addn0 is declared *)
Axiom addnC : forall m n, m + n = n + m.
(* addnC is declared *)
Lemma test x y z f : (x.+1 + y) + f (x.+1 + y) (z + (x + y).+1) = 0.
(* 1 subgoal

  x, y, z : nat
  f : nat -> nat -> nat
  ============================
  x.+1 + y + f (x.+1 + y) (z + (x + y).+1) = 0 *)
rewrite [in f _ _]addSn.
(* 1 subgoal

  x, y, z : nat
  f : nat -> nat -> nat
  ============================
  x.+1 + y + f (x + y).+1 (z + (x + y).+1) = 0 *)
rewrite addSn.

(* The bug. This works: *)
rewrite -[ER in (_ = ER)]addn0.
Undo.
(* So let's lift it into a tactic! But we can't: *)
Fail Ltac foo := rewrite -[ER in (_ = ER)]addn0.
(* The command has indeed failed with message:
The reference ER was not found in the current environment. *)

(* We need a hack. Note the extra parens! *)
Ltac foo := rewrite -[(ER in (_ = ER))]addn0.
foo.

Abort.