Fix `iSimpl .. in ..`.

Thanks to @Blaisorblade for reporting.

tests/proofmode.ref

@@ -74,6 +74,17 @@ Tactic failure: iSpecialize: cannot instantiate (⌜φ⌝ → P -∗ False)%I wi
   --------------------------------------∗
   ▷^(S n + S m) emp
   
+"test_iSimpl_in"
+     : string
+1 subgoal
+  
+  PROP : sbi
+  x, y : nat
+  ============================
+  "H" : ⌜S (S (S x)) = y⌝
+  --------------------------------------∗
+  ⌜S (S (S x)) = y⌝
+  
 "test_iFrame_later_1"
      : string
 1 subgoal

tests/proofmode.v

@@ -412,6 +412,10 @@ Proof.
   done.
 Qed.
 
+Check "test_iSimpl_in".
+Lemma test_iSimpl_in x y : ⌜ (3 + x)%nat = y ⌝ -∗ ⌜ S (S (S x)) = y ⌝ : PROP.
+Proof. iIntros "H". iSimpl in "H". Show. done. Qed.
+
 Lemma test_iIntros_pure_neg : (⌜ ¬False ⌝ : PROP)%I.
 Proof. by iIntros (?). Qed.
 

theories/proofmode/ltac_tactics.v

@@ -119,8 +119,8 @@ Tactic Notation "iEval" tactic(t) "in" constr(H) :=
     |pm_reflexivity
     |].
 
-Tactic Notation "iSimpl" := iEval simpl.
-Tactic Notation "iSimpl" "in" constr(H) := iEval simpl in H.
+Tactic Notation "iSimpl" := iEval (simpl).
+Tactic Notation "iSimpl" "in" constr(H) := iEval (simpl) in H.
 
 (* It would be nice to also have an `iSsrRewrite`, however, for this we need to
 pass arguments to Ssreflect's `rewrite` like `/= foo /bar` in Ltac, see: