Fix parentheses around optional module parameter

CHANGES.md

@@ -34,6 +34,7 @@
   + Remove some calls to if_newline and break_unless_newline and fix break before closing brackets (#1168) (Guillaume Petiot)
   + Fix unstable cmt in or-pattern (#1173) (Guillaume Petiot)
   + Fix location of comment attached to the underscore of an open record (#1208) (Guillaume Petiot)
+  + Fix parentheses around optional module parameter (#1212) (Christian Barcenas)
 
 #### Documentation
 

lib/Fmt_ast.ml

@@ -1184,10 +1184,15 @@ and fmt_fun_args c ?pro args =
              ( fmt_pattern c ~parens:false xpat
              $ fmt " =@;<1 2>" $ fmt_expression c xexp ))
     | Val (Optional l, xpat, Some xexp) ->
+        let parens =
+          match xpat.ast.ppat_desc with
+          | Ppat_unpack _ -> None
+          | _ -> Some false
+        in
         cbox 2
           ( str "?" $ str l
           $ wrap_k (fmt ":@,(") (str ")")
-              ( fmt_pattern c ~parens:false xpat
+              ( fmt_pattern c ?parens xpat
               $ fmt " =@;<1 2>" $ fmt_expression c xexp ) )
     | Val ((Labelled _ | Nolabel), _, Some _) ->
         impossible "not accepted by parser"

test/passing/module.ml

@@ -66,3 +66,8 @@ end
 module A (_ : S) = struct end
 
 module A : functor (_ : S) -> S' = functor (_ : S) -> struct end
+
+let helper ?x =
+  match x with Some (module X : X_typ) -> X.f | None -> X_add_one.f
+
+let helper ?x:((module X) = (module X_add_one : X_typ)) = X.f