Reproduce missing arity

Author: cknitt

tests/syntax_tests/data/parsing/grammar/expressions/arrow.res

@@ -107,4 +107,7 @@ let arr = (): array<nullable<int>> => []
 
 let fn = f => f;
 type f = int => unit;
-let a = fn(_ => (): f);
+let a = fn(_ => (): f);
+
+let returnsArrayOption = (): option<array<string>> => Some(["foo"])
+let usesIt = returnsArrayOption()

tests/syntax_tests/data/parsing/grammar/expressions/expected/arrow.res.txt

@@ -77,4 +77,6 @@ let c [arity:1]() = ((1, 2) : ('a, 'b) d)
 let arr () = ([||] : int nullable array)
 let fn [arity:1]f = f
 type nonrec f = int -> unit (a:1)
-let a = fn (fun [arity:1]_ -> () : f)
+let a = fn (fun [arity:1]_ -> () : f)
+let returnsArrayOption () = (Some [|{js|foo|js}|] : string array option)
+let usesIt = returnsArrayOption ()