outcome-printer: fix nullary uncurried function type

Author: glennsl

src/res_outcome_printer.ml

@@ -243,7 +243,7 @@ let printPolyVarIdent txt =
        ) ->
         (* Js.Fn.arity0<t> -> (.) => t *)
         Doc.concat [
-          Doc.text "(.) => ";
+          Doc.text "(. ()) => ";
           printOutTypeDoc typ;
         ]
      | Otyp_constr (

tests/oprint/expected/oprint.resi.txt

@@ -201,8 +201,8 @@ module Js: {
 }
 type arity0 = (. ()) => unit
 type arity0b = (. ()) => int
-type arity0c = (.) => (.) => array<int>
-type arity0d = (.) => unit => unit
+type arity0c = (. ()) => (. ()) => array<int>
+type arity0d = (. ()) => unit => unit
 type arity1 = (. int) => int
 type arity2 = (. int, int) => int
 type arity3 = (. int, int, int) => int
@@ -485,4 +485,4 @@ and ASet: {
 type emptyObject = {.}
 let f: (~x: 'a=?, ~y: 'b) => option<'a>
 type call = CleanStart
-let f: (~a: int=?, unit) => int
+let f: (~a: int=?, unit) => int