Precedence in parsing types

It looks to me like this should parse, but it doesn't:

var x: number | (string)=>void;

It works with added parens:

var x: number | ((string)=>void);

But if the parser is not too hacky, then maybe it's easy to make the first work?

(FWIW, I ran into this in a rest argument, where it would be nice to avoid the extra parens in

function foo(...xs: (number | ()=>void)[]): void { }

)

issue にある 2 つの型注釈の例と rest 引数の例を再現し、その後、TypeScript の parser におけるユニオン型と関数型の処理を調査します。括弧なしの形式が正常にパースされ、括弧付きの形式や rest 引数のケースにリグレッションが発生しなければ完了です。