function deco () { }
@deco
export class Comp {}

export let Comp = deco(_class = class Comp {}) || _class;

_class = class Comp{}; // Deduced from `deco(_class = class Comp {})` because `deco` is empty
export let Comp = _class; // Deduced from `/*...*/ || _class` because the left operand always yields `undefined`