Although Whedon has been serving as the director on Justice League during its reshoots, it was not generally expected that he would receive an actual co-directing credit on the film.
In addition to running the reshoots, Whedon has been helping out with the Justice League script.
Joss Whedon is getting an official co-writing credit for his contributions to the upcoming DC Extended Universe film, Justice League.
While Whedon may not get a directing credit on Justice League, it appears that he could have more influence over the future of the DCEU than Snyder will.