Does an ability that causes attacker to roll disadvantage need to be declared before roll?

@JeremyECrawford @ChrisPerkinsDnD does an ability that causes attacker to roll disadvantage, warding flare, need to be declared before roll?

— Gregory Cherry (@GregoryCherry69) March 7, 2017

Warding Flare must be used before an attack hits/misses, as indicated in the feature's second sentence (PH, 61). #DnD https://t.co/mtqxt2bYsh

— Jeremy Crawford (@JeremyECrawford) March 7, 2017