https://www.sageadvice.eu/war-caster-feat-booming-blade-as-a-reaction-to-enemy-provoking-at-5-10-is-a-reach-weapon-valid-for-the-melee-weapon-attack/
War Caster feat: Booming Blade as a reaction to enemy provoking at 5' -> 10', is a reach weapon valid for the melee weapon attack?