Heretic of The Seventh Circle
It is considered an action. It’s also considered an attack, but the part that interferes is that using it is an action, and you can’t combine actions.Right, but is a spell description that says ‘make a spell attack’ considered an attack?
As an action, you cast Booming Blade, and make an Attack with a melee weapon. You’re making an attack as part of the action of casting Booming Blade.