When you re-roll damage from Savage Attacker, would damage from a buff spell be included?

@mikemearls @ChrisPerkinsDnD newish DnD player here with a question for you guys. When you re-roll damage from Savage Attacker, would damage from a buff spell such as Thunderous Smite be included? We aren't 100% sure on the intended interaction. Thanks in advance! pic.twitter.com/Gw6eDJZclN

— Kevin S (@Optimal_Hunter) August 30, 2018

My reading – just the weapon’s damage dice

— Mike Mearls (@mikemearls) August 30, 2018