The PH is clear about what counts as an attack:
If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll, you're making an attack
However, it's a general principle, and we know that specific beats general. Are there any specific cases in 5e when you actually performing an attack (that will trigger any "when you hit with an attack" feature) without making an attack roll?
Grapple and Shove doesn't count — they do not count as a hit, so technically they are not "attacks", despite they are called "special melee attacks" in the PH.