Does Swashbuckler's Fancy Footwork apply if the attack was made with Booming Blade?

Question

The Roguish Archetype Swashbuckler (SCAG/XGtE) has the following feature:

Fancy Footwork

When you choose this archetype at 3rd level, you learn how to land a strike and then slip away without reprisal. During your turn, if you make a melee attack against a creature, that creature can't make opportunity attacks against you for the rest of your turn.

The cantrip Booming Blade (SCAG) says the following:

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails.

First Question:

Does Fancy Footwork apply (no OA from the attacked creature) if you attacked it with Booming Blade (or Green Flame Blade)?

Second Question:

More generally, since it does not specify a weapon attack, does Fancy Footwork apply to melee spell attacks as well?

Answer 1

Yes, Fancy Footwork applies in these instances

Your reading is correct. To trigger Fancy Footwork all you need to do is:

make a melee attack against a creature

The cantrips Booming Blade and Green-Flame Blade use identical wording when they say:

you must make a melee attack with a weapon against one creature

So both Booming Blade and Green-Flame Blade do trigger Fancy footwork. Making a melee attack does not require the Attack action to have been taken.

By the same reasoning, any melee spell attack (such as Thorn Whip) will also trigger Fancy Footwork - a melee spell attack is still a type of melee attack. It makes no difference for Fancy Footwork that that melee attack has been made via the Cast a Spell action rather than by an Attack action.