Would the Haste Spell allow you to cast a second, singular weapon attack effecting cantrip (such as Greenflame Blade)?

Question

So the Haste spell in 5e says that the targeted creature

gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

This means I technically have a second action, so would that allow me to use the Greenflame Blade cantrip a second time in the same turn (once with the actual action, once with this action) as the cantrip applies to one weapon attack in a similar fashion as a Paladin with Haste could apply Divine Smite onto the Haste-given attack?

Answer 1

No, you can't cast a spell with your extra action from haste.

Despite including an attack as part of the cantrip, all cantrips use the Cast a Spell action, like any other spell. Haste's options are limited as you indicated, and Cast a Spell is not among the available options.

But... Divine Smite!

The paladin's Divine Smite feature is not a spell, despite being fueled by spell slots. Paladins have other kinds of smiting that are spells, but Divine Smite is not. It triggers when you hit a creature with a melee weapon attack, but does not take any sort of action; any melee weapon attack that hits will suffice.

Answer 2

Quote from PHB pg. 250 in reference to the spell "Haste" "...gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object actions..."

Quote from PHB pg. 192 in reference to Actions in Combat: Attack "With this action, you make one melee or ranged attack."

So, while some spells are, quite literally, attacks, they do not fall under the "Attack" classification in regards to Actions in Combat, despite having to do an attack roll. There is a separate excerpt under Actions in Combat (PHB pg. 192) that references spellcasting, Cast a Spell; under which, spells are not technically even considered actions because of the fact "each spell has it's own casting time which specifies whether the caster must use an action, reaction, minutes or even hours..."

Actions in Combat clearly states what can be done during combat:

-Attack (melee or ranged, but not magic)

-Cast a spell

-Dash

-Disengage

-Dodge

-Help

-Hide

-Ready

-Search

-Use an Object

Haste clearly states that the action it allows the target can only be used for:

-Attack (melee or ranged; one weapon attack only, so no extra attack or weapon surges)

-Dash

-Disengage

-Hide

-Use an Object

"Cast a Spell" from the Actions in Combat section of PHB Pg.192, is clearly missing from that list of actions allowed by Haste

Answer 3

Yes, the bonus action from a Haste spell can be used to cast a second spell as long as the spell requires an attack roll.

The rules are quite clear that any spell that requires an attack roll is classed as an attack and is covered as an attack action.

The second paragraph of the description of the Attack Action states (PHB, page 192):

With this action, you make one melee or ranged attack. See "Making an Attack" section for the rules that govern an attack.

The first paragraph of the "Making an Attack" section states (PHB, page 194; this is just the fluff, BTW):

Whether you're striking with a melee weapon, firing a weapon at range, or making an attack roll as part of a spell, an attack has a simple structure.

The last paragraph in this section is the clincher:

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.

I don't think it could be any clearer.