Can you use a melee spell attack with the Hunter Ranger's Whirlwind Attack?

Question

The Hunter Ranger's Whirlwind Attack feature states:

You can use your action to make a melee attack against any number of creatures within 5 feet of you, with a separate attack roll for each target.

It does not specify that the attack needs to be a melee weapon attack but only that it must be a melee attack. Does this mean that you would be able to cast a spell such as inflict wounds if you multi-classed into a class with this spell or if you took the Magic Initiate feat and chose to learn the shocking grasp spell?

I am aware that Whirlwind Attack does not actually count as taking the Attack action; However, clearly you can make a melee weapon attack with this feature, an option that ordinarily would require the "Attack action". So why could you not also make a melee spell attack, an option that ordinarily would require the "Cast a Spell action"?

I would like answers to assume that the following ruling made in the Sage Advice Compendium is correct:

Whirlwind Attack is unusual, in that it’s a single attack with multiple attack rolls...

Answer 1

No

You can use your action to make a melee attack...

Whirlwind Attack is an action you can take. If you're taking the Whirlwind Attack action, you're not able to also take the Cast a spell action. You're also not getting any extra attacks if you have the Extra Attack feature, because you're not taking the Attack action.

Based on your questions and answers, you seem to be confused on the difference between Actions and things you do as part of an action. When Whirlwind Attacks says "make a melee attack", that is all you do, you make a melee attack. That does not mean you get to look through other actions such as "Cast a spell" or the "Attack action" for the words "make an attack" and then perform that action at the same time.

The path goes:

You: I want to take a whirlwind attack action

DM: Ok,make a melee attack roll against those 3 enemies

You: -Discuss results of rolls with DM and go from there.

Answer 2

Following the precedent of the Sage Advice Compendium, Whirlwind Attack will not allow you to make a melee spell attack

The section on Melee Attacks states:

A melee attack typically uses a handheld weapon such as a sword, a warhammer, or an axe. A typical monster makes a melee attack when it strikes with its claws, horns, teeth, tentacles, or other body part. A few spells also involve making a melee attack.

Thus we do know that certain spells are indeed considered melee attacks and so it would seem Whirlwind Attack would let us use them.
However, this is also the case if we were to look at the section on Opportunity Attacks which states:

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature.

It would seem we can use melee spell attacks for opportunity attacks; however, the Sage Advice Compendium has stated the following:

Q. Can you use a melee spell attack to make an opportunity attack?
A. You can’t if the spell attack is created by casting a spell. When a creature triggers an opportunity attack from you, you can use your reaction to make a melee attack against it. The opportunity attack doesn’t suddenly give you the ability to cast a spell, such as shocking grasp.

This is also showcased in this Q/A ("Can I use a spell to make an Opportunity Attack?").
Here we see the precedent set that even though opportunity attacks allow you to make a melee attack, they cannot be used to make melee spell attacks.
Following this logic we can conclude that even though the Whilrwind Attack feature allows us to make a melee attack, it cannot be used to make a melee spell attack.

Answer 3

You might with certain spells

Whirlwind attack requires you to take its special action to make a bunch of melee attacks. This locks you out of using the Cast a Spell action. However, you might be able to use a melee spell attack, if you have a to make such without taking the Cast a Spell action.

Ok, now we need a bit of a detour. Part of the Sage Advice answer to "Can you use a melee spell attack to make an opportunity attack?" includes the ruling that:

A few monsters can make opportunity attacks with melee spell attacks. Here’s how: certain monsters—including the banshee, the lich, and the specter—have a melee spell attack that isn’t delivered by a spell. For example, the banshee’s Corrupting Touch action is a melee spell attack but no spell is cast to make it. The banshee can, therefore, make opportunity attacks with Corrupting Touch.

Thus, a non-casting melee spell attack "action" can be used when a feature (such as the general rule on opportunity attacks) calls for an attack. Whirlwind similarly to opportunity attacks lets you make a melee attack as part of something else (ie. its special action vs. opportunity attacks reaction).

So now we just need to get ourselves an action which lets us make a melee spell attack:

• Flame blade (2nd level Druid spell).

  You can use your action to make a melee spell attack with the fiery blade. On a hit, the target takes 3d6 fire damage.

• Vampiric Touch (3rd level Warlock/Wizard spell).

  Until the spell ends, you can make the [melee spell] attack again on each of your turns as an action.

Both of these spells grant an action-option which is equivalent to the banshee's Corrupting Touch.

Alternately you could shapechange (let's not worry about how you get to cast it) into something with a melee spell action action. You would still have Whirlwind as shapechange includes:

You retain the benefit of any features from your class, race, or other source and can use them, provided that your new form is physically capable of doing so.

However, shapechange doesn't let you take the form of an undead (nor constucts for that matter) so the examples from SA are out. There are fortunately other monsters with such actions, including:

• Lamia (CR 4 monstrocity; MM)
• Kraken Priest (CR 5 humanoid; Volo's)
• Amnizu (CR 18 fiend; Mordenkainen's)

Answer 4

Technically Yes, but practically No.

Whirlwind Attack uses the phrase "make a melee attack". Note that this is the same wording as Opportunity Attack's "make one melee attack", and even the Attack action's "make one melee or ranged attack". It stands to reason that any melee attack you can make using the Attack action, you can also make using Opportunity Attacks or with the Whirlwind Attack action.

But what attacks can you make using the Attack action?

Technically, the rules are surprisingly silent on this.

We assume that we can use a weapon we are holding, but this is never actually stated in the rules. Grappling and Shoving are specifically called out as being possible using the Attack action. To me, this implies you can also make them using Whirlwind Attack, but it's not exactly clear if this is an exception or a clarification.

Let me ask you this: If a monster has an attack listed in its stat block under "Actions", can it use that attack as an Opportunity Attack? Can a Wolf use its claws against a fleeing opponent, potentially knocking them prone? I'm going to hazard a guess that most DMs rule that they can, without even considering the question.

Does it matter if the attack listed is a melee weapon attack or a melee spell attack? Can a Specter use its Life Drain attack as an opportunity attack? If a Specter was targeted by the Haste spell, could it use the additional Attack action to use Life Drain? If so, then a Specter that somehow uses Whirlwind Attack could indeed use Life Drain against multiple opponents.

According to the rules, there is no difference between a melee weapon attack and a melee spell attack for the purposes of the Attack action, nor Opportunity Attacks, nor Whirlwind Attack. If you can use one, you can use them all.

Therefore, a Hunter who has an unrestricted melee spell attack option (perhaps they have been Shapechanged into a Specter) can indeed use it with Whirlwind Attack, just as surely as they can use a held weapon.

However

That said, just because you can make an attack, doesn't mean you can perform an additional action that allows you to make that attack. Technically, ALL attacks require you to perform an action (or similar) to actually make the attack, so this isn't terribly helpful. However, I suspect that most DMs would not allow you to make the Cast a Spell action in the middle of the Attack action, therefore you would also not likely be able to cast Inflict Wounds as part of a Whirlwind Attack.

Vampiric Touch, on the other hand, is somewhat more reasonable to allow, as the spell effect grants you an attack that you can use on subsequent turns (the spell description does state that this attack requires an action, but like I said, ALL attacks require some kind of action, so if this is disallowed then as written you can't use a weapon either).

Hypothetically, if you use the Ready action to cast Inflict Wounds and hold the effect until the trigger occurs, you might then be considered to have the attack available, and could then Action Surge to use Whirlwind Attack with the readied attack from Inflict Wounds, but this would require a very specific interpretation of the rules that I suspect would not normally be allowed.