Fine. Why don't I use your own logic, then. According to you, in past threads, magic stone does not let you make an attack with a weapon. I actually agree with that in the case of no sling being used to make the attack, and since it's not the subject of the thread, let's ignore the case of slings. So, the attack you make with magic stone is not an attack with a weapon, according to you. How, then, can it be an attack with a nonmagical weapon?

You claim both that magic stone is an attack with a nonmagical weapon and an attack with no weapon at all. Which is it?

Its just a spell attack. It does the damage it says it does and nothing more. 

Just like there isn't a "magic fire damage" or a "magic acid damage," it just does bludgeoning damage unless stated otherwise. 

Here is my question for you: Is the attack described in magic stone made with a weapon? If the answer is no, then said attack is also not made with a nonmagical weapon. If it is not an attack made with a nonmagical weapon, then resistance or immunity to bludgeoning, piercing, or slashing damage from attacks with nonmagical weapons does not apply.

If the resistance was just worded to be about attacks from "nonmagic weapons," sure. 

But as things stand, go look at the phrasing today for ghosts or liches. The exact wording has been changed to "nonmagical attacks." It isn't a question of weapons or no weapons, but of damage that has been deemed "magical." 

Hence why Armor of Invulnerability has resistance to a dragon's breath weapon: the attack might have a magical source, but the cold damage is just cold damage.

Quote from Kronzypantz >>

Ok, so if I cast light on my staff it overcomes resistance to non-magic attacks? 

No. That status must be asserted in the spell/damage description. 

 
Of course not, the light spell doesn’t do any damage, the magic stone spell does.

What a silly debate.  This question seems really straightforward.  The spell says that when someone throws a magic pebble at a target it's a ranged spell attack that uses a spellcasting modifier for damage instead of the typical modifier that's used for a nonmagical range weapon attack (which would usually be DEX).  All attacks result in a type of damage, in this case it's bludgeoning damage.  It's clearly a magical attack.  For some reason, it's not even a weapon attack, it's simply a magical attack.  It's just like if you cast Fire Bolt to do fire damage.  Not all sources of fire damage are magical.  But the damage that is caused by the Fire Bolt is magical.  The same is true for Bludgeoning damage or any other possible type of damage.  Chill Touch does necrotic damage.  Eldritch Blast does force damage.  Ray of Frost does cold damage.  Shillelagh does Bludgeoning damage and it's even more spelled out in that case that the weapon is magical.  Thorn Whip does piercing damage.  These are all magical attacks.  Lots of damage types can also be caused by sources that are not magical so it's unclear why 3 specific damage types were questioned earlier in this thread.

Spells that deal bludgeoning, piercing, or slashing damage that don’t say “magical” are not magical.

As far as I know, that statement above is incorrect and unsupported.  We would need a direct quote from the rules that says this, otherwise it's just a made up homebrew.  There is no correlation between the damage type and whether or not it's a magical attack.  But whenever something says "spell attack" and uses spellcasting modifiers that's always a magical attack by definition.  Attacks with magic weapons or items are also magical attacks.

As far as answering the OP, if the target has resistance to bludgeoning damage then that would apply.  Resistance to non-magical attacks would not apply.

What damage does it do though? Does it say it does magical damage?

It’s a spell that does damage. There is technically no “magic damage” this edition, only magic sources of damage, and a spell is a magic source by default.

It doesn't matter what type of damage it says it does, and it certainly doesn't matter if it says the damage is "magical". What matters is if the attack is magical.

That brings us to the question: is the attack magical? Yes. Yes it is. Very obviously so. It's a spell attack made with a stone that a spell, in no uncertain terms, imbued with magic. It uses somebody's spellcasting ability. It at no point tries to pass itself off as anything but magical.

Quote from IamSposta >>

It’s a spell that does damage. There is technically no “magic damage” this edition, only magic sources of damage, and a spell is a magic source by default.

 I think that's an interesting counterpoint, especially to the idea that a, say... a weapon with the Light Spell cast on it does not count as magical when it deals damage, because the source of the damage is not the spell. The source of damage for Magic Stone is not the stone itself... what the stone is made out of and its size has no impact on the damage it deals.

The spell also literally says “you imbue the stones with magic.” Any way you slice it, the damage is coming from a magical source.

(Emphasis mine.)

A lone spellcaster cannot arm an entire village with magic stones.

And a Dragon's description is that its a creature of magic, yet in parsing out what is magical, the official ruling is that their breath weapon doesn't cause magical damage to override resistance to non-magical attacks. 

Its weird, because there are no creatures with resistance to elemental non-magical attacks, so we aren't given an example of where there would ever be a distinction for elemental damage. 

But spells only do what they explicitly say. Its fine to infer that a spell does magical damage, but given how specific the riders on weapons about overcoming resistances are its not explicit. 

Quote from Kronzypantz >>

But as things stand, go look at the phrasing today for ghosts or liches. The exact wording has been changed to "nonmagical attacks." It isn't a question of weapons or no weapons, but of damage that has been deemed "magical." 

Why did you switch from "attack" to "damage" here?

I'm not sure there's a creature in the game that lists resistance to "nonmagical damage". I'm pretty sure it's always been written as: "Bludgeoning, Piercing, and Slashing from Nonmagical Attacks". magic stone is very clearly a magical attack

About the only edge case I can think of where the wording is different for resistance, and refers to "nonmagical damage", is with stoneskin

Its a bit facetious, but "attack" here among immunities and resistances obviously refers to damage. Resistance to an attack itself isn't a thing in 5e. An attack can be made at disadvantage and its damage can be resisted, and there is even resistance to magical saving throws and effects. But not just "attacks" generally. 

Quote from Kronzypantz >>

Its a bit facetious, but "attack" here among immunities and resistances obviously refers to damage.

That doesn't track at all. The resistance is quite explicitly telling you it only applies to the outcomes of nonmagical attacks

What outcomes are there to non magical attacks except damage?

Quote from Kronzypantz >>

What outcomes are there to non magical attacks except damage?

What relevance is that question to the discussion?

"Resistance to Bludgeoning, Piercing, and Slashing from Nonmagical Attacks" very clearly states that it applies only to nonmagical attacks

Magic stone is clearly a “magical attack,” since it’s a spell attack made available by a magic spell. This isn’t rocket science.

Damage Resistance or Immunity to Bludgeoning, Piercing, and Slashing from Nonmagical Attacks is clearly bypassed by an attack delivered by the magic stone spell, as the Monster Manual provides what an magical attack actually is;

Vulnerabilities, Resistances, and Immunities: Some creatures have vulnerability, resistance, or immunity to certain types of damage. Particular creatures are even resistant or immune to damage from non-magical attacks (a magical attack is an attack delivered by a spell, a magic item, or another magical source). In addition, some creatures are immune to certain conditions.