The warlock's Pact of the Tome option for the Pact Boon feature says:
When you gain this feature, choose three cantrips from any class's spell list. While the book is on your person, you can cast those cantrips at will.
Are these cantrips considered warlock spells for the purposes of determining attack bonuses and save DCs?
I think that might be the intent, but unless I'm missing something, I don't think the rules as written support that. Similar features seem to specify when a spell becomes a class spell, such as a cleric's domain spells:
If you have a domain spell that doesn't appear on the cleric spell list, the spell is nonetheless a cleric spell for you.
Is my interpretation correct that while the warlock can cast those cantrips, they need to use the spellcasting ability of the class whose list the cantrip comes from when casting them?