The playable Firbolg race from Volo's Guide to Monsters has the Hidden Step racial feature (emphasis mine):
Hidden Step. As a bonus action, you can magically turn invisible until the start of your next turn or until you attack, make a damage roll, or force someone to make a saving throw. Once you use this trait, you can't use it again until you finish a short or long rest.
I can see how the text says it works, but there are situations where its wording ends invisibility without you taking any offensive action. That's really unusual for invisibility effects.
(For example, the spell Booming Blade makes you make a damage roll for the spell later, but it's not you personally taking new offensive action: it deals damage when a previously-hit opponent moves before the caster's next turn.)
Therefore my question: Have any errata or developer statements been made that clarify if “passive” delayed damage rolls or saving throws aren't meant to end Hidden Step?
I'm specifically looking for official statements clarifying this exact kind of interaction. Interpretations based on the text aren't useful answers because I can already see how the interaction works absent errata, and speculation on the intention aren't official clarification.
I myself have been unable to find an official statement that clarifies this issue, only this statement, which confirms that you are allowed to cast beneficial spells.
Best Answer
Yes, there is now an (un)official statement
Jeremy Crawford has clarified in a Tweet:
So, passive or not, as long as a creature is making a saving throw or taking damage from an effect you initiated (no matter when you initiated it) for any reason, hidden step will end.
This matches the intent we can understand when reading the ability itself.
Intent is clear from reading as well: if the user causes a harmful effect, hidden step deactivates.
The ability is explicitly written to restrict just about every way you can damage or harm an opponent (regardless of when said effect was initiated), so it seems clear that the intent was to prevent the user from doing harmful things. As such, allowing a loophole for spells and effects cast/initiated before the user used hidden step runs counter to that intent.
It may also be helpful to note that the designers also intentionally wrote this ability so as not to restrict beneficial spells and abilities being used.
The ability is already quite powerful and from a DM standpoint this argument would seem like an attempt to cheese additional power out of the ability by circumventing its primary restrictions.
This also seems wholly fair. In the example of booming blade, the only reason to cast such a spell is to try to cause damage. If you also choose to use hidden step you are taking the risk that the opponent triggers that damage and thus cancels your ability. It was player choice to cast the spell and to use the ability.
Allowing this opens the door for plenty of bad things/cheese
Our heroic firbolgs casts delayed blast fireball at a group of 4 enemies, uses hidden step, then immediately stops concentrating on the spell. It takes no action to stop concentrating on a spell so this is the exact same scenario as with booming blade. This causes 4 saving throws and 4 creatures to take up to 12d6 damage.
Does it seem to be intended to allow such an effect to not break hidden step? This seems like an overtly harmful action and I really do not think for one second that the designers intended this to be the case.
And this is only a cursory look at one spell. I'm sure that there are many more and possibly even worse spells/effects one could get away with through this loophole.
Neither RAW nor RAI support allowing a loophole for effects initiated before hidden step is activated.
As always, a DM may, of course, allow this if they want to for any reason.