The warlock's One with Shadows eldritch invocation presents an interesting opportunity: it gives you invisibility without requiring concentration. Specifically (PHB, p. 111):
One with Shadows
Prerequisite: 5th level
When you are in an area of dim light or darkness, you can use your
action to become invisible until you move or take an action or a
reaction.
Unlike the invisibility spell, this would not necessarily end if the warlock became unconscious. However, the wording that says that this spell ends if you "move or take an action or a reaction" seems to imply that this invisibility is usually intended to last for a very short duration.
But it occurred to me that outside of combat, people often don't do much that technically requires an action, especially if they are at rest. And at other times, it has been indicated that "moving" (for the purpose of magical triggers) refers to moving in the sense of spending movement to change your location on a 2D grid (not becoming prone, or standing up from prone).
So I was wondering: could a warlock use an action to Hide1, then use the One with Shadows invocation to become invisible, then simply lie down and go to sleep for 8 hours (for a long rest), while remaining invisible (and likely hidden)?
Put another way: is there some action, reaction, or move required during a long rest?
1 I included the part about Hiding because according to the rules as written, an unhidden creature that is invisible is still apparent to creatures around it (it can't be seen, but they know where it is). So I wanted to include the hiding part to avoid that argument. And I did so beforehand, because using the Hide action while invisible would break the invisibility.
Best Answer
This should work, if it's the last thing you do before going to sleep.
Outside of combat, we typically don't account for actions, but this invocation would require keeping track of whether you do something that would be an action. For example, you can eat during a rest, but that would use an action if done in combat, so it would break the invisibility (because the magic doesn't care whether you call it an action).
However, if the warlock goes into an enclosed, dark space, lies down, invokes the magic, and then goes to sleep, yeah, they can be invisible until waking up.
A caveat about doing this during a short rest
(not actually the question, but it seems relevant)
The short rest rules mention "tending to wounds" as a possible activity, and allow regaining hit points by spending Hit Dice, but don't actually say that you have to tend to your wounds to regain hit points. I would argue that the rules imply that wound care is an expected part of resting, and if you insist on spending the entire rest invisible instead of caring for your wounds, you can't spend Hit Dice. But depending on how your table treats the rules, and on how you interpret hit points, this could go either way.