Xanathar's Guide to Everything (p. 56) adds Aspect of the Moon as an option for one of their Eldritch Invocations:
Aspect of the Moon
Prerequisite: Pact of the Tome feature
You no longer need to sleep and can't be forced to sleep by any means. To gain the benefits of a long rest, you can spend all 8 hours doing light activity, such as reading your Book of Shadows and keeping watch.
What exactly is considered "light activity" for the purpose of this invocation? For example, would casting a spell, casting a ritual, making a short rest, copying spells and/or using a tool be considered light activity?