In the recently released preview of the Wild Magic Barbarian that will be in Tasha's Cauldron of Everything (preview here), I noticed the 6th level feature 'Bolstering Magic'. This feature has two applications. One acts as a Bless-type option, the second one reads:
Roll a d3. The creature [you're touching] regains one expended spell slot, the level of which equals the number rolled or lower (the creature’s choice). Once a creature receives this benefit, that creature can’t receive it again until after a long rest.
Suppose this effect is used on a Warlock of level 7 or above, and for the sake of argument suppose we rolled a 3 on the d3. All of their spell slots are of spell level 4. What happens?
- Nothing, the Warlock doesn't have the right type of spell slot to regain
- The Warlock has (expended) spell slots of Level 4 and higher, and now has a level 3 spell slot
- Something else happens, namely ...