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 …
Best Answer
While not a RAW answer, I would consider how the pearl of power works and has been errata'd over time in this scenario.
The original text of the item read:
Over time, Crawford suggested that warlocks should be allowed to regain slots with a pearl of power, though with the phrasing being a personal ruling moreso than an official one:
This was eventually errata'd into the item itself, whose text now begins with:
While it's certainly possible that the lack of such text in the new barbarian ability may have been intentional, historically it seems they haven't had a problem with restoring warlock spell slots at a lower level when such a feature is available.
Additionally, I would consider the transition from party level 6 to 7 in the scenario where warlocks are the primary/only spellcaster in a party with a Wild Magic barbarian; that part of the feature would effectively suddenly "turn off" at level 7 if restoring lower-level slots is not permitted, which is quite awkward.