If you have dis/advantage on a roll, do you have dis/advantage on a reroll?

Question

This might be a duplicate but I can't find it.

To be clear this has nothing to do with Halfling Luck trait. Or similar abilities that allow the reroll of a die that rolls a natural 1. (I was apparently incorrect though.)

This has to do with a situation such as the Path of the Zealot barbarian's Fanatical Focus feature (Xanathar's Guide to Everything, p. 11), which lets you reroll a save that you fail:

Starting at 6th level, the divine power that fuels your rage can protect you. If you fail a saving throw while you’re raging, you can reroll it, and you must use the new roll. You can use this ability only once per rage.

Situation: Barbarian fails his save and is afflicted with bestow curse. Now he has disadvantage on Constitution checks and saves. He is targeted with disintegrate and fails his save. Using Fanatical Focus, he chooses to reroll that save. He would obviously have disadvantage again since the curse is ongoing. I think we could all agree to that.

However, what if the disadvantage or advantage was only imposed for that effect? Such as a Sorcerer using the Heightened Spell metamagic option:

When you cast a spell that forces a creature to make a saving throw to resist its effects, you can spend 3 sorcery points to give one target of the spell disadvantage on its first saving throw made against the spell.

The ability says you "reroll that save", therefore I argue that you would have disadvantage again as it would still be the first saving throw against the spell albeit a meta-game solutioning of that resolution.

I was unable to find anything on Sageadvice.eu although it is getting harder to sift that data. And I did not find anything in the errata or the Sage Advice Compendium (2017).

Is there anything to support this ruling in the rules that I missed?

This seems intuitive and intended however I see nothing that alludes to it.

Answer 1

The same rule that applies to the halfling's Lucky trait applies here (PHB pg 173, Advantage/Disadvantage):

When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll the d20. you can reroll only one of the dice. You choose which one. For example, if a halfling has advantage on an ability check and rolls a 1 and a 13. the halfling could use the Lucky trait to reroll the 1.

So in this case, the ability would allow the player to reroll the lower die, but the second roll from the original disadvantage would still affect the outcome (as an upper bound on what could be rolled)

Answer 2

For features that reroll/replace the d20; you reroll/replace only one d20

The section on "Advantage and Disadvantage" reads (post errata, emphasis mine):

[...] When you have advantage or disadvantage and something in the game, such as the halfling's Lucky trait, lets you reroll or replace the d20, you can reroll or replace only one of the dice. You choose which one. For example, if a halfling has advantage or disadvantage on an ability check and rolls a 1 and a 13, the halfling could use the Lucky trait to reroll the 1. [...]

The example they use is the Halfling's Lucky Trait which states (emphasis mine):

When you roll a 1 on the d20 for an attack roll, ability check, or saving throw, you can reroll the die and must use the new roll.

For features that reroll the entire check... Ask the GM

Unfortunately, neither of these make it particularly clear what happens when the feature does not reroll/replace the d20 but instead rerolls the entire check. Without a clear rule here (and I can't find one anywhere else either) it is going to be up to the GM exactly how these interact though here are some things for the GM to consider in making their decision:

Usually whatever is causing (dis)advantage will still be causing (dis)advantage on the reroll anyway. This means that in most cases, it isn't going to matter because the reroll would have the same circumstances regardless.

Is the reroll actually a new attack/check/saving-throw?
This would matter for anything that affect only the next d20 roll somebody makes such as single-use advantage or any other similar effect.

I personally would rule that when you reroll something like this you are not actually making an entire second check; thus any sort of limited-use effect would apply to both the original roll and the reroll.

If your GM considers rerolls to be entirely new attacks/checks/saving-throws then anything affecting only the very next d20 roll a creature makes would behave differently with features that reroll the d20 and features that reroll the entire attack/check/saving-throw.

I found no rule clarifying how features that reroll the entire attack/check/saving-throw interact with (dis)advantage, but I personally would rule that the reroll is made under the exact same circumstances as the original roll.