Since both True Strike and Witch Bolt require concentration, can True Strike grant advantage to Witch Bolt's attack roll?
My answer to this question received a comment saying that Witch Bolt's attack roll wouldn't get advantage from True Strike since they are both Concentration spells. The point piqued my interest, and since I've seen True Strike used to grant advantage to Witch Bolt at my table and on this answer, I wanted to raise the question.
As I see it, it's one of the two:
In order to cast Witch Bolt you need to stop concentrating on True Strike, so you don't get advantage.
You stop concentrating on True Strike as you cast Witch Bolt, so you get the advantage.
I believe here RAI would side with (2) while RAW sides with (1), but I would like a definitive, objective RAW answer. Any commentary from an authority that would provide a definite RAI ruling would be appreciated, too.
I thought about making this a more general question, like "Can a concentration spell affect the casting of another concentration spell?", but I believe a specific test case can help focus the answer and most likely any rulings on this specific case would apply to the general case, unless otherwise explicitly specified.
True Strike: On your next turn, you gain advantage on your first attack roll against the target, provided that this spell hasn’t ended.