Version: 3.3.1-671-ge2331eb03

(Just noticed with this version, most likely is there since this was introduced)

I've been updating some scripts to use this, and ran into this bug. If you have two (or more) command substitutions inside parenthesis in a string, you get a parser error about mismatched parenthesis. An example:

$ math "($(random) - $(random))"
fish: Mismatched parenthesis
math "($(random) - $(random))"
     ^

This isn't just a problem with math, it's a general problem. You can replace it with any command, and you'll get the same error.

It does work with only one command substitution inside parenthesis:

math "($(random) / 2) x $(random)"