parentheses being set to variable in mixin

[aaarichter]

Hi, sorry if this has been asked before but I can't seem to find what option is causing this transform:

original stylus:

focus-outline($focusColor = $color-blue-600)
  0 0 3px 1px $focusColor

transformed to

focus-outline($focusColor = $color-blue-600)
  0 0 3px 1px {$focusColor}

The {} around the variable are causing the stylus compiler to throw expected ":", got "}"