This cop checks for ambiguous regexp literals in the first argument of a method invocation without parentheses.
# bad
# This is interpreted as a method invocation with a regexp literal,
# but it could possibly be `/` method invocations.
# (i.e. `do_something./(pattern)./(i)`)
do_something /pattern/i
# good
# With parentheses, there's no ambiguity.
do_something(/pattern/i)