What version of regex are you using?

1.9.3. The issue is present in regex 1.9.0 and later.

Describe the bug at a high level.

RegexSet::new([r"(?m)^ *v [0-9]"]).unwrap().is_match("v 0") incorrectly returns false in version 1.9.0 and later.

It returns true in 1.8.4.

It returns true if I use a Regex instead of a RegexSet.

What are the steps to reproduce the behavior?

fn main() { let pattern = r"(?m)^ *v [0-9]"; let text = "v 0"; let re = regex::Regex::new(pattern).unwrap(); println!("re is: {re:?}"); println!("{}", re.is_match(text)); // true (correct) let rs = regex::RegexSet::new([pattern]).unwrap(); println!("rs is: {rs:?}"); println!("{}", rs.is_match(text)); // false (incorrect) }

(playground link)

What is the actual behavior?

re is: Regex("(?m)^ *v [0-9]") true rs is: RegexSet(["(?m)^ *v [0-9]"]) false 

What is the expected behavior?

The last line should be true.