Unexpected match with end anchor in group

[vthib]

What version of regex are you using?

1.6.0

Describe the bug at a high level.

The regex (a$)b$ matches on input ab which is not expected.

What are the steps to reproduce the behavior?

fn main() {
    let regex = regex::Regex::new("(a$)b$").unwrap();
    println!("match: {:?}", regex.find("ab"));
    println!("captures: {:?}", regex.captures("ab"));
}

What is the actual behavior?

This prints:

match: Some(Match { text: "ab", start: 0, end: 2 })
captures: None

What is the expected behavior?

The regex should not match. The capture call gives the expected result, but not the find call.

a$b$ and (a$)b display the expected behavior, so this seems to be a weird corner case.

My first hypothesis was that it is caused by an invalid suffix extraction:

$ regex-debug prefixes '(a$)b$'
Cut(a)
$ regex-debug suffixes '(a$)b$'
Complete(ab)
$ regex-debug prefixes 'a$b$'
Cut(a)
$ regex-debug suffixes 'a$b$'
Cut(b)

But the regex (a$)b does not have the bug, and yet has the same suffix extraction:

$ regex-debug suffixes '(a$)b'
Complete(ab)

So i'm not sure it is related to this.

[BurntSushi]

Yeah, the Complete(ab) extraction for (a$)b$ does indeed look fishy.

This should be fixed once #656 lands. I've added it as a regression test in my WIP branch and can confirm it is fixed. Nice catch.