basic regex rule fails to match after updating to 0.2

[mhristache]

I have a very simple function used to strip ansi formatting, which used to work fine with regex 0.1:

extern crate regex;

fn main() {
    let input = "\x1b[34mfoo";
    assert_eq!(strip_formatting(input), "foo");
}

fn strip_formatting<'t>(input: &'t str) -> String {
    let re = regex::Regex::new(r#"\x1B\[.+?m"#).unwrap();
    re.replace_all(input, "")
}

After updating to regex 0.2, I did a small change to the function to adapt to the new API (no syntax change):

extern crate regex;
use std::borrow::Cow;

fn main() {
    let input = "\x1b[34mfoo";
    assert_eq!(strip_formatting(input), "foo");
}

fn strip_formatting<'t>(input: &'t str) -> Cow<'t, str> {
    let re = regex::Regex::new(r#"\x1B\[.+?m"#).unwrap();
    re.replace_all(input, "")
}

... but now it fails to match the regex rule:

   Compiling generic v0.0.1 (file:///Users/mX/projects/rust/tmp/generic)
    Finished debug [unoptimized + debuginfo] target(s) in 2.9 secs
     Running `target/debug/generic`
thread 'main' panicked at 'assertion failed: `(left == right)` (left: `"\u{1b}[34mfoo"`, right: `"foo"`)', src/main.rs:6
note: Run with `RUST_BACKTRACE=1` for a backtrace.

The strange thing is that it works if I replace with something instead of "", e.g. this works:

extern crate regex;
use std::borrow::Cow;

fn main() {
    let input = "\x1b[34mfoo";
    assert_eq!(strip_formatting(input), "something foo");
}

fn strip_formatting<'t>(input: &'t str) -> Cow<'t, str> {
    let re = regex::Regex::new(r#"\x1B\[.+?m"#).unwrap();
    re.replace_all(input, "something ")
}