regress 0.4.1

A regular expression engine targeting EcmaScript syntax
Documentation 
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fn test_1_error(pattern: &str, expected_err: &str) {
    let res = regress::Regex::new(pattern);
    assert!(res.is_err(), "Pattern should not have parsed: {}", pattern);

    let err = res.err().unwrap().text;
    assert!(
        err.contains(expected_err),
        "Error text '{}' did not contain '{}' for pattern '{}'",
        err,
        expected_err,
        pattern
    );
}

#[test]
fn test_excessive_capture_groups() {
    let mut captures = String::from("s");
    let mut loops = String::from("s");
    for _ in 0..65536 {
        captures.push_str("(x)");
        loops.push_str("x{3,5}");
    }
    test_1_error(captures.as_str(), "Capture group count limit exceeded");
    test_1_error(loops.as_str(), "Loop count limit exceeded");
}

#[test]
fn test_syntax_errors() {
    test_1_error(r"*", "Nothing to repeat");
    test_1_error(r"x**", "Nothing to repeat");
    test_1_error(r"?", "Nothing to repeat");
    test_1_error(r"{3,5}", "Nothing to repeat");
    test_1_error(r"x{5,3}", "Invalid quantifier");

    test_1_error(r"]", "Unbalanced bracket");
    test_1_error(r"[abc", "Unbalanced bracket");

    test_1_error(r"(", "Unbalanced parenthesis");
    test_1_error(r"(?!", "Unbalanced parenthesis");
    test_1_error(r"abc)", "Unbalanced parenthesis");

    test_1_error(r"[z-a]", "Invalid character range");
    test_1_error(r"[\d-z]", "Invalid character range");

    test_1_error("\\", "Incomplete escape");

    test_1_error("^*", "Quantifier not allowed here");
    test_1_error("${3}", "Quantifier not allowed here");
    test_1_error("(?=abc)*", "Quantifier not allowed here");
    test_1_error("(?!abc){3,}", "Quantifier not allowed here");

    test_1_error(r"\2(a)", "Invalid character escape");
}