html5ever 0.18.0

// Copyright 2014-2017 The html5ever Project Developers. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::fmt;

pub fn to_escaped_string<T: fmt::Debug>(x: &T) -> String {
    use std::fmt::Write;

    // FIXME: don't allocate twice
    let mut buf = String::new();
    let _ = buf.write_fmt(format_args!("{:?}", x));
    buf.shrink_to_fit();
    buf.chars().flat_map(|c| c.escape_default()).collect()
}

/// If `c` is an ASCII letter, return the corresponding lowercase
/// letter, otherwise None.
pub fn lower_ascii_letter(c: char) -> Option<char> {
    match c {
        'a' ... 'z' => Some(c),
        'A' ... 'Z' => Some((c as u8 - b'A' + b'a') as char),
        _ => None
    }
}

/// Is the character an ASCII alphanumeric character?
pub fn is_ascii_alnum(c: char) -> bool {
    matches!(c, '0'...'9' | 'a'...'z' | 'A'...'Z')
}

/// ASCII whitespace characters, as defined by
/// tree construction modes that treat them specially.
pub fn is_ascii_whitespace(c: char) -> bool {
    matches!(c, '\t' | '\r' | '\n' | '\x0C' | ' ')
}

#[cfg(test)]
#[allow(non_snake_case)]
mod test {
    use super::{is_ascii_alnum, lower_ascii_letter};

    test_eq!(lower_letter_a_is_a, lower_ascii_letter('a'), Some('a'));
    test_eq!(lower_letter_A_is_a, lower_ascii_letter('A'), Some('a'));
    test_eq!(lower_letter_symbol_is_None, lower_ascii_letter('!'), None);
    test_eq!(lower_letter_nonascii_is_None, lower_ascii_letter('\u{a66e}'), None);

    test_eq!(is_alnum_a, is_ascii_alnum('a'), true);
    test_eq!(is_alnum_A, is_ascii_alnum('A'), true);
    test_eq!(is_alnum_1, is_ascii_alnum('1'), true);
    test_eq!(is_not_alnum_symbol, is_ascii_alnum('!'), false);
    test_eq!(is_not_alnum_nonascii, is_ascii_alnum('\u{a66e}'), false);
}