paths-le 0.2.0

Extract every file path in a codebase, and say whether it still points at anything
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//! JavaScript's string primitives, where Rust's differ.
//!
//! The extension calls `String.prototype.trim` and matches `\s` in
//! several extractors. Neither means what the Rust equivalent means:
//! JavaScript's whitespace set includes U+FEFF, which Unicode's
//! `White_Space` property does not, and excludes U+0085, which it does.
//! A file beginning with a byte-order mark is ordinary, so the
//! difference is reachable rather than theoretical.
//!
//! Defining the set once, in two forms, and testing that the two agree
//! is the only way this stays correct — a character added to one form
//! and not the other is exactly the drift this guards against.

/// Every character JavaScript treats as whitespace: `WhiteSpace` plus
/// `LineTerminator` from the language spec.
pub(crate) const JS_WHITESPACE: [char; 25] = [
    '\u{9}',    // tab
    '\u{a}',    // line feed
    '\u{b}',    // vertical tab
    '\u{c}',    // form feed
    '\u{d}',    // carriage return
    '\u{20}',   // space
    '\u{a0}',   // no-break space
    '\u{1680}', // ogham space mark
    '\u{2000}', '\u{2001}', '\u{2002}', '\u{2003}', '\u{2004}', '\u{2005}', '\u{2006}', '\u{2007}',
    '\u{2008}', '\u{2009}', '\u{200a}', '\u{2028}', // line separator
    '\u{2029}', // paragraph separator
    '\u{202f}', '\u{205f}', '\u{3000}', '\u{feff}', // zero-width no-break space
];

/// The same set as a regex character-class body, for patterns that need
/// `[^\s…]`. Held equal to `JS_WHITESPACE` by a test below.
pub(crate) const JS_SPACE_CLASS: &str =
    r"\t\n\x0B\f\r \u{a0}\u{1680}\u{2000}-\u{200a}\u{2028}\u{2029}\u{202f}\u{205f}\u{3000}\u{feff}";

pub(crate) fn is_js_whitespace(c: char) -> bool {
    JS_WHITESPACE.contains(&c)
}

pub(crate) fn trim(value: &str) -> &str {
    value.trim_matches(is_js_whitespace)
}

pub(crate) fn trim_start(value: &str) -> &str {
    value.trim_start_matches(is_js_whitespace)
}

/// `content.trim().length === 0`, the guard every extractor opens with.
pub(crate) fn is_blank(value: &str) -> bool {
    trim(value).is_empty()
}

/// `value.split(/\s+/)[0]` — the first run of non-whitespace.
pub(crate) fn first_token(value: &str) -> &str {
    value.split(is_js_whitespace).next().unwrap_or("")
}

#[cfg(test)]
mod tests {
    use regex::Regex;

    use super::*;

    /// The two forms of the set must describe the same characters. A
    /// character added to one and not the other is silent drift between
    /// the trimmers and the patterns that use the class.
    #[test]
    fn the_char_list_and_the_regex_class_agree() {
        let class = Regex::new(&format!("^[{JS_SPACE_CLASS}]$")).expect("the class compiles");
        for c in JS_WHITESPACE {
            assert!(
                class.is_match(&c.to_string()),
                "{c:?} missing from the class"
            );
        }
        // Every code point the class matches must be in the list. The
        // class is BMP-only, so scanning the BMP is exhaustive for it.
        for code in 0u32..=0xffff {
            let Some(c) = char::from_u32(code) else {
                continue;
            };
            if class.is_match(&c.to_string()) {
                assert!(JS_WHITESPACE.contains(&c), "{c:?} missing from the list");
            }
        }
    }

    /// The two differences from Rust's own notion of whitespace, stated
    /// as tests so a future simplification to `str::trim` fails loudly.
    #[test]
    fn a_byte_order_mark_is_whitespace_here_and_not_in_rust() {
        assert!(is_js_whitespace('\u{feff}'));
        assert!(!'\u{feff}'.is_whitespace());
        assert_eq!(trim("\u{feff}a\u{feff}"), "a");
    }

    #[test]
    fn a_next_line_character_is_whitespace_in_rust_and_not_here() {
        assert!(!is_js_whitespace('\u{85}'));
        assert!('\u{85}'.is_whitespace());
        assert_eq!(trim("\u{85}a"), "\u{85}a");
    }

    #[test]
    fn trimming_matches_the_ordinary_cases() {
        assert_eq!(trim("  a b  "), "a b");
        assert_eq!(trim_start("  a  "), "a  ");
        assert_eq!(trim(""), "");
        assert!(is_blank(" \t\n "));
        assert!(!is_blank(" x "));
    }

    #[test]
    fn the_first_token_stops_at_whitespace() {
        assert_eq!(first_token("image.png 2x"), "image.png");
        assert_eq!(first_token("solo"), "solo");
        assert_eq!(first_token(""), "");
    }
}