css_to_xpath/

lib.rs

mod parser;
mod translate;

pub use translate::{Error, Mode, Translator};

/// The version of this crate, from `Cargo.toml`.
pub const VERSION: &str = env!("CARGO_PKG_VERSION");

/// Translate a CSS selector to an XPath 1.0 expression.
///
/// # Arguments
///
/// * `css` — A CSS selector string.
/// * `prefix` — An XPath path prefix prepended to the result
///   (e.g. `"descendant-or-self::"`).  Pass `""` for none.
/// * `mode` — The translator flavour: [`Mode::Generic`], [`Mode::Html`], or
///   [`Mode::Xhtml`].
///
/// # Errors
///
/// Returns an [`Error`] when the selector is syntactically invalid or uses
/// an unsupported construct.
pub fn css_to_xpath(css: &str, prefix: &str, mode: Mode) -> Result<String, Error> {
    Translator::new(mode).css_to_xpath(css, prefix)
}

#[cfg(test)]
mod tests {
    use crate::translate::{Mode, Translator};

    fn xpath(css: &str) -> String {
        Translator::new(Mode::Generic)
            .css_to_xpath(css, "")
            .unwrap()
    }

    /// Type, namespace, and attribute selector forms.
    #[test]
    fn simple_selectors() {
        assert_eq!(xpath("*"), "*");
        assert_eq!(xpath("e"), "e");
        assert_eq!(xpath("*|e"), "*[local-name() = 'e']");
        assert_eq!(xpath("|e"), "e");
        assert_eq!(xpath("|*"), "*[namespace-uri() = '']");
        assert_eq!(xpath("*|*"), "*");
        assert_eq!(xpath("e|f"), "e:f");
        assert_eq!(xpath("svg|*"), "svg:*");
        assert_eq!(xpath("e[foo]"), "e[@foo]");
        assert_eq!(xpath("e[foo|bar]"), "e[@foo:bar]");
        assert_eq!(xpath("[*|foo]"), "*[@*[local-name() = 'foo']]");
        assert_eq!(xpath("[|foo]"), "*[@foo]");
        assert_eq!(xpath("e[foo=\"bar\"]"), "e[@foo = 'bar']");
        assert_eq!(xpath("e[foo=\"\"]"), "e[@foo = '']");
        assert_eq!(
            xpath("e[foo|=\"\"]"),
            "e[@foo and (@foo = '' or starts-with(@foo, '-'))]"
        );
        assert_eq!(
            xpath("e[foo~=\"bar\"]"),
            "e[@foo and contains(concat(' ', normalize-space(@foo), ' '), ' bar ')]"
        );
        assert_eq!(
            xpath("e[foo^=\"bar\"]"),
            "e[@foo and starts-with(@foo, 'bar')]"
        );
        assert_eq!(
            xpath("e[foo$=\"bar\"]"),
            "e[@foo and substring(@foo, string-length(@foo)-2) = 'bar']"
        );
        assert_eq!(
            xpath("e[foo*=\"bar\"]"),
            "e[@foo and contains(@foo, 'bar')]"
        );
        assert_eq!(
            xpath("e[hreflang|=\"en\"]"),
            "e[@hreflang and (@hreflang = 'en' or starts-with(@hreflang, 'en-'))]"
        );
    }

    #[test]
    fn class_id_combinators() {
        assert_eq!(
            xpath("e.warning"),
            "e[@class and contains(concat(' ', normalize-space(@class), ' '), ' warning ')]"
        );
        assert_eq!(xpath("e#myid"), "e[@id = 'myid']");
        assert_eq!(xpath("e f"), "e//f");
        assert_eq!(xpath("e > f"), "e/f");
        assert_eq!(xpath("e + f"), "e/following-sibling::*[1][self::f]");
        assert_eq!(xpath("e ~ f"), "e/following-sibling::f");
        assert_eq!(
            xpath("e + f[bar]"),
            "e/following-sibling::*[1][self::f][@bar]"
        );
        assert_eq!(xpath("e + *"), "e/following-sibling::*[1][self::*]");
        assert_eq!(xpath("div#container p"), "div[@id = 'container']//p");
        assert_eq!(xpath("a , b"), "a | b");
    }

    #[test]
    fn unsafe_names_and_escapes() {
        assert_eq!(xpath("di\\[v"), "*[name() = 'di[v']");
        assert_eq!(xpath("[h\\]ref]"), "*[attribute::*[name() = 'h]ref']]");
        assert_eq!(xpath("di\u{a0}v"), "*[name() = 'di\u{a0}v']");
        // Unicode escapes are decoded to the characters they represent,
        // in idents, hashes, and strings alike.
        assert_eq!(xpath("#\\31 23"), "*[@id = '123']");
        assert_eq!(xpath("\\31 23"), "*[name() = '123']");
        assert_eq!(xpath("[\\31 23]"), "*[attribute::*[name() = '123']]");
        assert_eq!(xpath("e[foo='\\31 23']"), "e[@foo = '123']");
        assert_eq!(xpath("e[foo='x\\79 z']"), "e[@foo = 'xyz']");
        // '*|' bypasses the safe-name fallback: quoting handles it.
        assert_eq!(xpath("*|di\\[v"), "*[local-name() = 'di[v']");
        assert_eq!(xpath("[*|h\\]ref]"), "*[@*[local-name() = 'h]ref']]");
        // '|' with a name needing quoting keeps the no-namespace
        // constraint alongside the name() test.
        assert_eq!(
            xpath("|di\\[v"),
            "*[name() = 'di[v' and namespace-uri() = '']"
        );
        assert_eq!(xpath("|é"), "*[name() = 'é' and namespace-uri() = '']");
    }

    #[test]
    fn case_sensitivity_flags() {
        const LOWER_FOO: &str = "translate(@foo, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', \
                                 'abcdefghijklmnopqrstuvwxyz')";
        assert_eq!(xpath("e[foo=\"Bar\" i]"), format!("e[{LOWER_FOO} = 'bar']"));
        // Flag idents are themselves case-insensitive.
        assert_eq!(xpath("e[foo=\"Bar\" I]"), format!("e[{LOWER_FOO} = 'bar']"));
        assert_eq!(
            xpath("e[foo^=\"Bar\" i]"),
            format!("e[{LOWER_FOO} and starts-with({LOWER_FOO}, 'bar')]")
        );
        assert_eq!(
            xpath("e[foo$=\"Bar\" i]"),
            format!(
                "e[{LOWER_FOO} and substring({LOWER_FOO}, \
                 string-length({LOWER_FOO})-2) = 'bar']"
            )
        );
        // ASCII-only lowering: non-ASCII characters are left alone.
        assert_eq!(
            xpath("e[foo=\"B\u{e4}r\" i]"),
            format!("e[{LOWER_FOO} = 'b\u{e4}r']")
        );
        // An empty value keeps the exact translation.
        assert_eq!(xpath("e[foo=\"\" i]"), "e[@foo = '']");
        // 's' requests the default case-sensitive matching.
        assert_eq!(xpath("e[foo=\"Bar\" s]"), "e[@foo = 'Bar']");
        // The flag composes with namespaced attribute forms.
        assert_eq!(
            xpath("e[*|foo=\"Bar\" i]"),
            format!(
                "e[translate(@*[local-name() = 'foo'], \
                 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', \
                 'abcdefghijklmnopqrstuvwxyz') = 'bar']"
            )
        );
    }

    #[test]
    fn unsupported_errors() {
        let t = Translator::new(Mode::Generic);
        // The non-standard [a!=b] and :contains() are not supported.
        assert!(t.css_to_xpath("e[foo!=\"bar\"]", "").is_err());
        assert!(t.css_to_xpath("e:contains(\"foo\")", "").is_err());
        assert!(t.css_to_xpath("e::before", "").is_err());
        assert!(t.css_to_xpath("e:", "").is_err());
        assert!(t.css_to_xpath("", "").is_err());
        // A flag requires an operator and value.
        assert!(t.css_to_xpath("[rel i]", "").is_err());
        assert!(t.css_to_xpath("[rel=stylesheet k]", "").is_err());
        assert!(t.css_to_xpath("[rel=stylesheet i i]", "").is_err());
        // Unknown pseudo-classes error.
        assert!(t.css_to_xpath("e:unknown-pseudo", "").is_err());
        assert!(t.css_to_xpath("e:first-line", "").is_err()); // pseudo-element
        // The Level 4 column combinator and grid-structural pseudos have
        // no XPath 1.0 translation: column membership rests on
        // colspan/rowspan layout arithmetic. `||` is caught before Servo
        // misparses it as namespace syntax...
        assert!(t.css_to_xpath("col || td", "").is_err());
        assert!(t.css_to_xpath("col||td", "").is_err());
        assert!(t.css_to_xpath("e:nth-col(2)", "").is_err());
        assert!(t.css_to_xpath("e:nth-last-col(2n)", "").is_err());
        // ...while pipes in strings, escapes, and comments stay valid.
        assert!(t.css_to_xpath("[foo=\"a||b\"]", "").is_ok());
        assert!(t.css_to_xpath("a\\|\\|b", "").is_ok());
        assert!(t.css_to_xpath("a /* || */ b", "").is_ok());
        // Pseudo-classes outside the never-match policy (see PseudoClass)
        // error rather than silently matching nothing: form validity and
        // state could be at least partially translated some day, and
        // erroring keeps typos loud.
        assert!(t.css_to_xpath("e:valid", "").is_err());
        assert!(t.css_to_xpath("e:user-invalid", "").is_err());
        assert!(t.css_to_xpath("e:read-only", "").is_err());
        assert!(t.css_to_xpath("e:placeholder-shown", "").is_err());
        assert!(t.css_to_xpath("e:defined", "").is_err());
        // :scope is supported in the leftmost compound only, and never
        // inside functional pseudo-class arguments (the context node is
        // unreachable from an XPath 1.0 predicate).
        assert!(t.css_to_xpath("a :scope", "").is_err());
        assert!(t.css_to_xpath("a > :scope", "").is_err());
        assert!(t.css_to_xpath(":scope :scope", "").is_err());
        assert!(t.css_to_xpath("e:is(:scope)", "").is_err());
        assert!(t.css_to_xpath("e:not(:scope)", "").is_err());
        assert!(t.css_to_xpath("e:has(:scope)", "").is_err());
        assert!(t.css_to_xpath("e:nth-child(2 of :scope)", "").is_err());
        // A leading combinator is :has()-only; dangling and doubled
        // combinators are parse errors everywhere.
        assert!(t.css_to_xpath("e:is(> a)", "").is_err());
        assert!(t.css_to_xpath("e:has(> > a)", "").is_err());
        assert!(t.css_to_xpath("e:has(>)", "").is_err());
        assert!(t.css_to_xpath("e:has(a >)", "").is_err());
        // Nested :has() is rejected (selectors-4).
        assert!(t.css_to_xpath("e:has(a:has(b))", "").is_err());
        assert!(t.css_to_xpath("e:has(> a:has(b))", "").is_err());
        // of-type pseudos are not implemented on `*` — including compounds
        // that leave the type implicit (`.foo` is `*.foo`) or carry it
        // only inside a pseudo-class argument. XPath 1.0 cannot compare a
        // sibling's name with the matched element's own name, so only a
        // type named in the compound itself gives a sibling node test.
        assert!(t.css_to_xpath("*:first-of-type", "").is_err());
        assert!(t.css_to_xpath("*:nth-last-of-type(2)", "").is_err());
        assert!(t.css_to_xpath("*:only-of-type", "").is_err());
        assert!(t.css_to_xpath(".foo:first-of-type", "").is_err());
        assert!(t.css_to_xpath("[bar]:nth-of-type(2)", "").is_err());
        assert!(t.css_to_xpath(":is(e):first-of-type", "").is_err());
        // :lang()/:dir() argument validation; a lone '-' is not a valid
        // ident.
        assert!(t.css_to_xpath(":lang()", "").is_err());
        assert!(t.css_to_xpath(":lang(5)", "").is_err());
        assert!(t.css_to_xpath(":lang(-)", "").is_err());
        // An+B must be whitespace-exact and integer-valued.
        assert!(t.css_to_xpath("e:nth-child(3 7)", "").is_err());
        assert!(t.css_to_xpath("e:nth-child(2 n)", "").is_err());
        assert!(t.css_to_xpath("e:nth-child(2.5)", "").is_err());
        assert!(t.css_to_xpath("e:nth-child(2e1)", "").is_err());
    }

    /// The nth-* family and its an+b arithmetic.
    #[test]
    fn nth_family() {
        assert_eq!(
            xpath("e:nth-child(1)"),
            "e[count(preceding-sibling::*) = 0]"
        );
        assert_eq!(
            xpath("e:nth-child(3n+2)"),
            "e[count(preceding-sibling::*) >= 1 and (count(preceding-sibling::*) +2) mod 3 = 0]"
        );
        assert_eq!(
            xpath("e:nth-child(3n-2)"),
            "e[count(preceding-sibling::*) mod 3 = 0]"
        );
        assert_eq!(
            xpath("e:nth-child(-n+6)"),
            "e[count(preceding-sibling::*) <= 5]"
        );
        assert_eq!(xpath("e:nth-child(n)"), "e");
        assert_eq!(xpath("e:nth-child(odd)"), xpath("e:nth-child(2n+1)"));
        assert_eq!(xpath("e:nth-child(even)"), xpath("e:nth-child(2n)"));
        // An+B is ASCII case-insensitive per css-syntax; Servo handles it
        // natively.
        assert_eq!(xpath("e:nth-child(2N)"), xpath("e:nth-child(2n)"));
        assert_eq!(xpath("e:nth-child(ODD)"), xpath("e:nth-child(odd)"));
        assert_eq!(xpath("e:nth-child(EVEN)"), xpath("e:nth-child(even)"));
        assert_eq!(xpath("e:nth-child(-N+3)"), xpath("e:nth-child(-n+3)"));
        assert_eq!(
            xpath("e:nth-last-child(1)"),
            "e[count(following-sibling::*) = 0]"
        );
        assert_eq!(
            xpath("e:nth-last-child(2n)"),
            "e[(count(following-sibling::*) +1) mod 2 = 0]"
        );
        assert_eq!(
            xpath("e:nth-last-child(2n+1)"),
            "e[count(following-sibling::*) mod 2 = 0]"
        );
        assert_eq!(
            xpath("e:nth-last-child(2n+2)"),
            "e[count(following-sibling::*) >= 1 and (count(following-sibling::*) +1) mod 2 = 0]"
        );
        assert_eq!(
            xpath("e:nth-last-child(3n+1)"),
            "e[count(following-sibling::*) mod 3 = 0]"
        );
        assert_eq!(
            xpath("e:nth-last-child(-n+2)"),
            "e[count(following-sibling::*) <= 1]"
        );
        assert_eq!(
            xpath("e:nth-of-type(1)"),
            "e[count(preceding-sibling::e) = 0]"
        );
        assert_eq!(
            xpath("e:nth-last-of-type(1)"),
            "e[count(following-sibling::e) = 0]"
        );
        assert_eq!(
            xpath("div e:nth-last-of-type(1) .aclass"),
            "div//e[count(following-sibling::e) = 0]//*[@class and contains(concat(' ', normalize-space(@class), ' '), ' aclass ')]"
        );
        // Servo collapses :first-child & co. into nth data; the general
        // an+b form covers them (see translate::nth).
        assert_eq!(xpath("e:first-child"), "e[count(preceding-sibling::*) = 0]");
        assert_eq!(xpath("e:last-child"), "e[count(following-sibling::*) = 0]");
        assert_eq!(
            xpath("e:first-of-type"),
            "e[count(preceding-sibling::e) = 0]"
        );
        assert_eq!(
            xpath("e:last-of-type"),
            "e[count(following-sibling::e) = 0]"
        );
        assert_eq!(
            xpath("e:only-child"),
            "e[count(preceding-sibling::*) = 0 and count(following-sibling::*) = 0]"
        );
        assert_eq!(
            xpath("e:only-of-type"),
            "e[count(preceding-sibling::e) = 0 and count(following-sibling::e) = 0]"
        );
        // Element names needing quoting fold into a name() condition; the
        // of-type pseudos count same-type siblings through the same test.
        assert_eq!(
            xpath("é:first-of-type"),
            "*[name() = 'é' and count(preceding-sibling::*[name() = 'é']) = 0]"
        );
        assert_eq!(
            xpath("é:nth-of-type(2)"),
            "*[name() = 'é' and count(preceding-sibling::*[name() = 'é']) = 1]"
        );
        assert_eq!(
            xpath("é:nth-last-of-type(1)"),
            "*[name() = 'é' and count(following-sibling::*[name() = 'é']) = 0]"
        );
        assert_eq!(
            xpath("é:only-of-type"),
            "*[name() = 'é' and count(preceding-sibling::*[name() = 'é']) = 0 and count(following-sibling::*[name() = 'é']) = 0]"
        );
        assert_eq!(
            xpath("e ~ f:nth-child(3)"),
            "e/following-sibling::f[count(preceding-sibling::*) = 2]"
        );
        // Early exits: a=1 with b<=1 matches everything; a<0 with b<1 is
        // impossible.
        assert_eq!(xpath("e:nth-child(n+1)"), "e");
        assert_eq!(xpath("e:nth-child(n-5)"), "e");
        assert_eq!(xpath("e:nth-child(-n)"), "e[0]");
        assert_eq!(xpath("e:nth-child(-2n-1)"), "e[0]");
        assert_eq!(xpath("e:nth-child(-n+0)"), "e[0]");
        assert_eq!(
            xpath("e:nth-child(-n+1)"),
            "e[count(preceding-sibling::*) <= 0]"
        );
        assert_eq!(
            xpath("e:nth-child(-2n+2)"),
            "e[count(preceding-sibling::*) <= 1 and (count(preceding-sibling::*) +1) mod -2 = 0]"
        );
    }

    /// `of S` selector lists (CSS Level 4), nth-child only.
    #[test]
    fn nth_child_of() {
        assert_eq!(
            xpath("div:nth-child(2 of .foo)"),
            "div[count(preceding-sibling::*[@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ')]) = 1 and @class and contains(concat(' ', normalize-space(@class), ' '), ' foo ')]"
        );
        // a=1, b<=1: only the current-element check remains.
        assert_eq!(
            xpath("li:nth-child(n of .item)"),
            "li[@class and contains(concat(' ', normalize-space(@class), ' '), ' item ')]"
        );
        // Impossible series keeps the current-element check after the 0.
        assert_eq!(
            xpath("li:nth-child(-n of .item)"),
            "li[0 and @class and contains(concat(' ', normalize-space(@class), ' '), ' item ')]"
        );
        // An element argument folds into a name() test.
        assert_eq!(
            xpath("div:nth-child(2 of div.foo)"),
            "div[count(preceding-sibling::*[@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ') and name() = 'div']) = 1 and @class and contains(concat(' ', normalize-space(@class), ' '), ' foo ') and name() = 'div']"
        );
        // A universal argument makes the list match everything, like a
        // plain :nth-child.
        assert_eq!(
            xpath("li:nth-child(2 of .foo, *)"),
            "li[count(preceding-sibling::*) = 1]"
        );
    }

    /// Structural pseudos and the generic never-match set.
    #[test]
    fn structural_and_never_match_pseudos() {
        assert_eq!(xpath("e:empty"), "e[not(*) and not(string-length())]");
        assert_eq!(xpath("e:EmPTY"), "e[not(*) and not(string-length())]");
        assert_eq!(xpath("e:root"), "e[not(parent::*)]");
        // The generic never-match set.
        for pseudo in [
            "any-link",
            "link",
            "visited",
            "hover",
            "active",
            "focus",
            "focus-within",
            "focus-visible",
            "target",
            "target-within",
            "local-link",
            "enabled",
            "disabled",
            "checked",
            "required",
            "optional",
        ] {
            assert_eq!(xpath(&format!("a:{pseudo}")), "a[0]");
        }
        assert_eq!(xpath("a:dir(ltr)"), "a[0]");
    }

    #[test]
    fn negation_matching_where_has() {
        assert_eq!(
            xpath("e:not(:nth-child(odd))"),
            "e[not(count(preceding-sibling::*) mod 2 = 0)]"
        );
        assert_eq!(xpath("e:nOT(*)"), "e[0]");
        assert_eq!(xpath("e:not(a)"), "e[not(name() = 'a')]");
        assert_eq!(xpath("e:not(a, b)"), "e[not(name() = 'a' or name() = 'b')]");
        // A universal argument makes :not() unmatchable...
        assert_eq!(xpath("div:not(a, *)"), "div[0]");
        // :where() / :is() OR their arguments together into one condition
        // that ANDs with the rest of the compound.
        assert_eq!(xpath("div:where(p)"), "div[name() = 'p']");
        assert_eq!(
            xpath("div:where(p, span)"),
            "div[name() = 'p' or name() = 'span']"
        );
        assert_eq!(
            xpath("*:where(div.content)"),
            "*[@class and contains(concat(' ', normalize-space(@class), ' '), ' content ') and name() = 'div']"
        );
        assert_eq!(
            xpath("div:where(p):where(span)"),
            "div[name() = 'p' and name() = 'span']"
        );
        assert_eq!(xpath("div:is(p)"), "div[name() = 'p']");
        // :matches() is the legacy alias for :is().
        assert_eq!(xpath("div:matches(p)"), "div[name() = 'p']");
        // ...and :is()/:where() a no-op constraint.
        assert_eq!(xpath("e:is(*)"), "e");
        assert_eq!(xpath("div:is(a, *)"), "div");
        assert_eq!(xpath("div:where(a, *)"), "div");
        // :has().
        assert_eq!(xpath("div:has(p)"), "div[.//*[name() = 'p']]");
        assert_eq!(
            xpath("div:has(.foo)"),
            "div[.//*[@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ')]]"
        );
        assert_eq!(
            xpath("div:has(p, span)"),
            "div[.//*[name() = 'p'] | .//*[name() = 'span']]"
        );
        assert_eq!(
            xpath("div:has(p):has(span)"),
            "div[.//*[name() = 'p'] and .//*[name() = 'span']]"
        );
        assert_eq!(
            xpath("section:has(div.content)"),
            "section[.//*[@class and contains(concat(' ', normalize-space(@class), ' '), ' content ') and name() = 'div']]"
        );
        assert_eq!(xpath("div:has(*)"), "div[.//*]");
        // Leading combinators in :has() (selectors-4 relative selectors).
        assert_eq!(xpath("e:has(> img)"), "e[child::*[name() = 'img']]");
        assert_eq!(xpath("e:has(~ p)"), "e[following-sibling::*[name() = 'p']]");
        assert_eq!(
            xpath("e:has(+ p)"),
            "e[following-sibling::*[1][name() = 'p']]"
        );
        assert_eq!(
            xpath("e:has(> a, ~ p)"),
            "e[child::*[name() = 'a'] | following-sibling::*[name() = 'p']]"
        );
        assert_eq!(
            xpath("e:has(> .foo)"),
            "e[child::*[@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ')]]"
        );
        assert_eq!(
            xpath("e:has(+ p.foo)"),
            "e[following-sibling::*[1][@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ') and name() = 'p']]"
        );
        // Nested :not() (Selectors Level 4).
        assert_eq!(xpath(":not(:not(a))"), "*[not(not(name() = 'a'))]");
        assert_eq!(xpath("e:is(:not(f))"), "e[not(name() = 'f')]");
        assert_eq!(xpath("e:has(:not(f))"), "e[.//*[not(name() = 'f')]]");
        // Prefixed names inside arguments stay node tests, resolved
        // through the namespace map like a top-level `svg|g` — not a
        // string comparison against the document's prefix.
        assert_eq!(xpath("e:is(svg|g)"), "e[self::svg:g]");
        assert_eq!(xpath("e:not(svg|g)"), "e[not(self::svg:g)]");
        assert_eq!(xpath("e:is(svg|*)"), "e[self::svg:*]");
        assert_eq!(xpath("e:has(svg|g)"), "e[.//svg:g]");
        assert_eq!(xpath("e:has(> svg|g)"), "e[child::svg:g]");
        assert_eq!(xpath("e:has(~ svg|g)"), "e[following-sibling::svg:g]");
        assert_eq!(
            xpath("e:has(+ svg|g)"),
            "e[following-sibling::*[1][self::svg:g]]"
        );
        assert_eq!(
            xpath("e:has(svg|g.foo)"),
            "e[.//svg:g[@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ')]]"
        );
    }

    /// Complex selectors (with combinators) inside the functional
    /// pseudo-classes (Selectors Level 4). :is()/:where()/:not() and the
    /// nth `of S` lists match their argument at the candidate element, so
    /// each combinator becomes an existence test through the reversed
    /// axis; :has() looks forward, extending its path compound by
    /// compound.
    #[test]
    fn complex_pseudo_arguments() {
        // One reversed axis per combinator.
        assert_eq!(
            xpath("e:is(a b)"),
            "e[name() = 'b' and ancestor::*[name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(a > b)"),
            "e[name() = 'b' and parent::*[name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(a + b)"),
            "e[name() = 'b' and preceding-sibling::*[1][name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(a ~ b)"),
            "e[name() = 'b' and preceding-sibling::*[name() = 'a']]"
        );
        // Longer chains nest, each step wrapping the remainder.
        assert_eq!(
            xpath("e:is(a b c)"),
            "e[name() = 'c' and ancestor::*[name() = 'b' and ancestor::*[name() = 'a']]]"
        );
        assert_eq!(
            xpath("e:is(a > b ~ c)"),
            "e[name() = 'c' and preceding-sibling::*[name() = 'b' and parent::*[name() = 'a']]]"
        );
        assert_eq!(
            xpath("e:is(a + b > c)"),
            "e[name() = 'c' and parent::*[name() = 'b' and preceding-sibling::*[1][name() = 'a']]]"
        );
        // :not() negates the whole chain condition; complex and compound
        // arguments OR together ('and' binds tighter than 'or').
        assert_eq!(
            xpath("e:not(a b)"),
            "e[not(name() = 'b' and ancestor::*[name() = 'a'])]"
        );
        assert_eq!(
            xpath("e:not(a > b + c)"),
            "e[not(name() = 'c' and preceding-sibling::*[1][name() = 'b' and parent::*[name() = 'a']])]"
        );
        assert_eq!(
            xpath("e:is(a b, c)"),
            "e[name() = 'b' and ancestor::*[name() = 'a'] or name() = 'c']"
        );
        assert_eq!(
            xpath("e:is(a, b c)"),
            "e[name() = 'a' or name() = 'c' and ancestor::*[name() = 'b']]"
        );
        // Universal steps: a bare-`*` left-hand side is a bare axis test,
        // a bare-`*` rightmost compound leaves only the chain test, and a
        // universal *argument* still makes the list trivially true (or
        // :not() unmatchable).
        assert_eq!(xpath("e:is(* b)"), "e[name() = 'b' and ancestor::*]");
        assert_eq!(xpath("e:is(a *)"), "e[ancestor::*[name() = 'a']]");
        assert_eq!(xpath("e:not(a *)"), "e[not(ancestor::*[name() = 'a'])]");
        assert_eq!(xpath("e:is(a b, *)"), "e");
        assert_eq!(xpath("e:not(a b, *)"), "e[0]");
        // Conditions on chain steps come before each step's name test.
        assert_eq!(
            xpath("e:is(a.x b.y)"),
            "e[@class and contains(concat(' ', normalize-space(@class), ' '), ' y ') and \
             name() = 'b' and \
             ancestor::*[@class and contains(concat(' ', normalize-space(@class), ' '), ' x ') \
             and name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(a[foo='bar'] > b)"),
            "e[name() = 'b' and parent::*[@foo = 'bar' and name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(a:first-child b)"),
            "e[name() = 'b' and ancestor::*[count(preceding-sibling::*) = 0 and name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(a:hover b)"),
            "e[name() = 'b' and ancestor::*[0 and name() = 'a']]"
        );
        // Nested pseudo-classes inside chain steps; an or-group condition
        // is parenthesized when conjoined with the chain test.
        assert_eq!(
            xpath("e:is(:not(a) b)"),
            "e[name() = 'b' and ancestor::*[not(name() = 'a')]]"
        );
        assert_eq!(
            xpath("e:not(:is(a b))"),
            "e[not(name() = 'b' and ancestor::*[name() = 'a'])]"
        );
        assert_eq!(
            xpath("e:is(:not(a b) c)"),
            "e[name() = 'c' and ancestor::*[not(name() = 'b' and ancestor::*[name() = 'a'])]]"
        );
        assert_eq!(
            xpath("e:is(:is(a, b) c)"),
            "e[name() = 'c' and ancestor::*[name() = 'a' or name() = 'b']]"
        );
        assert_eq!(
            xpath("e:is(c :is(a, b))"),
            "e[(name() = 'a' or name() = 'b') and ancestor::*[name() = 'c']]"
        );
        // Prefixed names in chain steps stay self:: node tests.
        assert_eq!(
            xpath("ns|e:is(a b)"),
            "ns:e[name() = 'b' and ancestor::*[name() = 'a']]"
        );
        assert_eq!(
            xpath("e:is(ns|a b)"),
            "e[name() = 'b' and ancestor::*[self::ns:a]]"
        );
        assert_eq!(
            xpath("e:is(a ns|b)"),
            "e[self::ns:b and ancestor::*[name() = 'a']]"
        );
        // :has() walks forward: one joiner per combinator, with the
        // leading combinator choosing the first axis.
        assert_eq!(
            xpath("e:has(a b)"),
            "e[.//*[name() = 'a']//*[name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(a > b)"),
            "e[.//*[name() = 'a']/*[name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(a + b)"),
            "e[.//*[name() = 'a']/following-sibling::*[1][name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(a ~ b)"),
            "e[.//*[name() = 'a']/following-sibling::*[name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(> a b)"),
            "e[child::*[name() = 'a']//*[name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(> a > b)"),
            "e[child::*[name() = 'a']/*[name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(+ a > b)"),
            "e[following-sibling::*[1][name() = 'a']/*[name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(~ a + b)"),
            "e[following-sibling::*[name() = 'a']/following-sibling::*[1][name() = 'b']]"
        );
        assert_eq!(
            xpath("e:has(a > b + c)"),
            "e[.//*[name() = 'a']/*[name() = 'b']/following-sibling::*[1][name() = 'c']]"
        );
        assert_eq!(
            xpath("e:has(> a:is(b c))"),
            "e[child::*[name() = 'c' and ancestor::*[name() = 'b'] and name() = 'a']]"
        );
        assert_eq!(
            xpath("e:has(a.x > b.y)"),
            "e[.//*[@class and contains(concat(' ', normalize-space(@class), ' '), ' x ') \
             and name() = 'a']/*[@class and \
             contains(concat(' ', normalize-space(@class), ' '), ' y ') and name() = 'b']]"
        );
        // Prefixed names stay path node tests, except under `+` where the
        // [1] position predicate needs the node test to stay `*`.
        assert_eq!(xpath("e:has(ns|a > b)"), "e[.//ns:a/*[name() = 'b']]");
        assert_eq!(
            xpath("e:has(a + ns|b)"),
            "e[.//*[name() = 'a']/following-sibling::*[1][self::ns:b]]"
        );
        // `of S` with complex selectors: the chain condition filters the
        // counted siblings and constrains the current element.
        assert_eq!(
            xpath("e:nth-child(2n of a b)"),
            "e[(count(preceding-sibling::*[name() = 'b' and ancestor::*[name() = 'a']]) +1) \
             mod 2 = 0 and name() = 'b' and ancestor::*[name() = 'a']]"
        );
        assert_eq!(
            xpath("e:nth-child(2n of a > b)"),
            "e[(count(preceding-sibling::*[name() = 'b' and parent::*[name() = 'a']]) +1) \
             mod 2 = 0 and name() = 'b' and parent::*[name() = 'a']]"
        );
        assert_eq!(
            xpath("e:nth-last-child(3 of a b)"),
            "e[count(following-sibling::*[name() = 'b' and ancestor::*[name() = 'a']]) = 2 \
             and name() = 'b' and ancestor::*[name() = 'a']]"
        );
    }

    /// :scope (Selectors Level 4) anchors the expression at the node the
    /// XPath is evaluated from: the leftmost compound moves onto the
    /// self:: axis and the prefix is not applied.
    #[test]
    fn scope_pseudo() {
        let t = Translator::new(Mode::Generic);
        assert_eq!(xpath(":scope"), "self::*");
        assert_eq!(xpath(":ScoPE"), "self::*");
        assert_eq!(xpath(":scope > a"), "self::*/a");
        assert_eq!(xpath(":scope a"), "self::*//a");
        assert_eq!(
            xpath(":scope + a"),
            "self::*/following-sibling::*[1][self::a]"
        );
        assert_eq!(xpath(":scope ~ a"), "self::*/following-sibling::a");
        // Other simple selectors in the :scope compound constrain the
        // context node itself.
        assert_eq!(xpath("div:scope"), "self::div");
        assert_eq!(xpath("svg|g:scope"), "self::svg:g");
        assert_eq!(
            xpath(":scope.foo > a"),
            "self::*[@class and contains(concat(' ', normalize-space(@class), ' '), ' foo ')]/a"
        );
        assert_eq!(
            xpath(":scope:first-child"),
            "self::*[count(preceding-sibling::*) = 0]"
        );
        // The prefix is replaced by the self:: anchor, per selector group.
        assert_eq!(
            t.css_to_xpath(":scope > a", "descendant-or-self::")
                .unwrap(),
            "self::*/a"
        );
        assert_eq!(
            t.css_to_xpath("a, :scope > b", "descendant-or-self::")
                .unwrap(),
            "descendant-or-self::a | self::*/b"
        );
    }

    #[test]
    fn lang_and_dir() {
        // Generic: XPath's lang() does prefix matching natively.
        assert_eq!(xpath("e:lang(en)"), "e[lang('en')]");
        assert_eq!(xpath("e:lang(\"en\")"), "e[lang('en')]");
        assert_eq!(xpath("e:lang(en-*)"), "e[lang('en')]");
        assert_eq!(xpath("e:lang(*)"), "e[true()]");
        assert_eq!(xpath("e:lang(en, fr)"), "e[lang('en') or lang('fr')]");
        // Whitespace is a separator too.
        assert_eq!(xpath("e:lang(en fr)"), "e[lang('en') or lang('fr')]");
        // A bare * stays match-anything even alongside other ranges: it
        // must not be confused with the head of an interior wildcard.
        assert_eq!(xpath("e:lang(*, fr)"), "e[true() or lang('fr')]");
        // HTML: nearest lang-attributed ancestor, lowercased prefix match.
        let html = Translator::new(Mode::Html);
        assert_eq!(
            html.css_to_xpath("e:lang(EN)", "").unwrap(),
            "e[ancestor-or-self::*[@lang][1][starts-with(concat(translate(@lang, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), '-'), 'en-')]]"
        );
        assert_eq!(
            html.css_to_xpath("e:lang(*)", "").unwrap(),
            "e[ancestor-or-self::*[@lang]]"
        );
        // xhtml shares the HTML overrides.
        let xhtml = Translator::new(Mode::Xhtml);
        assert_eq!(
            xhtml.css_to_xpath("E:lang(*)", "").unwrap(),
            "E[ancestor-or-self::*[@lang]]"
        );
        // Interior wildcards (RFC 4647 extended filtering) are valid CSS
        // but inexpressible in XPath 1.0, so both spellings error rather
        // than over-match (unquoted *-CH) or never match (quoted "*-CH").
        let t = Translator::new(Mode::Generic);
        for sel in [
            "e:lang(*-CH)",
            "e:lang(\"*-CH\")",
            "e:lang(de-*-DE)",
            "e:lang(\"de-*-DE\")",
        ] {
            assert!(t.css_to_xpath(sel, "").is_err(), "{sel} should error");
            assert!(
                html.css_to_xpath(sel, "").is_err(),
                "{sel} should error (html)"
            );
        }
        // :dir() takes exactly one identifier (selectors-4) — none of
        // :lang()'s strings, wildcards, or lists. It never matches in any
        // translator: resolved directionality needs runtime bidi
        // resolution, and a nearest-@dir approximation is deliberately
        // not attempted (see apply_pseudo_class).
        assert_eq!(xpath("e:dir(rtl)"), "e[0]");
        assert_eq!(html.css_to_xpath("e:dir(rtl)", "").unwrap(), "e[0]");
        assert_eq!(xhtml.css_to_xpath("e:dir(ltr)", "").unwrap(), "e[0]");
        assert!(t.css_to_xpath("e:dir()", "").is_err());
        assert!(t.css_to_xpath("e:dir(ltr rtl)", "").is_err());
        assert!(t.css_to_xpath("e:dir(ltr, rtl)", "").is_err());
        assert!(t.css_to_xpath("e:dir(\"ltr\")", "").is_err());
        assert!(t.css_to_xpath("e:dir(*)", "").is_err());
    }

    /// The HTML translator's pseudo-class overrides.
    #[test]
    fn html_pseudo_overrides() {
        let html = Translator::new(Mode::Html);
        let h = |css: &str| html.css_to_xpath(css, "").unwrap();
        assert_eq!(
            h("a:link"),
            "a[@href and (name(.) = 'a' or name(.) = 'link' or name(.) = 'area')]"
        );
        // :any-link is :link plus :visited; with no visited state in a
        // static document the two coincide, so they share a translation.
        assert_eq!(h("a:any-link"), h("a:link"));
        assert_eq!(h("a:ANY-link"), h("a:link"));
        // @type comparisons fold case (HTML enumerated attribute), so
        // type="RADIO" reads as a radio. The fold is the same translate()
        // the `i` attribute flag uses.
        let t_lc = "translate(@type, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz')";
        assert_eq!(
            h("input:checked"),
            format!(
                "input[(@selected and name(.) = 'option') or (@checked and \
                 (name(.) = 'input' or name(.) = 'command')and \
                 ({t_lc} = 'checkbox' or {t_lc} = 'radio'))]"
            )
        );
        // :required/:optional test the @required attribute over the
        // elements it applies to; input types where it has no effect
        // match neither.
        assert_eq!(
            h("input:required"),
            format!(
                "input[@required and ((name(.) = 'input' and not(\
                 {t_lc} = 'hidden' or {t_lc} = 'range' or {t_lc} = 'color' or \
                 {t_lc} = 'submit' or {t_lc} = 'image' or {t_lc} = 'reset' or \
                 {t_lc} = 'button')) or name(.) = 'select' or name(.) = 'textarea')]"
            )
        );
        assert_eq!(
            h("select:optional"),
            format!(
                "select[not(@required) and ((name(.) = 'input' and not(\
                 {t_lc} = 'hidden' or {t_lc} = 'range' or {t_lc} = 'color' or \
                 {t_lc} = 'submit' or {t_lc} = 'image' or {t_lc} = 'reset' or \
                 {t_lc} = 'button')) or name(.) = 'select' or name(.) = 'textarea')]"
            )
        );
        // :disabled/:enabled fold @type case and apply HTML's
        // "actually disabled" carve-out: a control inside a disabled
        // fieldset's first legend is NOT disabled. Expressed by counting —
        // more disabled-fieldset ancestors than protecting first-legends.
        let fd = "count(ancestor::fieldset[@disabled]) > \
                  count(ancestor::legend[not(preceding-sibling::legend)]\
                  [parent::fieldset[@disabled]])";
        assert_eq!(
            h("input:disabled"),
            format!(
                "input[( @disabled and ( \
                 (name(.) = 'input' and not({t_lc} = 'hidden')) or \
                 name(.) = 'button' or name(.) = 'select' or \
                 name(.) = 'textarea' or name(.) = 'command' or \
                 name(.) = 'fieldset' or name(.) = 'optgroup' or \
                 name(.) = 'option' \
                 ) ) or ( ( \
                 (name(.) = 'input' and not({t_lc} = 'hidden')) or \
                 name(.) = 'button' or name(.) = 'select' or \
                 name(.) = 'textarea' \
                 ) \
                 and {fd} \
                 )]"
            )
        );
        assert_eq!(
            h("input:enabled"),
            format!(
                "input[(@href and (name(.) = 'a' or name(.) = 'link' or \
                 name(.) = 'area')) or \
                 ((name(.) = 'command' or name(.) = 'fieldset' or \
                 name(.) = 'optgroup') and not(@disabled)) or \
                 (((name(.) = 'input' and not({t_lc} = 'hidden')) \
                 or name(.) = 'button' or name(.) = 'select' \
                 or name(.) = 'textarea' or name(.) = 'keygen') \
                 and not (@disabled or {fd})) \
                 or (name(.) = 'option' and not(@disabled or \
                 ancestor::optgroup[@disabled]))]"
            )
        );
        // Non-overridden dynamic pseudos still never match.
        assert_eq!(h("a:hover"), "a[0]");
        assert_eq!(h("a:visited"), "a[0]");
        assert_eq!(h("a:focus-within"), "a[0]");
        assert_eq!(h("a:focus-visible"), "a[0]");
    }

    #[test]
    fn html_translator_lowercases_names_not_values() {
        let html = Translator::new(Mode::Html);
        assert_eq!(html.css_to_xpath("DIV", "").unwrap(), "div");
        assert_eq!(html.css_to_xpath("[FOO]", "").unwrap(), "*[@foo]");
        // Names lowercase, values keep their case.
        assert_eq!(
            html.css_to_xpath("DIV[Value=\"Mixed Case\"]", "").unwrap(),
            "div[@value = 'Mixed Case']"
        );
        // The element inside local-name() is lowercased too.
        assert_eq!(
            html.css_to_xpath("*|DIV", "").unwrap(),
            "*[local-name() = 'div']"
        );
        // xhtml preserves case
        let xhtml = Translator::new(Mode::Xhtml);
        assert_eq!(xhtml.css_to_xpath("DIV", "").unwrap(), "DIV");
    }

    #[test]
    fn prefix_applied_per_branch() {
        let t = Translator::new(Mode::Generic);
        assert_eq!(
            t.css_to_xpath("a, b", "descendant-or-self::").unwrap(),
            "descendant-or-self::a | descendant-or-self::b"
        );
    }
}