1 files changed, 145 insertions, 0 deletions
diff --git a/third_party/rust/cssparser/src/nth.rs b/third_party/rust/cssparser/src/nth.rs
new file mode 100644
index 0000000000..518de4d9b4
--- /dev/null
+++ b/third_party/rust/cssparser/src/nth.rs
@@ -0,0 +1,145 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use super::{BasicParseError, Parser, ParserInput, Token};
+
+/// Parse the *An+B* notation, as found in the `:nth-child()` selector.
+/// The input is typically the arguments of a function,
+/// in which case the caller needs to check if the arguments’ parser is exhausted.
+/// Return `Ok((A, B))`, or `Err(())` for a syntax error.
+pub fn parse_nth<'i, 't>(input: &mut Parser<'i, 't>) -> Result<(i32, i32), BasicParseError<'i>> {
+    match *input.next()? {
+        Token::Number {
+            int_value: Some(b), ..
+        } => Ok((0, b)),
+        Token::Dimension {
+            int_value: Some(a),
+            ref unit,
+            ..
+        } => {
+            match_ignore_ascii_case! {
+                unit,
+                "n" => Ok(parse_b(input, a)?),
+                "n-" => Ok(parse_signless_b(input, a, -1)?),
+                _ => match parse_n_dash_digits(&*unit) {
+                    Ok(b) => Ok((a, b)),
+                    Err(()) => {
+                        let unit = unit.clone();
+                        Err(input.new_basic_unexpected_token_error(Token::Ident(unit)))
+                    }
+                }
+            }
+        }
+        Token::Ident(ref value) => {
+            match_ignore_ascii_case! { value,
+                "even" => Ok((2, 0)),
+                "odd" => Ok((2, 1)),
+                "n" => Ok(parse_b(input, 1)?),
+                "-n" => Ok(parse_b(input, -1)?),
+                "n-" => Ok(parse_signless_b(input, 1, -1)?),
+                "-n-" => Ok(parse_signless_b(input, -1, -1)?),
+                _ => {
+                    let (slice, a) = if value.starts_with("-") {
+                        (&value[1..], -1)
+                    } else {
+                        (&**value, 1)
+                    };
+                    match parse_n_dash_digits(slice) {
+                        Ok(b) => Ok((a, b)),
+                        Err(()) => {
+                            let value = value.clone();
+                            Err(input.new_basic_unexpected_token_error(Token::Ident(value)))
+                        }
+                    }
+                }
+            }
+        }
+        Token::Delim('+') => match *input.next_including_whitespace()? {
+            Token::Ident(ref value) => {
+                match_ignore_ascii_case! { value,
+                    "n" => parse_b(input, 1),
+                    "n-" => parse_signless_b(input, 1, -1),
+                    _ => match parse_n_dash_digits(value) {
+                        Ok(b) => Ok((1, b)),
+                        Err(()) => {
+                            let value = value.clone();
+                            Err(input.new_basic_unexpected_token_error(Token::Ident(value)))
+                        }
+                    }
+                }
+            }
+            ref token => {
+                let token = token.clone();
+                Err(input.new_basic_unexpected_token_error(token))
+            }
+        },
+        ref token => {
+            let token = token.clone();
+            Err(input.new_basic_unexpected_token_error(token))
+        }
+    }
+}
+
+fn parse_b<'i, 't>(input: &mut Parser<'i, 't>, a: i32) -> Result<(i32, i32), BasicParseError<'i>> {
+    let start = input.state();
+    match input.next() {
+        Ok(&Token::Delim('+')) => parse_signless_b(input, a, 1),
+        Ok(&Token::Delim('-')) => parse_signless_b(input, a, -1),
+        Ok(&Token::Number {
+            has_sign: true,
+            int_value: Some(b),
+            ..
+        }) => Ok((a, b)),
+        _ => {
+            input.reset(&start);
+            Ok((a, 0))
+        }
+    }
+}
+
+fn parse_signless_b<'i, 't>(
+    input: &mut Parser<'i, 't>,
+    a: i32,
+    b_sign: i32,
+) -> Result<(i32, i32), BasicParseError<'i>> {
+    // FIXME: remove .clone() when lifetimes are non-lexical.
+    match input.next()?.clone() {
+        Token::Number {
+            has_sign: false,
+            int_value: Some(b),
+            ..
+        } => Ok((a, b_sign * b)),
+        token => Err(input.new_basic_unexpected_token_error(token)),
+    }
+}
+
+fn parse_n_dash_digits(string: &str) -> Result<i32, ()> {
+    let bytes = string.as_bytes();
+    if bytes.len() >= 3
+        && bytes[..2].eq_ignore_ascii_case(b"n-")
+        && bytes[2..].iter().all(|&c| matches!(c, b'0'..=b'9'))
+    {
+        Ok(parse_number_saturate(&string[1..]).unwrap()) // Include the minus sign
+    } else {
+        Err(())
+    }
+}
+
+fn parse_number_saturate(string: &str) -> Result<i32, ()> {
+    let mut input = ParserInput::new(string);
+    let mut parser = Parser::new(&mut input);
+    let int = if let Ok(&Token::Number {
+        int_value: Some(int),
+        ..
+    }) = parser.next_including_whitespace_and_comments()
+    {
+        int
+    } else {
+        return Err(());
+    };
+    if !parser.is_exhausted() {
+        return Err(());
+    }
+    Ok(int)
+}