swc-project/swc · error · Error

Expected 'n' character in Ident

Error message

Expected 'n' character in Ident

What it means

In the An+B microsyntax of :nth-* selectors, the ident at the `n` position must begin with (an optional `-` followed by) `n` or `N`; otherwise the parser rejects it with this error at the token's span.

Source

Thrown at crates/swc_css_parser/src/parser/selectors/mod.rs:1271

                let a;
                let a_raw;

                let n_value;

                match cur!(self) {
                    Token::Ident {  .. } => {
                        let ident_value = match bump!(self) {
                            Token::Ident { value, .. } => value,
                            _ => {
                                unreachable!();
                            }
                        };

                        let has_minus_sign = ident_value.starts_with('-');
                        let n_char = if has_minus_sign { ident_value.chars().nth(1) } else { ident_value.chars().next() };

                        if n_char != Some('n') && n_char != Some('N') {
                            return Err(Error::new(
                                span,
                                ErrorKind::Expected("'n' character in Ident"),
                            ));
                        }

                        a = Some(if has_minus_sign { -1 } else {1 });
                        a_raw = Some(self.input.atom(if has_plus_sign { "+" } else if has_minus_sign { "-" } else { "" }));

                        n_value = if has_minus_sign { ident_value[1..].to_string() } else { ident_value.to_string() };
                    }
                    tok!("dimension") => {
                        let dimension = match bump!(self) {
                            Token::Dimension { dimension } => {
                                let DimensionToken { value, raw_value, unit, .. } = *dimension;

                             (value, raw_value, unit)
                            }
                            _ => {

View on GitHub (pinned to 5176682b65)

Solutions

1. Use valid An+B forms like 2n, -n+3, odd, even
2. Collect parser errors for diagnostics
3. Fix the nth- expression

When it happens

Trigger: Thrown at crates/swc_css_parser/src/parser/selectors/mod.rs:1271 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/369d6aea65e0536f. Report an issue: GitHub.