swc-project/swc · error · swc_css_parser::Error

Expected declaration in parens

Error message

Expected declaration in parens

What it means

Inside a @supports parenthesized feature, try_to_parse_declaration_in_parens returned None — the content of the parentheses is neither a valid declaration nor a condition — so the parser reports this error at the current span.

Source

Thrown at crates/swc_css_parser/src/parser/at_rules/mod.rs:1182

}

impl<I> Parse<SupportsFeature> for Parser<I>
where
    I: ParserInput,
{
    fn parse(&mut self) -> PResult<SupportsFeature> {
        match cur!(self) {
            tok!("(") => {
                bump!(self);

                self.input.skip_ws();

                let declaration = match self.try_to_parse_declaration_in_parens() {
                    Some(declaration) => declaration,
                    None => {
                        let span = self.input.cur_span();

                        return Err(Error::new(
                            span,
                            ErrorKind::Expected("declaration in parens"),
                        ));
                    }
                };

                expect!(self, ")");

                Ok(SupportsFeature::Declaration(Box::new(declaration)))
            }
            Token::Function { value, .. }
                if matches_eq_ignore_ascii_case!(&**value, "selector") =>
            {
                // TODO improve me
                let ctx = Ctx {
                    in_supports_at_rule: true,
                    ..self.ctx
                };

View on GitHub (pinned to 5176682b65)

Solutions

1. Write a valid declaration such as (display: flex) inside the parens
2. Report the diagnostic from collected errors
3. Fix the @supports feature query

When it happens

Trigger: Thrown at crates/swc_css_parser/src/parser/at_rules/mod.rs:1182 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/83e7db9f8dcc14c8. Report an issue: GitHub.