swc-project/swc · error · Error

number, function (math functions) or ident (with 'none' valu

Error message

number, function (math functions) or ident (with 'none' value) token

What it means

Thrown by swc_css_parser when the THIRD component (b-axis) of lab()/oklab() begins with an unexpected token — anything that is not a percentage, number, math function, or ident. The catch-all arm (mod.rs:1139-1151) reports the expected-token message with the current token's span; a preceding var() suppresses it by ending the component list.

Source

Thrown at crates/swc_css_parser/src/parser/values_and_units/mod.rs:1141

                                        Ok(Some(ComponentValue::Function(parser.parse()?)))
                                    }
                                    tok!("ident") => {
                                        let ident: Box<Ident> = parser.parse()?;

                                        if ident.value.eq_ignore_ascii_case("none") {
                                            Ok(Some(ComponentValue::Ident(ident)))
                                        } else {
                                            Err(Error::new(
                                                ident.span,
                                                ErrorKind::Expected(
                                                    "'none' value of an ident token",
                                                ),
                                            ))
                                        }
                                    }
                                    _ => {
                                        if !has_variable_before {
                                            Err(Error::new(
                                                parser.input.cur_span(),
                                                ErrorKind::Expected(
                                                    "number, function (math functions) or ident \
                                                     (with 'none' value) token",
                                                ),
                                            ))
                                        } else {
                                            Ok(None)
                                        }
                                    }
                                },
                                &mut has_variable,
                            )?;

                            if let Some(number_or_none) = number_or_none {
                                values.push(number_or_none);
                            }

View on GitHub (pinned to 5176682b65)

Solutions

Use space-separated components: lab(50% 10 20).
Remove trailing commas before the closing parenthesis.
Ensure nested functions are real math functions (calc, min, max, clamp, round, ...) — arbitrary functions are rejected in this slot.
Wrap dynamic values in var().

Example fix

/* before */
color: lab(50% 10, 20);

/* after */
color: lab(50% 10 20);

Defensive patterns

Strategy: try-catch

Validate before calling

fn lab_third_token_ok(tok: &str) -> bool {
    let t = tok.trim();
    t.eq_ignore_ascii_case("none")
        || t.parse::<f64>().is_ok()
        || (t.ends_with('%') && t[..t.len() - 1].parse::<f64>().is_ok())
        || is_math_fn(t)
}

Type guard

fn no_trailing_comma(v: &str) -> bool {
    !v.trim_end_matches(')').trim().ends_with(',')
}

Try / catch

match swc_css_parser::parse_file::<swc_css_ast::Stylesheet>(&fm, None, config, &mut errs) {
    Err(e) if matches!(e.kind(), swc_css_parser::error::ErrorKind::Expected(m) if m.starts_with("number, function")) => {
        // stray token in lab/oklab third slot; log span, skip declaration
    }
    _ => {}
}

Prevention

Remove trailing commas inside color functions.
Only nest recognized math functions in component slots.
Normalize commas to spaces for lab/oklab in preprocessing.
Test generated CSS against parser fixtures.

When it happens

Trigger: `lab(50% 10,)` — trailing comma before ')'; `lab(50% 10, 20)` — legacy commas; `lab(50% 10 "20")` — string; `lab(50% 10 calc-summ(1))` — a non-math function.

Common situations: Comma-separated lab values from older tooling; stray trailing commas from generated CSS; interpolated strings.

Related errors

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/e4fc389ffbed5d9a. Report an issue: GitHub.