oxc-project/oxc · warning · OxcDiagnostic

Invalid group length in numeric value.

Error message

Invalid group length in numeric value.

What it means

Lint diagnostic from oxlint's `unicorn/numeric-separators-style` rule. It enforces how numeric separators (`_`) group digits: by default decimal digits in groups of 3, hex in groups of 2, and binary/octal in groups of 4 (configurable via `groupLength`, `minimumDigits`, `onlyIfContainsSeparator` per base). This message fires when a literal's separator grouping violates the configured style — wrong group length or a long number that should be grouped.

Source

Thrown at crates/oxc_linter/src/rules/unicorn/numeric_separators_style.rs:15

use cow_utils::CowUtils;
use oxc_ast::{
    AstKind,
    ast::{BigIntLiteral, BigintBase, NumberBase, NumericLiteral},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};

use crate::{AstNode, context::LintContext, rule::Rule};

fn numeric_separators_style_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Invalid group length in numeric value.")
        .with_help("Group digits with numeric separators (_) so longer numbers are easier to read.")
        .with_label(span)
}

#[derive(Debug, Clone, Default, PartialEq, Eq, Deserialize)]
pub struct NumericSeparatorsStyle(Box<NumericSeparatorsStyleConfig>);

#[derive(Debug, Clone, PartialEq, Eq, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NumericSeparatorsStyleConfig {
    /// Only enforce the rule when the numeric literal already contains a separator (`_`).
    ///
    /// When `true`, numbers without separators are left as-is; when `false` (default),
    /// grouping will be enforced for eligible numbers even if they don't include separators yet.
    only_if_contains_separator: bool,
    /// Configuration for hexadecimal literals (e.g. `0xAB_CD`, `0Xab_cd`, and bigint variants).
    /// Controls how digits are grouped and when separators are applied.
    hexadecimal: NumericBaseConfig,

View on GitHub (pinned to e1e7af627c)

Solutions

1. Regroup the literal to match the rule defaults: `1234567` -> `1_234_567`, `0xAABBCC` -> `0xAA_BB_CC`, `0b10100001` -> `0b1010_0001`.
2. If your project uses different group sizes, configure the rule in `.oxlintrc.json` under `rules` with `"unicorn/numeric-separators-style": ["error", {"hexadecimal": {"groupLength": 4}}]` etc.
3. Set `"onlyIfContainsSeparator": true` to leave numbers without `_` untouched if you only want consistency among already-separated numbers.
4. Run `oxlint --fix` for an automatic rewrite, then eyeball diffs on long constants.

Example fix

// before
const million = 1000000;
const rgb = 0xFF00FF;
const flags = 0b11110000;

// after
const million = 1_000_000;
const rgb = 0xFF_00_FF;
const flags = 0b1111_0000;

// Check config before enabling: put group lengths in .oxlintrc.json, e.g.
// "unicorn/numeric-separators-style": ["error", {
//   "hexadecimal": {"groupLength": 4},
//   "number": {"groupLength": 3, "minimumDigits": 5}
// }]
// Then: oxlint --fix .

When it happens

Trigger: Literals such as `const n = 1234567;` (no grouping despite 7 digits), `0xAABBCC` (hex groups of 2 expected -> `0xAA_BB_CC`), `0b1010_0001` is fine but `0b10_100001` is not, `1_0000.000_1` style mismatches. Also fires when config sets `groupLength: 4` but code uses `1_000_000`. Triggered during oxlint runs on numeric literals.

Common situations: Config mistakes: teams copy the ESLint unicorn config with custom `groupLength`/`minimumDigits` that differ from the code's existing style. Version changes: upgrading oxlint brought the rule in via the unicorn category and legacy constants (bit masks, protocol IDs) suddenly fail. Refactoring numbers across bases (dec -> hex) without regrouping separators.

Related errors

• Don't use a zero fraction in the number.
• Don't use a dangling dot in the number.
• Unexpected number literal prefix in uppercase.
• Unexpected exponential notation in uppercase.
• Unexpected hexadecimal digits in lowercase.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/73cb572a796a7445. Report an issue: GitHub.