oxc-project/oxc · warning · OxcDiagnostic

' :' is defined but never used.

Error message

'{label_name}:' is defined but never used.

What it means

Diagnostic from oxlint's no-unused-labels rule. A label declared on a loop or block is never targeted by any break/continue with that name, so it is dead syntax, typically leftover after the labeled break or the inner loop was removed.

Solutions

1. Delete the unused label and its colon.
2. If a labeled break was intended, restore break label; at the right spot.
3. Run oxlint --fix; removing an unused label is a purely mechanical, safe fix.

Example fix

// before
outer: for (const a of xs) {
  for (const b of ys) { handle(a, b); }
}
// after
for (const a of xs) {
  for (const b of ys) { handle(a, b); }
}

When it happens

Trigger: outer: for (...) { for (...) { ... } } with no break outer; or continue outer; anywhere in the function.

Common situations: The inner loop or the labeled break was deleted during refactoring; a flag or early return replaced the labeled control flow; generated code emits labels unconditionally.

Related errors

• This label ' ' is unnecessary
• ' ' is always 'undefined' because it's never assigned.
• Invalid loop. Its body allows only one iteration.
• ' ' is defined but never used.
• ' ' is imported but never used.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/66f05a2ba7396c09. Report an issue: GitHub.

Appendix: source

Thrown at crates/oxc_linter/src/rules/eslint/no_unused_labels.rs:9

use oxc_ast::AstKind;
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;

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

fn no_unused_labels_diagnostic(label_name: &str, span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn(format!("'{label_name}:' is defined but never used.")).with_label(span)
}

#[derive(Debug, Default, Clone)]
pub struct NoUnusedLabels;

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Disallow unused labels.
    ///
    /// ### Why is this bad?
    ///
    /// Labels that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring.
    ///
    /// ### Examples
    ///
    /// Examples of **incorrect** code for this rule:
    /// ```javascript

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