oxc-project/oxc · error · OxcDiagnostic

Negated expression is not allowed in equality check.

Error message

Negated expression is not allowed in equality check.

What it means

Raised by unicorn/no-negation-in-equality-check when one operand of an equality/inequality comparison (==, !=, ===, !==) is a negation (`!x`). The helper receives the current and suggested operators to build advice (e.g. swap === for !==); the faulting input is the negated operand comparison at the labeled span.

Source

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

use oxc_ast::{AstKind, ast::Expression};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};
use oxc_syntax::identifier::is_identifier_start;
use oxc_syntax::operator::{BinaryOperator, UnaryOperator};

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

fn no_negation_in_equality_check_diagnostic(
    span: Span,
    current_operator: BinaryOperator,
    suggested_operator: BinaryOperator,
) -> OxcDiagnostic {
    OxcDiagnostic::warn("Negated expression is not allowed in equality check.")
        .with_help(format!(
            "Remove the negation operator and use '{}' instead of '{}'.",
            suggested_operator.as_str(),
            current_operator.as_str()
        ))
        .with_label(span)
}

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

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Disallow negated expressions on the left of (in)equality checks.
    ///
    /// ### Why is this bad?
    ///

View on GitHub (pinned to e1e7af627c)

Solutions

1. Drop the negation and use the opposite operator: `!a === b` → `a !== b`
2. Move the negation outside the whole comparison if it applies to the result: `!(a === b)`
3. Restructure the boolean expression so no operand is negated

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/unicorn/no_negation_in_equality_check.rs:15 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/e7db54198166849c. Report an issue: GitHub.