astral-sh/ruff · error

Expected comparison operator

Error message

Expected comparison operator

What it means

An unreachable! in reverse_comparison (used by the yoda-conditions fixer): the CST comparison operator being rewritten is not one of the operators the fixer knows how to flip. Since the caller already validated the expression, hitting this arm indicates a mismatch between detection and fixing logic.

Source

Thrown at crates/ruff_linter/src/rules/flake8_simplify/rules/yoda_conditions.rs:199

            } => CompOp::LessThanEqual {
                whitespace_before: or_space(whitespace_before),
                whitespace_after: or_space(whitespace_after),
            },
            CompOp::Equal {
                whitespace_before,
                whitespace_after,
            } => CompOp::Equal {
                whitespace_before: or_space(whitespace_before),
                whitespace_after: or_space(whitespace_after),
            },
            CompOp::NotEqual {
                whitespace_before,
                whitespace_after,
            } => CompOp::NotEqual {
                whitespace_before: or_space(whitespace_before),
                whitespace_after: or_space(whitespace_after),
            },
            _ => panic!("Expected comparison operator"),
        };

        Ok(expression)
    })
}

/// SIM300
pub(crate) fn yoda_conditions(checker: &Checker, compare: &ast::ExprCompare) {
    let Some((left, op, right)) = compare.as_single() else {
        return;
    };

    if !matches!(
        op,
        CmpOp::Eq | CmpOp::NotEq | CmpOp::Lt | CmpOp::LtE | CmpOp::Gt | CmpOp::GtE,
    ) {
        return;
    }

View on GitHub (pinned to 15f3fe6b15)

Solutions

1. Add a match arm for the missing operator in reverse_comparison
2. Restrict the rule trigger to operators the fixer supports

When it happens

Trigger: Thrown at crates/ruff_linter/src/rules/flake8_simplify/rules/yoda_conditions.rs:200 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of astral-sh/ruff@15f3fe6b15 (2026-09-05). Data as JSON: /api/errors/000fab9861e10496. Report an issue: GitHub.