astral-sh/ruff · error

Expected one simple statement

Error message

Expected one simple statement

What it means

An anyhow bail! in the PT018 composite-condition fixer: after extracting the embedded statement, the block does not contain exactly one simple statement line, so the fixer cannot locate the assert to rewrite and aborts.

Source

Thrown at crates/ruff_linter/src/rules/flake8_pytest_style/rules/assertion.rs:769

    let mut tree = match_module(&module_text)?;

    // Extract the assert statement.
    let statements = if outer_indent.is_empty() {
        &mut tree.body
    } else {
        let [Statement::Compound(CompoundStatement::FunctionDef(embedding))] = &mut *tree.body
        else {
            bail!("Expected statement to be embedded in a function definition")
        };

        let indented_block = match_indented_block(&mut embedding.body)?;
        indented_block.indent = Some(outer_indent);

        &mut indented_block.body
    };

    let [Statement::Simple(simple_statement_line)] = statements.as_slice() else {
        bail!("Expected one simple statement")
    };

    let [SmallStatement::Assert(assert_statement)] = simple_statement_line.body.as_slice() else {
        bail!("Expected simple statement to be an assert")
    };

    // Extract the individual conditions.
    let mut conditions: Vec<Expression> = Vec::with_capacity(2);
    match &assert_statement.test {
        Expression::UnaryOperation(op) => {
            if matches!(op.operator, libcst_native::UnaryOp::Not { .. }) {
                if let Expression::BooleanOperation(boolean_operation) = &*op.expression {
                    if matches!(boolean_operation.operator, BooleanOp::Or { .. }) {
                        conditions.push(negate(&parenthesize(
                            &boolean_operation.left,
                            &op.expression,
                        )));
                        conditions.push(negate(&parenthesize(

View on GitHub (pinned to 26f38c119c)

Solutions

1. Ensure the reconstruction only wraps single-statement bodies
2. Skip the autofix when more than one simple statement is present

When it happens

Trigger: Thrown at crates/ruff_linter/src/rules/flake8_pytest_style/rules/assertion.rs:769 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of astral-sh/ruff@26f38c119c (2026-09-05). Data as JSON: /api/errors/81202ac71dd7caee. Report an issue: GitHub.