astral-sh/ruff · error

`{attr_name}` should have one argument

Error message

`{attr_name}` should have one argument

What it means

An unreachable! guard in the flake8-pie multiple-starts-ends-with rule: the let-else matched an expression shape the rule never intends to process (only calls of .startswith/.endswith reach here). Firing it means the rule's visitor let a non-matching expression through.

Source

Thrown at crates/ruff_linter/src/rules/flake8_pie/rules/multiple_starts_ends_with.rs:165

                        func: _,
                        arguments:
                            Arguments {
                                args,
                                keywords: _,
                                range: _,
                                node_index: _,
                            },
                        range_start: _,
                        node_index: _,
                    }) = expr
                    else {
                        unreachable!(
                            "{}",
                            format!("Indices should only contain `{attr_name}` calls")
                        )
                    };
                    args.first()
                        .unwrap_or_else(|| panic!("`{attr_name}` should have one argument"))
                })
                .collect();

            let node = Expr::Tuple(ast::ExprTuple {
                elts: words
                    .iter()
                    .flat_map(|value| {
                        if let Expr::Tuple(tuple) = value {
                            Left(tuple.iter())
                        } else {
                            Right(iter::once(*value))
                        }
                    })
                    .cloned()
                    .collect(),
                ctx: ExprContext::Load,
                range: TextRange::default(),
                node_index: ruff_python_ast::AtomicNodeIndex::NONE,

View on GitHub (pinned to 15f3fe6b15)

Solutions

1. Tighten the visitor so only matching call expressions reach the match
2. Handle the unexpected shape explicitly instead of unreachable!

When it happens

Trigger: Thrown at crates/ruff_linter/src/rules/flake8_pie/rules/multiple_starts_ends_with.rs:165 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/28e6656835f23ef1. Report an issue: GitHub.