astral-sh/ruff · error

We shouldn't be attempting an autofix if a sequence has < 2

Error message

We shouldn't be attempting an autofix if a sequence has < 2 elements; a sequence with 1 or 0 elements cannot be unsorted.

What it means

A deliberate panic in into_sorted_source_code: the sorter was asked to sort a literal sequence with fewer than two items. Sequences of length 0 or 1 cannot be unsorted, so the caller violated the method's documented precondition — a logic error in the rule that detected the sequence as unsorted.

Source

Thrown at crates/ruff_linter/src/rules/ruff/rules/sequence_sorting.rs:448

        })
    }

    /// Sort a multiline sequence of literal strings
    /// that is known to be unsorted.
    ///
    /// This function panics if it is called and `self.items`
    /// has length < 2. It's redundant to call this method in this case,
    /// since lists with < 2 items cannot be unsorted,
    /// so this is a logic error.
    pub(super) fn into_sorted_source_code(
        mut self,
        sorting_style: SortingStyle,
        locator: &Locator,
        stylist: &Stylist,
    ) -> String {
        let (first_item_start, last_item_end) = match self.items.as_slice() {
            [first_item, .., last_item] => (first_item.start(), last_item.end()),
            _ => panic!(
                "We shouldn't be attempting an autofix if a sequence has < 2 elements;
                a sequence with 1 or 0 elements cannot be unsorted."
            ),
        };

        // As well as the "items" in a multiline string sequence,
        // there is also a "prelude" and a "postlude":
        //  - Prelude == the region of source code from the opening parenthesis,
        //    up to the start of the first item in `__all__`/`__slots__`/etc.
        //  - Postlude == the region of source code from the end of the last
        //    item in `__all__`/`__slots__`/etc. up to and including the closing
        //    parenthesis.
        //
        // For example:
        //
        // ```python
        // __all__ = [  # comment0
        //   # comment1

View on GitHub (pinned to 26f38c119c)

Solutions

1. Fix the caller to only request a fix when the sequence has at least two items
2. Return an empty/unchanged result instead of panicking for short sequences

When it happens

Trigger: Thrown at crates/ruff_linter/src/rules/ruff/rules/sequence_sorting.rs:448 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/a15442c44fcae4ee. Report an issue: GitHub.