astral-sh/ruff · error

else clause

Error message

else clause

What it means

An .expect in the PLW0120 useless-else-on-loop rule: the code tries to locate the `else` keyword of a loop statement that the earlier guard confirmed has a non-empty orelse block. Firing it means the AST/range lookup for the else identifier failed despite the block existing — an internal invariant break, not a user error.

Source

Thrown at crates/ruff_linter/src/rules/pylint/rules/useless_else_on_loop.rs:75

    #[derive_message_formats]
    fn message(&self) -> String {
        "`else` clause on loop without a `break` statement; \
            remove the `else` and dedent its contents"
            .to_string()
    }

    fn fix_title(&self) -> Option<String> {
        Some("Remove `else`".to_string())
    }
}

/// PLW0120
pub(crate) fn useless_else_on_loop(checker: &Checker, stmt: &Stmt, body: &[Stmt], orelse: &[Stmt]) {
    if orelse.is_empty() || loop_exits_early(body) {
        return;
    }

    let else_range = identifier::else_(stmt, checker.locator().contents()).expect("else clause");

    let mut diagnostic = checker.report_diagnostic(UselessElseOnLoop, else_range);
    diagnostic.try_set_fix(|| {
        remove_else(
            stmt,
            orelse,
            else_range,
            checker.locator(),
            checker.indexer(),
            checker.stylist(),
        )
    });
}

/// Returns `true` if the given body contains a `break` statement.
fn loop_exits_early(body: &[Stmt]) -> bool {
    body.iter().any(|stmt| match stmt {
        Stmt::If(ast::StmtIf {

View on GitHub (pinned to 26f38c119c)

Solutions

1. Use the orelse block's range directly instead of re-locating the else keyword
2. Skip the diagnostic when the else identifier cannot be located

When it happens

Trigger: Thrown at crates/ruff_linter/src/rules/pylint/rules/useless_else_on_loop.rs:75 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/e8b141dd3ef2f8be. Report an issue: GitHub.