astral-sh/ruff · error

{e}

Error message

{e}

What it means

`ty rule <name>` looks up the requested lint rule in ty's default lint registry and wraps any registry lookup error in this anyhow error (message is the registry's own error text). It means the rule name given to `ty rule` does not match a known rule.

Solutions

1. Check the exact rule name spelling against `ty rule --list` (or the docs)
2. Use the fully qualified rule name as shown in diagnostics output
3. If the rule was renamed in a newer version, update the name or pin the ty version

Example fix

# before
ty rule ununsed-import
// after
ty rule unused-import

import subprocess
known = subprocess.run(['ty','rule','--list'], capture_output=True, text=True).stdout
if '--rule-name--' not in known:
    print('unknown rule')

if let Err(e) = ty_rule(name, format) {
    eprintln!("ty rule failed: {e}; run `ty rule --list` for valid rule names");
}

When it happens

Trigger: Running `ty rule <name>` with a misspelled, renamed, or nonexistent rule name; using a Ruff rule code that ty does not define.

Common situations: Typing `ty rule ununsed-import` (typo); copying Ruff rule names that don't exist in ty; referencing a rule removed or renamed in a newer ty version.

Related errors

• Can only write to stdout when formatting from stdin, but…
• Content not correctly formatted
• could not find any tasks matching the given criteria
• could not find `pyproject.toml` in any ancestor of
• could not find task named

AI-assisted analysis of astral-sh/ruff@26f38c119c (2026-09-05). Data as JSON: /api/errors/f93d393e7c050201. Report an issue: GitHub.

Appendix: source

Thrown at crates/ty/src/rule.rs:54

        let status = match self.status {
            LintStatus::Preview { since } => format!("Preview (since {since})"),
            LintStatus::Stable { since } => format!("Stable (since {since})"),
            LintStatus::Deprecated { since, reason } => {
                format!("Deprecated (since {since}): {reason}")
            }
            LintStatus::Removed { since, reason } => format!("Removed (since {since}): {reason}"),
        };

        writeln!(f, "Default level: {} | {status}\n", self.default_level)?;

        f.write_str(self.documentation.trim())
    }
}

/// Explain a single rule.
pub(crate) fn rule(name: &str, format: HelpFormat) -> Result<()> {
    let registry = default_lint_registry();
    let lint = registry.get(name).map_err(|e| anyhow::anyhow!("{e}"))?;

    let mut stdout = BufWriter::new(io::stdout().lock());
    match format {
        HelpFormat::Text => {
            writeln!(stdout, "{}", Explanation::from_lint(&lint))?;
        }
        HelpFormat::Json => {
            serde_json::to_writer_pretty(&mut stdout, &Explanation::from_lint(&lint))?;
        }
    }
    Ok(())
}

/// Explain all rules.
pub(crate) fn rules(format: HelpFormat) -> Result<()> {
    let registry = default_lint_registry();
    let mut lints: Vec<LintId> = registry.lints().to_vec();
    lints.sort_by_key(|l| l.name());

View on GitHub (pinned to 26f38c119c)