brew-cask: generate_completions_from_executable requires at

Error message

brew-cask: generate_completions_from_executable requires at least one shell

What it means

Thrown at the end of generate_completions_from_executable parsing. If the trailing options object has no 'shells' key, sensible defaults (bash/zsh/fish, plus pwsh for cobra/typer formats) are applied — but an explicitly present 'shells' array that resolves to empty means 'generate completions for zero shells', which is meaningless, so it bails.

Source

Thrown at src/system/packages/brew/cask.rs:5427

    let shells = options
        .and_then(|o| o.get("shells"))
        .and_then(Value::as_array)
        .map(|shells| {
            shells
                .iter()
                .map(|shell| {
                    let shell = shell.as_str().ok_or_else(|| {
                        eyre!("brew-cask: completion shell names must be strings")
                    })?;
                    CompletionShell::parse(shell)
                        .ok_or_else(|| eyre!("brew-cask: unsupported completion shell '{shell}'"))
                })
                .collect::<Result<Vec<_>>>()
        })
        .transpose()?
        .unwrap_or_else(|| default_generated_completion_shells(shell_parameter_format.as_deref()));
    if shells.is_empty() {
        bail!("brew-cask: generate_completions_from_executable requires at least one shell");
    }
    Ok(Some(GeneratedCompletionArtifact {
        executable,
        args,
        base_name: options
            .and_then(|o| o.get("base_name"))
            .and_then(Value::as_str)
            .map(str::to_string),
        shell_parameter_format,
        shells,
    }))
}

fn default_generated_completion_shells(format: Option<&str>) -> Vec<CompletionShell> {
    match format {
        Some("cobra") | Some("typer") => vec![
            CompletionShell::Bash,
            CompletionShell::Zsh,

View on GitHub (pinned to 6f52dcdf99)

Solutions

Omit the "shells" key entirely to get the default shell set
Or list at least one supported shell name, e.g. "shells": ["bash", "zsh", "fish", "pwsh"]

Example fix

// before
{"generate_completions_from_executable": ["mycli", {"shells": []}]}
// after
{"generate_completions_from_executable": ["mycli"]}

Defensive patterns

Strategy: validation

Validate before calling

fn completions_shells_ok(v: &serde_json::Value) -> bool {
    let arr = v.get("generate_completions_from_executable").and_then(|a| a.as_array());
    let Some(arr) = arr else { return true; };
    let opts = arr.last().and_then(|o| o.as_object());
    match opts.and_then(|o| o.get("shells")) {
        Some(serde_json::Value::Array(s)) => !s.is_empty(),
        None => true,
        Some(_) => false,
    }
}

Try / catch

match parse_generated_completion_artifact(&artifact) {
    Ok(c) => { /* proceed */ }
    Err(e) if e.to_string().contains("at least one shell") => {
        eprintln!("omit 'shells' to use defaults, or list bash/zsh/fish/pwsh explicitly");
    }
    Err(e) => return Err(e),
}

Prevention

Remember: defaults apply only when the shells key is ABSENT, not when it is empty
Render shells from a non-empty fallback in templates: shells = list or undefined

When it happens

Trigger: {"generate_completions_from_executable": ["mycli", {"shells": []}]} — the shells key exists and is an empty array; defaults are not consulted because the key was explicit.

Common situations: Templating that renders shells from an empty variable; users copying a stanza and trimming the list; YAML/JSON pipelines that collapse to empty arrays.

Related errors

AI-assisted analysis of jdx/mise@6f52dcdf99 (2026-08-22). Data as JSON: /api/errors/505f2118e7229545. Report an issue: GitHub.