brew-cask: generate_completions_from_executable requires an

Error message

brew-cask: generate_completions_from_executable requires an executable

What it means

Thrown while parsing a generate_completions_from_executable artifact. The stanza is an array whose first element must be the executable (string) that generates completions, optionally followed by args and a trailing options object. An empty array provides no executable, so parsing fails immediately; a non-string first element fails the same way via the follow-on lookup.

Source

Thrown at src/system/packages/brew/cask.rs:5381

        }
        _ => Ok(None),
    }
}

fn parse_generated_completion_artifact(
    value: &Value,
) -> Result<Option<GeneratedCompletionArtifact>> {
    let Some(generated) = value
        .as_object()
        .and_then(|o| o.get("generate_completions_from_executable"))
    else {
        return Ok(None);
    };
    let Value::Array(values) = generated else {
        return Ok(None);
    };
    if values.is_empty() {
        bail!("brew-cask: generate_completions_from_executable requires an executable");
    }
    let options = values.last().and_then(Value::as_object);
    let command_values = if options.is_some() {
        &values[..values.len() - 1]
    } else {
        values.as_slice()
    };
    let executable = command_values
        .first()
        .and_then(Value::as_str)
        .ok_or_else(|| {
            eyre!("brew-cask: generate_completions_from_executable requires an executable")
        })?
        .to_string();
    let args = command_values
        .iter()
        .skip(1)
        .map(|value| {

View on GitHub (pinned to 6f52dcdf99)

Solutions

Make the first array element the executable string: ["mycli"] or ["mycli", "completions", "--shell"]
Keep the optional options object (base_name, shells, shell_parameter_format) as the LAST element, never the first
If the cask JSON is upstream and malformed, update mise/brew metadata caches and report the cask token

Example fix

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

Defensive patterns

Strategy: validation

Validate before calling

fn completions_artifact_ok(v: &serde_json::Value) -> bool {
    match v.get("generate_completions_from_executable") {
        Some(serde_json::Value::Array(a)) => a.first().map(|f| f.is_string()).unwrap_or(false),
        _ => true,
    }
}

Type guard

fn is_completions_stanza(v: &serde_json::Value) -> bool {
    matches!(v, serde_json::Value::Array(a) if !a.is_empty() && a[0].is_string())
}

Try / catch

match parse_generated_completion_artifact(&artifact) {
    Ok(c) => { /* proceed */ }
    Err(e) if e.to_string().contains("requires an executable") => {
        eprintln!("completions stanza needs the generator binary as the first array element");
    }
    Err(e) => return Err(e),
}

Prevention

Always start the array with the executable string; options object goes last
Omit the stanza entirely for CLI tools without completion support
Never ship empty placeholder arrays from templates

When it happens

Trigger: {"generate_completions_from_executable": []} in a cask's artifact list; also an array whose first element is a number/object (e.g. [{"shell": "bash"}, "tool"]) where no string executable can be extracted.

Common situations: Templates or generators that emit the stanza with a placeholder that got emptied; cask JSON hand-authored for completion generation; reordering mistakes where the options object is placed first.

Related errors

AI-assisted analysis of jdx/mise@6f52dcdf99 (2026-08-22). Data as JSON: /api/errors/7f33d47940db73e6. Report an issue: GitHub.