What causes "brew-cask:{}: unsupported {kind} run guard condition" in jdx/mise?

Add "condition" as one of "on", "if_exists", "unless_exists"

brew-cask:{}: unsupported {kind} run guard condition

Error message

brew-cask:{}: unsupported {kind} run guard condition

What it means

Thrown when a guard object has no readable condition at all: object.get("condition").and_then(as_str) returns None because the key is absent or holds a non-string. Without a condition the guard cannot be classified, so parsing the whole cask fails. The message has no value placeholder, distinguishing it from the unknown-condition-string variant.

Source

Thrown at src/system/packages/brew/cask.rs:5930

            None => bail!(
                "brew-cask:{}: unsupported {kind} run guard platform",
                cask.token
            ),
        },
        Some(condition @ ("if_exists" | "unless_exists")) => {
            let path = parse_context_flight_path(cask, kind, "run guard", object)?;
            if condition == "if_exists" {
                Ok(FlightGuard::IfExists(path))
            } else {
                Ok(FlightGuard::UnlessExists(path))
            }
        }
        Some(condition) => bail!(
            "brew-cask:{}: unsupported {kind} run guard condition {}",
            cask.token,
            condition
        ),
        None => bail!(
            "brew-cask:{}: unsupported {kind} run guard condition",
            cask.token
        ),
    }
}

fn parse_context_flight_path(
    cask: &Cask,
    kind: &str,
    field: &str,
    object: &serde_json::Map<String, Value>,
) -> Result<FlightPath> {
    let path = object
        .get("path")
        .and_then(Value::as_str)
        .ok_or_else(|| eyre!("brew-cask:{}: unsupported {kind} {field} path", cask.token))?;
    let base = match object.get("base").and_then(Value::as_str) {
        Some("staged_path") => FlightPathBase::StagedPath,

View on GitHub (pinned to 6f52dcdf99)

Solutions

Add "condition" as one of "on", "if_exists", "unless_exists"
If the guard was meant to be a platform check, also add the matching "value"

Example fix

// before
{"guards": [{"path": "/tmp/lock"}]}
// after
{"guards": [{"condition": "unless_exists", "path": "/tmp/lock"}]}

Defensive patterns

Strategy: validation

Validate before calling

fn guard_has_condition(g: &serde_json::Value) -> bool {
    g.get("condition").and_then(|c| c.as_str()).is_some()
}

Try / catch

match parse_flight_guard(&cask, kind, &guard) {
    Ok(g) => { /* proceed */ }
    Err(e) if e.to_string().contains("run guard condition") && !e.to_string().contains("condition ") => {
        eprintln!("every guard object needs a string 'condition' key");
    }
    Err(e) => return Err(e),
}

Prevention

Always include a string 'condition' as the first key of a guard
Lint generated cask JSON for guard objects that lack a condition

When it happens

Trigger: {"guards": [{"path": "/tmp/x"}]} — a guard with path fields but no "condition" key; or {"condition": ["on"]} where condition is an array.

Common situations: Typing the key wrongly ("conditions", "when", "check"); templating that drops empty condition variables; refactors that renamed the field.

Related errors

AI-assisted analysis of jdx/mise@6f52dcdf99 (2026-08-22). Data as JSON: /api/errors/dd77164a18460778. Report an issue: GitHub.