What causes "brew-cask: invalid completion target '{}'" in jdx/mise?

Give the completion target an actual file name under the prefix (e.g. $HOMEBREW_PREFIX/etc/bash_completion.d/mytool).

brew-cask: invalid completion target

Error message

brew-cask: invalid completion target '{}'

What it means

This error is thrown by caskroom_completion_path when a validated completion target, after being stripped of the Homebrew prefix, has no remaining components — i.e. the target equals the prefix directory itself rather than a file inside it. Since there would be no relative path to mirror into the caskroom, the operation is rejected.

Solutions

Give the completion target an actual file name under the prefix (e.g. $HOMEBREW_PREFIX/etc/bash_completion.d/mytool).
Remove the degenerate completion entry pointing at the prefix root.
Fix the manifest/template so the file-name segment is not lost when building the target path.
Log/inspect the resolved target path to confirm it names a file, not the prefix directory.

Example fix

// before
completions = [{ target = "$HOMEBREW_PREFIX" }]
// after
completions = [{ target = "$HOMEBREW_PREFIX/share/zsh/site-functions/_mytool" }]

Defensive patterns

Strategy: validation

Validate before calling

let relative = target.strip_prefix(&prefix).map_err(|_| "target outside prefix")?;
if relative.as_os_str().is_empty() || relative.components().next().is_none() {
    return Err("target must name a file under the prefix, not the prefix itself".into());
}

Prevention

Ensure completion targets always include a file-name component beneath $HOMEBREW_PREFIX.
Reject targets that normalize to the prefix root ('' or '.') during manifest validation.
When building targets programmatically, assert the joined path is strictly deeper than the prefix.

When it happens

Trigger: A cask completion target that resolves exactly to the Homebrew prefix root (e.g. target_name "" or "." combined with prefix joining, or $HOMEBREW_PREFIX alone), so target.strip_prefix(prefix) yields an empty relative path and relative.components().next() is None.

Common situations: A cask whose completion target is set to just the $HOMEBREW_PREFIX placeholder or "."; a mis-templated manifest where the file-name portion of the target is dropped; programmatically assembled paths that end up as the prefix itself.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of jdx/mise@533346cc37 (2026-09-17). Data as JSON: /api/errors/e2998b339b3288a2. Report an issue: GitHub.

Appendix: source

Thrown at src/system/packages/brew/cask/mod.rs:3253

        }
    };
    if normalized.is_empty() {
        bail!("brew-cask: invalid completion target '{target_name}'");
    }
    Ok(normalized)
}

fn caskroom_completion_path(caskroom: &Path, target: &Path) -> Result<PathBuf> {
    let prefix = prefix::prefix();
    let relative = target.strip_prefix(&prefix).map_err(|_| {
        eyre!(
            "brew-cask: completion target '{}' must be under {}",
            target.display(),
            prefix.display()
        )
    })?;
    if relative.components().next().is_none() {
        bail!(
            "brew-cask: invalid completion target '{}'",
            target.display()
        );
    }
    Ok(caskroom.join(relative))
}

fn previous_completion_targets(cask: &Cask) -> Result<Vec<PathBuf>> {
    Ok(previous_receipt(cask)?
        .map(|receipt| receipt.completions)
        .unwrap_or_default())
}

fn remove_obsolete_completions(
    cask: &Cask,
    previous_targets: &[PathBuf],
    current_targets: &[PathBuf],
) -> Result<()> {

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