jdx/mise · error

brew-cask: : conflicts with installed cask

Error message

brew-cask:{}: conflicts with installed cask {}

What it means

Before installing, the cask's `conflicts_with cask` list is checked against currently installed casks (via installed_versions). If any conflicting cask has installed versions, the install is aborted because Homebrew casks declare hard conflicts that would produce broken or duplicated system state.

Solutions

  1. Uninstall the conflicting cask first (`brew uninstall --cask <conflict>`) then retry.
  2. If both are truly needed, remove the conflicts_with entry in a local/forked cask (at your own risk).
  3. Choose an alternative cask that does not declare the conflict.
  4. Check which installed cask triggered it via the conflict name in the message and decide whether you still need it.

Example fix

// before
brew install --cask newapp   # conflicts with installed 'oldapp'
// after
brew uninstall --cask oldapp && install newapp via manager
Defensive patterns

Strategy: try-catch

Validate before calling

use std::process::Command;
fn cask_conflicts_with_installed(conflicts: &[&str]) -> Vec<String> {
    conflicts.iter().filter(|c| {
        Command::new("brew").args(["list", "--cask", c]).output()
            .map(|o| o.status.success()).unwrap_or(false)
    }).map(|c| c.to_string()).collect()
}

Try / catch

match install_result {
    Err(e) if e.to_string().contains("conflicts with installed cask") => {
        let conflict = e.to_string().rsplit(' ').next().unwrap_or("<unknown>");
        eprintln!("uninstall the conflicting cask first: brew uninstall --cask {conflict}");
    }
    other => other?,
}

Prevention

When it happens

Trigger: Installing cask X whose stanza lists `conflicts_with cask: 'Y'` while cask Y is already installed (installed_versions(Y) non-empty).

Common situations: Conflicting GUI apps from different vendors (e.g. two Dropbox-like clients); switching between alternative tools where the old cask was installed outside this manager; Homebrew adding a new conflicts_with entry to an existing cask.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

AI-assisted analysis of jdx/mise@533346cc37 (2026-09-17). Data as JSON: /api/errors/3016ef1f61b9dbd8. Report an issue: GitHub.

Appendix: source

Thrown at src/system/packages/brew/cask/mod.rs:616

                cask.token
            );
            return Ok(version);
        }
        let artifacts = cask_artifacts(&cask)?;
        validate_platform_support(&cask, &artifacts)?;
        // Validate the whole app batch before dependencies, downloads, or hooks
        // can mutate anything, including when producing a dry-run plan.
        artifacts.app_target_paths()?;
        let installed_version = mise_installed_cask_version(&cask)?;
        if let Some(reason) =
            installed_skip_reason(&cask, &artifacts, installed_version.as_deref(), mode)?
        {
            info!("brew-cask:{}: {reason}", cask.token);
            return Ok(reason.to_string());
        }
        for conflict in &cask.conflicts_with.cask {
            if !installed_versions(conflict).is_empty() {
                bail!(
                    "brew-cask:{}: conflicts with installed cask {}",
                    cask.token,
                    conflict
                );
            }
        }
        if !cask.depends_on.formula.is_empty() {
            let dependencies = cask
                .depends_on
                .formula
                .iter()
                .map(|name| PackageRequest {
                    name: name.clone(),
                    version: None,
                    tap_url: None,
                    desired: super::super::PackageDesiredState::Present,
                })
                .collect::<Vec<_>>();

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