What causes "{}" in jdx/mise?

Read unavailable_reason() output in the message to confirm the platform limitation.

{}

Error message

{}

What it means

This error is returned by target_user on non-unix platforms, where resolving the current user's name and login shell is not supported. The message is the reason produced by unavailable_reason(), explaining why the feature cannot work on this platform. It prevents the login-shell detection code path from silently returning wrong data.

Source

Thrown at src/system/login_shell.rs:106

fn target_user() -> Result<nix::unistd::User> {
    use eyre::eyre;
    use nix::unistd::{User, geteuid};

    if geteuid().is_root()
        && let Ok(sudo_user) = crate::env::var("SUDO_USER")
        && !sudo_user.is_empty()
        && sudo_user != "root"
    {
        return User::from_name(&sudo_user)?
            .ok_or_else(|| eyre!("failed to find user from SUDO_USER={sudo_user}"));
    }
    let uid = geteuid();
    User::from_uid(uid)?.ok_or_else(|| eyre!("failed to find user for uid {uid}"))
}

#[cfg(not(unix))]
fn target_user() -> Result<TargetUser> {
    eyre::bail!("{}", unavailable_reason())
}

#[cfg(not(unix))]
struct TargetUser {
    name: String,
    shell: PathBuf,
}

fn display_shell(shell: PathBuf) -> String {
    shell.to_string_lossy().to_string()
}

#[cfg(unix)]
fn chsh_args(request: &LoginShellRequest, user: &nix::unistd::User) -> Vec<String> {
    chsh_args_for_user_name(request, &user.name)
}

#[cfg(unix)]

View on GitHub (pinned to afd2eddd3a)

Solutions

Read unavailable_reason() output in the message to confirm the platform limitation.
Run the operation on a unix platform (macOS/Linux) if the feature is required.
Configure the shell/user explicitly in settings if the tool offers an override, bypassing target_user detection.
If you maintain the caller, gate the feature behind cfg(unix) or provide a Windows implementation.

Defensive patterns

Strategy: fallback

Validate before calling

#[cfg(unix)]
fn login_shell_supported() -> bool { true }
#[cfg(not(unix))]
fn login_shell_supported() -> bool { false }

Try / catch

match target_user() {
    Err(e) if !cfg!(unix) => {
        // fall back to $SHELL / configured default shell
        let shell = std::env::var("SHELL").unwrap_or_else(|_| "/bin/sh".into());
        ...
    }
    other => other?,
}

Prevention

Feature-gate login-shell-dependent functionality with cfg(unix).
Provide an explicit config override for shell/user on unsupported platforms.
Document platform requirements so Windows users don't hit the dead end.

When it happens

Trigger: Any call into login_shell::target_user() (and thus higher-level login-shell lookup APIs) compiled/running on a non-unix platform (e.g. Windows), where the cfg(not(unix)) branch is active.

Common situations: Running the tool on Windows when a feature assumes POSIX user/shell detection; CI images or cross-platform builds where the login-shell feature is exercised on an unsupported OS.

Understand the failure class

Background: "unsupported platform" / "not supported on this platform" errors: what they mean and how to fix them — this error's family across 47 libraries.

Related errors

AI-assisted analysis of jdx/mise@afd2eddd3a (2026-09-09). Data as JSON: /api/errors/74673bfb5313f9db. Report an issue: GitHub.