What causes "unhash output missing hash" in nikivdev/code?

Check the command's stderr/exit status and surface it instead of stdout alone

unhash output missing hash

Error message

unhash output missing hash

What it means

run computes a hash via an external command (unhash/hash tool), reads the first non-empty stdout line, and throws this error when the output has no lines at all. It protects the LINK_PREFIX link construction from an empty hash.

Source

Thrown at src/hash.rs:40

    if env::var("UNHASH_KEY").is_err() {
        if let Ok(Some(value)) = flow_env::get_personal_env_var("UNHASH_KEY") {
            cmd.env("UNHASH_KEY", value);
        }
    }

    let output = cmd.output().context("failed to run unhash")?;
    if !output.status.success() {
        let stdout = String::from_utf8_lossy(&output.stdout);
        let stderr = String::from_utf8_lossy(&output.stderr);
        bail!("unhash failed: {}\n{}{}", output.status, stdout, stderr);
    }

    let stdout = String::from_utf8_lossy(&output.stdout);
    let mut lines = stdout.lines().filter(|line| !line.trim().is_empty());
    let hash = lines
        .next()
        .ok_or_else(|| anyhow::anyhow!("unhash output missing hash"))?
        .trim()
        .to_string();

    let link = format!("{LINK_PREFIX}{hash}");
    copy_to_clipboard(&link)?;

    println!("{hash}");
    println!("{link}");

    if let Some(path_line) = lines.next() {
        println!("{}", path_line.trim());
    }

    Ok(())
}

fn copy_to_clipboard(text: &str) -> Result<()> {
    if std::env::var("FLOW_NO_CLIPBOARD").is_ok() || !std::io::stdin().is_terminal() {

View on GitHub (pinned to a747e741ae)

Solutions

Check the command's stderr/exit status and surface it instead of stdout alone
Verify the hash tool is installed and on PATH and produces output for your input
Ensure you pass non-empty input to hash

Example fix

// before
let hash = lines.next().ok_or_else(|| anyhow::anyhow!("unhash output missing hash"))?;
// after
if !output.status.success() {
    anyhow::bail!("hash command failed: {}", String::from_utf8_lossy(&output.stderr));
}
let hash = lines.next().ok_or_else(|| anyhow::anyhow!("unhash output missing hash"))?;

Defensive patterns

Strategy: try-catch

Validate before calling

let out = Command::new("f").args(["hash", input]).output()?;
if !out.status.success() || out.stdout.iter().all(|&b| b.is_ascii_whitespace()) {
    anyhow::bail!("hash tool produced no output: {}", String::from_utf8_lossy(&out.stderr));
}

Try / catch

match run(input) {
    Err(e) if e.to_string().contains("missing hash") => {
        eprintln!("hash tool returned empty output; check stderr of the hash command");
    }
    other => other?,
}

Prevention

Check exit status/stderr of external commands, not just stdout
Pin/verify the hash tool version your parser expects
Never pipe empty input into hash

When it happens

Trigger: The underlying hash command exits with empty stdout (failed silently, wrong subcommand, empty input) so lines.next() is None.

Common situations: Hash tool not installed or returning empty due to error on stderr, piping empty input, version change that renamed the output field.

Related errors

AI-assisted analysis of nikivdev/code@a747e741ae (2026-09-01). Data as JSON: /api/errors/09002e8a1a90bfe3. Report an issue: GitHub.