nikivdev/code · error

`f pr preview --mode` requires a value

Error message

`f pr preview --mode` requires a value

What it means

The `--mode` flag of `f pr preview` requires a value (e.g. draft or feedback). This error is thrown when the flag is the last argument on the command line, so args.get(index + 1) returns None.

Source

Thrown at src/pr_preview.rs:285

    let mut repo_path = match opts.paths.len() {
        0 => None,
        1 => Some(PathBuf::from(&opts.paths[0])),
        _ => bail!("`f pr preview --path` accepts at most one repo path override"),
    };
    let mut requested_base = opts.base.clone();
    let mut mode = opts.mode.unwrap_or(PrPreviewModeArg::Draft);
    let mut json = opts.json;

    let mut index = 1;
    while index < args.len() {
        match args[index].as_str() {
            "--json" => {
                json = true;
                index += 1;
            }
            "--mode" => {
                let Some(value) = args.get(index + 1) else {
                    bail!("`f pr preview --mode` requires a value");
                };
                mode = parse_mode_arg(value)?;
                index += 2;
            }
            "--base" => {
                let Some(value) = args.get(index + 1) else {
                    bail!("`f pr preview --base` requires a value");
                };
                requested_base = value.clone();
                index += 2;
            }
            "--path" => {
                let Some(value) = args.get(index + 1) else {
                    bail!("`f pr preview --path` requires a value");
                };
                repo_path = Some(PathBuf::from(value));
                index += 2;
            }

View on GitHub (pinned to a747e741ae)

Solutions

  1. Append a value: `f pr preview --mode draft` (or `feedback`)
  2. Check shell scripts for truncated or line-wrapped commands
  3. Ensure the value is not accidentally consumed by quoting issues

Example fix

// before
f pr preview --mode
// after
f pr preview --mode feedback
Defensive patterns

Strategy: validation

Validate before calling

if args.iter().any(|a| a == "--mode") {
    let i = args.iter().position(|a| a == "--mode").unwrap();
    if args.get(i + 1).is_none() { anyhow::bail!("--mode needs a value"); }
}

Try / catch

if let Err(e) = run_pr_preview(cmd) {
    if e.to_string().contains("--mode`) requires a value") {
        eprintln!("Usage: f pr preview --mode draft|feedback");
    }
}

Prevention

When it happens

Trigger: Running `f pr preview --mode` with nothing following it, so no value can be consumed for the flag.

Common situations: Truncated command lines in shell scripts; forgetting to pass draft/feedback after --mode; shell quoting mistakes that drop the value.

Related errors

AI-assisted analysis of nikivdev/code@a747e741ae (2026-09-01). Data as JSON: /api/errors/ae89bfee4f3eda7a. Report an issue: GitHub.