Refuse to prompt when stdin is not a TTY

byob-prompter.3 iostreamsprompter

Problem: a command that prompts for confirmation works interactively but hangs in CI or in a pipeline with no stdin attached. Worse, naive prompt libraries read EOF, interpret it as "no", and silently skip a destructive action without failing.

Idea: every Prompter method checks IO.IsStdinTTY() first (byob-iostreams.1 exposes this on IOStreams). If false, return a sentinel ErrNotTTY. The caller is responsible for handling it — typically by requiring --yes/-y (see byob-prompter.5) or failing with a clear message ("pass --yes to skip confirmation in non-interactive environments").

Tradeoffs: every Prompter caller now has to think about the non-TTY case. That's the point — the failure mode goes from "silently wrong" to "explicitly unsupported." --yes (byob-prompter.5) already covers the "skip prompts despite a TTY" case; no separate env-var escape hatch is needed.

Design

var ErrNotTTY = errors.New("no TTY available for prompting")

func (p *live) Confirm(ctx context.Context, msg string, def bool) (bool, error) {
    if !p.io.IsStdinTTY() {
        return false, ErrNotTTY
    }
    // ...prompt (see byob-prompter.2 for the ctx-select pattern)
}

// Caller:
yes, err := f.Prompter.Confirm(ctx, "Delete all?", false)
switch {
case errors.Is(err, prompt.ErrNotTTY):
    return fmt.Errorf("not a TTY; pass --yes to confirm non-interactively")
case err != nil:
    return err
case !yes:
    return ErrCancel // see byob-errors.1
}

Pairs with the prompter-tty-check memory — same rule, one-line form, always-on.