ColorScheme honors NO_COLOR + TTY, degrades to identity function

byob-iostreams.2 iostreams

Problem: terminal color codes embedded across the codebase create three failure modes: (1) garbage in pipes and log files, (2) ignoring the user's NO_COLOR preference, (3) ugly if isTTY guards at every print site.

Idea: attach a ColorScheme to IOStreams. It exposes Red(s), Green(s), Bold(s), etc. When colors are disabled (non-TTY stdout, NO_COLOR env var set, or explicit --no-color), those methods return the input unchanged. Call sites always write cs.Red("error") without guarding.

Tradeoffs: method-per-color grows the surface slightly. Respecting the NO_COLOR standard is table stakes in 2025; costs nothing to honor.

Design

type ColorScheme struct{ enabled bool }

func NewColorScheme(isTTY bool) *ColorScheme {
    _, noColor := os.LookupEnv("NO_COLOR")
    return &ColorScheme{enabled: isTTY && !noColor}
}

func (c *ColorScheme) Red(s string) string {
    if !c.enabled { return s }
    return "\x1b[31m" + s + "\x1b[0m"
}

// usage:
fmt.Fprintln(io.ErrOut, io.ColorScheme().Red("error: ") + err.Error())