supports-color/index.js

Detect whether a terminal supports color

import process from 'node:process';
import os from 'node:os';
import tty from 'node:tty';

// From: https://github.com/sindresorhus/has-flag/blob/main/index.js
/// function hasFlag(flag, argv = globalThis.Deno?.args ?? process.argv) {
function hasFlag(flag, argv = globalThis.Deno ? globalThis.Deno.args : process.argv) {
	const prefix = flag.startsWith('-') ? '' : (flag.length === 1 ? '-' : '--');
	const position = argv.indexOf(prefix + flag);
	const terminatorPosition = argv.indexOf('--');
	return position !== -1 && (terminatorPosition === -1 || position < terminatorPosition);
}

const {env} = process;

let flagForceColor;
if (
	hasFlag('no-color')
	|| hasFlag('no-colors')
	|| hasFlag('color=false')
	|| hasFlag('color=never')
) {
	flagForceColor = 0;
} else if (
	hasFlag('color')
	|| hasFlag('colors')
	|| hasFlag('color=true')
	|| hasFlag('color=always')
) {
	flagForceColor = 1;
}

function envForceColor() {
	if (!('FORCE_COLOR' in env)) {
		return;
	}

	if (env.FORCE_COLOR === 'true') {
		return 1;
	}

	if (env.FORCE_COLOR === 'false') {
		return 0;
	}

	if (env.FORCE_COLOR.length === 0) {
		return 1;
	}

	if (!/^\d+$/v.test(env.FORCE_COLOR)) {
		return;
	}

	const level = Math.min(Number(env.FORCE_COLOR), 3);

	if (![0, 1, 2, 3].includes(level)) {
		return;
	}

	return level;
}

function translateLevel(level) {
	if (level === 0) {
		return false;
	}

	return {
		level,
		hasBasic: true,
		has256: level >= 2,
		has16m: level >= 3,
	};
}

// eslint-disable-next-line complexity -- Color support detection necessarily handles multiple environments.
function _supportsColor(haveStream, {streamIsTTY, sniffFlags = true} = {}) {
	const noFlagForceColor = envForceColor();
	if (noFlagForceColor !== undefined) {
		flagForceColor = noFlagForceColor;
	}

	const forceColor = sniffFlags ? flagForceColor : noFlagForceColor;

	if (forceColor === 0) {
		return 0;
	}

	if (sniffFlags) {
		if (hasFlag('color=16m')
			|| hasFlag('color=full')
			|| hasFlag('color=truecolor')) {
			return 3;
		}

		if (hasFlag('color=256')) {
			return 2;
		}
	}

	// A numeric `FORCE_COLOR` requests an exact level, while `FORCE_COLOR=true` and `FORCE_COLOR=` only enable color and let the level be detected.
	if (forceColor !== undefined && /^\d+$/v.test(env.FORCE_COLOR)) {
		return forceColor;
	}

	// Check for Azure DevOps pipelines.
	// Has to be above the `!streamIsTTY` check.
	if ('TF_BUILD' in env && 'AGENT_NAME' in env) {
		return 1;
	}

	if (haveStream && !streamIsTTY && forceColor === undefined) {
		return 0;
	}

	const min = forceColor || 0;

	if (env.TERM === 'dumb') {
		return min;
	}

	if (process.platform === 'win32') {
		// Windows 10 build 10586 is the first Windows release that supports 256 colors.
		// Windows 10 build 14931 is the first release that supports 16m/TrueColor.
		const osRelease = os.release().split('.');
		if (
			Number(osRelease[0]) >= 10
			&& Number(osRelease[2]) >= 10_586
		) {
			return Number(osRelease[2]) >= 14_931 ? 3 : 2;
		}

		return 1;
	}

	if ('CI' in env) {
		if (['GITHUB_ACTIONS', 'GITEA_ACTIONS', 'CIRCLECI'].some(key => Object.hasOwn(env, key))) {
			return 3;
		}

		if (['TRAVIS', 'APPVEYOR', 'GITLAB_CI', 'BUILDKITE', 'DRONE'].some(sign => Object.hasOwn(env, sign)) || env.CI_NAME === 'codeship') {
			return 1;
		}

		return min;
	}

	if ('TEAMCITY_VERSION' in env) {
		return /^(?:9\.0*[1-9]\d*\.|\d{2,}\.)/v.test(env.TEAMCITY_VERSION) ? 1 : 0;
	}

	if (env.COLORTERM === 'truecolor') {
		return 3;
	}

	if (env.TERM === 'xterm-kitty') {
		return 3;
	}

	if (env.TERM === 'xterm-ghostty') {
		return 3;
	}

	if (env.TERM === 'wezterm') {
		return 3;
	}

	if ('TERM_PROGRAM' in env) {
		const version = Number((env.TERM_PROGRAM_VERSION || '').split('.', 1)[0]);

		switch (env.TERM_PROGRAM) {
			case 'iTerm.app': {
				return version >= 3 ? 3 : 2;
			}

			case 'Apple_Terminal': {
				return 2;
			}
			// No default
		}
	}

	if (/-256(?:color)?$/iv.test(env.TERM)) {
		return 2;
	}

	if (/^screen|^xterm|^vt100|^vt220|^rxvt|color|ansi|cygwin|linux/iv.test(env.TERM)) {
		return 1;
	}

	if ('COLORTERM' in env) {
		return 1;
	}

	return min;
}

export function createSupportsColor(stream, options = {}) {
	const level = _supportsColor(stream, {
		streamIsTTY: stream && stream.isTTY,
		...options,
	});

	return translateLevel(level);
}

const supportsColor = {
	stdout: createSupportsColor({isTTY: tty.isatty(1)}),
	stderr: createSupportsColor({isTTY: tty.isatty(2)}),
};

export default supportsColor;