Source

File: wp-includes/admin-bar.php

function is_admin_bar_showing() {
	global $show_admin_bar, $pagenow;

	// For all these types of requests, we never want an admin bar.
	if ( defined( 'XMLRPC_REQUEST' ) || defined( 'DOING_AJAX' ) || defined( 'IFRAME_REQUEST' ) || wp_is_json_request() ) {
		return false;
	}

	if ( is_embed() ) {
		return false;
	}

	// Integrated into the admin.
	if ( is_admin() ) {
		return true;
	}

	if ( ! isset( $show_admin_bar ) ) {
		if ( ! is_user_logged_in() || 'wp-login.php' === $pagenow ) {
			$show_admin_bar = false;
		} else {
			$show_admin_bar = _get_admin_bar_pref();
		}
	}

	/**
	 * Filters whether to show the admin bar.
	 *
	 * Returning false to this hook is the recommended way to hide the admin bar.
	 * The user's display preference is used for logged in users.
	 *
	 * @since 3.1.0
	 *
	 * @param bool $show_admin_bar Whether the admin bar should be shown. Default false.
	 */
	$show_admin_bar = apply_filters( 'show_admin_bar', $show_admin_bar );

	return $show_admin_bar;
}