xprofile_sync_wp_profile( int $user_id,  $field_id = null )

function xprofile_sync_wp_profile( $user_id = 0, $field_id = null ) {

	// Bail if profile syncing is disabled.
	if ( bp_disable_profile_sync() ) {
		return true;
	}

	if ( empty( $user_id ) ) {
		$user_id = bp_loggedin_user_id();
	}

	if ( empty( $user_id ) ) {
		return false;
	}

	$firstname_id = bp_xprofile_firstname_field_id();
	$lastname_id  = bp_xprofile_lastname_field_id();
	$nickname_id  = bp_xprofile_nickname_field_id();

	if ( ! $field_id || $field_id == $firstname_id ) {
		$firstname = xprofile_get_field_data( bp_xprofile_firstname_field_id(), $user_id );
		bp_update_user_meta( $user_id, 'first_name', $firstname );
	}

	if ( ! $field_id || $field_id == $lastname_id ) {
		$lastname = xprofile_get_field_data( bp_xprofile_lastname_field_id(), $user_id );
		bp_update_user_meta( $user_id, 'last_name', $lastname );
	}

	if ( ! $field_id || $field_id == $nickname_id ) {
		$nickname = xprofile_get_field_data( bp_xprofile_nickname_field_id(), $user_id );
		bp_update_user_meta( $user_id, 'nickname', $nickname );
	}

	bp_xprofile_update_display_name( $user_id );
}