サイドバーに各種投稿の新着を出す。テキストウィジェットにショートコードOKな感じで

for_sidebar_widget_recent_post.php

<?php
function update_list( $atts ) {

	extract( shortcode_atts( array(
		'post_type'	=>	array( 'ranking', 'magazinenavi', 'topics' ),
		'num'					=>	8,
		'class'				=>	'recent_post',
		'order'				=>	'DESC',
		'orderby'			=>	'',
		'post_parent'	=>	null,
	), $atts ) );
	
	global $post;
	$args = array(
	  'post_type'			=>	$post_type,
	  'numberposts'		=>	$num,
	  'order'					=>	$order,
	  'orderby'				=>	$orderby,
	  'post_parent'		=>	$post_parent,
	);
	$relational_posts = get_posts( $args );
	setup_postdata( $post );
		$html = '';
		foreach( $relational_posts as $post ) {
		$post_date = esc_attr( get_the_time( 'Y.m.d', $post->ID ) );
		$post_link = esc_url( get_permalink( $post->ID ) );
		$post_title = esc_attr( get_the_title( $post->ID ) );
		$post_type = get_post_type( $post->ID );
		
		$html .= "<li class='$post_type'><a href='$post_link'>$post_title</a><span class='post_date'>$post_date</span></li>";
	}
	wp_reset_postdata();
	return "<ul class='$class'>$html</ul>";
} 
add_shortcode( 'recent_update', 'update_list' );

// add widget area
add_filter('widget_text', 'do_shortcode');