[WordPress] Contact Form 7 に独自ショートコードを追加

cf7_shortcode.php

<?php
add_action('init', 'my_wpcf7_shortcode');
function my_wpcf7_shortcode(){
  wpcf7_add_shortcode('my_shortcode', 'my_wpcf7_shortcode_handler', true);
}

function my_wpcf7_shortcode_handler( $tag ) {
  $tag = new WPCF7_Shortcode( $tag );
  if ( empty( $tag->name ) )
    return '';

  $args = array(
    'size'      => $tag->get_size_option( '40' ),
    'maxlength' => $tag->get_maxlength_option(),
    'class'     => $tag->get_class_option( wpcf7_form_controls_class( $tag->type, $tag->name ) ),
    'id'        => $tag->get_option( 'id', 'id', true ),
    'tabindex'  => $tag->get_option( 'tabindex', 'int', true ),
    'pre'       => $tag->get_option( 'pre', '.*', true ),
    'post'      => $tag->get_option( 'post', '.*', true ),
    );
  $defaults = array(
    'size'      => '40',
    'maxlength' => '40',
    'class'     => $tag->name,
    'id'        => $tag->name,
    'tabindex'  => 0,
    'pre'       => '<span class="wpcf7-form-control-wrap">',
    'post'      => '</span>',
    );
  wp_parse_args( $args, $defaults );

  $value = '';
  if ( wpcf7_is_posted() && isset($_POST[$tag->name]) )
    $value = stripslashes_deep( $_POST[$tag->name] );

  return sprintf(
    $args['pre'] . '<input type="%2$s" name="%1$s" value="%3$s" />' . $args['post'],
    $tag->name,
    $tag->type,
    esc_attr($value)
    );
}