WordPress│参照した記事にショートコードでカスタムフィールドの値を割り当てる方法

<?php
function waza_scf_post_id($value) {
    $id = absint($value ?: get_queried_object_id());
    $post = get_post($id);
    return $post && is_post_publicly_viewable($post) && !post_password_required($post) ? $id : 0;
}
function waza_scf_value($field, $id) {
    // 公開するフィールドだけを列挙。秘密情報や内部キーは追加しない。
    $allowed = ['scf_text', 'scf_textarea', 'scf_image', 'scf_checkbox', 'scf_radio', 'scf_btn', 'scf_map'];
    if (!class_exists('SCF') || !$id || !in_array($field, $allowed, true)) return null;
    return SCF::get($field, $id);
}
function waza_scf_text($atts) {
    $a = shortcode_atts(['field'=>'scf_text', 'type'=>'text', 'post_id'=>'0'], $atts);
    $value = waza_scf_value($a['field'], waza_scf_post_id($a['post_id']));
    if ($value === null || $value === '' || $value === false) return '';
    switch ($a['type']) {
        case 'text': case 'radio':
            return is_scalar($value) ? esc_html((string) $value) : '';
        case 'textarea':
            return is_scalar($value) ? nl2br(esc_html((string) $value)) : '';
        case 'checkbox':
            return is_array($value) ? esc_html(implode(', ', array_filter($value, 'is_scalar'))) : '';
        case 'image':
            return is_numeric($value) ? wp_get_attachment_image(absint($value), 'large') : '';
        default: return '';
    }
}
add_shortcode('custom_field', 'waza_scf_text');
add_shortcode('scf_btn', function ($atts) {
    $a = shortcode_atts(['field_name'=>'scf_btn', 'text'=>'詳しく見る', 'post_id'=>'0'], $atts);
    $value = waza_scf_value($a['field_name'], waza_scf_post_id($a['post_id']));
    if (!is_string($value) || !preg_match('~^https?://~i', $value)) return '';
    $url = esc_url($value, ['http','https']);
    if (!$url) return '';
    return '<div class="swell-block-button is-style-btn_normal"><a class="swell-block-button__link" href="' . $url . '">' . esc_html($a['text']) . '</a></div>';
});
add_shortcode('scf_map', function ($atts) {
    $a = shortcode_atts(['post_id'=>'0'], $atts);
    $value = waza_scf_value('scf_map', waza_scf_post_id($a['post_id']));
    if (!is_string($value)) return '';
    $url = wp_parse_url($value);
    if (($url['scheme'] ?? '') !== 'https' || ($url['host'] ?? '') !== 'www.google.com' || !str_starts_with($url['path'] ?? '', '/maps/embed') || isset($url['user']) || isset($url['pass'])) return '';
    return '<iframe title="所在地の地図" src="' . esc_url($value) . '" width="600" height="450" style="max-width:100%;border:0" loading="lazy" allowfullscreen></iframe>';
});

[custom_field field="scf_text" type="text" post_id="123"]
[custom_field field="scf_textarea" type="textarea" post_id="123"]
[custom_field field="scf_checkbox" type="checkbox" post_id="123"]
[custom_field field="scf_radio" type="radio" post_id="123"]
[custom_field field="scf_image" type="image" post_id="123"]
[scf_btn text="詳しく見る" post_id="123"]
[scf_map post_id="123"]