yoast-cjk-auto-generate-excerpt-fix.php

add_filter( 'wpseo_metadesc', function ($trim) {
  if ( is_singular() ) {
    if ( empty( $trim ) ) {
    
      // If excerpt is empty, use core's auto-generate excerpt to put excerpt string back in to the var.
      // 返ってきた抜粋が空白の場合、コアの自動抜粋・抜粋取得処理を使って抜粋を入れ直す.
      $trim = get_the_excerpt();
      
      // If you prefer to, additionally, trimm at "。" (full stop, if any), then you can do this instead of above.
      // コアが作る自動抜粋の中に句点がもしあれば、句点の後は切り捨てたい場合.
      // $excerpt = get_the_excerpt();
      // $punctuation = mb_strrpos( $excerpt, '。' );
      // $punctuation = ( false !== $punctuation ) ? $punctuation + 1 : null;
      // $trim = mb_substr( $excerpt, 0, $punctuation );
    }
  }
  return $trim;
}, 10, 1 );