yii\gii\CodeFile::diff PHP Method

    public function diff()
    {
        $type = strtolower($this->getType());
        if (in_array($type, ['jpg', 'gif', 'png', 'exe'])) {
            return false;
        } elseif ($this->operation === self::OP_OVERWRITE) {
            return $this->renderDiff(file($this->path), $this->content);
        } else {
            return '';
        }
    }