Nested Jekyll page navigation without plugins

navigation.html

{% capture html %}

{% assign childCount = '' %}
{% comment %} Make sure there will be pages before making the ul tag. {% endcomment %}
{% assign entries = site.pages | sort: "path" %}
{% for entry in entries %}
    {% capture slug    %}{{ entry.url | split: "/"   | last                       }}{% endcapture %}
    {% capture current %}{{ entry.url | remove: slug | remove: "//" | append: "/" }}{% endcapture %}

    {% if current == include.context %}
        {% capture childCount %}{{ childCount }}*{% endcapture %}
    {% endif %}

{% endfor %}

{% if childCount.size > 0 %}
<ul>
    {% if include.context == "/" %}
        <li class="{% if page.url == "/" %}active{% endif %}">
            <a href="{{ site.baseurl }}/">{{ site.title }}</a>
        </li>
    {% endif %}

    {% assign entries = site.pages | sort: "path" %}
    {% for entry in entries %}
        {% capture slug    %}{{ entry.url | split: "/"   | last                       }}{% endcapture %}
        {% capture current %}{{ entry.url | remove: slug | remove: "//" | append: "/" }}{% endcapture %}

        {% if current == include.context %}
            <li class="{% if page.url contains entry.url %}active{% endif %}">
                {% capture subMenu %}{% include navigation.html context=entry.url %}{% endcapture %}
                {% if subMenu.size > 0 %}
                    <a href="{{ site.baseurl }}{{ entry.url }}">{{ entry.title }}</a>
                {% endif %}
                {% unless subMenu.size > 0 %}
                    {% comment %} 
                        This if/unless is optional.  Useful if you want clicking on the non-text part 
                        of the <li> row to expand, but you want have the leaf nodes of the navigation
                        tree browse when anywhere in the <li> is clicked, not just the text of the <a>.
                        If not, just remove the unless entirely and remove the if/endif around the <a>
                        above.
                    {% endcomment %}
                    <a class="make-the-internal-a-tag-inline-block-and-100%w/h" href="{{ site.baseurl }}{{ entry.url }}">{{ entry.title }}</a>
                {% endunless %}
                {{ subMenu }}
            </li>
        {% endif %}

    {% endfor %}
</ul>
{% endif %}
{% endcapture %}{{ html | strip_newlines | replace:'    ','' | replace:'    ','' | replace:'  ',' ' }}