Fix liquid variable leakage in navigation components (#1243)

* Refactor nav, breadcrumbs, children_nav

Fix #1118

Improve the modularity of building the nav-panel, breadcrumbs, and children-nav
by making them independent. This also significantly simplifies the Liquid code.

* Fix order of breadcrumbs

* Update breadcrumbs.html

Revert inclusion of single breadcrumb for top-level pages.

* Update breadcrumbs.html

* Update children_nav.html

Revert to the previous layout in the HTML, to allow the use of `diff` to check the built site.

* Update minimal.html

Remove the previously required workaround involving `nav.html`.

* Add docs pages about layouts

The aim of the initial version of these docs pages is to illustrate the difference between the default and minimal layouts.

* Update CHANGELOG.md

_includes/components/breadcrumbs.html

@@ -1,15 +1,43 @@
-{% unless page.url == "/" %}
-  {% if page.parent %}
-    <nav aria-label="Breadcrumb" class="breadcrumb-nav">
-      <ol class="breadcrumb-nav-list">
-        {% if page.grand_parent %}
-          <li class="breadcrumb-nav-list-item"><a href="{{ first_level_url }}">{{ page.grand_parent }}</a></li>
-          <li class="breadcrumb-nav-list-item"><a href="{{ second_level_url }}">{{ page.parent }}</a></li>
-        {% else %}
-          <li class="breadcrumb-nav-list-item"><a href="{{ first_level_url }}">{{ page.parent }}</a></li>
-        {% endif %}
-        <li class="breadcrumb-nav-list-item"><span>{{ page.title }}</span></li>
-      </ol>
-    </nav>
-  {% endif %}
-{% endunless %}
+{%- comment -%}
+  Include as: {%- include components/breadcrumbs.html -%}
+  Depends on: page, site.
+  Results in: HTML for the breadcrumbs component.
+  Overwrites:
+    pages_list, parent_page, grandparent_page.
+{%- endcomment -%}
+
+{%- if page.url != "/" and page.parent -%}
+
+  {%- assign pages_list = site[page.collection]
+      | default: site.html_pages
+      | where_exp: "item", "item.title != nil"
+      | where_exp: "item", "item.has_children != nil" -%}
+
+  {%- if page.grand_parent -%}
+    {%- assign parent_page = pages_list
+        | where: "title", page.parent
+        | where: "parent", page.grand_parent
+        | first -%}
+    {%- assign grandparent_page = pages_list
+        | where: "title", page.grand_parent
+        | first -%}
+  {%- else -%}
+    {%- assign parent_page = pages_list
+        | where: "title", page.parent
+        | where_exp: "item", "item.parent == nil"
+        | first -%}
+  {%- endif -%}
+
+<nav aria-label="Breadcrumb" class="breadcrumb-nav">
+  <ol class="breadcrumb-nav-list">
+  {% if page.parent -%}
+  {%- if page.grand_parent %}
+    <li class="breadcrumb-nav-list-item"><a href="{{ grandparent_page.url | relative_url }}">{{ page.grand_parent }}</a></li>
+  {%- endif %}
+    <li class="breadcrumb-nav-list-item"><a href="{{ parent_page.url | relative_url }}">{{ page.parent }}</a></li>
+  {% endif -%}
+    <li class="breadcrumb-nav-list-item"><span>{{ page.title }}</span></li>
+  </ol>
+</nav>
+
+{%- endif -%}

_includes/components/children_nav.html

@@ -1,9 +1,33 @@
+{%- comment -%}
+  Include as: {%- include components/children_nav.html -%}
+  Depends on: page, site.
+  Results in: HTML for the children-navigation component.
+  Includes:
+    sorted_pages.html
+    toc_heading_custom.html
+  Overwrites:
+    child_pages.
+{%- endcomment -%}
+
+{%- if page.has_children == true and page.has_toc != false -%}
+  {%- assign child_pages = site[page.collection]
+        | default: site.html_pages
+        | where: "parent", page.title
+        | where: "grand_parent", page.parent -%}
+
+  {%- include sorted_pages.html pages = child_pages -%}
+
+  {%- if page.child_nav_order == 'desc' or page.child_nav_order == 'reversed' -%}
+    {%- assign sorted_pages = sorted_pages | reverse -%}
+  {%- endif -%}
+{%- endif -%}
+
 <hr>
 {% include toc_heading_custom.html %}
 <ul>
-  {% for child in include.toc_list %}
-    <li>
-      <a href="{{ child.url | relative_url }}">{{ child.title }}</a>{% if child.summary %} - {{ child.summary }}{% endif %}
-    </li>
-  {% endfor %}
+{% for child in sorted_pages %}
+  <li>
+    <a href="{{ child.url | relative_url }}">{{ child.title }}</a>{% if child.summary %} - {{ child.summary }}{% endif %}
+  </li>
+{% endfor %}
 </ul>