Stop using request variants to determine layout

This removes the code for the taxonomy_navigation requests variants and
uses `if` statements in the views instead.

This makes it clearer what's going on. It shouldn't make any change in
the pages.

I suspect that most of these `if` statements aren't actually meaningful
and can be removed. That's for a follow up PR.

Author: tijmenb

app/controllers/content_items_controller.rb

@@ -84,17 +84,7 @@ def set_expiry
   end
 
   def set_up_navigation
-    # Setting a variant on a request is a type of Rails Dark Magic that will
-    # use a convention to automagically load an alternative partial, view or
-    # layout.  For example, if I set a variant of :taxonomy_navigation and we render
-    # a partial called _breadcrumbs.html.erb then Rails will attempt to load
-    # _breadcrumbs.html+taxonomy_navigation.erb instead. If this file doesn't exist,
-    # then it falls back to _breadcrumbs.html.erb.  See:
-    # http://edgeguides.rubyonrails.org/4_1_release_notes.html#action-pack-variants
     @navigation = NavigationType.new(@content_item.content_item)
-    if @navigation.should_present_taxonomy_navigation?
-      request.variant = :taxonomy_navigation
-    end
   end
 
   def with_locale

app/views/shared/_breadcrumbs.html+taxonomy_navigation.erb

@@ -1,3 +1,11 @@
-<% if @content_item.breadcrumbs.any? %>
-  <%= render 'govuk_component/breadcrumbs', breadcrumbs: @content_item.breadcrumbs %>
+<% if @navigation.should_present_taxonomy_navigation? %>
+  <% if @content_item.taxon_breadcrumbs.any? %>
+    <%= render 'govuk_component/breadcrumbs',
+      breadcrumbs: @content_item.taxon_breadcrumbs,
+      collapse_on_mobile: true %>
+  <% end %>
+<% else %>
+  <% if @content_item.breadcrumbs.any? %>
+    <%= render 'govuk_component/breadcrumbs', breadcrumbs: @content_item.breadcrumbs %>
+  <% end %>
 <% end %>

app/views/shared/_breadcrumbs.html.erb

@@ -1,3 +1,15 @@
 <div class="column-third add-title-margin">
-  <%= render partial: 'govuk_component/related_items', locals: content_item.related_items %>
+  <% if @navigation.should_present_taxonomy_navigation? %>
+    <%=
+      render(
+        partial: 'govuk_component/taxonomy_sidebar',
+        locals: content_item.taxonomy_sidebar
+      ) %>
+  <% else %>
+    <%=
+      render(
+        partial: 'govuk_component/related_items',
+        locals: content_item.related_items
+      ) %>
+  <% end %>
 </div>

app/views/shared/_related_items.html+taxonomy_navigation.erb

@@ -1,6 +1,11 @@
-<div class="grid-row">
-  <div class="column-two-thirds">
-    <%= render 'govuk_component/title', @content_item.title_and_context %>
+<% if @navigation.should_present_taxonomy_navigation? %>
+  <%= render 'govuk_component/title', @content_item.title_and_context %>
+  <%= render 'shared/translations', translations: @content_item.available_translations %>
+<% else %>
+  <div class="grid-row">
+    <div class="column-two-thirds">
+      <%= render 'govuk_component/title', @content_item.title_and_context %>
+    </div>
+    <%= render 'shared/translations' %>
   </div>
-  <%= render 'shared/translations' %>
-</div>
+<% end %>

app/views/shared/_related_items.html.erb

@@ -1,6 +1,11 @@
 <% if @content_item.available_translations.length > 1 %>
-  <div class="column-third">
+  <% if @navigation.should_present_taxonomy_navigation? %>
     <%= render 'components/translation-nav',
         translations: @content_item.available_translations %>
-  </div>
+  <% else %>
+    <div class="column-third">
+      <%= render 'components/translation-nav',
+          translations: @content_item.available_translations %>
+    </div>
+  <% end %>
 <% end %>