Refactor darkfish's classes sidebar implementation (#1296)

The current logic written in ERB template is super hard to read and
understand. I think given its complexity is makes sense to implement
those logic in pure Ruby methods instead of ERB code in a view.

Author: st0012

lib/rdoc/generator/darkfish.rb

@@ -824,6 +824,50 @@ def generate_ancestor_list(ancestors, klass)
     content << '</li></ul>'
   end
 
+  def generate_class_link(klass, rel_prefix)
+    if klass.display?
+      %(<code><a href="#{rel_prefix}/#{klass.path}">#{klass.name}</a></code>)
+    else
+      %(<code>#{klass.name}</code>)
+    end
+  end
+
+  def generate_class_index_content(classes, rel_prefix)
+    grouped_classes = group_classes_by_namespace_for_sidebar(classes)
+    return '' unless top = grouped_classes[nil]
+
+    solo = top.one? { |klass| klass.display? }
+    traverse_classes(top, grouped_classes, rel_prefix, solo)
+  end
+
+  def traverse_classes(klasses, grouped_classes, rel_prefix, solo = false)
+    content = +'<ul class="link-list">'
+
+    klasses.each do |index_klass|
+      if children = grouped_classes[index_klass.full_name]
+        content << %(<li><details#{solo ? ' open' : ''}><summary>#{generate_class_link(index_klass, rel_prefix)}</summary>)
+        content << traverse_classes(children, grouped_classes, rel_prefix)
+        content << '</details></li>'
+        solo = false
+      elsif index_klass.display?
+        content << %(<li>#{generate_class_link(index_klass, rel_prefix)}</li>)
+      end
+    end
+
+    "#{content}</ul>"
+  end
+
+  def group_classes_by_namespace_for_sidebar(classes)
+    grouped_classes = classes.group_by do |klass|
+      klass.full_name[/\A[^:]++(?:::[^:]++(?=::))*+(?=::[^:]*+\z)/]
+    end.select do |_, klasses|
+      klasses.any?(&:display?)
+    end
+
+    grouped_classes.values.each(&:uniq!)
+    grouped_classes
+  end
+
   private
 
   def nesting_namespaces_to_class_modules klass

lib/rdoc/generator/template/darkfish/_sidebar_classes.rhtml

@@ -1,34 +1,5 @@
 <div id="classindex-section" class="nav-section">
   <h3>Class and Module Index</h3>
 
-  <%-
-  all_classes = @classes.group_by do |klass|
-    klass.full_name[/\A[^:]++(?:::[^:]++(?=::))*+(?=::[^:]*+\z)/]
-  end.delete_if do |_, klasses|
-    !klasses.any?(&:display?)
-  end
-  link = proc do |index_klass, display = index_klass.display?|
-    if display
-      -%><code><a href="<%= rel_prefix %>/<%= index_klass.path %>"><%= index_klass.name %></a></code><%-
-    else
-      -%><code><%= index_klass.name %></code><%-
-    end
-  end
-  if top = all_classes[nil]
-    solo = top.one? {|klass| klass.display?}
-    traverse = proc do |klasses| -%>
-  <ul class="link-list">
-      <%- klasses.uniq!(&:full_name) -%>
-      <%- klasses.each do |index_klass| -%>
-        <%- if children = all_classes[index_klass.full_name] -%>
-  <li><details<% if solo; solo = false %> open<% end %>><summary><% link.call(index_klass) %></summary>
-          <%- traverse.call(children) -%>
-  </ul></details>
-        <%- elsif index_klass.display? -%>
-  <li><% link.call(index_klass, true) %>
-        <%- end -%>
-      <%- end -%>
-    <%- end -%>
-    <%- traverse.call(top) -%>
-  <%- end -%>
+  <%= generate_class_index_content(@classes, rel_prefix) %>
 </div>