Keep guidelines menu in sync with ToC (#2856)

_data/topnav.yml

@@ -11,30 +11,10 @@ topnav_dropdowns:
   - title: Topnav Dropdowns
     folders:
       - title: Guidelines
-        folderitems:
-            - title: General
-              url: /general_introduction.html
-            - title: Android (Draft)
-              url: /android_design.html
-            - title: C (Draft)
-              url: /clang_design.html
-            - title: C++ (Draft)
-              url: /cpp_introduction.html
-            - title: C#.NET
-              url: /dotnet_introduction.html
-            - title: Go (Draft)
-              url: /golang_introduction.html
-            - title: iOS (Draft)
-              url: /ios_introduction.html
-            - title: Java
-              url: /java_introduction.html
-            - title: Python
-              url: /python_design.html
-            - title: TypeScript
-              url: /typescript_introduction.html
+        guidelines: true
       - title: API References
         folderitems:
-          - title: C#.NET
+          - title: .NET
             external_url: https://aka.ms/net-docs
           - title: Java
             external_url: https://aka.ms/java-docs

_includes/topnav.html

@@ -20,6 +20,7 @@
 
 {% assign topnav = site.data[page.topnav] %}
 {% assign topnav_dropdowns = site.data[page.topnav].topnav_dropdowns %}
+{% assign topnav_guidelines = site.data.sidebars.general_sidebar.entries[0] %}
 
                 {% for entry in topnav.topnav %}
                 {% for item in entry.items %}
@@ -39,6 +40,11 @@
                 <li class="dropdown">
                     <a href="#" class="dropdown-toggle" data-toggle="dropdown">{{ folder.title }}<b class="caret"></b></a>
                     <ul class="dropdown-menu">
+                        {% if folder.guidelines %}
+                        {% for folderitem in topnav_guidelines.folders %}
+                        <li><a href="{{folderitem.folderitems[0].url}}" rel="noopener">{{folderitem.title}}</a></li>
+                        {% endfor %}
+                        {% else %}
                         {% for folderitem in folder.folderitems %}
                         {% if folderitem.external_url %}
                         <li><a href="{{folderitem.external_url}}" rel="noopener">{{folderitem.title}}</a></li>
@@ -48,6 +54,7 @@
                         <li><a href="{{folderitem.url | relative_url }}">{{folderitem.title}}</a></li>
                         {% endif %}
                         {% endfor %}
+                        {% endif %}
                     </ul>
                 </li>
                 {% endfor %}