Show some useful links on 404 default page

readthedocs/core/views/__init__.py

@@ -124,11 +124,33 @@ def server_error_404(request, exception=None, template_name='404.html'):  # pyli
             )
         else:
             return response
-    r = render(request, template_name)
+    r = render(request, template_name, context=_get_404_context(request))
     r.status_code = 404
     return r
 
 
+def _get_404_context(request):
+    from readthedocs.redirects.utils import project_and_path_from_request, language_and_version_from_path
+    project = None
+    language = None
+    version_slug = None
+
+    full_path = request.get_full_path()
+    project, path = project_and_path_from_request(request, full_path)
+    if project and not project.single_version:
+        language, version_slug, path = language_and_version_from_path(path)
+
+    context = {
+        'default_docs_url': project.get_docs_url(),
+        'version_docs_url': project.get_docs_url(
+            version_slug=version_slug,
+            lang_slug=language,
+        ),
+        'full_path': full_path,
+    }
+    return context
+
+
 def do_not_track(request):
     dnt_header = request.META.get('HTTP_DNT')
 

readthedocs/core/views/serve.py

@@ -150,6 +150,11 @@ def serve_docs(
         request, project, subproject, lang_slug=None, version_slug=None,
         filename=''):
     """Exists to map existing proj, lang, version, filename views to the file format."""
+
+    # TODO: remove this, it's only for debugging purposes
+    # from readthedocs.core.views import server_error_404
+    # return server_error_404(request)
+
     if not version_slug:
         version_slug = project.get_default_version()
     try:

readthedocs/templates/404.html

@@ -16,25 +16,20 @@
 {% block language-select-form %}{% endblock %}
 
 {% block content %}
-    {% if suggestion %}
-      <div class="suggestions">
-          <h1>You've found something that doesn't exist.</h1>
-          <p>{{ suggestion.message }}</p>
-          {% ifequal suggestion.type 'top' %}
-          <p>
-              <a href="{{ suggestion.href }}">Go to the top of the documentation.</a>
-          </p>
-          {% endifequal %}
-          {% ifequal suggestion.type 'list' %}
-          <ul>
-            {% for item in suggestion.list %}
-              <li><a href="{% doc_url item.project item.version_slug item.pagename %}">{{ item.label }}</a></li>
-            {% endfor %}
-          </ul>
-          {% endifequal %}
-      </div>
+
+  {% block 404_useful_links %}
+    {% if default_docs_url %}
+      Top site default documentation: {{ default_docs_url }} </br>
+    {% endif %}
+    {% if version_docs_url %}
+      Version/Language site documentation: {{ version_docs_url }} </br>
     {% endif %}
-<pre style="line-height: 1.25; white-space: pre;">
+    {% if full_path %}
+      The page requested is {{ full_path }}</br>
+    {% endif %}
+  {% endblock %}
+
+  <pre style="%; line-height: 1.25; white-space: pre;">
 
         \          SORRY            /
          \                         /
@@ -58,5 +53,5 @@ <h1>You've found something that doesn't exist.</h1>
           /          N            \
          /           q,            \
         /                           \
-</pre>
+  </pre>
 {% endblock %}