Enhance 404 error page by adding search form and loading additional docs tags

djangoproject/templates/404.html

@@ -1,9 +1,18 @@
 {% extends 'base_error.html' %}
-{% load i18n %}
+{% load i18n docs %}
 
 {% block title %}{% translate "Page not found" %}{% endblock %}
 
-{% block header %}<h1>404</h1>{% endblock %}
+{% block header %}
+  <div class="copy-banner">
+    <div class="container--flex container--flex--wrap--mobile">
+      <h1>404</h1>
+      {% if request.host.regex == 'docs' %}
+        {% search_form %}
+      {% endif %}
+    </div>
+  </div>
+{% endblock %}
 
 {% block content %}
   <h2>{% translate "Page not found" %}</h2>
@@ -12,7 +21,8 @@ <h2>{% translate "Page not found" %}</h2>
     {% blocktranslate trimmed %}
       Looks like you followed a bad link. If you think it's our fault, please
       <a href="https://code.djangoproject.com/">let us know</a>.
-    {% endblocktranslate %}</p>
+    {% endblocktranslate %}
+  </p>
 
   {% url 'homepage' as homepage_url %}
   <p>

docs/templatetags/docs.py

@@ -15,14 +15,23 @@
 @register.inclusion_tag("docs/search_form.html", takes_context=True)
 def search_form(context):
     request = context["request"]
+    version = ""
+    lang = ""
+    exception = context.get("exception", "")
+    if exception:
+        lang = context["LANGUAGE_CODE"]
+        version = context["DOCS_VERSION"]
+    else:
+        version = context["version"]
+        lang = context["lang"]
     release = DocumentRelease.objects.get_by_version_and_lang(
-        context["version"],
-        context["lang"],
+        version,
+        lang,
     )
     return {
         "form": DocSearchForm(request.GET, release=release),
-        "version": context["version"],
-        "lang": context["lang"],
+        "version": version,
+        "lang": lang,
     }