Preserve relative path when switching between versions of the documentation

layouts/404.html

@@ -1,4 +1,5 @@
 {{ define "main" }}
+{{ partial "handle-version-switch-404.html" . }}
 <div class="container-404">
     <h4>
         Perhaps you were looking for:

layouts/partials/handle-version-switch-404.html

@@ -0,0 +1,11 @@
+{{/*
+If a 404 occurs and the referrer is a different version of the Kubernetes documentation,
+don't show the regular 404 error page, but instead redirect to the site root
+*/}}
+<script type="text/javascript">
+  var sameBaseUrlRegExp = new RegExp("^" + location.protocol + "//" + location.host.replace(".", "\\.") + "/.*", "i");
+  var kubernetesDocumentationUrlRegExp = new RegExp("^https?://(.+\\.)?kubernetes.io/.*", "i");
+  if (!sameBaseUrlRegExp.test(document.referrer) && kubernetesDocumentationUrlRegExp.test(document.referrer)) {
+    location.replace("/");
+  }
+</script>

layouts/partials/navbar-version-selector.html

@@ -2,7 +2,8 @@
 	{{ T "version_menu" }}
 </a>
 <div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdownMenuLink">
+	{{ $p := . }}
 	{{ range .Site.Params.versions }}
-	<a class="dropdown-item" href="{{ .url }}">{{ .version }}</a>
+	<a class="dropdown-item" href="{{ .url }}{{ $p.RelPermalink }}">{{ .version }}</a>
 	{{ end }}
 </div>