Fix 404 page (missing tabs property was making it render funny).

Also added code to detect if the 404 is on a documentation page.
The version switcher in the documentation attempts to preserve the
path (so that if you are looking at, say, JobExecutor in a version, you'd
also potentially be looking at JobExecutor after the switch). However,
there is no guarantee that the docs structure is the same in the two
versions, so you may land on a page that's not there. The code looks
at whether you are hitting a 404 on a docs page and offers a link to the
main docs page for that version.

Also, a minor fix in `getCurrentVersion`

Author: hategan

web/404.html

@@ -1,11 +1,20 @@
 ---
 permalink: /404.html
 layout: default
+tab: 100
 ---
 
 <div class="container">
-  <h1>404</h1>
+    <div v-if="isDocsPage()">
+        <h1>404</h1>
+        <p><strong>Page not found</strong></p>
+        <p>This version of the documentation does not contain this page. Please go to the <a :href="getMainDocsPage()">main documentation page</a>.
+    </div>
+    <div v-else>
 
-  <p><strong>Page not found :(</strong></p>
-  <p>The requested page could not be found.</p>
+        <h1>404</h1>
+
+        <p><strong>Page not found</strong></p>
+        <p>The requested page could not be found.</p>
+    </div>
 </div>

web/_includes/vueinit.html

@@ -9,7 +9,9 @@
             },
             methods: {
                 getSortedVersionLabels: getSortedVersionLabels,
-                setVersion: setVersion
+                setVersion: setVersion,
+                getMainDocsPage: getMainDocsPage,
+                isDocsPage: isDocsPage
             }
         });
 

web/versioning.js

@@ -219,7 +219,7 @@ function setVersion() {
  *                     currently displayed documentation version.
  */
 function getCurrentVersion() {
-    v = splitLocation()[1];
+    var v = splitLocation()[1];
     if (v == "") {
         return v;
     }
@@ -228,4 +228,22 @@ function getCurrentVersion() {
     }
 }
 
+/**
+ * Returns the main documentation page for the current version by removing
+ * everything after <code>"../docs/v/x.y.z/"</code> from the current URL.
+ */
+function getMainDocsPage() {
+    var s = splitLocation();
+
+    return s[0] + "/" + s[1] + "/";
+}
+
+/**
+ * Returns true if the current URL points to a versioned documentation
+ * page.
+ */
+function isDocsPage() {
+    return window.location.href.includes("/docs/v/");
+}
+
 initVersions();