docs(docs): preserve path to current doc page when switching versions

Preserve URL path when switching between doc versions.

Closes #4661
Closes #5773

docs/src/templates/js/docs.js

@@ -5,11 +5,19 @@ var docsApp = {
   filter: {}
 };
 
-docsApp.controller.DocsVersionsCtrl = ['$scope', '$window', 'NG_VERSIONS', 'NG_VERSION', function($scope, $window, NG_VERSIONS, NG_VERSION) {
+docsApp.controller.DocsVersionsCtrl = ['$scope', '$rootScope', '$window', 'NG_VERSIONS', 'NG_VERSION', function($scope, $rootScope, $window, NG_VERSIONS, NG_VERSION) {
   $scope.docs_versions = NG_VERSIONS;
   $scope.docs_version  = NG_VERSIONS[0];
+
   $scope.jumpToDocsVersion = function(version) {
-    $window.location = version.url;
+    var currentPagePath = '';
+
+    // preserve URL path when switching between doc versions
+    if (angular.isObject($rootScope.currentPage) && $rootScope.currentPage.section && $rootScope.currentPage.id) {
+      currentPagePath = '/' + $rootScope.currentPage.section + '/' + $rootScope.currentPage.id;
+    }
+
+    $window.location = version.url + currentPagePath;
   };
 }];
 
@@ -645,7 +653,7 @@ docsApp.serviceFactory.sections = ['NG_PAGES', function sections(NG_PAGES) {
 }];
 
 
-docsApp.controller.DocsController = function($scope, $location, $window, $cookies, sections) {
+docsApp.controller.DocsController = function($scope, $rootScope, $location, $window, $cookies, sections) {
   $scope.fold = function(url) {
     if(url) {
       $scope.docs_fold = '/notes/' + url;
@@ -736,9 +744,9 @@ docsApp.controller.DocsController = function($scope, $location, $window, $cookie
         sectionName = SECTION_NAME[sectionId] || sectionId,
         page = sections.getPage(sectionId, partialId);
 
-      $scope.currentPage = sections.getPage(sectionId, partialId);
+      $rootScope.currentPage = sections.getPage(sectionId, partialId);
 
-      if (!$scope.currentPage) {
+      if (!$rootScope.currentPage) {
         $scope.partialTitle = 'Error: Page Not Found!';
       }