Cherry picked Adolfo's commits and addressed Braden's observations

common/static/common/js/discussion/views/discussion_inline_view.js

@@ -126,7 +126,8 @@
                 course_settings: this.courseSettings,
                 topicId: discussionId,
                 startHeader: this.startHeader,
-                is_commentable_divided: response.is_commentable_divided
+                is_commentable_divided: response.is_commentable_divided,
+                user_group_id: response.user_group_id,
             });
 
             this.newPostView.render();

common/static/common/js/discussion/views/discussion_topic_menu_view.js

@@ -15,6 +15,7 @@
             initialize: function(options) {
                 this.course_settings = options.course_settings;
                 this.currentTopicId = options.topicId;
+                this.group_name = options.group_name;
                 _.bindAll(this,
                     'handleTopicEvent'
                 );

common/static/common/js/discussion/views/new_post_view.js

@@ -42,6 +42,7 @@
                 }
                 this.course_settings = options.course_settings;
                 this.is_commentable_divided = options.is_commentable_divided;
+                this.user_group_id = options.user_group_id;
                 this.topicId = options.topicId;
                 this.discussionBoardView = options.discussionBoardView;
             };
@@ -53,6 +54,7 @@
                 _.extend(context, {
                     group_options: this.getGroupOptions(),
                     is_commentable_divided: this.is_commentable_divided,
+                    is_discussion_division_enabled: this.course_settings.get('is_discussion_division_enabled'),
                     mode: this.mode,
                     startHeader: this.startHeader,
                     form_id: this.mode + (this.topicId ? '-' + this.topicId : '')
@@ -68,10 +70,17 @@
                 if (this.isTabMode()) {
                     this.topicView = new DiscussionTopicMenuView({
                         topicId: this.topicId,
-                        course_settings: this.course_settings
+                        course_settings: this.course_settings,
+                        group_name: this.getGroupName()
                     });
-                    this.topicView.on('thread:topic_change', this.toggleGroupDropdown);
+                    this.topicView.on('thread:topic_change', this.toggleGroupDropDown);
+                    if (this.course_settings.get('is_discussion_division_enabled')) {
+                        this.topicView.on('thread:topic_change', this.updateVisibilityMessage);
+                    }
                     this.addField(this.topicView.render());
+                } else {
+                    this.group_name = this.getGroupName();
+                    this.updateVisibilityMessage(null, this.is_commentable_divided);
                 }
                 return DiscussionUtil.makeWmdEditor(this.$el, $.proxy(this.$, this), 'js-post-body');
             };
@@ -100,6 +109,26 @@
                 }
             };
 
+            NewPostView.prototype.getGroupName = function() {
+                var userGroupId;
+                var group;
+                var group_name = null;
+                if (this.course_settings.get('is_discussion_division_enabled')) {
+                    userGroupId = $('#discussion-container').data('user-group-id');
+                    if (!userGroupId) {
+                        userGroupId = this.user_group_id;
+                    }
+                    group = this.course_settings.get('groups').find(function(group) {
+                        return group.id == userGroupId;
+                    });
+                    if (group) {
+                        group_name = group.name;
+                    }
+                }
+
+                return group_name;
+            };
+
             NewPostView.prototype.events = {
                 'keypress .forum-new-post-form input:not(.wmd-input)': function(event) {
                     return DiscussionUtil.ignoreEnterKey(event);
@@ -121,6 +150,17 @@
                 }
             };
 
+            NewPostView.prototype.updateVisibilityMessage = function($target, force_divided) {
+                var visEl = $('.group-visibility .field-label-text');
+                var visTemplate = edx.HtmlUtils.template($('#new-post-visibility-template').html());
+                var group_name = null;
+                if (($target && $target.data('divided')) || force_divided) {
+                    group_name = this.group_name;
+                }
+
+                edx.HtmlUtils.setHtml(visEl, visTemplate({group_name: group_name}));
+            };
+
             NewPostView.prototype.postOptionChange = function(event) {
                 var $optionElem, $target;
                 $target = $(event.target);

common/static/common/templates/discussion/new-post-visibility.underscore

@@ -0,0 +1,11 @@
+<% if (group_name) { %>
+    <%-
+    interpolate(
+        gettext('This post will be visible only to %(group_name)s.'),
+        {group_name: group_name},
+        true
+    )
+    %>
+<% } else { %>
+    <%- gettext('This post will be visible to everyone.') %>
+<% } %>

common/static/common/templates/discussion/new-post.underscore

@@ -29,6 +29,13 @@
             </div>
         </label>
     </div>
+    <% } else if (is_discussion_division_enabled) { %>
+    <div class="post-field group-visibility">
+        <label class="field-label">
+            <!-- Wrapper for the visibility message filled out by a separate template -->
+            <span class="field-label-text"></span>
+	</label>
+    </div>
     <% } %>
     <div class="post-field">
         <label class="field-label">