don't infer the current user for nil DiscussionTopic#user in the stream

fixes #8403

test plan:
 * import an external content package with discussion topics
 * make sure to find a discussion topic that has no author
 * on the dashboard of a user that has a stream item about that topic
   it should not show that the current user is the author

Change-Id: I681be31462a82591d60665dce967aa1548ef3a07
Reviewed-on: https://gerrit.instructure.com/10579
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>

app/models/discussion_topic.rb

@@ -26,7 +26,7 @@ class DiscussionTopic < ActiveRecord::Base
 
   attr_accessible :title, :message, :user, :delayed_post_at, :assignment,
     :plaintext_message, :podcast_enabled, :podcast_has_student_posts,
-    :require_initial_post, :threaded, :discussion_type
+    :require_initial_post, :threaded, :discussion_type, :context
 
   module DiscussionTypes
     SIDE_COMMENT = 'side_comment'

app/models/stream_item.rb

@@ -30,7 +30,7 @@ class StreamItem < ActiveRecord::Base
   def stream_data(viewing_user_id)
     res = data.is_a?(OpenObject) ? data : OpenObject.new
     res.assert_hash_data
-    res.user_id ||= viewing_user_id
+    res.user_id ||= viewing_user_id unless res.type == 'DiscussionTopic'
     post_process(res, viewing_user_id)
   end
   

app/views/context/_dashboard_topic.html.erb

@@ -12,7 +12,9 @@
       <a href="<%= context_prefix(context_code) %>/discussion_topics/<%= topic ? topic.id : "{{ id }}" %>" class="title"><%= topic.try_rescue(:title) || t('no_title', "No Title") %></a>
       <div class="sub_title">
         <span class="context_code group_<%= context_code || 'blank' %>"><%= cached_context_short_name(context_code) %></span>
-        <a title="<%= t 'titles.author_name', "Author's name" %>" href="<%= context_prefix(context_code) %>/users/<%= topic ? topic.user_id : "{{ user_id }}" %>" class="user_name"><%= context_user_name(context_code, topic.try_rescue(:user_id)) %></a>
+        <% if topic && topic.user_id || !topic || topic.new_record? %>
+          <a title="<%= t 'titles.author_name', "Author's name" %>" href="<%= context_prefix(context_code) %>/users/<%= topic ? topic.user_id : "{{ user_id }}" %>" class="user_name"><%= context_user_name(context_code, topic.try_rescue(:user_id)) %></a>
+        <% end %>
       </div>
     </div>
     <div class="post_date time_ago_date"><%= datetime_string(post_date) || nbsp %></div>

spec/models/stream_item_spec.rb

@@ -0,0 +1,32 @@
+#
+# Copyright (C) 2011 Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper.rb')
+
+describe StreamItem do
+  it "should not infer a user_id for DiscussionTopic" do
+    user
+    context = Course.create!
+    dt = DiscussionTopic.create!(:context => context)
+    dt.generate_stream_items([@user])
+    si = @user.stream_item_instances.first.stream_item
+    data = si.stream_data(@user.id)
+    data.type.should == 'DiscussionTopic'
+    data.user_id.should be_nil
+  end
+end

spec/views/context/_dashboard_topic.html.erb_spec.rb

@@ -20,10 +20,11 @@ require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper')
 require File.expand_path(File.dirname(__FILE__) + '/../views_helper')
 
 describe "context/dashboard_topic" do
-  it "should render" do
+  it "should not show the author for nil user_id" do
     render :partial => "context/dashboard_topic", :locals =>
         { :dashboard_topic => OpenObject.new({:root_discussion_entries => nil,
-                                              :created_at => Time.now.utc})}
+                                              :created_at => Time.now.utc, :user_id => nil})}
     response.should_not be_nil
+    response.body.should_not match /Author/
   end
 end