FEATURE: Warn when reviving a topic that has been inactive for X days. Setting warn_reviving_old_topic_age controls when the warning is shown. Set it to 0 to disable this feature.

config/locales/server.en.yml

@@ -170,6 +170,13 @@ en:
 
       Instead of adding another reply, please consider editing your previous replies, or visiting other topics.
 
+    reviving_old_topic: |
+      ### Revive this topic?
+
+      The last reply to this topic is now over %{days} days old. Your reply will bump the topic to the top of its list and notify anyone previously involved in the conversation.
+
+      Are you sure you want to continue this old conversation?
+
   activerecord:
     attributes:
       category:
@@ -838,6 +845,7 @@ en:
     invites_shown: "Maximum invites shown on a user page"
     short_progress_text_threshold: "After the number of posts in a topic goes above this number, the progress bar will only show the current post number. If you change the progress bar's width, you may need to change this value."
     default_code_lang: "Default programming language syntax highlighting applied to GitHub code blocks (lang-auto, ruby, python etc.)"
+    warn_reviving_old_topic_age: "When someone starts replying to a topic older than this many days, a warning will be displayed to discourage the user from reviving an old discussion. Disable by setting to 0."
 
     embeddable_host: "Host that can embed the comments from this Discourse forum"
     feed_polling_enabled: "Whether to import a RSS/ATOM feed as posts"

config/site_settings.yml

@@ -238,6 +238,7 @@ posting:
   default_code_lang:
     client: true
     default: "lang-auto"
+  warn_reviving_old_topic_age: 180
 
 email:
   email_time_window_mins: 10

lib/composer_messages_finder.rb

@@ -6,6 +6,7 @@ class ComposerMessagesFinder
   end
 
   def find
+    check_reviving_old_topic ||
     check_education_message ||
     check_new_user_many_replies ||
     check_avatar_notification ||
@@ -123,6 +124,21 @@ class ComposerMessagesFinder
      body: PrettyText.cook(I18n.t('education.dominating_topic', percent: (ratio * 100).round)) }
   end
 
+  def check_reviving_old_topic
+    return unless @details[:topic_id]
+
+    topic = Topic.where(id: @details[:topic_id]).first
+
+    return if topic.nil? ||
+              SiteSetting.warn_reviving_old_topic_age < 1 ||
+              topic.last_posted_at > SiteSetting.warn_reviving_old_topic_age.days.ago
+
+    {templateName: 'composer/education',
+     wait_for_typing: false,
+     extraClass: 'urgent',
+     body: PrettyText.cook(I18n.t('education.reviving_old_topic', days: (Time.zone.now - topic.last_posted_at).round / 1.day)) }
+  end
+
   private
 
     def creating_topic?

spec/components/composer_messages_finder_spec.rb

@@ -14,6 +14,7 @@ describe ComposerMessagesFinder do
       finder.expects(:check_avatar_notification).once
       finder.expects(:check_sequential_replies).once
       finder.expects(:check_dominating_topic).once
+      finder.expects(:check_reviving_old_topic).once
       finder.find
     end
 
@@ -277,5 +278,51 @@ describe ComposerMessagesFinder do
 
   end
 
+  context '.check_reviving_old_topic' do
+    let(:user)  { Fabricate(:user) }
+    let(:topic) { Fabricate(:topic) }
+
+    it "does not give a message without a topic id" do
+      described_class.new(user, composerAction: 'createTopic').check_reviving_old_topic.should be_blank
+      described_class.new(user, composerAction: 'reply').check_reviving_old_topic.should be_blank
+    end
+
+    context "a reply" do
+      let(:finder) { described_class.new(user, composerAction: 'reply') }
+
+      context "warn_reviving_old_topic_age is 180 days" do
+        before do
+          SiteSetting.stubs(:warn_reviving_old_topic_age).returns(180)
+        end
+
+        it "does not notify if last post is recent" do
+          topic = Fabricate(:topic, last_posted_at: 1.hour.ago)
+          described_class.new(user, composerAction: 'reply', topic_id: topic.id).check_reviving_old_topic.should be_blank
+        end
+
+        it "notifies if last post is old" do
+          topic = Fabricate(:topic, last_posted_at: 181.days.ago)
+          described_class.new(user, composerAction: 'reply', topic_id: topic.id).check_reviving_old_topic.should_not be_blank
+        end
+      end
+
+      context "warn_reviving_old_topic_age is 0" do
+        before do
+          SiteSetting.stubs(:warn_reviving_old_topic_age).returns(0)
+        end
+
+        it "does not notify if last post is new" do
+          topic = Fabricate(:topic, last_posted_at: 1.hour.ago)
+          described_class.new(user, composerAction: 'reply', topic_id: topic.id).check_reviving_old_topic.should be_blank
+        end
+
+        it "does not notify if last post is old" do
+          topic = Fabricate(:topic, last_posted_at: 365.days.ago)
+          described_class.new(user, composerAction: 'reply', topic_id: topic.id).check_reviving_old_topic.should be_blank
+        end
+      end
+    end
+  end
+
 end