remove rails-observers

Rails yanked out observers many many years ago, instead the functionality
was yanked out to a gem that is very lightly maintained.

For example: if we want to upgrade to rails 5 there is no published gem

Internally the usage of observers had quite a few problem.

The series of refactors renamed a bunch of classes to give us more clarity
and removed some magic.

spec/services/post_action_notifier_spec.rb

@@ -0,0 +1,99 @@
+require 'rails_helper'
+require_dependency 'post_destroyer'
+
+describe PostActionNotifier do
+
+  before do
+    PostActionNotifier.enable
+  end
+
+  let!(:evil_trout) { Fabricate(:evil_trout) }
+  let(:post) { Fabricate(:post) }
+
+  context 'liking' do
+    context 'when liking a post' do
+      it 'creates a notification' do
+        expect {
+          PostAction.act(evil_trout, post, PostActionType.types[:like])
+          # one like (welcome badge deferred)
+        }.to change(Notification, :count).by(1)
+      end
+    end
+
+    context 'when removing a liked post' do
+      it 'removes a notification' do
+        PostAction.act(evil_trout, post, PostActionType.types[:like])
+        expect {
+          PostAction.remove_act(evil_trout, post, PostActionType.types[:like])
+        }.to change(Notification, :count).by(-1)
+      end
+    end
+  end
+
+  context 'when editing a post' do
+    it 'notifies a user of the revision' do
+      expect {
+        post.revise(evil_trout, { raw: "world is the new body of the message" })
+      }.to change(post.user.notifications, :count).by(1)
+    end
+
+    context "edit notifications are disabled" do
+
+      before { SiteSetting.stubs(:disable_edit_notifications).returns(true) }
+
+
+      it 'notifies a user of the revision made by another user' do
+        expect {
+          post.revise(evil_trout, { raw: "world is the new body of the message" })
+        }.to change(post.user.notifications, :count).by(1)
+      end
+
+      it 'does not notifiy a user of the revision made by the system user' do
+        expect {
+          post.revise(Discourse.system_user, { raw: "world is the new body of the message" })
+        }.not_to change(post.user.notifications, :count)
+      end
+
+    end
+
+  end
+
+  context 'private message' do
+    let(:user) { Fabricate(:user) }
+    let(:mention_post) { Fabricate(:post, user: user, raw: 'Hello @eviltrout')}
+    let(:topic) do
+      topic = mention_post.topic
+      topic.update_columns archetype: Archetype.private_message, category_id: nil
+      topic
+    end
+
+    it "won't notify someone who can't see the post" do
+      expect {
+        Guardian.any_instance.expects(:can_see?).with(instance_of(Post)).returns(false)
+        mention_post
+        PostAlerter.post_created(mention_post)
+      }.not_to change(evil_trout.notifications, :count)
+    end
+
+    it 'creates like notifications' do
+      other_user = Fabricate(:user)
+      topic.allowed_users << user << other_user
+      expect {
+        PostAction.act(other_user, mention_post, PostActionType.types[:like])
+      }.to change(user.notifications, :count)
+    end
+  end
+
+  context 'moderator action post' do
+    let(:user) { Fabricate(:user) }
+    let(:first_post) { Fabricate(:post, user: user, raw: 'A useless post for you.')}
+    let(:topic) { first_post.topic }
+
+    it 'should not notify anyone' do
+      expect {
+        Fabricate(:post, topic: topic, raw: 'This topic is CLOSED', post_type: Post.types[:moderator_action])
+      }.to_not change { Notification.count }
+    end
+  end
+
+end

spec/services/post_alerter_spec.rb

@@ -63,8 +63,7 @@ describe PostAlerter do
 
   context 'edits' do
     it 'notifies correctly on edits' do
-
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')
 
@@ -89,7 +88,7 @@ describe PostAlerter do
   context 'likes' do
 
     it 'notifies on likes after an undo' do
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')
 
@@ -101,7 +100,7 @@ describe PostAlerter do
     end
 
     it 'notifies on does not notify when never is selected' do
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')
 
@@ -110,12 +109,11 @@ describe PostAlerter do
 
       PostAction.act(evil_trout, post, PostActionType.types[:like])
 
-
       expect(Notification.where(post_number: 1, topic_id: post.topic_id).count).to eq(0)
     end
 
     it 'notifies on likes correctly' do
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')