Original implementation to allow users to subscribe to labels

1. Allow subscribing (the current user) to a label

- Refactor the `Subscription` coffeescript class
  - The main change is that it accepts a container, and conducts all
    DOM queries within its scope. We need this because the labels
    page has multiple instances of `Subscription` on the same page.

2. Creating an issue or MR with labels notifies users subscribed to those labels

- Label `has_many` subscribers through subscriptions.

3. Adding a label to an issue or MR notifies users subscribed to those labels

- This only applies to subscribers of the label that has just been
  added, not all labels for the issue.

1 files changed, 7 insertions, 2 deletions

diff --git a/app/controllers/projects/labels_controller.rb b/app/controllers/projects/labels_controller.rb
index ecac3c395ec..d0334c37b67 100644
--- a/app/controllers/projects/labels_controller.rb
+++ b/app/controllers/projects/labels_controller.rb
@@ -1,8 +1,8 @@
 class Projects::LabelsController < Projects::ApplicationController
   before_action :module_enabled
-  before_action :label, only: [:edit, :update, :destroy]
+  before_action :label, only: [:edit, :update, :destroy, :toggle_subscription]
   before_action :authorize_read_label!
-  before_action :authorize_admin_labels!, except: [:index]
+  before_action :authorize_admin_labels!, except: [:index, :toggle_subscription]
 
   respond_to :js, :html
 
@@ -60,6 +60,11 @@ class Projects::LabelsController < Projects::ApplicationController
     end
   end
 
+  def toggle_subscription
+    @label.toggle_subscription(current_user)
+    render nothing: true
+  end
+
   protected
 
   def module_enabled