4 files changed, 37 insertions, 3 deletions
diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index 2556f06e2d3..63025c10fb0 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -54,7 +54,7 @@ class IssuableBaseService < BaseService
     if params.present? && issuable.update_attributes(params.merge(updated_by: current_user))
       issuable.reset_events_cache
       handle_common_system_notes(issuable, old_labels: old_labels)
-      handle_changes(issuable)
+      handle_changes(issuable, old_labels: old_labels)
       issuable.create_new_cross_references!(current_user)
       execute_hooks(issuable, 'update')
     end
diff --git a/app/services/issues/update_service.rb b/app/services/issues/update_service.rb
index e6afcb91652..fb9571247cc 100644
--- a/app/services/issues/update_service.rb
+++ b/app/services/issues/update_service.rb
@@ -4,7 +4,11 @@ module Issues
       update(issue)
     end
 
-    def handle_changes(issue)
+    def handle_changes(issue, options = {})
+      if have_changes?(issue, options)
+        task_service.mark_as_done(issue, current_user)
+      end
+
       if issue.previous_changes.include?('milestone_id')
         create_milestone_note(issue)
       end
@@ -23,5 +27,22 @@ module Issues
     def close_service
       Issues::CloseService
     end
+
+    private
+
+    def have_changes?(issue, options = {})
+      valid_attrs = [:title, :description, :assignee_id, :milestone_id]
+
+      attrs_changed = valid_attrs.any? do |attr|
+        issue.previous_changes.include?(attr.to_s)
+      end
+
+      old_labels = options[:old_labels]
+      labels_changed = old_labels && issue.labels != old_labels
+
+      if attrs_changed || labels_changed
+        task_service.mark_as_done(issue, current_user)
+      end
+    end
   end
 end
diff --git a/app/services/merge_requests/update_service.rb b/app/services/merge_requests/update_service.rb
index 5ff2cc03dda..55322bf47bb 100644
--- a/app/services/merge_requests/update_service.rb
+++ b/app/services/merge_requests/update_service.rb
@@ -14,7 +14,7 @@ module MergeRequests
       update(merge_request)
     end
 
-    def handle_changes(merge_request)
+    def handle_changes(merge_request, options = {})
       if merge_request.previous_changes.include?('target_branch')
         create_branch_change_note(merge_request, 'target',
                                   merge_request.previous_changes['target_branch'].first,
diff --git a/app/services/task_service.rb b/app/services/task_service.rb
index 35d258a70c2..2c312331ae9 100644
--- a/app/services/task_service.rb
+++ b/app/services/task_service.rb
@@ -26,6 +26,15 @@ class TaskService
     end
   end
 
+  # When we mark a task as done we should:
+  #
+  #  * mark all pending tasks related to the target for the user as done
+  #
+  def mark_as_done(target, user)
+    pending_tasks = pending_tasks_for(user, target.project, target)
+    pending_tasks.update_all(state: :done)
+  end
+
   private
 
   def create_task(project, target, author, user, action)
@@ -40,4 +49,8 @@ class TaskService
 
     Task.create(attributes)
   end
+
+  def pending_tasks_for(user, project, target)
+    user.tasks.pending.where(project: project, target: target)
+  end
 end