6 files changed, 52 insertions, 3 deletions
diff --git a/app/mailers/emails/issues.rb b/app/mailers/emails/issues.rb
index 6f54c42146c..d64e48f774b 100644
--- a/app/mailers/emails/issues.rb
+++ b/app/mailers/emails/issues.rb
@@ -6,6 +6,11 @@ module Emails
       mail_new_thread(@issue, issue_thread_options(@issue.author_id, recipient_id))
     end
 
+    def new_mention_in_issue_email(recipient_id, issue_id, updated_by_user_id)
+      setup_issue_mail(issue_id, recipient_id)
+      mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id))
+    end
+
     def reassigned_issue_email(recipient_id, issue_id, previous_assignee_id, updated_by_user_id)
       setup_issue_mail(issue_id, recipient_id)
 
diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index 2d96efe1042..b0ea7c905f8 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -104,11 +104,12 @@ class IssuableBaseService < BaseService
     change_subscription(issuable)
     filter_params
     old_labels = issuable.labels.to_a
+    old_mentioned_users = issuable.mentioned_users.to_a
 
     if params.present? && update_issuable(issuable, params)
       issuable.reset_events_cache
       handle_common_system_notes(issuable, old_labels: old_labels)
-      handle_changes(issuable, old_labels: old_labels)
+      handle_changes(issuable, old_labels: old_labels, old_mentioned_users: old_mentioned_users)
       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 c7d406cc331..a2111b3806b 100644
--- a/app/services/issues/update_service.rb
+++ b/app/services/issues/update_service.rb
@@ -4,7 +4,7 @@ module Issues
       update(issue)
     end
 
-    def handle_changes(issue, old_labels: [])
+    def handle_changes(issue, old_labels: [], old_mentioned_users: [])
       if has_changes?(issue, old_labels: old_labels)
         todo_service.mark_pending_todos_as_done(issue, current_user)
       end
@@ -32,6 +32,11 @@ module Issues
       if added_labels.present?
         notification_service.relabeled_issue(issue, added_labels, current_user)
       end
+
+      added_mentions = issue.mentioned_users - old_mentioned_users
+      if added_mentions.present?
+        notification_service.new_mentions_in_issue(issue, added_mentions, current_user)
+      end
     end
 
     def reopen_service
diff --git a/app/services/notification_service.rb b/app/services/notification_service.rb
index ab6e51209ee..73df572514f 100644
--- a/app/services/notification_service.rb
+++ b/app/services/notification_service.rb
@@ -35,6 +35,20 @@ class NotificationService
     new_resource_email(issue, issue.project, :new_issue_email)
   end
 
+  # When issue text is updated, we should send an email to:
+  #
+  #  * newly mentioned project team members with notification level higher than Participating
+  #
+  def new_mentions_in_issue(issue, new_mentioned_users, current_user)
+    new_mentions_in_resource_email(
+      issue,
+      issue.project,
+      new_mentioned_users,
+      current_user,
+      :new_mention_in_issue_email
+    )
+  end
+
   # When we close an issue we should send an email to:
   #
   #  * issue author if their notification level is not Disabled
@@ -177,7 +191,7 @@ class NotificationService
 
     # build notify method like 'note_commit_email'
     notify_method = "note_#{note.noteable_type.underscore}_email".to_sym
-    
+
     recipients.each do |recipient|
       mailer.send(notify_method, recipient.id, note.id).deliver_later
     end
@@ -471,6 +485,14 @@ class NotificationService
     end
   end
 
+  def new_mentions_in_resource_email(target, project, new_mentioned_users, current_user, method)
+    recipients = build_recipients(target, project, current_user) & new_mentioned_users
+
+    recipients.each do |recipient|
+      mailer.send(method, recipient.id, target.id, current_user.id).deliver_later
+    end
+  end
+
   def close_resource_email(target, project, current_user, method)
     action = method == :merged_merge_request_email ? "merge" : "close"
     recipients = build_recipients(target, project, current_user, action: action)
diff --git a/app/views/notify/new_mention_in_issue_email.html.haml b/app/views/notify/new_mention_in_issue_email.html.haml
new file mode 100644
index 00000000000..f42b150c0d6
--- /dev/null
+++ b/app/views/notify/new_mention_in_issue_email.html.haml
@@ -0,0 +1,9 @@
+- if current_application_settings.email_author_in_body
+  %div
+    #{link_to @issue.author_name, user_url(@issue.author)} wrote:
+-if @issue.description
+  = markdown(@issue.description, pipeline: :email, author: @issue.author)
+
+- if @issue.assignee_id.present?
+  %p
+    Assignee: #{@issue.assignee_name}
diff --git a/app/views/notify/new_mention_in_issue_email.text.erb b/app/views/notify/new_mention_in_issue_email.text.erb
new file mode 100644
index 00000000000..457e94b4800
--- /dev/null
+++ b/app/views/notify/new_mention_in_issue_email.text.erb
@@ -0,0 +1,7 @@
+You have been mentioned in an issue.
+
+Issue <%= @issue.iid %>: <%= url_for(namespace_project_issue_url(@issue.project.namespace, @issue.project, @issue)) %>
+Author:    <%= @issue.author_name %>
+Assignee:  <%= @issue.assignee_name %>
+
+<%= @issue.description %>