Send email to recipients

app/mailers/emails/issues.rb

@@ -6,6 +6,12 @@ module Emails
       mail_new_thread(@issue, issue_thread_options(@issue.author_id, recipient_id, reason))
     end
 
+    def issue_due_email(recipient_id, issue_id, reason = nil)
+      setup_issue_mail(issue_id, recipient_id)
+
+      mail_new_thread(@issue, issue_thread_options(@issue.author_id, recipient_id, reason))
+    end
+
     def new_mention_in_issue_email(recipient_id, issue_id, updated_by_user_id, reason = nil)
       setup_issue_mail(issue_id, recipient_id)
       mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id, reason))

app/services/notification_recipient_service.rb

@@ -230,14 +230,20 @@ module NotificationRecipientService
 
         add_subscribed_users
 
-        if [:new_issue, :new_merge_request].include?(custom_action)
+        if [:new_issue, :new_merge_request, :due_date_issue].include?(custom_action)
           # These will all be participants as well, but adding with the :mention
           # type ensures that users with the mention notification level will
           # receive them, too.
           add_mentions(current_user, target: target)
 
           # Add the assigned users, if any
-          assignees = custom_action == :new_issue ? target.assignees : target.assignee
+          assignees = case custom_action
+                      when :new_issue, :due_date_issue
+                        target.assignees
+                      else
+                        target.assignee
+                      end
+
           # We use the `:participating` notification level in order to match existing legacy behavior as captured
           # in existing specs (notification_service_spec.rb ~ line 507)
           add_recipients(assignees, :participating, NotificationReason::ASSIGNED) if assignees

app/services/notification_service.rb

@@ -363,6 +363,19 @@ class NotificationService
     end
   end
 
+  def issue_due_email(issue)
+    recipients = NotificationRecipientService.build_recipients(
+      issue,
+      issue.author,
+      action: "due_date",
+      skip_current_user: false,
+    )
+
+    recipients.each do |recipient|
+      mailer.send(:issue_due_email, recipient.user.id, issue.id, recipient.reason).deliver_later
+    end
+  end
+
   protected
 
   def new_resource_email(target, method)

app/views/notify/issue_due_email.html.haml

+- if Gitlab::CurrentSettings.email_author_in_body
+  %p.details
+    #{link_to @issue.author_name, user_url(@issue.author)} updated the issue's due date:
+
+- if @issue.assignees.any?
+  %p
+    Assignee: #{@issue.assignee_list}
+
+%p
+  This Issue has a new due date: #{ @issue.due_date }
+
+- if @issue.description
+  %div
+  = markdown(@issue.description, pipeline: :email, author: @issue.author)

app/views/notify/issue_due_email.text.erb

+An Issue had its due date updated.
+
+Issue <%= @issue.iid %>: <%= url_for(project_issue_url(@issue.project, @issue)) %>
+Author:    <%= @issue.author_name %>
+Assignee:  <%= @issue.assignee_list %>
+New Due Date: <%= @issue.due_date %>
+
+<%= @issue.description %>

app/workers/issue_due_worker.rb

@@ -3,9 +3,8 @@ class IssueDueWorker
 
   def perform(issue_id)
     issue = Issue.find_by_id(issue_id)
-    # How do we want to deal with noops?
     if issue.due_date == Date.today
-      # execute
+      NotificationService.new.issue_due_email(issue)
     end
   end
 end