Add email notification for milestone changes

app/mailers/emails/issues.rb

@@ -45,6 +45,20 @@ module Emails
       mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id, reason))
     end
+    def removed_milestone_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))
+    end
+
+    def changed_milestone_issue_email(recipient_id, issue_id, milestone, updated_by_user_id, reason = nil)
+      setup_issue_mail(issue_id, recipient_id)
+
+      @milestone = milestone
+      @milestone_url = milestone_url(@milestone)
+      mail_answer_thread(@issue, issue_thread_options(updated_by_user_id, recipient_id, reason))
+    end
+
     def issue_status_changed_email(recipient_id, issue_id, status, updated_by_user_id, reason = nil)
       setup_issue_mail(issue_id, recipient_id)

app/mailers/emails/merge_requests.rb

@@ -40,6 +40,20 @@ module Emails
       mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
     end
+    def removed_milestone_merge_request_email(recipient_id, merge_request_id, updated_by_user_id, reason = nil)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+
+      mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
+    end
+
+    def changed_milestone_merge_request_email(recipient_id, merge_request_id, milestone, updated_by_user_id, reason = nil)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+
+      @milestone = milestone
+      @milestone_url = milestone_url(@milestone)
+      mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
+    end
+
     def closed_merge_request_email(recipient_id, merge_request_id, updated_by_user_id, reason = nil)
       setup_merge_request_mail(merge_request_id, recipient_id)

app/services/issues/update_service.rb

@@ -48,6 +48,8 @@ module Issues
         notification_service.async.relabeled_issue(issue, added_labels, current_user)
       end
+      handle_milestone_change(issue)
+
       added_mentions = issue.mentioned_users - old_mentioned_users
       if added_mentions.present?
@@ -91,6 +93,16 @@ module Issues
     private
+    def handle_milestone_change(issue)
+      if issue.previous_changes.include?('milestone_id')
+        if issue.milestone.nil?
+          notification_service.async.removed_milestone_issue(issue, current_user)
+        else
+          notification_service.async.changed_milestone_issue(issue, issue.milestone, current_user)
+        end
+      end
+    end
+
     # rubocop: disable CodeReuse/ActiveRecord
     def get_issue_if_allowed(id, board_group_id = nil)
       return unless id

app/services/merge_requests/update_service.rb

@@ -58,6 +58,8 @@ module MergeRequests
         merge_request.mark_as_unchecked
       end
+      handle_milestone_change(merge_request)
+
       added_labels = merge_request.labels - old_labels
       if added_labels.present?
         notification_service.async.relabeled_merge_request(
@@ -105,6 +107,16 @@ module MergeRequests
     private
+    def handle_milestone_change(merge_request)
+      if merge_request.previous_changes.include?('milestone_id')
+        if merge_request.milestone.nil?
+          notification_service.async.removed_milestone_merge_request(merge_request, current_user)
+        else
+          notification_service.async.changed_milestone_merge_request(merge_request, merge_request.milestone, current_user)
+        end
+      end
+    end
+
     def create_branch_change_note(issuable, branch_type, old_branch, new_branch)
       SystemNoteService.change_branch(
         issuable, issuable.project, current_user, branch_type,

app/services/notification_service.rb

@@ -129,6 +129,14 @@ class NotificationService
     relabeled_resource_email(issue, added_labels, current_user, :relabeled_issue_email)
   end
+  def removed_milestone_issue(issue, current_user)
+    removed_milestone_resource_email(issue, current_user, :removed_milestone_issue_email)
+  end
+
+  def changed_milestone_issue(issue, new_milestone, current_user)
+    changed_milestone_resource_email(issue, new_milestone, current_user, :changed_milestone_issue_email)
+  end
+
   # When create a merge request we should send an email to:
   #
   #  * mr author
@@ -138,7 +146,7 @@ class NotificationService
   #  * users with custom level checked with "new merge request"
   #
   # In EE, approvers of the merge request are also included
-  #
+
   def new_merge_request(merge_request, current_user)
     new_resource_email(merge_request, :new_merge_request_email)
   end
@@ -208,6 +216,14 @@ class NotificationService
     relabeled_resource_email(merge_request, added_labels, current_user, :relabeled_merge_request_email)
   end
+  def removed_milestone_merge_request(merge_request, current_user)
+    removed_milestone_resource_email(merge_request, current_user, :removed_milestone_merge_request_email)
+  end
+
+  def changed_milestone_merge_request(merge_request, new_milestone, current_user)
+    changed_milestone_resource_email(merge_request, new_milestone, current_user, :changed_milestone_merge_request_email)
+  end
+
   def close_mr(merge_request, current_user)
     close_resource_email(merge_request, current_user, :closed_merge_request_email)
   end
@@ -500,6 +516,30 @@ class NotificationService
     end
   end
+  def removed_milestone_resource_email(target, current_user, method)
+    recipients = NotificationRecipientService.build_recipients(
+      target,
+      current_user,
+      action: 'removed_milestone'
+    )
+
+    recipients.each do |recipient|
+      mailer.send(method, recipient.user.id, target.id, current_user.id).deliver_later
+    end
+  end
+
+  def changed_milestone_resource_email(target, milestone, current_user, method)
+    recipients = NotificationRecipientService.build_recipients(
+      target,
+      current_user,
+      action: 'changed_milestone'
+    )
+
+    recipients.each do |recipient|
+      mailer.send(method, recipient.user.id, target.id, milestone, current_user.id).deliver_later
+    end
+  end
+
   def reopen_resource_email(target, current_user, method, status)
     recipients = NotificationRecipientService.build_recipients(target, current_user, action: "reopen")

app/views/notify/_changed_milestone_issue_email.html.haml

+%p
+  #{'Milestone'} changed to
+  %strong= link_to(@milestone.name, @milestone_url)

app/views/notify/_changed_milestone_issue_email.text.erb

+Milestone changed to <%= @milestone.name %> ( <%= @milestone_url %> )

app/views/notify/_changed_milestone_merge_request_email.html.haml

+%p
+  #{'Milestone'} changed to
+  %strong= link_to(@milestone.name, @milestone_url)

app/views/notify/_changed_milestone_merge_request_email.text.erb

+Milestone changed to <%= @milestone.name %> ( <%= @milestone_url %> )

app/views/notify/_removed_milestone_issue_email.html.haml

+%p
+  #{'Milestone'} removed

app/views/notify/_removed_milestone_issue_email.text.erb

+Milestone removed

app/views/notify/_removed_milestone_merge_request_email.html.haml

+%p
+  #{'Milestone'} removed

app/views/notify/_removed_milestone_merge_request_email.text.erb

+Milestone removed

app/views/notify/changed_milestone_issue_email.html.haml

+= render 'changed_milestone_issue_email', issuable: @issue

app/views/notify/changed_milestone_issue_email.text.erb

+<%= render 'changed_milestone_issue_email', issuable: @issue %>

app/views/notify/changed_milestone_merge_request_email.html.haml

+= render 'changed_milestone_merge_request_email', issuable: @merge_request

app/views/notify/changed_milestone_merge_request_email.text.erb

+<%= render 'changed_milestone_merge_request_email', issuable: @merge_request %>

app/views/notify/removed_milestone_issue_email.html.haml

+= render 'removed_milestone_issue_email', issuable: @issue

app/views/notify/removed_milestone_issue_email.text.erb

+<%= render 'removed_milestone_issue_email', issuable: @issue %>

app/views/notify/removed_milestone_merge_request_email.html.haml

+= render 'removed_milestone_merge_request_email', issuable: @merge_request