Merge branch '2451-fix-mentions-in-issue-updates' into 'master'

Send notification emails when users are newly mentioned in issue or MR edits

## What does this MR do?

Introduces "new mention in issue" and "new mention in MR" email notifications.  Editing a Mentionable title or description and adding a mention to a user who was not previously mentioned will now send them a notification email, following usual permissions for doing so.

## Why was this MR needed?

Issues & MRs may be edited to include mentions to new people. We don't currently send out email notifications of these edits to anyone, although they do create TODOs. This brings email notifications into parity with TODOs.

## What are the relevant issue numbers?

Closes #2451

See merge request !5800

10 files changed, 109 insertions, 4 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/mailers/emails/merge_requests.rb b/app/mailers/emails/merge_requests.rb
index 9dd11d20ea6..95810b0ac6e 100644
--- a/app/mailers/emails/merge_requests.rb
+++ b/app/mailers/emails/merge_requests.rb
@@ -6,6 +6,11 @@ module Emails
       mail_new_thread(@merge_request, merge_request_thread_options(@merge_request.author_id, recipient_id))
     end
 
+    def new_mention_in_merge_request_email(recipient_id, merge_request_id, updated_by_user_id)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+      mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id))
+    end
+
     def reassigned_merge_request_email(recipient_id, merge_request_id, previous_assignee_id, updated_by_user_id)
       setup_merge_request_mail(merge_request_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/merge_requests/update_service.rb b/app/services/merge_requests/update_service.rb
index 026a37997d4..30c5f24988c 100644
--- a/app/services/merge_requests/update_service.rb
+++ b/app/services/merge_requests/update_service.rb
@@ -16,7 +16,7 @@ module MergeRequests
       update(merge_request)
     end
 
-    def handle_changes(merge_request, old_labels: [])
+    def handle_changes(merge_request, old_labels: [], old_mentioned_users: [])
       if has_changes?(merge_request, old_labels: old_labels)
         todo_service.mark_pending_todos_as_done(merge_request, current_user)
       end
@@ -55,6 +55,15 @@ module MergeRequests
           current_user
         )
       end
+
+      added_mentions = merge_request.mentioned_users - old_mentioned_users
+      if added_mentions.present?
+        notification_service.new_mentions_in_merge_request(
+          merge_request,
+          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..2291bc0f127 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
@@ -75,6 +89,20 @@ class NotificationService
     new_resource_email(merge_request, merge_request.target_project, :new_merge_request_email)
   end
 
+  # When merge request text is updated, we should send an email to:
+  #
+  #  * newly mentioned project team members with notification level higher than Participating
+  #
+  def new_mentions_in_merge_request(merge_request, new_mentioned_users, current_user)
+    new_mentions_in_resource_email(
+      merge_request,
+      merge_request.target_project,
+      new_mentioned_users,
+      current_user,
+      :new_mention_in_merge_request_email
+    )
+  end
+
   # When we reassign a merge_request we should send an email to:
   #
   #  * merge_request old assignee if their notification level is not Disabled
@@ -177,7 +205,7 @@ 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 +499,15 @@ 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, action: "new")
+    recipients = recipients & 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..4f3d36bd9ca
--- /dev/null
+++ b/app/views/notify/new_mention_in_issue_email.html.haml
@@ -0,0 +1,12 @@
+%p
+  You have been mentioned in an issue.
+
+- 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 %>
diff --git a/app/views/notify/new_mention_in_merge_request_email.html.haml b/app/views/notify/new_mention_in_merge_request_email.html.haml
new file mode 100644
index 00000000000..32aedb9e6b9
--- /dev/null
+++ b/app/views/notify/new_mention_in_merge_request_email.html.haml
@@ -0,0 +1,15 @@
+%p
+  You have been mentioned in Merge Request #{@merge_request.to_reference}
+
+- if current_application_settings.email_author_in_body
+  %div
+    #{link_to @merge_request.author_name, user_url(@merge_request.author)} wrote:
+%p.details
+  != merge_path_description(@merge_request, '&rarr;')
+
+- if @merge_request.assignee_id.present?
+  %p
+    Assignee: #{@merge_request.author_name} &rarr; #{@merge_request.assignee_name}
+
+-if @merge_request.description
+  = markdown(@merge_request.description, pipeline: :email, author: @merge_request.author)
diff --git a/app/views/notify/new_mention_in_merge_request_email.text.erb b/app/views/notify/new_mention_in_merge_request_email.text.erb
new file mode 100644
index 00000000000..5bf0282e097
--- /dev/null
+++ b/app/views/notify/new_mention_in_merge_request_email.text.erb
@@ -0,0 +1,9 @@
+You have been mentioned in Merge Request <%= @merge_request.to_reference %>
+
+<%= url_for(namespace_project_merge_request_url(@merge_request.target_project.namespace, @merge_request.target_project, @merge_request)) %>
+
+<%= merge_path_description(@merge_request, 'to') %>
+Author:    <%= @merge_request.author_name %>
+Assignee:  <%= @merge_request.assignee_name %>
+
+<%= @merge_request.description %>