Notify with email when merge request became unmergeable

Display MR unmergeable reasons

7 files changed, 82 insertions, 0 deletions

diff --git a/app/mailers/emails/merge_requests.rb b/app/mailers/emails/merge_requests.rb
index b3f2aeb08ca..c2333180663 100644
--- a/app/mailers/emails/merge_requests.rb
+++ b/app/mailers/emails/merge_requests.rb
@@ -56,6 +56,14 @@ module Emails
       mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id, reason))
     end
 
+    def merge_request_unmergeable_email(recipient_id, merge_request_id, reason = nil)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+
+      @merge_request_presenter = MergeRequestPresenter.new(@merge_request, current_user: current_user)
+
+      mail_answer_thread(@merge_request, merge_request_thread_options(@merge_request.author_id, recipient_id, reason))
+    end
+
     def resolved_all_discussions_email(recipient_id, merge_request_id, resolved_by_user_id, reason = nil)
       setup_merge_request_mail(merge_request_id, recipient_id)
 
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index dd4daf3711b..99687d305e7 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -125,6 +125,10 @@ class MergeRequest < ActiveRecord::Base
       Gitlab::Timeless.timeless(merge_request, &block)
     end
 
+    after_transition unchecked: :cannot_be_merged do |merge_request, transition|
+      NotificationService.new.merge_request_unmergeable(merge_request)
+    end
+
     def check_state?(merge_status)
       [:unchecked, :cannot_be_merged_recheck].include?(merge_status.to_sym)
     end
diff --git a/app/presenters/merge_request_presenter.rb b/app/presenters/merge_request_presenter.rb
index 4b4132af2d0..ad839d9840a 100644
--- a/app/presenters/merge_request_presenter.rb
+++ b/app/presenters/merge_request_presenter.rb
@@ -20,6 +20,17 @@ class MergeRequestPresenter < Gitlab::View::Presenter::Delegated
     end
   end
 
+  def unmergeable_reasons
+    strong_memoize(:unmergeable_reasons) do
+      reasons = []
+      reasons << "no commits" if merge_request.has_no_commits?
+      reasons << "source branch is missing" unless merge_request.source_branch_exists?
+      reasons << "target branch is missing" unless merge_request.target_branch_exists?
+      reasons << "has merge conflicts" unless merge_request.project.repository.can_be_merged?(merge_request.diff_head_sha, merge_request.target_branch)
+      reasons
+    end
+  end
+
   def cancel_merge_when_pipeline_succeeds_path
     if can_cancel_merge_when_pipeline_succeeds?(current_user)
       cancel_merge_when_pipeline_succeeds_project_merge_request_path(project, merge_request)
diff --git a/app/services/notification_recipient_service.rb b/app/services/notification_recipient_service.rb
index 5658699664d..4fa38665abc 100644
--- a/app/services/notification_recipient_service.rb
+++ b/app/services/notification_recipient_service.rb
@@ -18,6 +18,10 @@ module NotificationRecipientService
     Builder::NewNote.new(*a).notification_recipients
   end
 
+  def self.build_merge_request_unmergeable_recipients(*a)
+    Builder::MergeRequestUnmergeable.new(*a).notification_recipients
+  end
+
   module Builder
     class Base
       def initialize(*)
@@ -330,5 +334,26 @@ module NotificationRecipientService
         note.author
       end
     end
+
+    class MergeRequestUnmergeable < Base
+      attr_reader :target
+      def initialize(merge_request)
+        @target = merge_request
+      end
+
+      def build!
+        target.merge_participants.each do |user|
+          add_recipients(user, :participating, nil)
+        end
+      end
+
+      def custom_action
+        :unmergeable_merge_request
+      end
+
+      def acting_user
+        nil
+      end
+    end
   end
 end
diff --git a/app/services/notification_service.rb b/app/services/notification_service.rb
index 8b3ddab5e19..636cfbf5b45 100644
--- a/app/services/notification_service.rb
+++ b/app/services/notification_service.rb
@@ -149,6 +149,15 @@ class NotificationService
     end
   end
 
+  # When a merge request is found to be unmergeable, we should send an email to:
+  #
+  #  * mr author
+  #  * mr merge user if set
+  #
+  def merge_request_unmergeable(merge_request)
+    merge_request_unmergeable_email(merge_request)
+  end
+
   # When merge request text is updated, we should send an email to:
   #
   #  * newly mentioned project team members with notification level higher than Participating
@@ -485,6 +494,14 @@ class NotificationService
     end
   end
 
+  def merge_request_unmergeable_email(merge_request)
+    recipients = NotificationRecipientService.build_merge_request_unmergeable_recipients(merge_request)
+
+    recipients.each do |recipient|
+      mailer.merge_request_unmergeable_email(recipient.user.id, merge_request.id).deliver_later
+    end
+  end
+
   def mailer
     Notify
   end
diff --git a/app/views/notify/merge_request_unmergeable_email.html.haml b/app/views/notify/merge_request_unmergeable_email.html.haml
new file mode 100644
index 00000000000..f51a31c0eda
--- /dev/null
+++ b/app/views/notify/merge_request_unmergeable_email.html.haml
@@ -0,0 +1,6 @@
+%p
+  Merge Request #{link_to @merge_request.to_reference, project_merge_request_url(@merge_request.target_project, @merge_request)} can no longer be merged due to the following reason(s):
+
+  %ul
+    - @merge_request_presenter.unmergeable_reasons.each do |reason|
+      %li= reason
diff --git a/app/views/notify/merge_request_unmergeable_email.text.haml b/app/views/notify/merge_request_unmergeable_email.text.haml
new file mode 100644
index 00000000000..2acf0de34fc
--- /dev/null
+++ b/app/views/notify/merge_request_unmergeable_email.text.haml
@@ -0,0 +1,11 @@
+Merge Request #{@merge_request.to_reference} can no longer be merged due to the following reason(s):
+
+- @merge_request_presenter.unmergeable_reasons.each do |reason|
+  * #{reason}
+
+Merge Request url: #{project_merge_request_url(@merge_request.target_project, @merge_request)}
+
+= merge_path_description(@merge_request, 'to')
+
+Author: #{@merge_request.author_name}
+Assignee: #{@merge_request.assignee_name}