Merge branch '18757-fix' into 'master'

Fallback to group's owners/masters when a project has none for the "access requested email"

## What does this MR do?

From b31c5052:

    Fallback to group's owners/masters when a project has none
    
    A project in a group can have no explicit owners/masters,
    in that case we fallbacks to the group's owners/masters.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

Because of #18757.

## What are the relevant issue numbers?

Fixes #18757.

## Does this MR meet the acceptance criteria?

- [x] No need for CHANGELOG.
- [x] No need for documentation.
- [x] No API support added.
- [x] Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4791

app/mailers/emails/members.rb

@@ -12,6 +12,11 @@ module Emails
       @member_id = member_id
 
       admins = member_source.members.owners_and_masters.includes(:user).pluck(:notification_email)
+      # A project in a group can have no explicit owners/masters, in that case
+      # we fallbacks to the group's owners/masters.
+      if admins.empty? && member_source.respond_to?(:group) && member_source.group
+        admins = member_source.group.members.owners_and_masters.includes(:user).pluck(:notification_email)
+      end
 
       mail(to: admins,
            subject: subject("Request to join the #{member_source.human_name} #{member_source.model_name.singular}"))

spec/mailers/notify_spec.rb

@@ -401,7 +401,8 @@ describe Notify do
     end
 
     describe 'project access requested' do
-      let(:project) { create(:project) }
+      context 'for a project in a user namespace' do
+        let(:project) { create(:project).tap { |p| p.team << [p.owner, :master, p.owner] } }
         let(:user) { create(:user) }
         let(:project_member) do
           project.request_access(user)
@@ -414,6 +415,10 @@ describe Notify do
         it_behaves_like "a user cannot unsubscribe through footer link"
 
         it 'contains all the useful information' do
+          to_emails = subject.header[:to].addrs
+          expect(to_emails.size).to eq(1)
+          expect(to_emails[0].address).to eq(project.members.owners_and_masters.first.user.notification_email)
+
           is_expected.to have_subject "Request to join the #{project.name_with_namespace} project"
           is_expected.to have_body_text /#{project.name_with_namespace}/
           is_expected.to have_body_text /#{namespace_project_project_members_url(project.namespace, project)}/
@@ -421,6 +426,34 @@ describe Notify do
         end
       end
 
+      context 'for a project in a group' do
+        let(:group_owner) { create(:user) }
+        let(:group) { create(:group).tap { |g| g.add_owner(group_owner) } }
+        let(:project) { create(:project, namespace: group) }
+        let(:user) { create(:user) }
+        let(:project_member) do
+          project.request_access(user)
+          project.members.request.find_by(user_id: user.id)
+        end
+        subject { Notify.member_access_requested_email('project', project_member.id) }
+
+        it_behaves_like 'an email sent from GitLab'
+        it_behaves_like 'it should not have Gmail Actions links'
+        it_behaves_like "a user cannot unsubscribe through footer link"
+
+        it 'contains all the useful information' do
+          to_emails = subject.header[:to].addrs
+          expect(to_emails.size).to eq(1)
+          expect(to_emails[0].address).to eq(group.members.owners_and_masters.first.user.notification_email)
+
+          is_expected.to have_subject "Request to join the #{project.name_with_namespace} project"
+          is_expected.to have_body_text /#{project.name_with_namespace}/
+          is_expected.to have_body_text /#{namespace_project_project_members_url(project.namespace, project)}/
+          is_expected.to have_body_text /#{project_member.human_access}/
+        end
+      end
+    end
+
     describe 'project access denied' do
       let(:project) { create(:project) }
       let(:user) { create(:user) }