Display custom service desk email

When a custom service desk email is set, prefer this address
on the service desk issues page.

app/controllers/projects_controller.rb

@@ -38,6 +38,9 @@ class ProjectsController < Projects::ApplicationController
   before_action only: [:new, :create] do
     frontend_experimentation_tracking_data(:new_create_project_ui, 'click_tab')
     push_frontend_feature_flag(:new_create_project_ui) if experiment_enabled?(:new_create_project_ui)
+  end
+
+  before_action only: [:edit] do
     push_frontend_feature_flag(:service_desk_custom_address, @project)
   end
 

app/models/project.rb

@@ -2468,6 +2468,10 @@ class Project < ApplicationRecord
   alias_method :service_desk_enabled?, :service_desk_enabled
 
   def service_desk_address
+    service_desk_custom_address || service_desk_incoming_address
+  end
+
+  def service_desk_incoming_address
     return unless service_desk_enabled?
 
     config = Gitlab.config.incoming_email
@@ -2476,6 +2480,16 @@ class Project < ApplicationRecord
     config.address&.gsub(wildcard, "#{full_path_slug}-#{id}-issue-")
   end
 
+  def service_desk_custom_address
+    return unless ::Gitlab::ServiceDeskEmail.enabled?
+    return unless ::Feature.enabled?(:service_desk_custom_address, self)
+
+    key = service_desk_setting&.project_key
+    return unless key.present?
+
+    ::Gitlab::ServiceDeskEmail.address_for_key("#{full_path_slug}-#{key}")
+  end
+
   def root_namespace
     if namespace.has_parent?
       namespace.root_ancestor

app/services/service_desk_settings/update_service.rb

@@ -9,6 +9,8 @@ module ServiceDeskSettings
         params.delete(:project_key)
       end
 
+      params[:project_key] = nil if params[:project_key].blank?
+
       if settings.update(params)
         success
       else

app/views/projects/_service_desk_settings.html.haml

@@ -10,7 +10,8 @@
     - if ::Gitlab::ServiceDesk.supported?
       .js-service-desk-setting-root{ data: { endpoint: project_service_desk_path(@project),
         enabled: "#{@project.service_desk_enabled}",
-        incoming_email: (@project.service_desk_address if @project.service_desk_enabled),
+        incoming_email: (@project.service_desk_incoming_address if @project.service_desk_enabled),
+        custom_email: (@project.service_desk_custom_address if @project.service_desk_enabled),
         selected_template: "#{@project.service_desk_setting&.issue_template_key}",
         outgoing_name: "#{@project.service_desk_setting&.outgoing_name}",
         project_key: "#{@project.service_desk_setting&.project_key}",

lib/gitlab/service_desk_email.rb

@@ -17,6 +17,12 @@ module Gitlab
       def config
         Gitlab.config.service_desk_email
       end
+
+      def address_for_key(key)
+        return if config.address.blank?
+
+        config.address.sub(Gitlab::IncomingEmail::WILDCARD_PLACEHOLDER, key)
+      end
     end
   end
 end

spec/lib/gitlab/service_desk_email_spec.rb

@@ -56,4 +56,26 @@ RSpec.describe Gitlab::ServiceDeskEmail do
       end
     end
   end
+
+  describe '.address_for_key' do
+    context 'when service desk address is set' do
+      before do
+        stub_service_desk_email_setting(address: 'address+%{key}@example.com')
+      end
+
+      it 'returns address' do
+        expect(described_class.address_for_key('foo')).to eq('address+foo@example.com')
+      end
+    end
+
+    context 'when service desk address is not set' do
+      before do
+        stub_service_desk_email_setting(address: nil)
+      end
+
+      it 'returns nil' do
+        expect(described_class.key_from_address('foo')).to be_nil
+      end
+    end
+  end
 end

spec/models/project_spec.rb

@@ -1449,12 +1449,15 @@ RSpec.describe Project do
   end
 
   describe '#service_desk_address' do
-    let_it_be(:project) { create(:project, service_desk_enabled: true) }
+    let_it_be(:project, reload: true) { create(:project, service_desk_enabled: true) }
 
+    subject { project.service_desk_address }
+
+    shared_examples 'with incoming email address' do
+      context 'when incoming email is enabled' do
         before do
-      allow(Gitlab::ServiceDesk).to receive(:enabled?).and_return(true)
-      allow(Gitlab.config.incoming_email).to receive(:enabled).and_return(true)
-      allow(Gitlab.config.incoming_email).to receive(:address).and_return("test+%{key}@mail.com")
+          config = double(enabled: true, address: 'test+%{key}@mail.com')
+          allow(::Gitlab.config).to receive(:incoming_email).and_return(config)
         end
 
         it 'uses project full path as service desk address key' do
@@ -1462,6 +1465,56 @@ RSpec.describe Project do
         end
       end
 
+      context 'when incoming email is disabled' do
+        before do
+          config = double(enabled: false)
+          allow(::Gitlab.config).to receive(:incoming_email).and_return(config)
+        end
+
+        it 'uses project full path as service desk address key' do
+          expect(project.service_desk_address).to be_nil
+        end
+      end
+    end
+
+    context 'when service_desk_email is disabled' do
+      before do
+        allow(::Gitlab::ServiceDeskEmail).to receive(:enabled?).and_return(false)
+      end
+
+      it_behaves_like 'with incoming email address'
+    end
+
+    context 'when service_desk_email is enabled' do
+      before do
+        config = double(enabled: true, address: 'foo+%{key}@bar.com')
+        allow(::Gitlab::ServiceDeskEmail).to receive(:config).and_return(config)
+      end
+
+      context 'when service_desk_custom_address flag is enabled' do
+        before do
+          stub_feature_flags(service_desk_custom_address: true)
+        end
+
+        it 'returns custom address when project_key is set' do
+          create(:service_desk_setting, project: project, project_key: 'key1')
+
+          expect(subject).to eq("foo+#{project.full_path_slug}-key1@bar.com")
+        end
+
+        it_behaves_like 'with incoming email address'
+      end
+
+      context 'when service_desk_custom_address flag is disabled' do
+        before do
+          stub_feature_flags(service_desk_custom_address: false)
+        end
+
+        it_behaves_like 'with incoming email address'
+      end
+    end
+  end
+
   describe '.find_by_service_desk_project_key' do
     it 'returns the correct project' do
       project1 = create(:project)

spec/services/service_desk_settings/update_service_spec.rb

@@ -31,6 +31,17 @@ RSpec.describe ServiceDeskSettings::UpdateService do
       end
     end
 
+    context 'when project_key is an empty string' do
+      let(:params) { { project_key: '' } }
+
+      it 'sets nil project_key' do
+        result = described_class.new(settings.project, user, params).execute
+
+        expect(result[:status]).to eq :success
+        expect(settings.reload.project_key).to be_nil
+      end
+    end
+
     context 'with invalid params' do
       let(:params) { { outgoing_name: 'x' * 256 } }