Support an alert template field to allow for customization

ee/app/presenters/projects/prometheus/alert_presenter.rb

@@ -3,6 +3,8 @@
 module Projects
   module Prometheus
     class AlertPresenter < Gitlab::View::Presenter::Delegated
+      RESERVED_ANNOTATIONS = %w(gitlab_incident_markdown)
+
       def full_title
         [environment_name, alert_title].compact.join(': ')
       end
@@ -40,6 +42,10 @@ module Projects
         MARKDOWN
       end
 
+      def alert_markdown
+        annotations.find { |annotation| annotation.label == 'gitlab_incident_markdown' }&.value
+      end
+
       private
 
       def alert_title
@@ -64,6 +70,7 @@ module Projects
       def annotation_list
         strong_memoize(:annotation_list) do
           annotations
+            .reject { |annotation| RESERVED_ANNOTATIONS.include?(annotation.label) }
             .map { |annotation| bullet(annotation.label, annotation.value) }
             .join("\n")
         end

ee/app/services/incident_management/create_issue_service.rb

@@ -33,17 +33,23 @@ module IncidentManagement
     end
 
     def issue_description
-      return alert_summary unless issue_template_content
-
       horizontal_line = "\n---\n\n"
 
-      alert_summary + horizontal_line + issue_template_content
+      [
+        alert_summary,
+        alert_markdown,
+        issue_template_content
+      ].compact.join(horizontal_line)
     end
 
     def alert_summary
       alert.issue_summary_markdown
     end
 
+    def alert_markdown
+      alert.alert_markdown
+    end
+
     def alert
       strong_memoize(:alert) do
         Gitlab::Alerting::Alert.new(project: project, payload: params).present

ee/spec/services/incident_management/create_issue_service_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 describe IncidentManagement::CreateIssueService do
-  let(:project) { create(:project, :repository) }
+  set(:project) { create(:project, :repository) }
   let(:service) { described_class.new(project, nil, alert_payload) }
   let(:alert_starts_at) { Time.now }
   let(:alert_title) { 'TITLE' }
@@ -20,7 +20,7 @@ describe IncidentManagement::CreateIssueService do
     Gitlab::Alerting::Alert.new(project: project, payload: alert_payload).present
   end
 
-  let!(:setting) do
+  set(:setting) do
     create(:project_incident_management_setting, project: project)
   end
 
@@ -45,21 +45,16 @@ describe IncidentManagement::CreateIssueService do
       end
     end
 
-    context 'with issue_template_content' do
-      before do
-        create_issue_template('bug', issue_template_content)
-        setting.update!(issue_template_key: 'bug')
-      end
-
+    shared_examples 'GFM template' do
       context 'plain content' do
-        let(:issue_template_content) { 'some content' }
+        let(:template_content) { 'some content' }
 
         it 'creates an issue appending issue template' do
           expect(subject).to include(status: :success)
 
           expect(issue.description).to include(alert_presenter.issue_summary_markdown)
           expect(issue.description).to include(summary_separator)
-          expect(issue.description).to include(issue_template_content)
+          expect(issue.description).to include(template_content)
         end
       end
 
@@ -67,7 +62,7 @@ describe IncidentManagement::CreateIssueService do
         let(:user) { create(:user) }
         let(:plain_text) { 'some content' }
 
-        let(:issue_template_content) do
+        let(:template_content) do
           <<~CONTENT
             #{plain_text}
             /due tomorrow
@@ -87,6 +82,40 @@ describe IncidentManagement::CreateIssueService do
           expect(issue.assignees).to eq([user])
         end
       end
+    end
+
+    context 'with gitlab_incident_markdown' do
+      let(:alert_annotations) do
+        { title: alert_title, gitlab_incident_markdown: template_content }
+      end
+
+      it_behaves_like 'GFM template'
+    end
+
+    context 'with issue_template_content' do
+      before do
+        create_issue_template('bug', template_content)
+        setting.update!(issue_template_key: 'bug')
+      end
+
+      it_behaves_like 'GFM template'
+
+      context 'and gitlab_incident_markdown' do
+        let(:template_content) { 'plain text'}
+        let(:alt_template) { 'alernate text' }
+        let(:alert_annotations) do
+          { title: alert_title, gitlab_incident_markdown: alt_template }
+        end
+
+        it 'includes both templates' do
+          expect(subject).to include(status: :success)
+
+          expect(issue.description).to include(alert_presenter.issue_summary_markdown)
+          expect(issue.description).to include(template_content)
+          expect(issue.description).to include(alt_template)
+          expect(issue.description.count(summary_separator)).to eq(2)
+        end
+      end
 
       private