Loosen Danger requirements for security MRs

Security MRs in the `gitlab-org/security` group don't require merge
request IDs for changelog entries, nor do they have strict target branch
requirements.

danger/changelog/Dangerfile

@@ -26,7 +26,7 @@ def check_changelog(path)
   fail "`title` should be set, in #{gitlab.html_link(path)}! #{SEE_DOC}" if yaml["title"].nil?
   fail "`type` should be set, in #{gitlab.html_link(path)}! #{SEE_DOC}" if yaml["type"].nil?
 
-  if yaml["merge_request"].nil?
+  if yaml["merge_request"].nil? && !helper.security_mr?
     message "Consider setting `merge_request` to #{gitlab.mr_json["iid"]} in #{gitlab.html_link(path)}. #{SEE_DOC}"
   elsif yaml["merge_request"] != gitlab.mr_json["iid"] && !changelog.ce_port_changelog?(path)
     fail "Merge request ID was not set to #{gitlab.mr_json["iid"]}! #{SEE_DOC}"

danger/metadata/Dangerfile

@@ -32,7 +32,7 @@ end
 
 has_pick_into_stable_label = gitlab.mr_labels.find { |label| label.start_with?('Pick into') }
 
-if gitlab.branch_for_base != "master" && !has_pick_into_stable_label
+if gitlab.branch_for_base != "master" && !has_pick_into_stable_label && !helper.security_mr?
   warn "Most of the time, merge requests should target `master`. Otherwise, please set the relevant `Pick into X.Y` label."
 end
 

lib/gitlab/danger/helper.rb

@@ -174,6 +174,12 @@ module Gitlab
         labels - current_mr_labels
       end
 
+      def security_mr?
+        return false unless gitlab_helper
+
+        gitlab_helper.mr_json['web_url'].include?('/gitlab-org/security/')
+      end
+
       private
 
       def has_database_scoped_labels?(current_mr_labels)

spec/lib/gitlab/danger/changelog_spec.rb

@@ -34,6 +34,7 @@ describe Gitlab::Danger::Changelog do
       { docs: nil, none: nil }
     ].each do |categories|
       let(:changes_by_category) { categories }
+
       it "is falsy when categories don't require a changelog" do
         is_expected.to be_falsy
       end

spec/lib/gitlab/danger/helper_spec.rb

@@ -312,4 +312,26 @@ describe Gitlab::Danger::Helper do
       it { is_expected.to match_array(['database', 'database::review pending']) }
     end
   end
+
+  describe '#security_mr?' do
+    it 'returns false when `gitlab_helper` is unavailable' do
+      expect(helper).to receive(:gitlab_helper).and_return(nil)
+
+      expect(helper).not_to be_security_mr
+    end
+
+    it 'returns false when on a normal merge request' do
+      expect(fake_gitlab).to receive(:mr_json)
+        .and_return('web_url' => 'https://gitlab.com/gitlab-org/gitlab/merge_requests/1')
+
+      expect(helper).not_to be_security_mr
+    end
+
+    it 'returns true when on a security merge request' do
+      expect(fake_gitlab).to receive(:mr_json)
+        .and_return('web_url' => 'https://gitlab.com/gitlab-org/security/gitlab/merge_requests/1')
+
+      expect(helper).to be_security_mr
+    end
+  end
 end