Dont cache root path in file_paths method

While migrating .com to k8s it an issue was found that when the root
path changes, that our file_paths cache is not accurate, nor is it
busted.

This MR removes the root path from the cache, and rejoins it when the
method is called.

part of:
https://gitlab.com/gitlab-org/gitlab/-/issues/338288

app/models/release_highlight.rb

@@ -49,8 +49,12 @@ class ReleaseHighlight
   end
 
   def self.file_paths
-    @file_paths ||= Rails.cache.fetch(self.cache_key('file_paths'), expires_in: CACHE_DURATION) do
-      Dir.glob(FILES_PATH).sort.reverse
+    @file_paths ||= self.relative_file_paths.map { |path| path.prepend(Rails.root.to_s) }
+  end
+
+  def self.relative_file_paths
+    Rails.cache.fetch(self.cache_key('file_paths'), expires_in: CACHE_DURATION) do
+      Dir.glob(FILES_PATH).sort.reverse.map { |path| path.delete_prefix(Rails.root.to_s) }
     end
   end
 

ee/spec/models/release_highlight_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe ReleaseHighlight, :clean_gitlab_redis_cache do
-  let(:fixture_dir_glob) { Dir.glob(File.join('spec', 'fixtures', 'whats_new', '*.yml')).grep(/\d*\_(\d*\_\d*)\.yml$/) }
+  let(:fixture_dir_glob) { Dir.glob(File.join(Rails.root, 'spec', 'fixtures', 'whats_new', '*.yml')).grep(/\d*\_(\d*\_\d*)\.yml$/) }
   let(:starter_plan) { create(:license, plan: License::STARTER_PLAN) }
   let(:premium_plan) { create(:license, plan: License::PREMIUM_PLAN) }
   let(:ultimate_plan) { create(:license, plan: License::ULTIMATE_PLAN) }

spec/models/release_highlight_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe ReleaseHighlight, :clean_gitlab_redis_cache do
-  let(:fixture_dir_glob) { Dir.glob(File.join('spec', 'fixtures', 'whats_new', '*.yml')).grep(/\d*\_(\d*\_\d*)\.yml$/) }
+  let(:fixture_dir_glob) { Dir.glob(File.join(Rails.root, 'spec', 'fixtures', 'whats_new', '*.yml')).grep(/\d*\_(\d*\_\d*)\.yml$/) }
 
   before do
     allow(Dir).to receive(:glob).with(Rails.root.join('data', 'whats_new', '*.yml')).and_return(fixture_dir_glob)
@@ -193,4 +193,12 @@ RSpec.describe ReleaseHighlight, :clean_gitlab_redis_cache do
       expect(subject).to eq('Free')
     end
   end
+
+  describe '.file_paths' do
+    it 'joins relative file paths with the root path to avoid caching the root url' do
+      allow(described_class).to receive(:relative_file_paths).and_return([+'/a.yml'])
+
+      expect(described_class.file_paths.first).to eq("#{Rails.root}/a.yml")
+    end
+  end
 end