ci: Add a new 'scripts/rubocop-max-files-in-cache-check'

This new script will fail if AllCops.MaxFilesInCache is too low compared
to the number of RuboCop target files.
Signed-off-by: Rémy Coutable <remy@rymai.me>

scripts/rubocop-max-files-in-cache-check

+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'yaml'
+
+MINIMUM_MAX_FILES_IN_CACHE_MARGIN = 1.05
+RECOMMENDED_MAX_FILES_IN_CACHE_MARGIN = 1.25
+RUBOCOP_LIST_TARGET_FILES_COMMAND = 'bundle exec rubocop --list-target-files | wc -l'
+
+RuboCopMaxFilesInCacheIsTooSmall = Class.new(StandardError)
+
+rubocop_target_files_count = `#{RUBOCOP_LIST_TARGET_FILES_COMMAND}`.strip.to_i
+
+raise Error, "#{RUBOCOP_LIST_TARGET_FILES_COMMAND} failed with status #{$?}!" if rubocop_target_files_count == 0
+
+rubocop_target_files_count = rubocop_target_files_count.to_i
+rubocop_current_max_files_in_cache = YAML.load_file(File.expand_path('../.rubocop.yml', __dir__)).dig('AllCops', 'MaxFilesInCache').to_i
+minimum_max_files_in_cache = (rubocop_target_files_count * MINIMUM_MAX_FILES_IN_CACHE_MARGIN).round(-3)
+
+# We want AllCops.MaxFilesInCache to be at least 5% above the actual files count at any time to give us enough time to increase it accordingly
+if rubocop_current_max_files_in_cache <= minimum_max_files_in_cache
+  recommended_max_files_in_cache = (rubocop_target_files_count * RECOMMENDED_MAX_FILES_IN_CACHE_MARGIN).round(-3)
+  raise RuboCopMaxFilesInCacheIsTooSmall, "Current count of RuboCop target file is #{rubocop_target_files_count} but AllCops.MaxFilesInCache is set to #{rubocop_current_max_files_in_cache}. We recommend to increase it to #{recommended_max_files_in_cache}."
+else
+  puts "Current count of RuboCop target file is #{rubocop_target_files_count} and AllCops.MaxFilesInCache is set to #{rubocop_current_max_files_in_cache}. All good."
+  exit(0)
+end

scripts/static-analysis

@@ -54,6 +54,7 @@ class StaticAnalysis
     Task.new(%w[bin/rake gettext:lint], 85),
     Task.new(%W[bundle exec license_finder --decisions-file config/dependency_decisions.yml --project-path #{project_path}], 20),
     Task.new(%w[bin/rake lint:static_verification], 35),
+    Task.new(%w[scripts/rubocop-max-files-in-cache-check], 20),
     Task.new(%w[bin/rake config_lint], 10),
     Task.new(%w[bin/rake gitlab:sidekiq:all_queues_yml:check], 15),
     (Gitlab.ee? ? Task.new(%w[bin/rake gitlab:sidekiq:sidekiq_queues_yml:check], 11) : nil),