Reviewer roulette via Danger

What does this MR do?

(Tries to) add reviewer roulette via Danger. The idea is that danger can scan the MR and determine what reviews it needs. Once decided, it can randomly pick a reviewer and maintainer for each category, perhaps taking OOO status into account along with any other information. It could even take CODEOWNERS information into account.

The final choice of which reviewers to use should remain with the author of the merge request - these are just suggestions to ease selection when the author doesn't have a strong opinion.

I'm new to danger - let's see what I can do!

What are the relevant issue numbers?

Closes #56087 (closed)

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• Documentation created/updated via this MR
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the style guides
• Security reports checked/validated by reviewer

danger/plugins/helper.rb

@@ -3,17 +3,17 @@
 require 'net/http'
 require 'yaml'
 
-Teammate = Struct.new(:name, :projects, :gitlab, keyword_init: true) do
-  def self.build(hash)
-    new(name: hash['name'], projects: hash['projects'], gitlab: hash['gitlab'])
-  end
+class Teammate
+  attr_reader :name, :projects, :gitlab
 
-  def initialize(*args, &blk)
-    super
+  def initialize(options = {})
+    @name = options['name']
+    @projects = options['projects']
+    @gitlab = options['gitlab']
   end
 
   def in_project?(name)
-    projects.has_key?(name)
+    projects&.has_key?(name)
   end
 
   # Traintainers also count as reviewers
@@ -69,7 +69,6 @@ def all_changed_files
         .sort
     end
 
-    # @return [Boolean]
     def ee?
       ENV['CI_PROJECT_NAME'] == 'gitlab-ee' || File.exist?('../../CHANGELOG-EE.md')
     end
@@ -78,45 +77,63 @@ def project_name
       ee? ? 'gitlab-ee' : 'gitlab-ce'
     end
 
+    # Looks up the current list of GitLab team members and parses it into a
+    # useful form
+    #
+    # @return [Array<Teammate>]
     def team
-      Psych.safe_load(Net::HTTP.get(TEAM_DATA_URL)).map { |hash| Teammate.build(hash) }
+      @team ||=
+        begin
+          data = Psych.safe_load(Net::HTTP.get(TEAM_DATA_URL), [Date])
+
+          data.map { |hash| Teammate.new(hash) }
+        end
     end
 
+    # Like +team+, but only returns teammates in the current project, based on
+    # project_name.
+    #
+    # @return [Array<Teammate>]
     def project_team
       team.select { |member| member.in_project?(project_name) }
     end
 
     # @return [Hash<String,Array<String>>]
     def changes_by_category
-      all_changed_files.inject(Hash.new { |h, k| h[k] = [] }) do |hsh, file|
-        hsh[category_for_file(file)] << file
+      all_changed_files.each_with_object(Hash.new { |h, k| h[k] = [] }) do |file, hash|
+        hash[category_for_file(file)] << file
+        hash
       end
     end
 
+    # Determines the category a file is in, e.g., `:frontend` or `:backend`
+    # @return[Symbol]
     def category_for_file(file)
       _, category = CATEGORIES.find { |regexp, _| regexp.match?(file) }
 
       category || :unknown
     end
 
+    # rubocop:disable Style/RegexpLiteral
     CATEGORIES = {
       %r{\Adoc/} => :documentation,
       %r{\A(CONTRIBUTING|LICENSE|MAINTENANCE|PHILOSOPHY|PROCESS|README)(\.md)?\z/} => :documentation,
 
-      %r{\A(/ee)?/app/(assets|views)/} => :frontend,
-      %r{\A(/ee)?/public/} => :frontend,
-      %r{\A(/ee)?/vendor/assets/} => :frontend,
-      %r{\A/(jest\.config\.js|package\.json|yarn\.lock)\z} => :frontend,
+      %r{\A(ee/)?app/(assets|views)/} => :frontend,
+      %r{\A(ee/)?public/} => :frontend,
+      %r{\A(ee/)?vendor/assets/} => :frontend,
+      %r{\A(jest\.config\.js|package\.json|yarn\.lock)\z} => :frontend,
 
-      %r{\A(/ee)?/app/(controllers|finders|graphql|helpers|mailers|models|policies|presenters|serializers|services|uploaders|validators|workers)/} => :backend,
-      %r{\A(/ee)?/(bin|config|danger|generator_templates|lib|rubocop|scripts|spec)/} => :backend,
-      %r{\A(/ee)?/vendor/(cert_manager|Dockerfile|gitignore|ingress|jupyter|project_templates|prometheus|runner)/} => :backend,
-      %r{\A(/ee)?/vendor/(languages\.yml|licenses\.csv)\z/} => :backend,
-      %r{\A/(Gemfile|Gemfile.lock)\z} => :backend,
-      %r{\A/(GITALY_SERVER_VERSION|GITLAB_PAGES_VERSION|GITLAB_SHELL_VERSION|GITLAB_WORKHORSE_VERSION|Rakefile)\z} => :backend,
+      %r{\A(ee/)?app/(controllers|finders|graphql|helpers|mailers|models|policies|presenters|serializers|services|uploaders|validators|workers)/} => :backend,
+      %r{\A(ee/)?(bin|config|danger|generator_templates|lib|rubocop|scripts|spec)/} => :backend,
+      %r{\A(ee/)?vendor/(cert_manager|Dockerfile|gitignore|ingress|jupyter|project_templates|prometheus|runner)/} => :backend,
+      %r{\A(ee/)?vendor/(languages\.yml|licenses\.csv)\z/} => :backend,
+      %r{\A(Dangerfile|Gemfile|Gemfile.lock|Procfile|Rakefile)\z} => :backend,
+      %r{\A(GITALY_SERVER_VERSION|GITLAB_PAGES_VERSION|GITLAB_SHELL_VERSION|GITLAB_WORKHORSE_VERSION|Rakefile)\z} => :backend,
 
-      %r{\A(/ee)?/db/} => :database,
-      %r{\A(/ee)?/qa/} => :qa
+      %r{\A(ee/)?db/} => :database,
+      %r{\A(ee/)?qa/} => :qa
     }.freeze
+    # rubocop:enable Style/RegexpLiteral
   end
 end