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

@@ -3,137 +3,13 @@
 require 'net/http'
 require 'yaml'
 
-class Teammate
-  attr_reader :name, :projects, :gitlab
-
-  def initialize(options = {})
-    @name = options['name']
-    @projects = options['projects']
-    @gitlab = options['gitlab']
-  end
-
-  def in_project?(name)
-    projects&.has_key?(name)
-  end
-
-  # Traintainers also count as reviewers
-  def reviewer?(project, category)
-    capabilities(project) == "reviewer #{category}" || traintainer?(project, category)
-  end
-
-  def traintainer?(project, category)
-    capabilities(project) == "trainee_maintainer #{category}"
-  end
-
-  def maintainer?(project, category)
-    capabilities(project) == "maintainer #{category}"
-  end
-
-  private
-
-  def capabilities(project)
-    projects.fetch(project, '')
-  end
-end
+require_relative '../../lib/gitlab/danger/helper'
 
 module Danger
-  # Common helper functions for our danger scripts
-  # If we find ourselves repeating code in our danger files, we might as well put them in here.
+  # Common helper functions for our danger scripts. See Gitlab::Danger::Helper
+  # for more details
   class Helper < Plugin
-    TEAM_DATA_URL = URI.parse('https://gitlab.com/gitlab-com/www-gitlab-com/raw/master/data/team.yml').freeze
-
-    # Returns a list of all files that have been added, modified or renamed.
-    # `git.modified_files` might contain paths that already have been renamed,
-    # so we need to remove them from the list.
-    #
-    # Considering these changes:
-    #
-    # - A new_file.rb
-    # - D deleted_file.rb
-    # - M modified_file.rb
-    # - R renamed_file_before.rb -> renamed_file_after.rb
-    #
-    # it will return
-    # ```
-    # [ 'new_file.rb', 'modified_file.rb', 'renamed_file_after.rb' ]
-    # ```
-    #
-    # @return [Array<String>]
-    def all_changed_files
-      Set.new
-        .merge(git.added_files.to_a)
-        .merge(git.modified_files.to_a)
-        .merge(git.renamed_files.map { |x| x[:after] })
-        .subtract(git.renamed_files.map { |x| x[:before] })
-        .to_a
-        .sort
-    end
-
-    def ee?
-      ENV['CI_PROJECT_NAME'] == 'gitlab-ee' || File.exist?('../../CHANGELOG-EE.md')
-    end
-
-    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
-      @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.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/(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
-    }.freeze
-    # rubocop:enable Style/RegexpLiteral
+    # Put the helper code somewhere it can be tested
+    include Gitlab::Danger::Helper
   end
 end