Reviewer roulette via Danger

Dangerfile

@@ -11,3 +11,4 @@ danger.import_dangerfile(path: 'danger/commit_messages')
 danger.import_dangerfile(path: 'danger/duplicate_yarn_dependencies')
 danger.import_dangerfile(path: 'danger/prettier')
 danger.import_dangerfile(path: 'danger/eslint')
+danger.import_dangerfile(path: 'danger/roulette')

danger/plugins/helper.rb

 # frozen_string_literal: true
 
+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
+
 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.
   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.
@@ -36,6 +74,18 @@ def ee?
       ENV['CI_PROJECT_NAME'] == 'gitlab-ee' || File.exist?('../../CHANGELOG-EE.md')
     end
 
+    def project_name
+      ee? ? 'gitlab-ee' : 'gitlab-ce'
+    end
+
+    def team
+      Psych.safe_load(Net::HTTP.get(TEAM_DATA_URL), [Date]).map { |hash| Teammate.new(hash) }
+    end
+
+    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|
@@ -50,7 +100,23 @@ def category_for_file(file)
     end
 
     CATEGORIES = {
-      %r{\Adoc/} => :documentation
-    }
+      %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/(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)?/db/} => :database,
+      %r{\A(/ee)?/qa/} => :qa
+    }.freeze
   end
 end

danger/roulette/Dangerfile

+# frozen_string_literal: true
+
+HANDLED_CHANGES = [:backend, :frontend].freeze
+
+MESSAGE = <<MARKDOWN
+Changes that require review have been detected! A merge request is normally
+reviewed by both a reviewer and a maintainer in its primary category (e.g.
+~frontend or ~backend), and by a maintainer in all other categories.
+
+To spread load more evenly across eligible reviewers, Danger has randomly picked
+a candidate for each review slot. Feel free to override this selection if you
+think someone else would be better-suited, or the chosen person is unavailable.
+
+Once you've decided who will review this merge request, mention them as you
+normally would! Danger does not (yet?) automatically notify them for you.
+
+| Category | Reviewer | Maintainer |
+| -------- | -------- | ---------- |
+MARKDOWN
+
+def markdown_name(teammate)
+  return nil unless teammate
+
+  "`@#{teammate.gitlab}`"
+end
+
+def spin_the_wheel(category)
+  team = helper.project_team
+
+  reviewers = team.select { |member| member.reviewer?(helper.project, category) }
+  maintainers = team.select { |member| member.maintainer?(helper.project, category) }
+
+  # TODO: filter out people who are currently not in the office
+  # TODO: take CODEOWNERS into account?
+  # TODO: take OOO into account
+
+  reviewer = reviewers[rand(reviewers.size)]
+  maintainer = maintainers[rand(maintainers.size)]
+
+  "| #{category.capitalize} | #{markdown_name(reviewer)} | #{markdown_name(maintainer)} |
+end
+
+changes = helper.changes_by_category
+
+unless changes.empty?
+  categories = changes.keys & HANDLED_CHANGES
+  table = categories.map { |category| spin_the_wheel(team, category) }
+  markdown([message, *table].join("\n")
+end