Reviewer roulette via Danger

Make danger pick reviewers and maintainers at random, for feontend,
backend, database, etc, changes, whenever files belonging to those
teams get changed.

2 files changed, 173 insertions, 0 deletions

diff --git a/lib/gitlab/danger/helper.rb b/lib/gitlab/danger/helper.rb
new file mode 100644
index 00000000000..80760e41c7d
--- /dev/null
+++ b/lib/gitlab/danger/helper.rb
@@ -0,0 +1,131 @@
+# frozen_string_literal: true
+require 'net/http'
+require 'json'
+
+require_relative 'teammate'
+
+module Gitlab
+  module Danger
+    module Helper
+      ROULETTE_DATA_URL = URI.parse('https://about.gitlab.com/roulette.json').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
+            rsp = Net::HTTP.get_response(ROULETTE_DATA_URL)
+            raise "Failed to read #{ROULETTE_DATA_URL}: #{rsp.code} #{rsp.message}" unless
+              rsp.is_a?(Net::HTTPSuccess)
+
+            data = JSON.parse(rsp.body)
+            data.map { |hash| ::Gitlab::Danger::Teammate.new(hash) }
+          rescue JSON::ParserError
+            raise "Failed to parse JSON response from #{ROULETTE_DATA_URL}"
+          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
+        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
+
+      # Returns the GFM for a category label, making its best guess if it's not
+      # a category we know about.
+      #
+      # @return[String]
+      def label_for_category(category)
+        CATEGORY_LABELS.fetch(category, "~#{category}")
+      end
+
+      CATEGORY_LABELS = {
+        docs: "~Documentation",
+        qa: "~QA"
+      }.freeze
+
+      # rubocop:disable Style/RegexpLiteral
+      CATEGORIES = {
+        %r{\Adoc/} => :docs,
+        %r{\A(CONTRIBUTING|LICENSE|MAINTENANCE|PHILOSOPHY|PROCESS|README)(\.md)?\z} => :docs,
+
+        %r{\A(ee/)?app/(assets|views)/} => :frontend,
+        %r{\A(ee/)?public/} => :frontend,
+        %r{\A(ee/)?spec/javascripts/} => :frontend,
+        %r{\A(ee/)?vendor/assets/} => :frontend,
+        %r{\A(jest\.config\.js|package\.json|yarn\.lock)\z} => :frontend,
+
+        %r{\A(ee/)?app/(?!assets|views)[^/]+} => :backend,
+        %r{\A(ee/)?(bin|config|danger|generator_templates|lib|rubocop|scripts)/} => :backend,
+        %r{\A(ee/)?spec/(?!javascripts)[^/]+} => :backend,
+        %r{\A(ee/)?vendor/(?!assets)[^/]+} => :backend,
+        %r{\A(ee/)?vendor/(languages\.yml|licenses\.csv)\z} => :backend,
+        %r{\A(Dangerfile|Gemfile|Gemfile.lock|Procfile|Rakefile)\z} => :backend,
+        %r{\A[A-Z_]+_VERSION\z} => :backend,
+
+        %r{\A(ee/)?db/} => :database,
+        %r{\A(ee/)?qa/} => :qa,
+
+        # Fallbacks in case the above patterns miss anything
+        %r{\.rb\z} => :backend,
+        %r{\.(md|txt)\z} => :docs,
+        %r{\.js\z} => :frontend
+      }.freeze
+      # rubocop:enable Style/RegexpLiteral
+    end
+  end
+end
diff --git a/lib/gitlab/danger/teammate.rb b/lib/gitlab/danger/teammate.rb
new file mode 100644
index 00000000000..4b822aa86c5
--- /dev/null
+++ b/lib/gitlab/danger/teammate.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Danger
+    class Teammate
+      attr_reader :name, :username, :projects
+
+      def initialize(options = {})
+        @name = options['name']
+        @username = options['username']
+        @projects = options['projects']
+      end
+
+      def markdown_name
+        "[#{name}](https://gitlab.com/#{username}) (`@#{username}`)"
+      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
+  end
+end