1 files changed, 70 insertions, 0 deletions
diff --git a/lib/rubygems/update_suggestion.rb b/lib/rubygems/update_suggestion.rb
new file mode 100644
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+++ b/lib/rubygems/update_suggestion.rb
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+# frozen_string_literal: true
+
+##
+# Mixin methods for Gem::Command to promote available RubyGems update
+
+module Gem::UpdateSuggestion
+  # list taken from https://github.com/watson/ci-info/blob/7a3c30d/index.js#L56-L66
+  CI_ENV_VARS = [
+    "CI", # Travis CI, CircleCI, Cirrus CI, Gitlab CI, Appveyor, CodeShip, dsari
+    "CONTINUOUS_INTEGRATION", # Travis CI, Cirrus CI
+    "BUILD_NUMBER", # Jenkins, TeamCity
+    "CI_APP_ID", "CI_BUILD_ID", "CI_BUILD_NUMBER", # Applfow
+    "RUN_ID" # TaskCluster, dsari
+  ].freeze
+
+  ONE_WEEK = 7 * 24 * 60 * 60
+
+  ##
+  # Message to promote available RubyGems update with related gem update command.
+
+  def update_suggestion
+    <<-MESSAGE
+
+A new release of RubyGems is available: #{Gem.rubygems_version} → #{Gem.latest_rubygems_version}!
+Run `gem update --system #{Gem.latest_rubygems_version}` to update your installation.
+
+    MESSAGE
+  end
+
+  ##
+  # Determines if current environment is eglible for update suggestion.
+
+  def eglible_for_update?
+    # explicit opt-out
+    return false if Gem.configuration[:prevent_update_suggestion]
+    return false if ENV["RUBYGEMS_PREVENT_UPDATE_SUGGESTION"]
+
+    # focus only on human usage of final RubyGems releases
+    return false unless Gem.ui.tty?
+    return false if Gem.rubygems_version.prerelease?
+    return false if Gem.disable_system_update_message
+    return false if ci?
+
+    # check makes sense only when we can store of last try
+    # otherwise we will not be able to prevent annoying update message
+    # on each command call
+    return unless Gem.configuration.config_file_writable?
+
+    # load time of last check, ensure the difference is enough to repeat the suggestion
+    check_time = Time.now.to_i
+    last_update_check = Gem.configuration[:last_update_check] || 0
+    return false if (check_time - last_update_check) < ONE_WEEK
+
+    # compare current and latest version, this is the part where
+    # latest rubygems spec is fetched from remote
+    (Gem.rubygems_version < Gem.latest_rubygems_version).tap do |eglible|
+      if eglible
+        # store the time of last successful check into config file
+        Gem.configuration[:last_update_check] = check_time
+        Gem.configuration.write
+      end
+    end
+  rescue # don't block install command on any problem
+    false
+  end
+
+  def ci?
+    CI_ENV_VARS.any? {|var| ENV.include?(var) }
+  end
+end