render notice when viewing an archived gem

app/controllers/rubygems_controller.rb

@@ -23,6 +23,9 @@ def index
   def show
     @versions = @rubygem.public_versions.limit(5)
     @adoption = @rubygem.ownership_call
+
+    flash[:notice] = t(".archived_notice") if @rubygem.archived?
+
     if @versions.to_a.any?
       render "show"
     else

config/locales/en.yml

@@ -699,6 +699,7 @@ en:
       show_all_versions: Show all versions (%{count} total)
       versions_header: Versions
       yanked_notice: This version has been yanked, and it is not available for download directly or for other gems that may have depended on it.
+      archived_notice: This gem has been archived. It is now read-only and will not accept new versions.
     show_yanked:
       not_hosted_notice: This gem is not currently hosted on RubyGems.org. Yanked versions of this gem may already exist.
       reserved_namespace_html:

test/functional/rubygems_controller_test.rb

@@ -414,6 +414,17 @@ class RubygemsControllerTest < ActionController::TestCase
     end
   end
 
+  context "on GET to show for an archived gem" do
+    setup do
+      @rubygem = create(:rubygem, :archived)
+      get :show, params: { id: @rubygem.slug }
+    end
+
+    should "render a notice indicating the gem has been archived" do
+      assert page.has_content? I18n.t("rubygems.show.archived_notice")
+    end
+  end
+
   context "When not logged in" do
     context "On GET to show for a gem" do
       setup do