Fix rake routes error when Rails::Engine with empty routes is mounted; fixes rails/rails#13810

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actionpack/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Fix `rake routes` error when `Rails::Engine` with empty routes is mounted.
+
+    Fixes #13810.
+
+    *Maurizio De Santis*
+
 *   Automatically convert dashes to underscores for shorthand routes, e.g:
 
         get '/our-work/latest'

actionpack/lib/action_dispatch/routing/inspector.rb

@@ -194,9 +194,9 @@ module ActionDispatch
         end
 
         def widths(routes)
-          [routes.map { |r| r[:name].length }.max,
-           routes.map { |r| r[:verb].length }.max,
-           routes.map { |r| r[:path].length }.max]
+          [routes.map { |r| r[:name].length }.max || 0,
+           routes.map { |r| r[:verb].length }.max || 0,
+           routes.map { |r| r[:path].length }.max || 0]
         end
     end
 

actionpack/test/dispatch/routing/inspector_test.rb

@@ -54,6 +54,27 @@ module ActionDispatch
         ], output
       end
 
+      def test_displaying_routes_for_engines_without_routes
+        engine = Class.new(Rails::Engine) do
+          def self.inspect
+            "Blog::Engine"
+          end
+        end
+        engine.routes.draw do
+        end
+
+        output = draw do
+          mount engine => "/blog", as: "blog"
+        end
+
+        assert_equal [
+          "Prefix Verb URI Pattern Controller#Action",
+          "  blog      /blog       Blog::Engine",
+          "",
+          "Routes for Blog::Engine:"
+        ], output
+      end
+
       def test_cart_inspect
         output = draw do
           get '/cart', :to => 'cart#show'