Deprecate usage of nil as route path

In Rails 4 these kind of routes used to work:

```ruby
scope '/*id', controller: :builds, as: :build do
  get action: :show
end
```

But since 1a830cbd830c7f80936dff7e3c8b26f60dcc371d, routes are only created for
paths specified as strings or symbols. Implicit `nil` paths are just ignored,
with no deprecation warnings or errors. Routes are simply not created. This come
as a surprise for people migrating to Rails 5, since the lack of logs or errors
makes hard to understand where the problem is.

This commit introduces a deprecation warning in case of path as `nil`, while
still allowing the route definition.

1 files changed, 7 insertions, 0 deletions

diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index 75fdc9469f..d54cdf7247 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -373,6 +373,9 @@ class TestRoutingMapper < ActionDispatch::IntegrationTest
         post "create", :as => ""
         put  "update"
         get  "remove", :action => :destroy, :as => :remove
+        tc.assert_deprecated do
+          get action: :show, as: :show
+        end
       end
     end
 
@@ -391,6 +394,10 @@ class TestRoutingMapper < ActionDispatch::IntegrationTest
     get '/pagemark/remove'
     assert_equal 'pagemarks#destroy', @response.body
     assert_equal '/pagemark/remove', pagemark_remove_path
+
+    get '/pagemark'
+    assert_equal 'pagemarks#show', @response.body
+    assert_equal '/pagemark', pagemark_show_path
   end
 
   def test_admin