Rails uninitialized constant because of bad namespace coming out of nowhere

Question

I randomly run into errors where my framework complains about a missing class because of a bad namespace.

For some reasons Rails will try to look for class name namespaced from a different gem :

Suppose I have a ::ProfilesController in my root namespace, I sometimes get errors of

uninitialized constant Mongoid::Token::Collisions::ProfilesController

Where Mongoid::Token::Collisions (an example) is a module from a different gem used in models. I have several profiles controller declared the following way

class ::ProfilesController < Devise::RegistrationsController
class Registrations::ProfilesController < Devise::RegistrationsController
class Foo::ProfilesController < FooController
class Bar::ProfilesController < BarController
class Baz::Foo::ProfilesController < BazController

I don't understand how it's even possible to resolve ProfileController with the Mongoid::Token::Collisions namespace since I never write in my code ProfilesController as is without any namespace or the :: prefix

I actually had similar errors with different components. Usually the problem would go away when restarting the server. I'm wondering what may cause this behavior, which became more frequent. I'm not sure providing code would be of any help, the stack trace doesn't even start from my application code. Any idea where this may come from ?

ActionController::RoutingError (uninitialized constant Mongoid::Token::Collisions::ProfilesController):

activesupport (5.0.0.1) lib/active_support/inflector/methods.rb:283:in `const_get'
activesupport (5.0.0.1) lib/active_support/inflector/methods.rb:283:in `block in constantize'
activesupport (5.0.0.1) lib/active_support/inflector/methods.rb:266:in `each'
activesupport (5.0.0.1) lib/active_support/inflector/methods.rb:266:in `inject'
activesupport (5.0.0.1) lib/active_support/inflector/methods.rb:266:in `constantize'
actionpack (5.0.0.1) lib/action_dispatch/http/request.rb:93:in `controller_class'
actionpack (5.0.0.1) lib/action_dispatch/routing/route_set.rb:44:in `controller'
actionpack (5.0.0.1) lib/action_dispatch/routing/route_set.rb:30:in `serve'
actionpack (5.0.0.1) lib/action_dispatch/journey/router.rb:39:in `block in serve'
actionpack (5.0.0.1) lib/action_dispatch/journey/router.rb:26:in `each'
actionpack (5.0.0.1) lib/action_dispatch/journey/router.rb:26:in `serve'
actionpack (5.0.0.1) lib/action_dispatch/routing/route_set.rb:725:in `call'
rack-attack (5.0.1) lib/rack/attack.rb:147:in `call'
omniauth (1.3.2) lib/omniauth/strategy.rb:186:in `call!'
omniauth (1.3.2) lib/omniauth/strategy.rb:164:in `call'
omniauth (1.3.2) lib/omniauth/strategy.rb:186:in `call!'
omniauth (1.3.2) lib/omniauth/strategy.rb:164:in `call'
rack-tracker (1.1.0) lib/rack/tracker.rb:34:in `call'
rack-utm (0.0.2) lib/rack-utm.rb:59:in `call'
warden (1.2.6) lib/warden/manager.rb:35:in `block in call'
warden (1.2.6) lib/warden/manager.rb:34:in `catch'
warden (1.2.6) lib/warden/manager.rb:34:in `call'
rack (2.0.1) lib/rack/etag.rb:25:in `call'
rack (2.0.1) lib/rack/conditional_get.rb:25:in `call'
rack (2.0.1) lib/rack/head.rb:12:in `call'
rack (2.0.1) lib/rack/session/abstract/id.rb:222:in `context'
rack (2.0.1) lib/rack/session/abstract/id.rb:216:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/cookies.rb:613:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/callbacks.rb:38:in `block in call'
activesupport (5.0.0.1) lib/active_support/callbacks.rb:97:in `__run_callbacks__'
activesupport (5.0.0.1) lib/active_support/callbacks.rb:750:in `_run_call_callbacks'
activesupport (5.0.0.1) lib/active_support/callbacks.rb:90:in `run_callbacks'
actionpack (5.0.0.1) lib/action_dispatch/middleware/callbacks.rb:36:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/debug_exceptions.rb:49:in `call'
web-console (3.3.1) lib/web_console/middleware.rb:131:in `call_app'
web-console (3.3.1) lib/web_console/middleware.rb:28:in `block in call'
web-console (3.3.1) lib/web_console/middleware.rb:18:in `catch'
web-console (3.3.1) lib/web_console/middleware.rb:18:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
railties (5.0.0.1) lib/rails/rack/logger.rb:36:in `call_app'
railties (5.0.0.1) lib/rails/rack/logger.rb:24:in `block in call'
activesupport (5.0.0.1) lib/active_support/tagged_logging.rb:70:in `block in tagged'
activesupport (5.0.0.1) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (5.0.0.1) lib/active_support/tagged_logging.rb:70:in `tagged'
railties (5.0.0.1) lib/rails/rack/logger.rb:24:in `call'
ahoy_matey (1.5.2) lib/ahoy/engine.rb:22:in `call_with_quiet_ahoy'
request_store (1.3.1) lib/request_store/middleware.rb:9:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/request_id.rb:24:in `call'
rack (2.0.1) lib/rack/method_override.rb:22:in `call'
rack (2.0.1) lib/rack/runtime.rb:22:in `call'
activesupport (5.0.0.1) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.0.0.1) lib/action_dispatch/middleware/static.rb:136:in `call'
rack (2.0.1) lib/rack/sendfile.rb:111:in `call'
rack-cors (0.4.0) lib/rack/cors.rb:80:in `call'
railties (5.0.0.1) lib/rails/engine.rb:522:in `call'
puma (3.6.0) lib/puma/configuration.rb:225:in `call'
puma (3.6.0) lib/puma/server.rb:578:in `handle_request'
puma (3.6.0) lib/puma/server.rb:415:in `process_client'
puma (3.6.0) lib/puma/server.rb:275:in `block in run'
puma (3.6.0) lib/puma/thread_pool.rb:116:in `block in spawn_thread'

There is a lot of magic on how [rails loads constants](http://guides.rubyonrails.org/autoloading_and_reloading_constants.html). In almost every other language, you explicitly import/require classes as you need them. Rails decided to do that for you and with it comes a lot of complexity. — Anthony, Mar 15 '17 at 12:51
This might be related: http://stackoverflow.com/questions/17695557/rails-organizing-models-in-subfolders-having-warning-toplevel-constant-a-refer — MrYoshiji, Mar 15 '17 at 14:03
Hey @MrYoshiji this is likely related to Rails Autoloading magic'n'pitfalls but the question you linked deals with a different problem for a constant that already exists. In my case not only the constant is still not resolved, but rails is actually making up a constant that never existed anywhere by combining adding an irrelevant namespace to a class. — Cyril Duchon-Doris, Mar 15 '17 at 14:41
The request.rb:93 seems to call `constantize`, which (I think) does not prepend the string to constantize with `::` — MrYoshiji, Mar 15 '17 at 15:06
So somewhere there's dynamic code calling for a 'profiles_controller' that would get a weird namespace from somewhere... I suppose it could come from the `routes.rb` file ? Still don't understand why I would get a free bad namespace that doesn't even exist in the routes... — Cyril Duchon-Doris, Mar 15 '17 at 15:39

Rails uninitialized constant because of bad namespace coming out of nowhere

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