Zeitwerk error on devise mailer in production environment - ruby-on-rails

I have Rails 6, my preview class located in
mailer/previews/devise_mailer_preview.rb:
class DeviseMailerPreview < ActionMailer::Preview
...
end
And when I run application locally, everything is going fine, I can see my email previews on http://localhost:3000/rails/mailers/devise_mailer/confirmation_instructions address. But now Im trying to deploy application on server, and found that when I run bundle exec rails c production, I got the error:
/home/deploy/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/zeitwerk-2.3.0/lib/zeitwerk/loader/callbacks.rb:17:in
`on_file_autoloaded': expected file
/home/deploy/project/releases/20200627024908/app/mailer/previews/devise_mailer_preview.rb
to define constant Previews::DeviseMailerPreview, but didn't
(Zeitwerk::NameError)
After that I've checked locally RAILS_ENV=production rails c, and got same.
If I will rename DeviseMailerPreview class to Previews::DeviseMailerPreview, it will be broken and I cannot see emails on development, because Rails 6, accordingly to docs, expect exactly that name.
More of that, I've found in this article, that zeitwerk can be configured with autoload_paths param to avoid ruby's NameError. I found that I have it my config/application.rb:
config.load_defaults 6.0
Anyway I tried to add same row in my config/environments/production.rb file, but it didn't help.
What am I doing wrong and how can I fix it? Thanks in advance!

Add preview_path to the autoload_paths and zeitwerk will expect DeviseMailerPreview constant to be defined.
# development.rb
config.action_mailer.preview_path = Rails.root.join("app/mailers/previews")
# application.rb
config.autoload_paths << Rails.root.join("app/mailers/previews")

Your Mailer preview file is located in mailer/previews/devise_mailer_preview.rb, so I'm assuming it's full path is app/mailer/previews/devise_mailer_preview.rb
The docs says
In the above example, the preview class for UserMailer should be named UserMailerPreview and located in test/mailers/previews/user_mailer_preview.rb
So put your devise_mailer_preview.rb file to test/mailers/previews/devise_mailer_preview.rb
or in your config/application.rb add this line and restart:
config.action_mailer.preview_path = "#{Rails.root}/app/mailers/previews"
Actually the answer was in the docs itself.

In Rails 6, previews are added to the autoload paths only if options.show_previews is true, which is not by default in the production environment. See the source code here.
The reason for this is that previews are supposed to be an aid for development, and they are generally not something you want to be able to look at in production.
However, you can set that flag to true in production if you want.
There's another derivative: By storing the previews under app/mailers, Rails is going to eager load them because app/mailers is in the autoload paths. If app/mailers/previews is not in the autoload paths, eager loading will fail due to the namespace mismatch. Either you have them enabled in all environments, or else is better to have them in a separate location, like the default.

Related

LoadError: Unable to autoload constant in Rails

I am running a Rails application.
app/workers/sample/fetch_book_report_worker.rb
class Sample::FetchBookReportWorker
// body
end
app/workers/sample/fetch_student_report_worker.rb
class Sample::FetchStudentReportWorker
// body
end
app/workers/sample/fetch_teacher_report_worker.rb
class Sample::FetchTeacherReportWorker
// body
end
app/workers/sample/fetch_college_report_worker.rb
class Sample::FetchCollegeReportWorker
// body
end
When I ran the above worker individually, I didn't see an issue. But I ran all the workers at the same time. I got the below error.
LoadError: Unable to autoload constant Sample::FetchStudentReportWorker, expected /home/ubuntu/my-app/app/workers/sample/fetch_student_report_worker.rb to define it
How to solve this?
You can see autoload_paths to type this command.
bin/rails r 'puts ActiveSupport::Dependencies.autoload_paths'
If you can't see .../app/workers/sample, add the autoload_paths in config/application.rb
config.autoload_paths << Rails.root.join("app/workers/sample")
If it could causes problem in production mode, use the 'eager_load_paths'
referece from https://guides.rubyonrails.org/autoloading_and_reloading_constants.html
One likely root cause for the LoadError error is, that as of Rails 5.2.0, there are changes to autoload, that require submodules (namespaces) to (at the least) be defined (as a constant).
In the original post's example, the module Sample should be defined in the app/workers/sample.rb file (as commented by Vasfed above).
Refer to this related SO answer for more details.

Rails unable to autoload constant from file despite being defined in that file

This is a tricky one to explain. I have a module in another module namespace like so:
# app/models/points/calculator.rb
module Points
module Calculator
def self.included(base)
base.send(:include, CommonMethods)
base.send(:include, "Points::Calculator::#{base}Methods".constantize)
end
end
end
So then in other classes all I need to do is:
class User
include Points::Calculator
end
I've specified this directory in application.rb to be autoloadable...(even though i think rails recurses through models...)
config.autoload_paths += Dir[ Rails.root.join('app', 'models', "points") ]
In development env, everything works fine. When running tests(and production env), I get the following error:
Unable to autoload constant Points::Calculator, expected /Users/pete/work/recognize/app/models/points/calculator.rb to define it (LoadError)
I actually followed the advice here to fix the problem: Stop Rails from unloading a module in development mode by explicitly requiring calculator.rb in application.rb.
However, why is this happening??
I stuck some debug output in ActiveSupport's dependencies.rb file and noticed that this file is being required twice. The first time its required I can see that the constant is indeed loaded.
But the 2nd time its required the constant has been unloaded as far as Rails can tell, but when the actual require is called, ruby returns false because ruby knows its already required it. Then Rails throws the "unable to autoload constant" error because the constant still isn't present and ruby didn't "re-require" the file.
Can anyone shed light on why this might be happening?
Rails augments the constant lookup mechanism of ruby.
Constant lookup in Ruby:
Similar to method missing, a Module#constant-missing is invoked when a reference to a constant fails to be resolved. When we refer to a constant in a given lexical scope, that constant is searched for in:
Each entry in Module.nesting
Each entry in Module.nesting.first.ancestors
Each entry in Object.ancestors if Module.nesting.first is nil or a module.
When we refer to a constant, Ruby first attempts to find it according to this built-in lookup rules.
When ruby fails to find... rails kicks in, and using its own lookup convention and its knowledge about which constants have already been loaded (by ruby), Rails overrides Module#const_missing to load missing constants without the need for explicit require calls by the programmer.
Its own lookup convention?
Contrasting Ruby’s autoload (which requires the location of each autoloaded constant to be specified in advance) rails following a convention that maps constants to file names.
Points::Calculator # =>points/calculator.rb
Now for the constant Points::Calculator, rails searches this file path (ie 'points/calculator.rb') within the autoload paths, defined by the autoload_paths configuration.
In this case, rails searched for file path points/calculator in its autoloaded paths, but fails to find file and hence this error/warning is shown.
This answer is an abstract from this Urbanautomation blog.
Edit:
I wrote a blog about Zeitwerk, the new code reloader in Rails. Check it out at -> https://blog.bigbinary.com/2019/10/08/rails-6-introduces-new-code-loader-called-zeitwerk.html
If someone is having this issue in rails 6 which has zeitwerk autoloader,
Change ruby constant lookup back to classic in your application.rb
# config/application.rb
#...
config.autoloader = :classic
#...
Read more details here Rails Official Guides
Calculator should be a class to be autoloaded correctly
module Points
class Calculator
...
end
end

Local gem class is not found in Rails application

I have written a generator which creates the following ruby file and folder:
app/tests/test.rb
in the test.rb file I have a Test class which looks like this:
class Test < MyCustomModule::MyCustomClass::Base
...
end
Now, I want to use its functionality in one of the show.html.erb files creating new instance like this:
Test.new(...).render(...).html_safe
but I am getting the following error:
uninitialized constant MyCustomModule::MyCustomClass::Base
I have use the following answer to link my gem and my rails application. It seems to work as I am able to use the generator, but the gem module and class are not seen in the rails application.
Could anyone tell how to fix this issue?
I have try to follow the tips posted here but still nothing changed:
Adding config.autoload_paths += Dir["#{config.root}/lib/**/"] in application.rb file
I have created my gem structure looking at CarrierWave gem, so the naming should be correct
I try to disable config.threadsafe! but it is already disabled since config.cache_classes and config.eager_load are set to false in development
DEPRECATION WARNING: config.threadsafe! is deprecated. Rails
applications behave by default as thread safe in production as long as
config.cache_classes and config.eager_load are set to true.
Also, looking at adding-asset-to-your-gems rails documentation, it is said that:
A good example of this is the jquery-rails gem which comes with Rails
as the standard JavaScript library gem. This gem contains an engine
class which inherits from Rails::Engine. By doing this, Rails is
informed that the directory for this gem may contain assets and the
app/assets, lib/assets and vendor/assets directories of this engine
are added to the search path of Sprockets.
So, I have done this, and put my model class file in assets folder, but the result is the same.
The following screenshots demonstrate my real case:
The screenshot below displays my gem file structure
Here you can see how I am loading the gem in my Rails application Gemfile:
gem 'thumbnail_hover_effect', '0.0.3', github: 'thumbnail_hover_effec/thumbnail_hover_effec', branch: 'master'
Then I am using the gem generator a ruby file with a cutstom name in app/thumbnails/test.rb folder with the following code:
class Test < ThumbnailHoverEffect::Image::Base
...
end
and trying to use the Test class gives me uninitialized constant ThumbnailHoverEffect::Image::Base error.
Back in the gem files, these are how the thumbnail_hover_effect file looks like
require 'thumbnail_hover_effect/version'
require 'thumbnail_hover_effect/engine'
require 'thumbnail_hover_effect/image'
module ThumbnailHoverEffect
# Your code goes here...
end
and hoe the image file looks like:
module ThumbnailHoverEffect
#
class Image
...
end
end
From what you've posted here there is no ThumbnailHoverEffect::Image::Base defined. Rails autoloading conventions (which you should not be depending on a gem btw, more on that later) would be looking for this file in thumbnail_hover_effect/image/base.rb, but the directory structure you printed does not have that. Of course you could define the class in thumbnail_hover_effect/image.rb and it would work, but the abridged snippet you posted does not show that. So where is ThumbnailHoverEffect::Image::Base defined?
If it's in thumbnail_hover_effect/image/base.rb then that would indicate the file is not being loaded. You can sanity check this by putting a puts 'loading this stupid file' at the top of thumbnail_hover_effect/image/base.rb. That will allow you to bisect the problem by seeing whether there is a problem with your definition of the class, or whether the problem is with loading the proper files. Debugging is all about bisecting the problem.

Where do you put your Rack middleware files and requires?

I'm in the process of refactoring some logic built into a Rails application into middleware, and one annoyance I've run into is a seeming lack of convention for where to put them.
Currently I've settled on app/middleware but I could just as easily move it to vendor/middleware or maybe vendor/plugins/middleware...
The biggest problem is having to require the individual files at the top of config/environment.rb
require "app/middleware/system_message"
require "app/middleware/rack_backstage"
or else I get uninitialized constant errors on the config.middleware.use lines. That could get messy very quickly. I'd rather this was tucked away in an initializer somewhere.
Is there a conventional place to put this stuff?
The specific answer I'm looking for with this bounty is: where can I put the require lines so that they are not cluttering the environment.rb file but still get loaded before the config.middleware.use calls? Everything I have tried leads to uninitialized constant errors.
Update: Now that we're using Rails 3.0, I treat a Rails app like any other Rack app; code files for middleware go in lib (or a gem listed in Gemfile) and are required and loaded in config.ru.
As of Rails 3.2, Rack middleware belongs in the app/middleware directory.
It works "out-of-the-box" without any explicit require statements.
Quick example:
I'm using a middleware class called CanonicalHost which is implemented in app/middleware/canonical_host.rb. I've added the following line to production.rb (note that the middleware class is explicitly given, rather than as a quoted string, which works for any environment-specific config files):
config.middleware.use CanonicalHost, "example.com"
If you're adding middleware to application.rb, you'll need to include quotes, as per #mltsy's comment.
config.middleware.use "CanonicalHost", "example.com"
You can put it in lib/tableized/file_name.rb. As long as the class you're trying to load is discoverable by its filename, Rails will automatically load the file necessary. So, for example:
config.middleware.use "MyApp::TotallyAwesomeMiddleware"
You would keep in:
lib/my_app/totally_awesome_middleware.rb
Rails catches const_missing and attemts to load files corresponding to the missing constants automatically. Just make sure your names match and you're gravy. Rails even provides nifty helpers that'll help you identify the path for a file easily:
>> ChrisHeald::StdLib.to_s.tableize.singularize
=> "chris_heald/std_lib"
So my stdlib lives in lib/chris_heald/std_lib.rb, and is autoloaded when I reference it in code.
In my Rails 3.2 app, I was able to get my middleware TrafficCop loading by putting it at app/middleware/traffic_cop.rb, just as #MikeJarema described. I then added this line to my config/application.rb, as instructed:
config.middleware.use TrafficCop
However, upon application start, I kept getting this error:
uninitialized constant MyApp::Application::TrafficCop
Explicitly specifying the root namespace didn't help either:
config.middleware.use ::TrafficCop
# uninitialized constant TrafficCop
For some reason (which I've yet to discover), at this point in the Rails lifecycle, app/middleware wasn't included in the load paths. If I removed the config.middleware.use line, and ran the console, I could access the TrafficCop constant without any issue. But it couldn't find it in app/middleware at config time.
I fixed this by enclosing the middleware class name in quotes, like so:
config.middleware.use "TrafficCop"
This way, I would avoid the uninitialized constant error, since Rails isn't trying to find the TrafficCop class just yet. But, when it starts to build the middleware stack, it will constantize the string. By this time, app/middleware is in the load paths, and so the class will load correctly.
For Rails 3:
#config/application.rb
require 'lib/rack/my_adapter.rb'
module MyApp
class Application < Rails::Application
config.middleware.use Rack::MyAdapter
end
end
I'm not aware of a convention, but why not put it in the /lib directory? Files in there get automatically loaded by Rails.
You could create an initializer which requires the necessary files and then leave the files wherever you want.
According to this the initializers are executed before the rack middleware is loaded.
The working solution I have so far is moving the middleware requires to config/middleware.rb and requiring that file in environment.rb, reducing it to a single require which I can live with.
I'd still like to hear how other people have solved this seemingly basic problem of adding middleware to Rails.

Rails - why would a model inside RAILS_ROOT/lib not be available in production mode?

I have a class located inside RAILS_ROOT/lib folder, which I use in one of my helpers, and it works great in development.
When I switch to production, the application throws a NameError (uninitialized constant SomeHelper::SomeClass), and I have to load it manually in the helper:
load "#{Rails.root}/lib/some_class.rb"
module SomeHelper
def some_method
sc = SomeClass.new
# blah
end
end
I was under the impression that everything inside RAILS_ROOT/lib/* should be available all to the app - is there anything I need to configure to make this happen in prod mode? thanks.
When you call SomeHelper::SomeClass, Rails' autoloading mechanism will try to load file at lib/some_helper/some_class.rb
Rails won't load everything in lib/*, it will only try to load files when ConstMissing occurs.
You might need to check differences between the configuration settings between development and production environment:
config/environments/production.rb and config/environments/development.rb.
During the Rails initialization routine, load_plugins() is called which loads all plugins in config.plugin_paths. You need to make sure that your folder lib/ is included, like in
config.plugin_paths = ["#{RAILS_ROOT}/lib/plugins", "#{RAILS_ROOT}/vendor/plugins"]
In addition to config.plugin_paths, you can also name the plugins that should be loaded in config.plugins. If that variable contains :all then all plugins (found) will be loaded.
(By the way: configuration settings equal to either environment should go in config/environment.rb. Any differences between enviroments are due to settings in the respective .rb files.)

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