While debugging an unrelated issue in rspec, I'm coming across issues with constant loading.
The setup is as follows:
# app/models/foo.rb
class Foo << ApplicationRecord
include Foo::Searchable
end
# app/models/foo/searchable.rb
module Foo::Searchable
extend ActiveSupport::Concern
included do
#yada yada
end
end
I received the following error while debugging. NameError: uninitialized constant #<Class:0x00007fadd32ea580>::Searchable
Changing the naming to Foos::Searchable with corresponding folder move does fix the issue but I would like to understand what is actually happening.
Rails 6.0.3.1 Ruby 2.6.6
As well as using << instead of < you have fallen victim to really common issue due to missusing the scope resolution operator ::. It should not be used when declaring nested classes or modules as it leads to the wrong module nesting and will lead to a missing constant error unless the module which you are nesting in is already loaded.
You should always explitly declare nested modules/classes:
class Foo < ApplicationRecord
module Searchable
extend ActiveSupport::Concern
included do
#yada yada
end
end
end
The reason this issue is popping up everywhere after the transition to Rails 6 is that the old classic autoloader overloaded Module#const_missing and glassed over these bugs as it would autoload Foo.
Zeitwork which replaces the classic autoloader instead uses Module#autoload which is a relatively new addition to Ruby and a lot less hacky.
This turns out to be caused by incompatibility with Byebug. Byebug stops the events Zeitwerk uses for autoloading to fire off in a debugging session. The issue is described here.
The << was a typo and would not result in that error.
Perhaps you should replace << with <. You inherit, not redirect
class Foo < ApplicationRecord
include Foo::Searchable
end
Related
I am getting the "superclass mismatch for class" error when I run reload! in the Rails console. I have some super simple classes defined in ruby, something like this:
# base_class.rb
module A
module B
module C
class BaseClass
def close
#stub
end
end
end
end
end
And:
# more_specific.rb
module A
module B
module C
class MoreSpecific < BaseClass
def initialize
# ...
end
def close
end
end
end
end
end
I can see that in fact there's a problem because if I do this before I do reload!:
A::B::C::MoreSpecific.superclass.equal? A::B::C::BaseClass
I get true, and then if I do it after I get the error, I get a false. Additionally, the object_id of the BaseClass does in fact change.
Why might this happen? I've checked for additional references to the MoreSpecific class in the codebase because I thought that might lead to the BaseClass being established as a constant more than once, but did not see anything.
What could be causing the object_id of A:B:C::BaseClass to switch after the reload!?
Autoloading Modules Without a Require Statement
reload! is a Rails console method, not a standard Ruby method. While there could be other causes for the behavior you're seeing, it's worth noting that your C module in more_specific.rb doesn't require base_class at runtime, and may be losing its lookup; Rails may not autoload modules the way you're expecting without it.
Make sure that modules that depend on BaseClass contain a require base_class statement to be executed when the module reloads. If that doesn't resolve it, there may be other problems with your code as well that aren't shown in your current post.
I'm experiencing a failure to understand how Ruby module based namespacing is supposed to work. I've always understood it to be that if you have two classes with the same name you can put one in a module to clarify namespace.
At the moment this doesn't work and I can't see why. In app/models/something/baz.rb I have:
class Baz < ActiveRecord::Base
self.table_name = 'baz'
end
I'm not sure why the table_name assignment is in there. Perhaps because of the fact that this file is nested under something?
In lib/foo/bar/baz.rb I have:
module Foo
module Bar
class Baz
end
end
end
I've included, in order, the paths lib/foo, lib/bar in my autoload_paths config value in config/application.rb:
config.autoload_paths += %W(
#{config.root}/lib
#{config.root}/lib/import
#{config.root}/lib/foo
#{config.root}/lib/foo/bar
#{config.root}/app/models/concerns
#{config.root}/app/services
#{config.root}/app/controllers/concerns
#{config.root}/app
)
at the console I can successfully reference the Foo, Foo::Bar modules but when I try to do Foo::Bar::Baz I get the usual error
expected Baz to be defined in lib/foo/bar/baz.rb
now I change that class to be in lib/foo/bar/baz_thing.rb and refer to it in console as Foo::Bar::BazThing everything works. I've come to the possibly erroneous conclusion that the autoload implementation is mightly confused because there are two classes with the same name.
I've double, triple and quadruple checked names and paths on all of this.
I also read through all the suggested possible alternative/duplicate questions shown when creating this ticket and could find none that addressed my situation closely enough to answer my question.
Can anyone identify where I've gone wrong and why my expectations on module namespacing behavior are incorrect?
This is on ruby 2.2.2 and Rails 4.2.6
I have an existing codebase of unit tests where the same classes are defined for each test, and a program that iterates over them. Something like this:
test_files.each do |tf|
load "tests/#{tf}/"+tf
test= ::Kernel.const_get("my_class")
Test::Unit::UI::Console::TestRunner.run( test )
While working on these tests, I've realized that ruby allows you to require classes with the same name from different files, and it merges the methods of the two. This leads to problems as soon as the class hierarchy is not the same: superclass mismatch for class ...
Unfortunately, simply unloading the class is not enough, as there are many other classes in the hierarchy that remain loaded.
Is there a way to execute each test in a different global namespace?
While I figure that using modules would be the way to go, I'm not thrilled with idea of changing the hundreds of existing files by hand.
--EDIT--
Following Cary Swoveland's suggestion, I've moved the test running code to a separate .rb file and am running it using backticks. While this seems to work well, loading the ruby interpreter and requireing all the libraries again has a considerable overhead. Also, cross-platform compatibility requires some extra work.
first I wanted to propose the following solution:
#main.rb
modules = []
Dir.foreach('include') do |file|
if file =~ /\w/
new_module = Module.new
load "include/#{file}"
new_module.const_set("StandardClass", StandardClass)
Object.send(:remove_const, :StandardClass)
modules << new_module
end
end
modules.each do |my_module|
my_module::StandardClass.standard_method
end
#include/first.rb
class StandardClass
def self.standard_method
puts "first method"
end
end
#include/second.rb
class StandardClass
def self.standard_method
puts "second method"
end
end
this wraps each class with it's own module and calls the class inside it's module:
$ruby main.rb
second method
first method
But as you answered there are references to other classes so modules can break them.
I checked this by calling the third class from one of the wrapped classes and got:
include/second.rb:5:in `standard_method': uninitialized constant StandardClass::Independent (NameError)
so probably using backticks is better solution but I hope my answer will be helpful for some other similar situations.
I love the autoload functionality of Ruby; however, it's going away in future versions of Ruby since it was never thread-safe.
So right now I would like to pretend it's already gone and write my code without it, by implementing the lazy-loading mechanism myself. I'd like to implement it in the simplest way possible (I don't care about thread-safety right now). Ruby should allow us to do this.
Let's start by augmenting a class' const_missing:
class Dummy
def self.const_missing(const)
puts "const_missing(#{const.inspect})"
super(const)
end
end
Ruby will call this special method when we try to reference a constant under "Dummy" that's missing, for instance if we try to reference "Dummy::Hello", it will call const_missing with the Symbol :Hello. This is exactly what we need, so let's take it further:
class Dummy
def self.const_missing(const)
if :OAuth == const
require 'dummy/oauth'
const_get(const) # warning: possible endless loop!
else
super(const)
end
end
end
Now if we reference "Dummy::OAuth", it will require the "dummy/oauth.rb" file which is expected to define the "Dummy::OAuth" constant. There's a possibility of an endless loop when we call const_get (since it can call const_missing internally), but guarding against that is outside the scope of this question.
The big problem is, this whole solution breaks down if there exists a module named "OAuth" in the top-level namespace. Referencing "Dummy::OAuth" will skip its const_missing and just return the "OAuth" from the top-level. Most Ruby implementations will also make a warning about this:
warning: toplevel constant OAuth referenced by Dummy::OAuth
This was reported as a problem way back in 2003 but I couldn't find evidence that the Ruby core team was ever concerned about this. Today, most popular Ruby implementations carry the same behavior.
The problem is that const_missing is silently skipped in favor of a constant in the top-level namespace. This wouldn't happen if "Dummy::OAuth" was declared with Ruby's autoload functionality. Any ideas how to work around this?
This was raised in a Rails ticket some time ago and when I investigated it there appeared to be no way round it. The problem is that Ruby will search the ancestors before calling const_missing and since all classes have Object as an ancestor then any top-level constants will always be found. If you can restrict yourself to only using modules for namespacing then it will work since they do not have Object as an ancestor, e.g:
>> class A; end
>> class B; end
>> B::A
(irb):3: warning: toplevel constant A referenced by B::A
>> B.ancestors
=> [B, Object, Kernel, BasicObject]
>> module C; end
>> module D; end
>> D::C
NameError: uninitialized constant D::C
>> D.ancestors
=> [D]
I get your problem on ree 1.8.7 (you don't mention a specific version) if I use const_get inside const_missing, but not if I use ::. I don't love using eval, but it does work here:
class Dummy
def self.const_missing(const)
if :OAuth == const
require 'dummy/oauth'
eval "self::#{const}"
else
super(const)
end
end
end
module Hello
end
Dummy.const_get :Hello # => ::Hello
Dummy::Hello # => Dummy::Hello
I wish Module had a :: method so you could do self.send :"::", const.
Lazy loading is a very common design pattern, you can implementing it in many ways. like :
class Object
def bind(key, &block)
#hooks ||= Hash.new{|h,k|h[k]=[]}
#hooks[key.to_sym] << [self,block]
end
def trigger(key)
#hooks[key.to_sym].each { |context,block| block.call(context) }
end
end
Then you can
bind :json do
require 'json'
end
begin
JSON.parse("[1,2]")
rescue
trigger :json
retry
end
I'm new to Ruby, so I'm having some trouble understanding this weird exception problem I'm having. I'm using the ruby-aaws gem to access Amazon ECS: http://www.caliban.org/ruby/ruby-aws/. This defines a class Amazon::AWS:Error:
module Amazon
module AWS
# All dynamically generated exceptions occur within this namespace.
#
module Error
# An exception generator class.
#
class AWSError
attr_reader :exception
def initialize(xml)
err_class = xml.elements['Code'].text.sub( /^AWS.*\./, '' )
err_msg = xml.elements['Message'].text
unless Amazon::AWS::Error.const_defined?( err_class )
Amazon::AWS::Error.const_set( err_class,
Class.new( StandardError ) )
end
ex_class = Amazon::AWS::Error.const_get( err_class )
#exception = ex_class.new( err_msg )
end
end
end
end
end
This means that if you get an errorcode like AWS.InvalidParameterValue, this will produce (in its exception variable) a new class Amazon::AWS::Error::InvalidParameterValue which is a subclass of StandardError.
Now here's where it gets weird. I have some code that looks like this:
begin
do_aws_stuff
rescue Amazon::AWS::Error => error
puts "Got an AWS error"
end
Now, if do_aws_stuff throws a NameError, my rescue block gets triggered. It seems that Amazon::AWS::Error isn't the superclass of the generated error - I guess since it's a module everything is a subclass of it? Certainly if I do:
irb(main):007:0> NameError.new.kind_of?(Amazon::AWS::Error)
=> true
It says true, which I find confusing, especially given this:
irb(main):009:0> NameError.new.kind_of?(Amazon::AWS)
=> false
What's going on, and how am I supposed to separate out AWS errors from other type of errors? Should I do something like:
begin
do_aws_stuff
rescue => error
if error.class.to_s =~ /^Amazon::AWS::Error/
puts "Got an AWS error"
else
raise error
end
end
That seems exceptionally janky. The errors thrown aren't class AWSError either - they're raised like this:
error = Amazon::AWS::Error::AWSError.new( xml )
raise error.exception
So the exceptions I'm looking to rescue from are the generated exception types that only inherit from StandardError.
To clarify, I have two questions:
Why is NameError, a Ruby built in exception, a kind_of?(Amazon::AWS::Error), which is a module?
Answer: I had said include Amazon::AWS::Error at the top of my file, thinking it was kind of like a Java import or C++ include. What this actually did was add everything defined in Amazon::AWS::Error (present and future) to the implicit Kernel class, which is an ancestor of every class. This means anything would pass kind_of?(Amazon::AWS::Error).
How can I best distinguish the dynamically-created exceptions in Amazon::AWS::Error from random other exceptions from elsewhere?
Ok, I'll try to help here :
First a module is not a class, it allows you to mix behaviour in a class. second see the following example :
module A
module B
module Error
def foobar
puts "foo"
end
end
end
end
class StandardError
include A::B::Error
end
StandardError.new.kind_of?(A::B::Error)
StandardError.new.kind_of?(A::B)
StandardError.included_modules #=> [A::B::Error,Kernel]
kind_of? tells you that yes, Error does possess All of A::B::Error behaviour (which is normal since it includes A::B::Error) however it does not include all the behaviour from A::B and therefore is not of the A::B kind. (duck typing)
Now there is a very good chance that ruby-aws reopens one of the superclass of NameError and includes Amazon::AWS:Error in there. (monkey patching)
You can find out programatically where the module is included in the hierarchy with the following :
class Class
def has_module?(module_ref)
if self.included_modules.include?(module_ref) and not self.superclass.included_modules.include?(module_ref)
puts self.name+" has module "+ module_ref.name
else
self.superclass.nil? ? false : self.superclass.has_module?(module_ref)
end
end
end
StandardError.has_module?(A::B::Error)
NameError.has_module?(A::B::Error)
Regarding your second question I can't see anything better than
begin
#do AWS error prone stuff
rescue Exception => e
if Amazon::AWS::Error.constants.include?(e.class.name)
#awsError
else
whatever
end
end
(edit -- above code doesn't work as is : name includes module prefix which is not the case of the constants arrays. You should definitely contact the lib maintainer the AWSError class looks more like a factory class to me :/ )
I don't have ruby-aws here and the caliban site is blocked by the company's firewall so I can't test much further.
Regarding the include : that might be the thing doing the monkey patching on the StandardError hierarchy. I am not sure anymore but most likely doing it at the root of a file outside every context is including the module on Object or on the Object metaclass. (this is what would happen in IRB, where the default context is Object, not sure about in a file)
from the pickaxe on modules :
A couple of points about the include statement before we go on. First, it has nothing to do with files. C programmers use a preprocessor directive called #include to insert the contents of one file into another during compilation. The Ruby include statement simply makes a reference to a named module. If that module is in a separate file, you must use require to drag that file in before using include.
(edit -- I can't seem to be able to comment using this browser :/ yay for locked in platforms)
Well, from what I can tell:
Class.new( StandardError )
Is creating a new class with StandardError as the base class, so it is not going to be a Amazon::AWS::Error at all. It is just defined in that module, which is probably why it is a kind_of? Amazon::AWS::Error. It probably isn't a kind_of? Amazon::AWS because maybe modules don't nest for purposes of kind_of? ?
Sorry, I don't know modules very well in Ruby, but most definitely the base class is going to be StandardError.
UPDATE: By the way, from the ruby docs:
obj.kind_of?(class) => true or false
Returns true if class is the class of obj, or if class is one of the superclasses of obj or modules included in obj.
Just wanted to chime in: I would agree this is a bug in the lib code. It should probably read:
unless Amazon::AWS::Error.const_defined?( err_class )
kls = Class.new( StandardError )
Amazon::AWS::Error.const_set(err_class, kls)
kls.include Amazon::AWS::Error
end
One issue you're running into is that Amazon::AWS::Error::AWSError is not actually an exception. When raise is called, it looks to see if the first parameter responds to the exception method and will use the result of that instead. Anything that is a subclass of Exception will return itself when exception is called so you can do things like raise Exception.new("Something is wrong").
In this case, AWSError has exception set up as an attribute reader which it defines the value to on initialization to something like Amazon::AWS::Error::SOME_ERROR. This means that when you call raise Amazon::AWS::Error::AWSError.new(SOME_XML) Ruby ends up calling Amazon::AWS::Error::AWSError.new(SOME_XML).exception which will returns an instance of Amazon::AWS::Error::SOME_ERROR. As was pointed out by one of the other responders, this class is a direct subclass of StandardError instead of being a subclass of a common Amazon error. Until this is rectified, Jean's solution is probably your best bet.
I hope that helped explain more of what's actually going on behind the scenes.