fix: Faker::Config.lazy_loading configuration must be respected (WIP)

[thdaraujo]

(fixes #3248 )

This fix initializes lazy loading or eager loading after the first constant access, which can be a bit surprising.

But this guarantees that the Faker::Config.lazy_loading setting is respected.

We introduce a new Faker::Loader class responsible for taking care of the loading process.

The loader has a method Loader#install_on that adds lazy loading to a generator. It defines const_missing on namespace classes (Faker::Games, Faker::Music etc.), delegating back to the Loader, which resolves the constant either by requiring the single corresponding file (lazy) or by loading all generator files at once (eager).

The loading strategy (lazy vs eager) is snapshotted on the first const_missing call. Changing config after first use has no effect.

The loader also has a list of inflections to handle cases such as DnD -> dnd.rb.

Config.lazy_loading is now process-wide rather than thread-local, so it cannot be confired per-thread anymore (which didn't seem very useful to begin with, so we're simplifying this).

--

The main source of the problem is due to Faker having configuration set directly, which makes it hard to defer evaluation of the configuration before requiring the Faker library.

Other possible alternative could be:

• forcing eager loading when the lazy_loading config is first set to true
• exposing a configuration block that only loads files after the block is executed.

[thdaraujo]

testing script

require_relative "../faker/lib/faker"

lazy_loading = if ENV.key?('FAKER_LAZY_LOAD')
                 puts 'set via env...'
                 ENV['FAKER_LAZY_LOAD'] == '1'
               else
                 puts 'set via config...'
                 Faker::Config.lazy_loading = true
               end

puts "Number of constants: #{Faker.constants.size}"
puts "Faker::Name #{Faker::Name.name}"
puts "Number of constants: #{Faker.constants.size}"

if lazy_loading
  puts "faker is lazy loading..."

  if Faker.constants.size > 10
    raise "must be lazy loaded!"
  else
    "lazy loading success!"
  end
else
  puts "faker is NOT lazy loading..."

  if Faker.constants.size < 10
    raise "must be eager loaded!"
  else
    "eager loading success!"
  end
end

Call with env or config:

FAKER_LAZY_LOAD=0 ruby script.rb 
FAKER_LAZY_LOAD=1 ruby script.rb

# change `lazy_loading` config on the file itself, then run
ruby script.rb 

[thdaraujo]

this sets up loading the first time a generator is called, which could be a bit surprising/unexpected.

maybe it's a good enough solution for letting folks test it?

in the future, we aim to make lazy loading default, so this wouldn't be a problem anymore, in my view.

[thdaraujo]

stub Kernel#require to spy on files being required/loaded

[thdaraujo]

maybe I could pass require or Kernel via dependency injection to make it easier to test :/

It would also get rid of the warnings.

Could be a future improvement!

[stefannibrasil]

I tested on a Ruby project, and some generators raise this error:

Faker::Books::Dune.character =>

     NoMethodError:
       private method 'resolve_const' called for an instance of Faker::Loader