autoload-check.rb

#!/usr/bin/env ruby

# Place in your project (don't forget to chmod +x):
# bin/autoload-check

# Allow these files to be fixed later
allowlist = [
  "ExampleClass" # why?
]

# Load application instead of environment, so that we can configure the autoloader
require "./config/application"

# Hook into the Rails autoloader to track loading
autoloaded_constants = []
Rails.autoloaders.each do |loader|
  loader.on_load do |cpath, _value, _abspath|
    autoloaded_constants << [cpath, caller]
  end
end

# Hook into Active Support load_hooks too
ignorable_load_hooks = [:before_initialize, :after_routes_loaded]
ActiveSupport.singleton_class.send(:alias_method, :original_run_load_hooks, :run_load_hooks)
ActiveSupport.singleton_class.define_method(:run_load_hooks) do |name, base = Object|
  autoloaded_constants << ["#{base} (#{name})", caller] unless name.in?(ignorable_load_hooks)
  original_run_load_hooks(name, base)
end

# Boot the application
Rails.application.initialize!

# Remove the allowlisted constants
autoloaded_constants.reject! do |(name, _)|
  allowlist.include?(name)
end

# Try to find a clean caller
autoloaded_constants.each do |autoloaded_const|
  caller = autoloaded_const[1]
  autoloaded_const << Rails.backtrace_cleaner.clean(caller).first
end

if autoloaded_constants.any?
  puts <<~MESSAGE
    ❌ Autoloaded constants were referenced during during boot.
    These files/constants were autoloaded during the boot process,                                                           
    which will result in inconsistent behavior and will slow down and
    may break development mode. Remove references to these constants
    from code loaded at boot.

  MESSAGE

  # Print constants that do have a clean application caller
  autoloaded_constants.select { |c| c[2].present? }.tap do |constants|
    const_width = constants.map(&:first).map(&:length).max
    constants.each do |name, _caller, location|
      puts "🚨 #{name.ljust(const_width)} referenced by #{location}"
    end
  end

  # Print constants that are referenced inside framework/libraries
  autoloaded_constants.select { |c| c[2].blank? }.tap do |constants|
    const_width = constants.map(&:first).map(&:length).max
    constants.each do |name, caller, _location|
      puts "🚨 #{name}"
      puts caller.map { |line| "".ljust(const_width) + line }
    end
  end
  
  exit 1 # Failure
else
  puts "✅ No autoloading problems discovered! 🎉"
end