Load the constant named const_name which is missing from from_mod. If it is not possible to load the constant into from_mod, try its parent module using const_missing.

Source Code

# File active_support/dependencies.rb, line 221
def load_missing_constant(from_mod, const_name)
  log_call from_mod, const_name
  if from_mod == Kernel
    if ::Object.const_defined?(const_name)
      log "Returning Object::#{const_name} for Kernel::#{const_name}"
      return ::Object.const_get(const_name)
    else
      log "Substituting Object for Kernel"
      from_mod = Object
    end
  end

  # If we have an anonymous module, all we can do is attempt to load from Object.
  from_mod = Object if from_mod.name.blank?

  unless qualified_const_defined?(from_mod.name) && from_mod.name.constantize.object_id == from_mod.object_id
    raise ArgumentError, "A copy of #{from_mod} has been removed from the module tree but is still active!"
  end

  raise ArgumentError, "#{from_mod} is not missing constant #{const_name}!" if from_mod.const_defined?(const_name)

  qualified_name = qualified_name_for from_mod, const_name
  path_suffix = qualified_name.underscore
  name_error = NameError.new("uninitialized constant #{qualified_name}")

  file_path = search_for_file(path_suffix)
  if file_path && ! loaded.include?(File.expand_path(file_path)) # We found a matching file to load
    require_or_load file_path
    raise LoadError, "Expected #{file_path} to define #{qualified_name}" unless from_mod.const_defined?(const_name)
    return from_mod.const_get(const_name)
  elsif mod = autoload_module!(from_mod, const_name, qualified_name, path_suffix)
    return mod
  elsif (parent = from_mod.parent) && parent != from_mod &&
        ! from_mod.parents.any? { |p| p.const_defined?(const_name) }
    # If our parents do not have a constant named +const_name+ then we are free
    # to attempt to load upwards. If they do have such a constant, then this
    # const_missing must be due to from_mod::const_name, which should not
    # return constants from from_mod's parents.
    begin
      return parent.const_missing(const_name)
    rescue NameError => e
      raise unless e.missing_name? qualified_name_for(parent, const_name)
      raise name_error
    end
  else
    raise name_error
  end
end