Gem::SpecificationPolicy#validate_self_inclusion_in_files_list

# File tmp/rubies/ruby-3.3.0/lib/rubygems/specification_policy.rb, line 310
def validate_self_inclusion_in_files_list
  file_name = @specification.file_name

  return unless @specification.files.include?(file_name)

  error "#{@specification.full_name} contains itself (#{file_name}), check your files list"
end