Gem::Commands::BuildCommand#build_package

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/commands/build_command.rb, line 103
def build_package(gemspec)
  spec = Gem::Specification.load(gemspec)
  if spec
    # Gem::Specification#initialize applies --platform unless it is the local platform
    if options[:added_platform] && spec.platform == Gem::Platform::RUBY && Gem.platforms.last == Gem::Platform.local
      spec.platform = Gem::Platform.local
    end

    ruby_abi = options[:ruby_abi]
    if ruby_abi
      requirement = Gem::ContentAddress.ruby_abi_requirement(ruby_abi)
      existing = spec.required_ruby_version

      unless existing.none? || existing == requirement
        alert_warning "required_ruby_version was changed from \"#{existing}\" to \"#{requirement}\" for this build " \
          "because --ruby-abi #{ruby_abi} was given."
      end

      spec.required_ruby_version = requirement
    end

    Gem::Package.build(
      spec,
      options[:force],
      options[:strict],
      options[:output],
      content_addressable: options[:content_addressable]
    )
  else
    alert_error "Error loading gemspec. Aborting."
    terminate_interaction 1
  end
end