Gem::Resolver#build_spec_for_cache

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/resolver.rb, line 469
def build_spec_for_cache(name)
  # Rank sources by the order they were first supplied so that, when multiple
  # sources offer the same version and platform, the earlier source wins.
  source_rank = {}
  @all_specs[name].each do |s|
    source_rank[s.source] ||= source_rank.size
  end

  @all_specs[name].group_by(&:version).transform_values do |candidates|
    next candidates.first if candidates.length == 1

    # Prefer already-installed specs to avoid unnecessary downloads
    installed = candidates.select {|s| s.is_a?(Gem::Resolver::InstalledSpecification) }
    next installed.first if installed.length == 1
    candidates = installed if installed.any?

    # Among remaining candidates, prefer a content-addressed candidate
    # built for the running Ruby, then the most specific platform, then the
    # earlier-supplied source. The Ruby ABI ranks before platform
    # specificity so that gem install and bundle install choose the same
    # artifact: Bundler prefers compatible content-addressed candidates
    # before sorting by platform.
    candidates.min_by do |s|
      [Gem::ContentAddress.ruby_abi_specificity_match(s),
       Gem::Platform.platform_specificity_match(s.platform, Gem::Platform.local),
       source_rank[s.source]]
    end
  end
end