Gem::Resolver::InstallerSet#add_always_install

# File tmp/rubies/ruby-3.0.5/lib/rubygems/resolver/installer_set.rb, line 58
def add_always_install(dependency)
  request = Gem::Resolver::DependencyRequest.new dependency, nil

  found = find_all request

  found.delete_if do |s|
    s.version.prerelease? and not s.local?
  end unless dependency.prerelease?

  found = found.select do |s|
    Gem::Source::SpecificFile === s.source or
      Gem::Platform::RUBY == s.platform or
      Gem::Platform.local === s.platform
  end

  found = found.sort_by do |s|
    [s.version, s.platform == Gem::Platform::RUBY ? -1 : 1]
  end

  newest = found.last

  unless @force
    found_matching_metadata = found.reverse.find do |spec|
      metadata_satisfied?(spec)
    end

    if found_matching_metadata.nil?
      if newest
        ensure_required_ruby_version_met(newest.spec)
        ensure_required_rubygems_version_met(newest.spec)
      else
        exc = Gem::UnsatisfiableDependencyError.new request
        exc.errors = errors

        raise exc
      end
    else
      newest = found_matching_metadata
    end
  end

  @always_install << newest.spec
end