Gem::Installer#generate_bin_symlink

# File tmp/rubies/ruby-4.0.0/lib/rubygems/installer.rb, line 519
def generate_bin_symlink(filename, bindir)
  src = File.join gem_dir, spec.bindir, filename
  dst = File.join bindir, formatted_program_filename(filename)

  if File.exist? dst
    if File.symlink? dst
      link = File.readlink(dst).split File::SEPARATOR
      cur_version = Gem::Version.create(link[-3].sub(/^.*-/, ""))
      return if spec.version < cur_version
    end
    File.unlink dst
  end

  FileUtils.symlink src, dst, verbose: Gem.configuration.really_verbose
rescue NotImplementedError, SystemCallError
  alert_warning "Unable to use symlinks, installing wrapper"
  generate_bin_script filename, bindir
end