Gem::Commands::BuildCommand#find_gemspec

# File tmp/rubies/ruby-3.3.0/lib/rubygems/commands/build_command.rb, line 78
def find_gemspec(glob = "*.gemspec")
  gemspecs = Dir.glob(glob).sort

  if gemspecs.size > 1
    alert_error "Multiple gemspecs found: #{gemspecs}, please specify one"
    terminate_interaction(1)
  end

  gemspecs.first
end