Automatically bump and commit Xcode project version and build numbers

Rakefile

# Follow the instructions at https://developer.apple.com/library/archive/qa/qa1827/_index.html 
# ("Technical Q&A QA1827: Automating Version and Build Numbers Using agvtool")
#
# Then manage versions with `rake`:
#
#   $ rake bump[build]
#   $ rake bump[minor]
#   $ rake bump[major]

def perform_bump(level)
  versions = `agvtool mvers -terse1`.split(".").map(&:to_i)

  # Always bump the build number
  sh "agvtool bump" 
  build = `agvtool vers -terse`

  # Then bump the marketing version, if specified
  case level
  when :build
    return versions.join(".") + "-" + build
  when :minor
    versions[1] += 1
  when :major
    versions[0] += 1
    versions[1] = 0
  end

  new_version = versions.join(".")
  sh "agvtool new-marketing-version #{new_version}"
  return new_version + "-" + build
end

task :bump, [:level] => [:_index_clean?] do |t, args|
  level = args.level.to_sym
  raise "Cannot bump #{level}" unless [:major, :minor, :build].include?(level)
  version = perform_bump(level)
  sh "git commit -am 'Version #{version}'"
  sh "git tag #{version}"
end

task :_index_clean? do
  raise "Stash changes to the repository before running" unless system("git diff --quiet")
end