Add version command line flag.

cabal-prettify.cabal

@@ -63,6 +63,7 @@ executable cabal-prettify
   import: commons
   hs-source-dirs: executables/cabal-prettify
   main-is: Main.hs
+  other-modules: PackageInfo_cabal_prettify
   build-depends:
     , base
     , base-unicode-symbols

executables/cabal-prettify/Main.hs

@@ -10,12 +10,14 @@ import Control.Monad.Trans.Writer
 import Data.Bifunctor
 import Data.ByteString qualified as ByteArray
 import Data.Maybe
+import Data.Version
 import Distribution.Simple.Utils qualified as Cabal
 import Distribution.Verbosity qualified as Cabal
 import GHC.Generics (Generic)
 import Generics.Deriving.Monoid
 import Generics.Deriving.Semigroup
 import Options.Applicative
+import PackageInfo_cabal_prettify qualified as PackageInfo
 import Path
 import Path.IO
 import System.Exit
@@ -30,7 +32,10 @@ instance Exception CabalPrettifyException
 main ∷ IO ()
 main = do
   root ← getCurrentDir
-  command ← execParser (info (parseCommand root <**> helper) (fullDesc <> progDesc "Prettify your Cabal package configuration files!"))
+  command ← execParser do
+    info
+      do parseCommand root <**> helper <**> simpleVersioner (showVersion PackageInfo.version)
+      do fullDesc <> progDesc "Prettify your Cabal package configuration files!"
   run root command
 
 data Command = Command