add --version option

Main.hs

@@ -15,6 +15,7 @@ import qualified Database.LevelDB.Streaming as LS
 -- Error handling
 import Control.Exception     as BE
 import Control.Monad.Catch   as CE
+import qualified System.Exit as E
 
 -- Configuration
 import qualified Options.Applicative as O
@@ -27,6 +28,10 @@ import qualified Data.Text         as T
 import qualified Data.Text.IO      as T
 import qualified Data.ByteString   as B
 
+-- Version information
+import qualified Paths_bisc as Bisc
+import Data.Version (showVersion)
+
 -- Misc
 import Data.List             (nub)
 import Data.Maybe            (mapMaybe)
@@ -49,7 +54,8 @@ data Settings = Settings
 
 -- | Command line options
 data Options = Options
-  { dryRun     :: Bool      -- ^ don't delete anything
+  { version    :: Bool      -- ^ print version number
+  , dryRun     :: Bool      -- ^ don't delete anything
   , configPath :: FilePath  -- ^ config file path
   }
 
@@ -59,6 +65,11 @@ cliParser defConfig = O.info (O.helper <*> parser) infos
   where
     parser = Options
       <$> O.switch
+          (  O.long "version"
+          <> O.short 'v'
+          <> O.help "Print the version number and exit"
+          )
+      <*> O.switch
           (  O.long "dry-run"
           <> O.short 'n'
           <> O.help ("Don't actually remove anything, "<>
@@ -122,6 +133,10 @@ main = do
   defConfig <- D.getXdgDirectory D.XdgConfig ("bisc" </> "bisc.conf")
   opts <- O.execParser (cliParser defConfig)
 
+  when (version opts) $ do
+    putStrLn ("bisc " <> showVersion Bisc.version)
+    E.exitSuccess
+
   run <- runAction <$> loadSettings opts
   run "Cookies" deleteCookies
   run "QuotaManager" deleteQuotaOrigins