[#61] Add Util.Version module (#62)

CHANGES.md

@@ -1,6 +1,8 @@
 0.9.0
 =====
 
+* [#61](https://github.com/serokell/serokell-util/issues/61):
+  Add utility feature to extract git revision in `Serokell.Util.Version`.
 * [#45](https://github.com/serokell/serokell-util/issues/45):
   Move `Aeson.Options` to separate package [`aeson-options`][1].
 * [#34](https://github.com/serokell/serokell-util/issues/34):

serokell-util.cabal

@@ -38,6 +38,7 @@ library
                            Serokell.Util.Text
                            Serokell.Util.Trace
                            Serokell.Util.Verify
+                           Serokell.Util.Version
 
   other-modules:       Serokell.Data.Variant.Class
                        Serokell.Data.Variant.Helpers
@@ -64,12 +65,14 @@ library
                      , mtl
                      , o-clock ^>= 0.1.1
                      , parsec
+                     , process
                      , QuickCheck >= 2.8.1
                      , quickcheck-instances
                      , scientific
                      , template-haskell
                      , text
                      , text-format
+                     , th-lift-instances
                      , transformers
                      , universum ^>= 1.1.0
                      , unordered-containers >= 0.2.7.0

src/Serokell/Util.hs

@@ -16,3 +16,4 @@ import Serokell.Util.StaticAssert as Exports
 import Serokell.Util.Text as Exports
 import Serokell.Util.Trace as Exports
 import Serokell.Util.Verify as Exports
+import Serokell.Util.Version as Exports

src/Serokell/Util/Version.hs

@@ -0,0 +1,45 @@
+module Serokell.Util.Version
+       ( -- * Git revision
+         retrieveGitRev
+       ) where
+
+import Universum
+
+import Instances.TH.Lift ()
+import System.Environment (lookupEnv)
+import System.Exit (ExitCode (..))
+import System.Process (readProcessWithExitCode)
+
+import qualified Data.Text as Text
+import qualified Language.Haskell.TH as TH
+import qualified Language.Haskell.TH.Syntax as TH
+
+{- | Gets the git revision.
+For example, you can use it configuring CLI options:
+
+@
+versionOption = infoOption
+    ("Git revision: " <> toString $(retrieveGitRev))
+    (long "version" <> help "Show version")
+@
+
+You'll need @-XTemplateHaskell@.
+
+Also note, that in order to see the latest git revision for the latest commit
+you should force recompilation of the file which contains @$(retrieveGitRev)@.
+-}
+retrieveGitRev :: TH.Q TH.Exp
+retrieveGitRev = do
+    cti <- TH.runIO $ Text.strip . fromString <$> retrieveGit
+    TH.lift cti
+  where
+    retrieveGit :: IO String
+    retrieveGit = whenNothingM (lookupEnv "GITREV") retrieveFromGitExecutable
+
+    retrieveFromGitExecutable :: IO String
+    retrieveFromGitExecutable = do
+        (exitCode, output, _) <-
+            readProcessWithExitCode "git" ["rev-parse", "--verify", "HEAD"] ""
+        pure $ case exitCode of
+            ExitSuccess -> output
+            _           -> fail "Couldn't retrieve 'git' revision"