TH.hs

{-# LANGUAGE BlockArguments #-}
{-|
Module      : KMonad.Args.TH
Description : Template Haskell to use in the CLI
Copyright   : (c) slotThe, 2021
License     : MIT

Maintainer  : soliditsallgood@mailbox.org
Stability   : experimental
Portability : non-portable (TH)

-}
module KMonad.Args.TH (gitHash) where

import KMonad.Prelude

import Language.Haskell.TH (Exp, Q)
import Language.Haskell.TH.Syntax (runIO)
import UnliftIO.Directory (findExecutable)
import UnliftIO.Process (readProcessWithExitCode)

-- | Get the git hash of the current commit at compile time.
gitHash :: Q Exp
gitHash = do
  str <- runIO do
    findExecutable "git" >>= \case
      Nothing  -> pure ""                         -- Git not present
      Just git -> do
        (exitCode, hash, _) <- readProcessWithExitCode git ["rev-parse", "HEAD"] ""
        pure case exitCode of
          ExitSuccess -> takeWhile (/= '\n') hash
          _           -> ""                       -- Not in a git repo
  [| fromString str |]