ParseCabalFile.hs

{-# LANGUAGE ImportQualifiedPost #-}
{-# LANGUAGE LambdaCase #-}

import Data.ByteString qualified as BS
import Data.List (intercalate)
import Distribution.Package (packageVersion)
import Distribution.PackageDescription.Parsec (parseGenericPackageDescriptionMaybe)
import Distribution.Version (versionNumbers)
import System.Environment (getArgs)
import System.IO (hPutStrLn, stderr, stdout)

main :: IO ()
main = do
  cabalFile <-
    getArgs >>= \case
      [cabalFile] -> return cabalFile
      _ -> errorWithoutStackTrace "Expected exactly one argument: CABAL_FILE"

  cabalFileContents <- BS.readFile cabalFile
  packageDesc <-
    maybe (errorWithoutStackTrace "Could not parse cabal file") return $
      parseGenericPackageDescriptionMaybe cabalFileContents

  output
    [ ("version", intercalate "." . map show . versionNumbers . packageVersion $ packageDesc)
    ]

output :: [(String, String)] -> IO ()
output = mapM_ (uncurry output')
  where
    output' key value = do
      let kv = key ++ "=" ++ value
      -- log to stderr
      hPutStrLn stderr $ "Setting: " ++ kv
      -- output to stdout into $GITHUB_OUTPUT
      hPutStrLn stdout kv