exec: use POSIX 'execve' system call (#527)

src/Stack/Exec.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE OverloadedStrings #-}
@@ -7,15 +8,21 @@
 
 module Stack.Exec where
 
-import           Control.Exception.Lifted
 import           Control.Monad.Reader
 import           Control.Monad.Logger
 import           Control.Monad.Catch hiding (try)
 import           Control.Monad.Trans.Control (MonadBaseControl)
-import           Data.Streaming.Process (ProcessExitedUnsuccessfully(..))
 import           Stack.Types
+
+#ifdef mingw32_HOST_OS
+import           Control.Exception.Lifted
+import           Data.Streaming.Process (ProcessExitedUnsuccessfully(..))
 import           System.Exit
-import           System.Process.Run
+import           System.Process.Run (callProcess)
+#else
+import           System.Process.Read (envHelper, preProcess)
+import           System.Posix.Process (executeFile)
+#endif
 
 -- | Default @EnvSettings@ which includes locals and GHC_PACKAGE_PATH
 defaultEnvSettings :: EnvSettings
@@ -36,10 +43,15 @@ plainEnvSettings = EnvSettings
 -- | Execute a process within the Stack configured environment.
 exec :: (HasConfig r, MonadReader r m, MonadIO m, MonadLogger m, MonadThrow m, MonadBaseControl IO m)
      => EnvSettings -> String -> [String] -> m b
-exec envSettings cmd args = do
+exec envSettings cmd0 args = do
     config <- asks getConfig
     menv <- liftIO (configEnvOverride config envSettings)
-    e <- try (callProcess Nothing menv cmd args)
+#ifdef mingw32_HOST_OS
+    e <- try (callProcess Nothing menv cmd0 args)
     liftIO $ case e of
         Left (ProcessExitedUnsuccessfully _ ec) -> exitWith ec
         Right () -> exitSuccess
+#else
+    cmd <- preProcess Nothing menv cmd0
+    liftIO $ executeFile cmd False args (envHelper menv)
+#endif