Add --mingw-path switch to 'ghcup run'

lib/GHCup/Prelude/Process/Windows.hs

@@ -217,6 +217,25 @@ exec exe args chdir env = do
   exit_code <- liftIO $ withCreateProcess cp $ \_ _ _ p -> waitForProcess p
   pure $ toProcessError exe args exit_code
 
+-- | Like 'exec', except doesn't add msys2 stuff to PATH.
+execNoMinGW :: MonadIO m
+     => FilePath       -- ^ thing to execute
+     -> [FilePath]     -- ^ args for the thing
+     -> Maybe FilePath   -- ^ optionally chdir into this
+     -> Maybe [(String, String)] -- ^ optional environment
+     -> m (Either ProcessError ())
+execNoMinGW exe args chdir env = do
+  -- https://gitlab.haskell.org/haskell/ghcup-hs/-/issues/375
+  forM_ (Map.fromList <$> env) $ \cEnv -> do
+    let paths = ["PATH", "Path"]
+        curPaths = (\x -> maybe [] splitSearchPath (Map.lookup x cEnv)) =<< paths
+        newPath = intercalate [searchPathSeparator] curPaths
+    setEnv "PATH" ""
+    setEnv "Path" newPath
+  let cp = (proc exe args) { cwd = chdir, env = env }
+  exit_code <- liftIO $ withCreateProcess cp $ \_ _ _ p -> waitForProcess p
+  pure $ toProcessError exe args exit_code
+
 
 -- | Thin wrapper around `executeFile`.
 execShell :: MonadIO m