error handling

Author: pepeiborra

ghcide/src/Development/IDE/Main.hs

@@ -11,12 +11,13 @@ import           Control.Concurrent.Extra              (newLock, readVar,
                                                         withLock,
                                                         withNumCapabilities)
 import           Control.Exception.Safe                (Exception (displayException),
-                                                        catchAny)
-import           Control.Monad.Extra                   (concatMapM, unless,
-                                                        when)
+                                                        SomeException (SomeException),
+                                                        catch, catchAny)
+import           Control.Monad.Extra                   (concatMapM, join,
+                                                        unless, when)
 import qualified Data.Aeson.Encode.Pretty              as A
 import           Data.Default                          (Default (def))
-import           Data.Foldable                         (for_, traverse_)
+import           Data.Foldable                         (traverse_)
 import qualified Data.HashMap.Strict                   as HashMap
 import           Data.Hashable                         (hashed)
 import           Data.List.Extra                       (intercalate, isPrefixOf,
@@ -255,8 +256,6 @@ defaultMain Arguments{..} = do
         PrintDefaultConfig ->
             LT.putStrLn $ decodeUtf8 $ A.encodePretty $ pluginsToDefaultConfig argsHlsPlugins
         LSP -> withNumCapabilities (maybe (numProcessors `div` 2) fromIntegral argsThreads) $ do
-            server <- for argsMonitoringPort $ \p ->
-                Monitoring.forkServer "localhost" (fromIntegral p)
             t <- offsetTime
             logInfo logger "Starting LSP server..."
             logInfo logger "If you are seeing this in a terminal, you probably should have run WITHOUT the --lsp option!"
@@ -293,6 +292,15 @@ defaultMain Arguments{..} = do
                     hPutStrLn stderr $
                         "Currently, HLS supports GHC 9 only partially. "
                         <> "See [issue #297](https://github.com/haskell/haskell-language-server/issues/297) for more detail."
+
+                -- this can fail if the port is busy
+                server <- fmap join $ for argsMonitoringPort $ \p ->
+                      (Just <$> Monitoring.forkServer "localhost" (fromIntegral p))
+                    `catch` \e@SomeException{} -> do
+                        logInfo logger $ T.pack $
+                            "Unable to bind monitoring server on port " <> show p <> ":" <> show e
+                        return Nothing
+
                 initialise
                     argsDefaultHlsConfig
                     rules