lsp-test: fromJust crash in sendRequest

[pepeiborra]

My tests randomly crash with:

test-binary: Maybe.fromJust: Nothing
CallStack (from HasCallStack):
  error, called at libraries/base/Data/Maybe.hs:148:21 in base:Data.Maybe
  fromJust, called at src/Language/LSP/Test.hs:327:20 in lsp-test-0.14.0.0-26fxKpgpCT6HDpy4E8JMz7:Language.LSP.Test

                                          
### Error in:   Unit tests - Dirties generateTargets after file edit
Timed out waiting to receive a message from the server.
Cases: 1  Tried: 1  Errors: 1  Failures: 0

Could this be a concurrency issue? The code doesn't seem thread-safe:

lsp/lsp-test/src/Language/LSP/Test.hs

Lines 318 to 327 in 6b34b5b

	idn <- curReqId <$> get
	modify $ \c -> c { curReqId = idn+1 }
	let id = IdInt idn
	let mess = RequestMessage "2.0" id method params
	-- Update the request map
	reqMap <- requestMap <$> ask
	liftIO $ modifyMVar_ reqMap $
	\r -> return $ fromJust $ updateRequestMap r id method

[bosu]

I am seeing this as curReqId conflict between SInitialize and SShutdown requests.

Both of them start with curReqId == 0 (SShutdown is being called from its own Session monad instance). Therefore there is a possibility that shutdown sees outstanding initialize request
on the shared requestMap MVar.

The following naive patch fixes this for me:

diff --git a/lsp-test/src/Language/LSP/Test.hs b/lsp-test/src/Language/LSP/Test.hs
index 46bb8e4..60484ca 100644
--- a/lsp-test/src/Language/LSP/Test.hs
+++ b/lsp-test/src/Language/LSP/Test.hs
@@ -232,7 +232,9 @@ runSessionWithHandles' serverProc serverIn serverOut config' caps rootDir ses
sio
   where
   -- | Asks the server to shutdown and exit politely
   exitServer :: Session ()
-  exitServer = request_ SShutdown Empty >> sendNotification SExit Empty
+  exitServer = do
+    modify $ \c -> c { curReqId = -1 }
+    request_ SShutdown Empty >> sendNotification SExit Empty
 
   -- | Listens to the server output until the shutdown ack,
   -- makes sure it matches the record and signals any semaphores