lsp
Haskell library for the Microsoft Language Server Protocol. It currently implements all of the 3.15 specification.
It is split into three separate packages, lsp, lsp-types, and lsp-test:
-
lsp-typesprovides type-safe definitions that match up with the typescript definitions laid out in the specification -
lspis a library for building language servers, handling:- JSON-RPC transport
- Keeping track of the document state in memory with the Virtual File System (VFS)
- Responding to notifications and requests via handlers
- Setting the server capabilities in the initialize request based on registered handlers
- Dynamic registration of capabilities
- Cancellable requests and progress notifications
- Publishing and flushing of diagnostics
-
lsp-testis a functional testing framework for Language Server Protocol servers.
Language servers built on lsp
Example language servers
There are two example language servers in the lsp/example/ folder. Simple.hs provides a minimal example:
{-# LANGUAGE OverloadedStrings #-}
import Language.LSP.Server
import Language.LSP.Types
import Control.Monad.IO.Class
import qualified Data.Text as T
handlers :: Handlers (LspM ())
handlers = mconcat
[ notificationHandler SInitialized $ \_not -> do
let params = ShowMessageRequestParams MtInfo "Turn on code lenses?"
(Just [MessageActionItem "Turn on", MessageActionItem "Don't"])
_ <- sendRequest SWindowShowMessageRequest params $ \res ->
case res of
Right (Just (MessageActionItem "Turn on")) -> do
let regOpts = CodeLensRegistrationOptions Nothing Nothing (Just False)
_ <- registerCapability STextDocumentCodeLens regOpts $ \_req responder -> do
let cmd = Command "Say hello" "lsp-hello-command" Nothing
rsp = List [CodeLens (mkRange 0 0 0 100) (Just cmd) Nothing]
responder (Right rsp)
pure ()
Right _ ->
sendNotification SWindowShowMessage (ShowMessageParams MtInfo "Not turning on code lenses")
Left err ->
sendNotification SWindowShowMessage (ShowMessageParams MtError $ "Something went wrong!\n" <> T.pack (show err))
pure ()
, requestHandler STextDocumentHover $ \req responder -> do
let RequestMessage _ _ _ (HoverParams _doc pos _workDone) = req
Position _l _c' = pos
rsp = Hover ms (Just range)
ms = HoverContents $ markedUpContent "lsp-demo-simple-server" "Hello world"
range = Range pos pos
responder (Right $ Just rsp)
]
main :: IO Int
main = runServer $ ServerDefinition
{ onConfigurationChange = const $ pure $ Right ()
, doInitialize = \env _req -> pure $ Right env
, staticHandlers = \_caps -> handlers
, interpretHandler = \env -> Iso (runLspT env) liftIO
, options = defaultOptions
}Whilst Reactor.hs shows how a reactor design can be used to handle all
requests on a separate thread, such in a way that we could then execute them on
multiple threads without blocking server communication. They can be installed
from source with
cabal install lsp-demo-simple-server lsp-demo-reactor-server
stack install :lsp-demo-simple-server :lsp-demo-reactor-server --flag haskell-lsp:demo
Examples of using lsp-test
Setting up a session
import Language.LSP.Test
main = runSession "hie" fullCaps "proj/dir" $ do
doc <- openDoc "Foo.hs" "haskell"
skipMany anyNotification
symbols <- getDocumentSymbols docUnit tests with HSpec
describe "diagnostics" $
it "report errors" $ runSession "hie" fullCaps "test/data" $ do
openDoc "Error.hs" "haskell"
[diag] <- waitForDiagnosticsSource "ghcmod"
liftIO $ do
diag ^. severity `shouldBe` Just DsError
diag ^. source `shouldBe` Just "ghcmod"Replaying captured session
replaySession "hie" "test/data/renamePass"Parsing with combinators
skipManyTill loggingNotification publishDiagnosticsNotification
count 4 (message :: Session ApplyWorkspaceEditRequest)
anyRequest <|> anyResponseTry out the example tests in the lsp-test/example directory with cabal test.
For more examples check the Wiki, or see this introductory blog post.
Whilst writing your tests you may want to debug them to see what's going wrong.
You can set the logMessages and logStdErr options in SessionConfig to see what the server is up to.
There are also corresponding environment variables so you can turn them on from the command line:
LSP_TEST_LOG_MESSAGES=1 LSP_TEST_LOG_STDERR=1 cabal test
Troubleshooting
Seeing funny stuff when running lsp-test via stack? If your server is built upon Haskell tooling, keep in mind that stack sets some environment variables related to GHC, and you may want to unset them.
Useful links
Other resources
See #haskell-language-server on IRC freenode.
