Add no-op semanticTokens handlers (#202)

`lsp` falsely advertises `semanticTokens` capabilities, regardless of
what we support. Register some no-op handlers so that clients which
trust the LSP server don't crash out.

See: haskell/lsp#640

Author: 9999years

src/StaticLS/Handlers.hs

@@ -112,6 +112,24 @@ handleResolveInlayHint :: Handlers (LspT c StaticLsM)
 handleResolveInlayHint = LSP.requestHandler LSP.SMethod_InlayHintResolve $ \_ _ -> do
   pure ()
 
+-- The lsp library (>=2.7.0.1) unconditionally advertises `semanticTokensProvider`
+-- in initialize, even when no semantic-token handlers are registered. Clients
+-- (notably Neovim's built-in LSP client) then send `textDocument/semanticTokens/*`
+-- requests, which fall through to the library's `missingRequestHandler` and are
+-- logged at Error severity -- the default logger surfaces those as `window/showMessage`
+-- popups. Register stub handlers that return Null so the requests resolve quietly.
+handleSemanticTokensFull :: Handlers (LspT c StaticLsM)
+handleSemanticTokensFull = LSP.requestHandler LSP.SMethod_TextDocumentSemanticTokensFull $ \_ res ->
+  res $ Right $ InR Null
+
+handleSemanticTokensFullDelta :: Handlers (LspT c StaticLsM)
+handleSemanticTokensFullDelta = LSP.requestHandler LSP.SMethod_TextDocumentSemanticTokensFullDelta $ \_ res ->
+  res $ Right $ InR $ InR Null
+
+handleSemanticTokensRange :: Handlers (LspT c StaticLsM)
+handleSemanticTokensRange = LSP.requestHandler LSP.SMethod_TextDocumentSemanticTokensRange $ \_ res ->
+  res $ Right $ InR Null
+
 handleReferencesRequest :: Handlers (LspT c StaticLsM)
 handleReferencesRequest = LSP.requestHandler LSP.SMethod_TextDocumentReferences $ \req res -> do
   let params = req._params

src/StaticLS/Server.hs

@@ -227,6 +227,9 @@ serverDef options logger = do
                 , handleDocumentSymbols
                 , handleCompletion
                 , handleCompletionItemResolve
+                , handleSemanticTokensFull
+                , handleSemanticTokensFullDelta
+                , handleSemanticTokensRange
                 ]
                   <> (if options.provideInlays then [handleInlayHintRequest options, handleResolveInlayHint] else [])
                   <> ( case options.fourmoluCommand of