Crash when client advertises `workspace/workspaceFolders` but doesn’t implement handler

[csacca]

Describe the bug

When a client advertises workspace.workspaceFolders but does not implement the workspace/workspaceFolders request, the server assumes success and later code dereferences a missing/failed result, causing a crash.

To Reproduce

1. Start the server with a client that sets capabilities.workspace.workspaceFolders = true but does not handle workspace/workspaceFolders (e.g., powernap/crush).
2. Complete initialize/initialized.
3. The server requests workspace/workspaceFolders; the client returns a JSON-RPC error; the server crashes or becomes unstable.

Expected behavior

• No crash. Treat request errors/null as no folders and continue.
• Prefer InitializeParams.workspaceFolders when present and cache for later use.

Useful Information

• MATLAB-language-server Version: v1.3.6
• MATLAB Version: R2025b Update 1 (25.2.0.3042426) 64-bit (glnxa64)
• OS Version: Ubuntu 24.04.3 LTS as devcontainer (mcr.microsoft.com/devcontainers/base:ubuntu-24.04) with MATLAB feature (ghcr.io/mathworks/devcontainer-features/matlab)
• Language Server Client: crush v0.13.6
  • LSP Client Library: crush v0.13.6 uses powernap v0.0.0-20251015113943-25f979b54ad4

Additional context

• Affected code: src/server.ts (capability gate), src/lifecycle/MatlabSession.ts (launch dir), src/lifecycle/PathSynchronizer.ts (on connect), src/indexing/WorkspaceIndexer.ts (index roots).
• Repro: node build from source; ran /opt/matlab-language-server/out/index.js with the client above (crush).
• Fix: defensively wrap all getWorkspaceFolders() calls; only enable PathSynchronizer if the request succeeds; fall back to InitializeParams.workspaceFolders or [] and log a warning when clients error.

I will be submitting a pull request.

Example traffic between `crush` and `matlab-langauge-server`

Example traffic between crush and matlab-langauge-server

stdin:

Content-Length: 2837

{"id":0,"jsonrpc":"2.0","method":"initialize","params":{"capabilities":{"general":{"markdown":{"parser":"marked","version":"1.1.0"},"positionEncodings":["utf-16"],"regularExpressions":{"engine":"ECMAScript","version":"ES2020"}},"textDocument":{"codeAction":{"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}},"dataSupport":true,"dynamicRegistration":true,"isPreferredSupport":true,"resolveSupport":{"properties":["edit"]}},"completion":{"completionItem":{"commitCharactersSupport":true,"deprecatedSupport":true,"documentationFormat":["markdown","plaintext"],"insertReplaceSupport":true,"preselectSupport":true,"resolveSupport":{"properties":["documentation","detail","additionalTextEdits"]},"snippetSupport":false,"tagSupport":{"valueSet":[1]}},"contextSupport":true,"dynamicRegistration":true},"definition":{"dynamicRegistration":true,"linkSupport":true},"documentHighlight":{"dynamicRegistration":true},"documentSymbol":{"dynamicRegistration":true,"hierarchicalDocumentSymbolSupport":true},"formatting":{"dynamicRegistration":true},"hover":{"contentFormat":["markdown","plaintext"],"dynamicRegistration":true},"publishDiagnostics":{"codeDescriptionSupport":true,"dataSupport":true,"relatedInformation":true,"tagSupport":{"valueSet":[1,2]},"versionSupport":true},"rangeFormatting":{"dynamicRegistration":true},"references":{"dynamicRegistration":true},"rename":{"dynamicRegistration":true,"prepareSupport":true},"synchronization":{"didSave":true,"dynamicRegistration":true,"willSave":true,"willSaveWaitUntil":true}},"window":{"showDocument":{"support":true},"showMessage":{"messageActionItem":{"additionalPropertiesSupport":true}},"workDoneProgress":true},"workspace":{"applyEdit":true,"configuration":true,"didChangeConfiguration":{"dynamicRegistration":true},"didChangeWatchedFiles":{"dynamicRegistration":true,"relativePatternSupport":true},"fileOperations":{"didCreate":true,"didDelete":true,"didRename":true,"dynamicRegistration":true,"willCreate":true,"willDelete":true,"willRename":true},"symbol":{"dynamicRegistration":true},"workspaceEdit":{"documentChanges":true,"failureHandling":"textOnlyTransactional","normalizesLineEndings":true,"resourceOperations":["create","rename","delete"]},"workspaceFolders":true}},"clientInfo":{"name":"powernap","version":"0.1.0"},"initializationOptions":{"MATLAB":{"indexWorkspace":true,"installPath":"/opt/matlab/R2025b","matlabConnectionTiming":"onStart","prewarmGraphics":false,"signIn":true,"telemetry":false}},"locale":"en-us","processId":26471,"rootPath":"/workspaces/agentic-matlab-example","rootUri":"file:///workspaces/agentic-matlab-example","trace":"off","workspaceFolders":[{"uri":"file:///workspaces/agentic-matlab-example","name":"agentic-matlab-example"}]}}Content-Length: 52

{"jsonrpc":"2.0","method":"initialized","params":{}}Content-Length: 38

{"id":0,"result":null,"jsonrpc":"2.0"}Content-Length: 38

{"id":1,"result":[{}],"jsonrpc":"2.0"}Content-Length: 38

{"id":2,"result":null,"jsonrpc":"2.0"}Content-Length: 105

{"id":3,"error":{"code":0,"message":"no handler for method: workspace/workspaceFolders"},"jsonrpc":"2.0"}

stdout:

Content-Length: 134

{"jsonrpc":"2.0","method":"window/logMessage","params":{"type":4,"message":"(17:12:36) matlabls: Log Directory: /tmp/matlabls_26511"}}Content-Length: 583

{"jsonrpc":"2.0","id":0,"result":{"capabilities":{"codeActionProvider":true,"completionProvider":{"triggerCharacters":[".","("," ",",","/","\\"]},"definitionProvider":true,"documentFormattingProvider":true,"documentRangeFormattingProvider":true,"executeCommandProvider":{"commands":["matlabls.lint.suppress.line","matlabls.lint.suppress.file"]},"foldingRangeProvider":true,"referencesProvider":true,"signatureHelpProvider":{"triggerCharacters":["(",","]},"documentSymbolProvider":true,"renameProvider":{"prepareProvider":true},"documentHighlightProvider":true,"textDocumentSync":2}}}Content-Length: 201

{"jsonrpc":"2.0","id":0,"method":"client/registerCapability","params":{"registrations":[{"id":"91b68732-e3ec-49a1-bfb6-1202b45aad6f","method":"workspace/didChangeConfiguration","registerOptions":{}}]}}Content-Length: 101

{"jsonrpc":"2.0","id":1,"method":"workspace/configuration","params":{"items":[{"section":"MATLAB"}]}}Content-Length: 204

{"jsonrpc":"2.0","id":2,"method":"client/registerCapability","params":{"registrations":[{"id":"93246463-a499-485b-b7af-5c7110954b4d","method":"workspace/didChangeWorkspaceFolders","registerOptions":{}}]}}Content-Length: 103

{"jsonrpc":"2.0","method":"matlab/connection/update/server","params":{"connectionStatus":"connecting"}}Content-Length: 62

{"jsonrpc":"2.0","id":3,"method":"workspace/workspaceFolders"}

stderr:

(node:26511) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
/opt/matlab-language-server/out/index.js:43412
                        responsePromise.reject(new messages_1.ResponseError(error.code, error.message, error.data));
                                               ^

ResponseError: no handler for method: workspace/workspaceFolders
    at handleResponse (/opt/matlab-language-server/out/index.js:43412:48)
    at handleMessage (/opt/matlab-language-server/out/index.js:43192:13)
    at processMessageQueue (/opt/matlab-language-server/out/index.js:43209:17)
    at Immediate.<anonymous> (/opt/matlab-language-server/out/index.js:43181:13)
    at process.processImmediate (node:internal/timers:485:21) {
  code: 0,
  data: undefined
}

Node.js v22.21.1

Example `crush.json` lsp config for `matlab-language-server`

Example crush.json lsp config for matlab-language-server

{
  "$schema": "https://charm.land/crush.json",
  "lsp": {
    "matlab": {
      "command": "/usr/local/bin/matlab-language-server",
      "args": [
        "--stdio"
      ],
      "env": {
        "MLM_LICENSE_FILE": "27000@host"
      },
      "init_options": {
        "MATLAB": {
          "installPath": "/opt/matlab/R2025b",
          "indexWorkspace": true,
          "matlabConnectionTiming": "onStart",
          "telemetry": false,
          "signIn": true,
          "prewarmGraphics": false
        }
      }
    }
  },
  ...
}