Issue hooking up redhat-developer/yaml-language-server


I’m new to Nova extensions and Language Servers and I’m trying to add redhat-developer/yaml-language-server.

The Language server is quite similar to json-langauge-server which @apexskier has ported, but for yaml files instead. It lints yaml, validates against known json-scheams and has special support for Kubernetes resources.

I’ve got the server installed in my extension storage using apexskier/nova-extension-utils and have it starting up with a LanguageClient instance.

I’m getting this error in the extension console after the server starts:

Error: Invalid parameter: registrations
Registrations must be of type Registration[]

After quite a bit of hackery, I’ve been debugging the JSON RPC messages to see what’s going on. I managed this by setting my LanguageClient path to be my node.js path, then changing the args to be ["--inspect-brk", languageServerPath, "--stdio"]. So it starts the node process and immediately breakpoints until I connect a nodejs debugger (vs code :roll_eyes:).

It seems to initialize fine and send up an initialized too. The server then requests a client/registerCapability with the payload below but the response is the error.

The client/registerCapability:

  "jsonrpc": "2.0",
  "id": 0,
  "method": "client/registerCapability",
  "params": {
    "registrations": [
        "id": "69a84b93-43ca-46bf-b556-45ca3ac357ef",
        "method": "workspace/didChangeWorkspaceFolders",
        "registerOptions": {}

The response:

  "jsonrpc": "2.0",
  "id": 0,
  "error": {
    "message": "Invalid parameter: registrations\nRegistrations must be of type Registration[]",
    "code": -32602

It logs that error to the Nova debug pane too, but the stack trace isn’t very useful

Is this capability not supported by Nova, is something else going on here or am I doing something horribly wrong?

Thanks for any help or advice,



// add '--inspect-brk=9231' as the first arg to debug on that port
const serverOptions: ServerOptions = {
  type: "stdio",
  path: nodePath,
  args: ["--trace-warnings", serverPath, "--stdio"],

const settings = {
  yaml: {
    format: {
      enable: true,
      singleQuote: true,
    validate: true,
    hover: true,
    completion: true,
    schemas: {},
    schemaStore: { enable: false },

const clientOptions: ClientOptions = {
  syntaxes: ["yaml"],
  initializationOptions: settings,

client = new LanguageClient(


Device Info:

  • Nova 3.1 build 221256
  • macOS 11.0.1 (20B29)

Yes. The dynamic registration parts of the Language Server Protocol are not currently supported by Nova. We’re hoping to support them at some point in the future, and are tracking the feature. I’m sorry that I don’t have a better response here. I’d hope that the YAML language server would be falling back gracefully, but it may be that it’s only behaving as such when interfacing with LSP IDEs that support that capability.

1 Like

Thanks for your reply, it helped narrow down what I was doing wrong with the YAML server. It seems it doesn’t break the YAML server but it does create an unhandled promise rejection, which can be made warning-only with a Node.js CLI flag for now. I’ve got a first version of the extension working now!