neoclide/coc.nvim · error · Error

Unsupported position encoding (${result.capabilities.positio

Error message

Unsupported position encoding (${result.capabilities.positionEncoding}) received from server ${this.name}

What it means

During doInitialize, the client validates the server's InitializeResult: any server that advertises a positionEncoding other than UTF-16 is rejected with this error. The client (like vscode) only supports UTF-16 position encoding, so a server claiming 'utf-8' or 'utf-32' capability is incompatible.

Source

Thrown at src/language-client/client.ts:1228

      const part = new ProgressPart(connection, token)
      part.begin({ title: `Initializing ${this.id}`, kind: 'begin' })
      return this.doInitialize(connection, initParams).then(result => {
        part.done()
        return result
      }, (error: Error) => {
        part.done()
        return Promise.reject(error)
      })
    } else {
      return this.doInitialize(connection, initParams)
    }
  }

  private async doInitialize(connection: Connection, initParams: InitializeParams): Promise<InitializeResult> {
    try {
      const result = await connection.initialize(initParams)
      if (result.capabilities.positionEncoding !== undefined && result.capabilities.positionEncoding !== PositionEncodingKind.UTF16) {
        throw new Error(`Unsupported position encoding (${result.capabilities.positionEncoding}) received from server ${this.name}`)
      }

      this._initializeResult = result
      this.$state = ClientState.Running
      let textDocumentSyncOptions: TextDocumentSyncOptions | undefined
      if (Is.number(result.capabilities.textDocumentSync)) {
        if (result.capabilities.textDocumentSync === TextDocumentSyncKind.None) {
          textDocumentSyncOptions = {
            openClose: false,
            change: TextDocumentSyncKind.None,
            save: undefined
          }
        } else {
          textDocumentSyncOptions = {
            openClose: true,
            change: result.capabilities.textDocumentSync,
            save: {
              includeText: false

View on GitHub (pinned to 50e974d969)

Solutions

1. Configure the server to use UTF-16 offsets (e.g. rust-analyzer: {"lsp":{"positionEncoding":"utf-16"}} or {"offsetEncoding":["utf-16"]}).
2. Downgrade or switch to a server build that doesn't force utf-8 position encoding.
3. Update coc.nvim — newer versions may support more encodings.
4. If the server has no encoding option, open an issue upstream or use an alternative server.

Example fix

// before (rust-analyzer config)
{ "rust-analyzer.lsp.enable": true }  // server defaults to utf-8

// after (settings.json of the server)
// ~/.config/rust-analyzer/settings.json or RA args
{ "lsp": { "positionEncoding": "utf-16" } }

function supportsUtf16(initResult: InitializeResult): boolean {
  const enc = initResult.capabilities.positionEncoding
  return enc === undefined || enc === 1 /* PositionEncodingKind.UTF16 */
}

try {
  await client.start()
} catch (e) {
  if (String(e).includes('Unsupported position encoding')) {
    // reconfigure the server to utf-16 or switch servers
  }
}

When it happens

Trigger: Connecting to a language server whose capabilities.positionEncoding is set to UTF-8 or UTF-32 (per LSP 3.17 spec) — e.g. servers using rust-analyzer's lsp-server crate or other toolkits defaulting to utf-8; server built against newer LSP features while client pins UTF-16.

Common situations: Using a cutting-edge server (rust-analyzer with utf-8 position encoding enabled, newer jdtls/helix-ecosystem servers) with coc.nvim; server config enabling `positionEncoding: utf-8` / `offsetEncoding`; LSP 3.17 servers under vim clients that don't negotiate encoding.

Related errors

• Language server ${id} not found
• ${uri} changed before apply edit
• Unable to getCallHierarchyItem at current position
• Action "${action.title}" is disabled: ${action.disabled.reas
• Format provider not found for buffer: ${doc.bufnr}

AI-assisted analysis of neoclide/coc.nvim@50e974d969 (2026-08-31). Data as JSON: /api/errors/e48f7c663a91ffee. Report an issue: GitHub.