Neovim LSP Attachment Troubleshooting Guide

When Neovim’s LSP client won’t attach, completions, diagnostics, and hover info are missing. Use this step‑by‑step diagnostic checklist—starting with the server binary, configuration, root‑dir detection, and debug logs—to pinpoint and resolve the issue.

Problem Overview

When a Language Server Protocol (LSP) client in Neovim does not attach, you’ll notice a lack of code completion, diagnostics, hover information, or signature help. The server may be installed, but the client never initiates a connection. This guide walks you through a structured diagnostic process to pinpoint the root cause and apply the appropriate fix.

Diagnostic Table

Condition	Likely Cause	Quick Check	Fix
No completions or diagnostics appear	Server binary not found or not executable	Run `which <server>` in a terminal	Install the binary or add its directory to `PATH`
Client shows `Inactive` in `:LspInfo`	Root directory detection failed (no .git, package.json, etc.)	Check `vim.lsp.get_active_clients()` output	Add a marker file or adjust `root_dir` in config
Errors in `:messages` about `cmd` execution	Incorrect command passed to `lspconfig`	Review `lua/config/lsp/*.lua`	Correct the `cmd` array
Server starts but never reports diagnostics	Log level too low; handshake failures hidden	Run `:lua vim.lsp.set_log_level('debug')`	Inspect `~/.local/share/nvim/lsp.log`
Multiple LSP managers installed simultaneously	Binary path conflicts	Check `which <server>` vs. `mason.nvim` path	Remove duplicate managers or set `cmd` to absolute path

Step‑by‑Step Checks

Verify the Server Binary
Open a terminal (outside Neovim) and run:
```
which pyright
```
Replace pyright with your server name. The output should be an absolute path, and the file must be executable (chmod +x if not). If which returns nothing, install the server or add its location to PATH.
Check LSP Configuration
Review your Lua LSP setup, typically in lua/config/lsp/pyright.lua (or similar). A minimal correct configuration looks like:
```
local lspconfig = require('lspconfig')

lspconfig.pyright.setup({
  cmd = { 'pyright-langserver', '--stdio' },
  filetypes = { 'python' },
  root_dir = lspconfig.util.root_pattern('pyproject.toml', 'setup.cfg', '.git'),
})
```
Ensure that cmd is an array of strings, not a single string, and that filetypes matches the file you’re editing. A common mistake is passing a relative path or omitting the --stdio flag.
Validate Root Directory Detection
Open the file that should trigger the LSP, then run:
```
:LspInfo
```
Look for the Root Directory field. If it shows “None”, Neovim couldn’t find a marker file. Add a .git folder, package.json, or whatever the server expects, or override root_dir in the config.
Inspect LSP Log for Handshake Issues
Enable debug logging:
```
:lua vim.lsp.set_log_level('debug')
```
Reopen the file, then check the log:
```
cat ~/.local/share/nvim/lsp.log | tail -n 50
```
Look for entries like error: cmd failed or error: failed to start client. These indicate problems with the command or environment.
Review :messages for Immediate Errors
After attempting to open a file, run:
```
:messages
```
Search for lines containing cmd or LSP. Errors such as cannot open file: No such file or directory point to mis‑configured cmd or missing binaries.
Confirm Neovim and Lua API Compatibility
Neovim 0.10 introduced breaking changes to the LSP Lua API. If you upgraded recently, double‑check that your require('lspconfig') calls match the current API. The root_pattern helper, for example, is still available but its signature changed.
Check for Multiple LSP Managers
If you use mason.nvim alongside manual installs, ensure that the cmd you specify points to the correct binary. You can force the path by using an absolute path in cmd.
Re‑start Neovim After Changes
After editing any config file, reload Neovim or run :source % if editing the file directly. Then re‑run :LspInfo to verify that the client is now Active.

Escalation Path

If the server binary is present, the config looks correct, but :LspInfo still shows Inactive, try mason.nvim’s :MasonInstall <server> to reinstall the server.
When debug logs show handshake failures, consult the server’s own documentation for required environment variables or additional command flags.
For persistent issues, bump Neovim to the latest stable release and ensure your lua/config/lsp files are compatible with the new API.
As a last resort, open an issue on the server’s GitHub repository or on the Neovim community forum, attaching the relevant log excerpts and config snippets.

Limitations & Caveats

Some servers (e.g., tsserver) require a package.json in the project root; absence of this file will prevent attachment even if the binary exists.
Neovim’s built‑in LSP client does not support binary downloads; you must manually install or use a manager like mason.nvim.
Changing the log level to debug can generate large log files; remember to reset it with vim.lsp.set_log_level('info') after troubleshooting.

Practical Verification Checklist

which <server> returns a path.
Configuration cmd array matches the binary signature.
Root directory marker file exists or root_dir is overridden.
After :LspInfo, status shows Active and the buffer’s filetype is listed.
Log file contains no “error” entries for the current session.

Conclusion

By following this ordered diagnostic flow, you can systematically eliminate the most common reasons a Neovim LSP client fails to attach. The key is to confirm the binary’s presence, validate the configuration, and use the built‑in tools (:LspInfo, :messages, and the debug log) to surface hidden errors. Once the root cause is identified, applying the corresponding fix will restore full LSP functionality in your Neovim environment.

Fixing Neovim LSP Attachment Failures: A Diagnostic Checklist