# Neovim LSP (Language Server Protocol)

**Language servers** provide IDE features: autocomplete, diagnostics (error highlighting), go-to-definition, rename, hover docs. Neovim has a built-in LSP client; you install language servers separately.

## Architecture

Neovim's LSP client communicates with language servers (external processes). Each language needs its own server: `pyright` for Python, `clangd` for C/C++, `eslint` for JavaScript, etc.

Server types:

- **Installed locally** — `npm install -g pyright`, `pip install pylsp` (common for interpreted languages)
- **Binary** — download and add to PATH
- **Package manager** — brew, apt, etc.

## Basic setup with nvim-lspconfig

Install plugin:

```lua
-- ~/.config/nvim/lua/plugins/init.lua
{
  "neovim/nvim-lspconfig",
}
```

Then configure servers in `~/.config/nvim/init.lua`:

```lua
local lspconfig = require("lspconfig")

-- Python
lspconfig.pyright.setup({})

-- C/C++
lspconfig.clangd.setup({})

-- JavaScript/TypeScript
lspconfig.tsserver.setup({})
```

## Install language servers

Before using a server, install it:

```bash
# Python
pip install pyright

# JavaScript/TypeScript
npm install -g typescript-language-server

# C/C++
apt install clangd          # Linux
brew install llvm           # macOS
```

## LSP keybindings

After setup, use vim.lsp functions in keybindings:

```lua
vim.keymap.set('n', 'gd', vim.lsp.buf.definition)     -- go to definition
vim.keymap.set('n', 'gr', vim.lsp.buf.references)     -- find references
vim.keymap.set('n', 'K', vim.lsp.buf.hover)           -- hover info
vim.keymap.set('n', '<leader>rn', vim.lsp.buf.rename) -- rename
vim.keymap.set('n', '<leader>ca', vim.lsp.buf.code_action) -- code action
```

## Diagnostics

LSP shows errors/warnings inline. Check status:

```vim
:LspInfo           " show LSP status
:LspStart          " start LSP for current file
:LspStop           " stop LSP
```

Jump to diagnostics:

```vim
:lua vim.diagnostic.goto_next()     " next error
:lua vim.diagnostic.goto_prev()     " prev error
```

Map these:

```lua
vim.keymap.set('n', '<leader>e', vim.diagnostic.goto_next)
vim.keymap.set('n', '<leader>E', vim.diagnostic.goto_prev)
```

Diagnostics show in sign column and as virtual text. Customize display:

```lua
vim.diagnostic.config({
  virtual_text = true,
  underline = true,
  signs = true,
})
```

## Autocomplete with nvim-cmp

LSP sends completion suggestions to nvim-cmp (autocomplete plugin):

```lua
{
  "hrsh7th/nvim-cmp",
  dependencies = {
    "hrsh7th/cmp-nvim-lsp",
    "L3MON4D3/LuaSnip",
  },
}
```

Configure:

```lua
local cmp = require("cmp")
cmp.setup({
  sources = {
    { name = "nvim_lsp" },
    { name = "luasnip" },
  },
  mapping = cmp.mapping.preset.insert({
    ["<C-b>"] = cmp.mapping.scroll_docs(-4),
    ["<C-f>"] = cmp.mapping.scroll_docs(4),
    ["<C-Space>"] = cmp.mapping.complete(),
    ["<CR>"] = cmp.mapping.confirm({ select = true }),
  }),
})
```

Then `<C-Space>` triggers autocomplete.

## Troubleshooting

**LSP not starting**: Check `:LspInfo`. Missing language server? Install it and add to PATH.

**No diagnostics**: Server may not be configured. Read server docs and init settings.

**Slow autocomplete**: Language server may be resource-intensive. Some servers (pylance) need powerful hardware.

**Hover not working**: Some servers need specific configuration. Check server docs or try hover alternative: `:help lsp-hover`.

LSP is powerful but needs setup. Start with one language, expand as needed.