fredrikaverpil/nvim-plugin

Writing Neovim Plugins

Reference: https://neovim.io/doc/user/lua-plugin/

File Structure

A standard Neovim plugin layout:

myplugin.nvim/
├── plugin/
│   └── myplugin.lua      ← eagerly loaded at startup (keep minimal)
├── lua/
│   └── myplugin/
│       ├── init.lua      ← main module (required as 'myplugin')
│       ├── config.lua    ← option defaults + validation
│       └── health.lua    ← health checks (:checkhealth)
├── ftplugin/
│   └── rust.lua          ← filetype-specific init (optional)
├── doc/
│   └── myplugin.txt      ← vimdoc (generate with panvimdoc)
└── README.md

Neovim auto-discovers files in these paths — no registration needed.

Lazy Loading

Keep plugin/myplugin.lua minimal. Defer require() into command/mapping bodies, not at the top of the file. This preserves startup time.

-- BAD: eager load
local myplugin = require("myplugin")
vim.api.nvim_create_user_command("MyCommand", function()
  myplugin.run()
end, {})

-- GOOD: deferred load
vim.api.nvim_create_user_command("MyCommand", function()
  require("myplugin").run()
end, {})

Keymapping Patterns

Avoid creating keymaps automatically — it conflicts with user config. Two preferred approaches:

<Plug> Mappings (recommended for simple actions)

-- In plugin/myplugin.lua
vim.keymap.set("n", "<Plug>(MyPluginAction)", function()
  require("myplugin").do_action()
end)

Users then bind it themselves:

vim.keymap.set("n", "<leader>a", "<Plug>(MyPluginAction)")

Lua Functions (recommended for extensible actions)

-- Expose the function; let users decide the mapping
require("myplugin").do_action()  -- callable directly

For buffer-local mappings (custom UI, ftplugin), always pass buffer = bufnr:

vim.keymap.set("n", "<Plug>(MyPluginBufferAction)", function()
  require("myplugin").buffer_action()
end, { buffer = bufnr })

Initialization: setup() Patterns

Pattern 1: Separated config + init (preferred)

Plugin works out-of-the-box. setup() only overrides defaults — no require() calls, side effects, or expensive work. Initialization happens in plugin/ or ftplugin/ scripts, not inside setup().

-- lua/myplugin/config.lua
local M = {}

M.defaults = {
  enabled = true,
  timeout = 500,
}

M.options = {}

function M.setup(opts)
  M.options = vim.tbl_deep_extend("force", M.defaults, opts or {})
  M.validate()
end

function M.validate()
  vim.validate({
    enabled = { M.options.enabled, "boolean" },
    timeout = { M.options.timeout, "number" },
  })
end

return M

Pattern 2: Combined setup() (use when init is complex/risky)

Requires the user to call setup() explicitly — even with defaults. Only choose this when misconfiguration risk is high.

-- lua/myplugin/init.lua
local M = {}

function M.setup(opts)
  local config = require("myplugin.config")
  config.setup(opts)
  -- initialization logic here
  M._initialized = true
end

return M

Guard Variables

Prevent re-initialization (e.g. from sourcing the same file twice):

-- plugin/myplugin.lua
if vim.g.loaded_myplugin then
  return
end
vim.g.loaded_myplugin = true

For ftplugin (per-buffer, not per-session):

-- ftplugin/rust.lua
local bufnr = vim.api.nvim_get_current_buf()
-- no session-level guard needed; ftplugin is intentionally per-buffer

Set filetype as late as possible in custom UI buffers so users can override buffer-local settings via FileType autocmds.

Health Checks

Create lua/{plugin}/health.lua. :checkhealth {plugin} auto-discovers it.

-- lua/myplugin/health.lua
local M = {}

function M.check()
  vim.health.start("myplugin")

  -- Check initialization
  local ok, config = pcall(require, "myplugin.config")
  if not ok then
    vim.health.error("myplugin not loaded")
    return
  end

  -- Check config
  if config.options.timeout < 100 then
    vim.health.warn("timeout < 100ms may cause issues")
  else
    vim.health.ok("configuration looks good")
  end

  -- Check external deps
  if vim.fn.executable("some-tool") == 1 then
    vim.health.ok("some-tool found")
  else
    vim.health.error("some-tool not found in PATH")
  end
end

return M

Type Annotations (LuaCATS)

Annotate public APIs with LuaCATS for lua-language-server (luals):

---@class MyPlugin.Config
---@field enabled boolean
---@field timeout integer

---@param opts? MyPlugin.Config
function M.setup(opts) end

---@return MyPlugin.Config
function M.get_config() end

Integrate lua-typecheck-action in CI to catch type errors before users do.

In-Process LSP Actions (advanced UI pattern)

For plugins with custom UIs, expose actions as LSP code-actions so users can invoke them via standard vim.lsp.buf.code_action():

-- Users can then filter and apply specific actions:
vim.lsp.buf.code_action({
  apply = true,
  filter = function(a)
    return a.title == "My Plugin Action"
  end,
})

Versioning & Deprecation

• Follow SemVer: MAJOR.MINOR.PATCH
• Use vim.deprecate() when removing or renaming APIs:

function M.old_function(opts)
  vim.deprecate("myplugin.old_function", "myplugin.new_function", "2.0.0", "myplugin")
  return M.new_function(opts)
end

• Automate releases with luarocks-tag-release or release-please-action
• Publish to luarocks if the plugin has Lua dependencies or is itself a dependency

Documentation (vimdoc)

Provide vimdoc so users can access :h myplugin in Neovim.

Generate from Markdown using panvimdoc, then regenerate help-tags:

:helptags doc/

Development Workflow

• Use :restart to reload plugin changes during development
• Profile startup impact: nvim --startuptime /tmp/nvim-startup.log
• Add dev = true to your lazy.nvim spec to load from local path:

{
  "username/myplugin.nvim",
  dev = true,  -- loads from opts.dev.path/myplugin.nvim
}

Code Style

Follow the project's Lua style (per .stylua.toml):

• 2-space indentation
• Double quotes
• 120 char line width
• Sort requires via stylua