Introduction#

In the world of Neovim plugin development. One of superpowers enabled by the Lua language in Neovim is type annotations using EmmyLua-style comments (—@). These annotations supercharge documentation, IDE integration, and code readability.

In lazydocker.nvim, a plugin that embeds LazyDocker into a Neovim floating window, I extensively used these annotations.

Lua Type Annotations#

Lua is dynamically typed, but Neovim’s LSP (via nvim-lspconfig and emmy-lua) supports EmmyLua annotations:

---@class MyClass
---@field field string A description.

---@param param string Input param.
---@return boolean Success?
function myFunc(param) end

These generate:

• Hover docs in Neovim (K)
• Autocomplete for fields/methods
• Vim help pages (:help lazydocker.nvim)
• Type checking warnings

Type Hierarchy in lazydocker.nvim#

The plugin defines a rich type system:

---@class LazyDocker
---@field config LazyDocker.Config Module config table. See |LazyDocker.config|.
---@field setup fun(config?: LazyDocker.Config) Module Setup. See |LazyDocker.setup()|.
...

Nested Types:

---@class LazyDocker.Config
---@field window LazyDocker.WindowConfig

---@class LazyDocker.WindowConfig
---@field settings LazyDocker.WindowSettings

---@class LazyDocker.WindowSettings
---@field width number Width of the floating panel...
---@field height number Height...
---@field border string Style...
---@field relative string Layout relative to...

Aliases for enums:

---@alias LazyDocker.Engine string only accepts the values 'podman' and 'docker'

Enhancing Readability#

Without types:

-- What is this? Magic table?
local config = { window = { settings = { width = 0.618 } } }
require('lazydocker').setup(config)

With types (hover config generates a full schema!):

local config: LazyDocker.Config = {
  window = {
    settings = {
      width = 0.618,  -- 0-1 percentage
      border = 'rounded',  -- Valid: 'rounded', 'single', etc.
    }
  }
}

Validation helpers reference types implicitly:

function H._is_percentage(a)  -- Ensures 0 < width/height <= 1
vim.validate({ ['width'] = { settings.width, H._is_percentage, '0-1' } })

Supercharged IDE Features#

1. Autocomplete Everywhere:

   • Type LazyDocker.config.window.settings. generates a popup with width|height|border|relative.
   • LazyDocker.open({ engine = ‘ generates an autocompletion with ‘docker’|‘podman’.

2. Hover Documentation (hit K):

   • On LazyDocker.open: Full @usage examples + param types.
   • Cross-references like |LazyDocker.config| link to help sections.

3. Error Prevention:

   • LSP warns: opts.engine must be ‘docker’|‘podman’.
   • Invalid border = ‘invalid’ generates an error message.

4. Help Integration:

   ---

   • |LazyDocker.types|
   • |LazyDocker.setup|

   ---

   :help LazyDocker.types renders the @class docs beautifully.