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Getting started using Lua in Neovim
Introduction
The integration of Lua as a first-class language inside Neovim is shaping up to be one of its killer features. However, the amount of teaching material for learning how to write plugins in Lua is not as large as what you would find for writing them in Vimscript. This is an attempt at providing some basic information to get people started.
This guide assumes you are using the latest nightly build of Neovim. Since version 0.5 of Neovim is a development version, keep in mind that some APIs that are being actively worked on are not quite stable and might change before release.
Learning Lua
If you are not already familiar with the language, there are plenty of resources to get started:
- The Learn X in Y minutes page about Lua should give you a quick overview of the basics
- If videos are more to your liking, Derek Banas has a 1-hour tutorial on the language
- The lua-users wiki is full of useful information on all kinds of Lua-related topics
- The official reference manual for Lua should give you the most comprehensive tour of the language
It should also be noted that Lua is a very clean and simple language. It is easy to learn, especially if you have experience with similar scripting languages like JavaScript. You may already know more Lua than you realise!
Note: the version of Lua that Neovim embeds is LuaJIT 2.1.0, which maintains compatibility with Lua 5.1 (with a few 5.2 extensions)
Existing tutorials for writing Lua in Neovim
A few tutorials have already been written to help people write plugins in Lua. Some of them helped quite a bit when writing this guide. Many thanks to their authors.
- teukka.tech - From init.vim to init.lua
- 2n.pl - How to write neovim plugins in Lua
- 2n.pl - How to make UI for neovim plugins in Lua
- ms-jpq - Neovim Async Tutorial
Where to put Lua files
Lua files are typically found inside a lua/ folder in your runtimepath (for most users, this will mean ~/.config/nvim/lua on *nix systems and ~/AppData/Local/nvim/lua on Windows). The package.path and package.cpath globals are automatically adjusted to include Lua files in this folder. This means you can require() these files as Lua modules.
Let's take the following folder structure as an example:
📂 ~/.config/nvim
├── 📁 after
├── 📁 ftplugin
├── 📂 lua
│ ├── 🌑 myluamodule.lua
│ └── 📂 other_modules
│ ├── 🌑 anothermodule.lua
│ └── 🌑 init.lua
├── 📁 pack
├── 📁 plugin
├── 📁 syntax
└── 🇻 init.vim
The following Lua code will load myluamodule.lua:
require('myluamodule')
Notice the absence of a .lua extension.
Similarly, loading other_modules/anothermodule.lua is done like so:
require('other_modules.anothermodule')
-- or
require('other_modules/anothermodule')
Path separators are denoted by either a dot . or a slash /.
A folder containing an init.lua file can be required directly, without have to specify the name of the file.
require('other_modules') -- loads other_modules/init.lua
For more information: :help lua-require
Caveats
Unlike .vim files, .lua files are not automatically sourced from directories in your runtimepath. Instead, you have to source/require them from Vimscript. There are plans to add the option to load an init.lua file as an alternative to init.vim:
Tips
Several Lua plugins might have identical filenames in their lua/ folder. This could lead to namespace clashes.
If two different plugins have a lua/main.lua file, then doing require('main') is ambiguous: which file do we want to source?
It might be a good idea to namespace your config or your plugin with a top-level folder, like so: lua/plugin_name/main.lua
Using Lua from Vimscript
:lua
This command executes a chunk of Lua code.
:lua require('myluamodule')
Multi-line scripts are possible using heredoc syntax:
echo "Here's a bigger chunk of Lua code"
lua << EOF
local mod = require('mymodule')
local tbl = {1, 2, 3}
for k, v in ipairs(tbl) do
mod.method(v)
end
print(tbl)
EOF
See also:
:help :lua:help :lua-heredoc
Caveats
You don't get correct syntax highlighting when writing Lua in a .vim file. It might be more convenient to use the :lua command as an entry point for requiring external Lua files.
:luado
This command executes a chunk of Lua code that acts on a range of lines in the current buffer. If no range is specified, the whole buffer is used instead. Whatever string is returned from the chunk is used to determine what each line should be replaced with.
The following command would replace every line in the current buffer with the text hello world:
:luado return 'hello world'
Two implicit line and linenr variables are also provided. line is the text of the line being iterated upon whereas linenr is its number. The following command would make every line whose number is divisible by 2 uppercase:
:luado if linenr % 2 == 0 then return line:upper() end
See also:
:help :luado
:luafile
This command sources a Lua file.
:luafile ~/foo/bar/baz/myluafile.lua
It is analogous to the :source command for .vim files or the built-in dofile() function in Lua.
See also:
:help :luafile
luaeval()
This built-in Vimscript function evaluates a Lua expression string and returns its value. Lua data types are automatically converted to Vimscript types (and vice versa).
" You can store the result in a variable
let variable = luaeval('1 + 1')
echo variable
" 2
let concat = luaeval('"Lua".." is ".."awesome"')
echo concat
" 'Lua is awesome'
" List-like tables are converted to Vim lists
let list = luaeval('{1, 2, 3, 4}')
echo list[0]
" 1
echo list[1]
" 2
" Note that unlike Lua tables, Vim lists are 0-indexed
" Dict-like tables are converted to Vim dictionaries
let dict = luaeval('{foo = "bar", baz = "qux"}')
echo dict.foo
" 'bar'
" Same thing for booleans and nil
echo luaeval('true')
" v:true
echo luaeval('nil')
" v:null
" You can create Vimscript aliases for Lua functions
let LuaMathPow = luaeval('math.pow')
echo LuaMathPow(2, 2)
" 4
let LuaModuleFunction = luaeval('require("mymodule").myfunction')
call LuaModuleFunction()
luaeval() takes an optional second argument that allows you to pass data to the expression. You can then access that data from Lua using the magic global _A:
echo luaeval('_A[1] + _A[2]', [1, 1])
" 2
echo luaeval('string.format("Lua is %s", _A)', 'awesome')
" 'Lua is awesome'
See also:
:help luaeval()
v:lua
This global Vim variable allows you to call global Lua functions directly from Vimscript. Again, Vim data types are converted to Lua types and vice versa.
call v:lua.print('Hello from Lua!')
" 'Hello from Lua!'
let scream = v:lua.string.rep('A', 10)
echo scream
" 'AAAAAAAAAA'
" Requiring modules works
call v:lua.require('mymodule').myfunction()
" How about a nice statusline?
lua << EOF
function _G.statusline()
local filepath = '%f'
local align_section = '%='
local percentage_through_file = '%p%%'
return string.format(
'%s%s%s',
filepath,
align_section,
percentage_through_file
)
end
EOF
set statusline=%!v:lua.statusline()
" Also works in expression mappings
lua << EOF
function _G.check_back_space()
local col = vim.fn.col('.') - 1
if col == 0 or vim.fn.getline('.'):sub(col, col):match('%s') then
return true
else
return false
end
end
EOF
inoremap <silent> <expr> <Tab>
\ pumvisible() ? '\<C-n>' :
\ v:lua.check_back_space() ? '\<Tab>' :
\ completion#trigger_completion()
See also:
:help v:lua:help v:lua-call
Caveats
This variable can only be used to call functions. The following will always throw an error:
" Aliasing functions doesn't work
let LuaPrint = v:lua.print
" Accessing dictionaries doesn't work
echo v:lua.some_global_dict['key']
" Using a function as a value doesn't work
echo map([1, 2, 3], v:lua.global_callback)
The vim namespace
Neovim exposes a global vim variable which serves as an entry point to interact with its APIs from Lua. It provides users with an extended "standard library" of functions as well as various sub-modules.
Some notable functions and modules include:
vim.inspect: pretty-print Lua objects (useful for inspecting tables)vim.regex: use Vim regexes from Luavim.api: module that exposes API functions (the same API used by remote plugins)vim.loop: module that exposes the functionality of Neovim's event-loop (using LibUV)vim.lsp: module that controls the built-in LSP clientvim.treesitter: module that exposes the functionality of the tree-sitter library
This list is by no means comprehensive. If you wish to know more about what's made available by the vim variable, :help lua-stdlib and :help lua-vim are the way to go. Alternatively, you can do :lua print(vim.inspect(vim)) to get a list of every module.
Tips
Writing print(vim.inspect(x)) every time you want to inspect the contents of an object can get pretty tedious. It might be worthwhile to have a global wrapper function somewhere in your configuration:
function _G.dump(...)
local objects = vim.tbl_map(vim.inspect, {...})
print(unpack(objects))
end
You can then inspect the contents of an object very quickly in your code or from the command-line:
dump({1, 2, 3})
:lua dump(vim.loop)
Additionally, you may find that built-in Lua functions (such as math.max() or string.rep()) are sometimes lacking compared to what you would find in other languages (for example os.clock() only returns a value in seconds, not milliseconds). Be sure to look at the Neovim stdlib (and vim.fn, more on that later), it probably has what you're looking for.
Using Vimscript from Lua
vim.api.nvim_eval()
This function evaluates a Vimscript expression string and returns its value. Vimscript data types are automatically converted to Lua types (and vice versa).
It is the Lua equivalent of the luaeval() function in Vimscript
-- Data types are converted correctly
print(vim.api.nvim_eval('1 + 1')) -- 2
print(vim.inspect(vim.api.nvim_eval('[1, 2, 3]'))) -- { 1, 2, 3 }
print(vim.inspect(vim.api.nvim_eval('{"foo": "bar", "baz": "qux"}'))) -- { baz = "qux", foo = "bar" }
print(vim.api.nvim_eval('v:true')) -- true
print(vim.api.nvim_eval('v:null')) -- nil
Caveats
Unlike luaeval(), vim.api.nvim_eval() does not provide an implicit _A variable to pass data to the expression.
vim.api.nvim_exec()
This function evaluates a chunk of Vimscript code. It takes in a string containing the source code to execute and a boolean to determine whether the output of the code should be returned by the function (you can then store the output in a variable, for example).
local result = vim.api.nvim_exec(
[[
let text = 'hello world'
echo text
function! MyFunction()
" do something inside this function
endfunction
call MyFunction()
]],
true)
print(result) -- 'hello world'
vim.api.nvim_command()
This function executes an ex command. It takes in a string containing the command to execute.
vim.api.nvim_command('new')
vim.api.nvim_command('wincmd H')
vim.api.nvim_command('set nonumber')
vim.api.nvim_command('%s/foo/bar/g')
Note: vim.cmd is a shorter alias to this function (currently not documented in :help)
vim.cmd('buffers')
Tips
Since you have to pass strings to these functions, you often end up having to escape backslashes:
vim.cmd('%s/\\Vfoo/bar/g')
Literal strings are easier to use as they do not require escaping characters:
vim.cmd([[%s/\Vfoo/bar/g]])