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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.

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 Lua
vim.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 client
vim.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

TODO: is it possible for vim.api.nvim_eval() to return a funcref?

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 for 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]])

Managing vim options

Using api functions

Neovim provides a set of API functions to either set an option or get its current value:

Global options:
- vim.api.nvim_set_option()
- vim.api.nvim_get_option()
Buffer-local options:
- vim.api.nvim_buf_set_option()
- vim.api.nvim_buf_get_option()
Window-local options:
- vim.api.nvim_win_set_option()
- vim.api.nvim_win_get_option()

They take a string containing the name of the option to set/get as well as the value you want to set it to.

Boolean options (like (no)number) have to be set to either true or false:

vim.api.nvim_set_option('smarttab', false)
print(vim.api.nvim_get_option('smarttab')) -- false

Unsurprisingly, string options have to be set to a string:

vim.api.nvim_set_option('selection', 'exclusive')
print(vim.api.nvim_get_option('selection')) -- 'exclusive'

Number options accept a number:

vim.api.nvim_set_option('updatetime', 3000)
print(vim.api.nvim_get_option('updatetime')) -- 3000

Buffer-local and window-local options also need a buffer number or a window number (using 0 will set/get the option for the current buffer/window):

vim.api.nvim_win_set_option(0, 'number', true)
vim.api.nvim_buf_set_option(10, 'shiftwidth', 4)
print(vim.api.nvim_win_get_option(0, 'number')) -- true
print(vim.api.nvim_buf_get_option(10, 'shiftwidth')) -- 4

Using meta-accessors

A few meta-accessors are available if you want to set options in a more "idiomatic" way. They essentially wrap the above API functions and allow you to manipulate options as if they were variables:

vim.o.{option}: global options
vim.bo.{option}: buffer-local options
vim.wo.{option}: window-local options

vim.o.smarttab = false
print(vim.o.smarttab) -- false

vim.bo.shiftwidth = 4
print(vim.bo.shiftwidth) -- 4

You can specify a number for buffer-local and window-local options. If no number is given, the current buffer/window is used:

vim.bo[4].expandtab = true -- same as vim.api.nvim_buf_set_option(4, 'expandtab', true)
vim.wo.number = true -- same as vim.api.nvim_win_set_option(0, 'number', true)

See also:

:help lua-vim-internal-options

Caveats

WARNING: The following section is based on a few experiments I did. The docs don't seem to mention this behavior and I haven't checked the source code to verify my claims.
TODO: Can anyone confirm this?

If you've only ever dealt with options using the :set command, the behavior of some options might surprise you.

Essentially, options can either be global, local to a buffer/window, or have both a global and a local value.

The :setglobal command sets the global value of an option. The :setlocal command sets the local value of an option. The :set command sets the global and local value of an option.

Here's a handy table from :help :setglobal:

Command	global value	local value
:set option=value	set	set
:setlocal option=value	-	set
:setglobal option=value	set	-

There is no equivalent to the :set command in Lua, you either set an option globally or locally.

You might expect the number option to be global, but the documentation describes it as being "local to window". Such options are actually "sticky": their value is copied over from the current window when you open a new one.

So if you were to set the option from your init.lua, you would do it like so:

vim.wo.number = true

Options that are "local to buffer" like shiftwidth, expandtab or undofile are even more confusing. Let's say your init.lua contains the following code:

vim.bo.expandtab = true

When you launch Neovim and start editing, everything is fine: pressing <Tab> inserts spaces instead of a tab character. Open another buffer and you're suddenly back to tabs...

Setting it globally has the opposite problem:

vim.o.expandtab = true

This time, you insert tabs when you first launch Neovim. Open another buffer and pressing <Tab> does what you expect.

In short, options that are "local to buffer" have to be set like this if you want the correct behavior:

vim.bo.expandtab = true
vim.o.expandtab = true

See also:

:help :setglobal
:help global-local

TODO: Why does this happen? Do all buffer-local options behave this way? Might be related to neovim/neovim#7658 and vim/vim#2390. Also for window-local options: neovim/neovim#11525 and vim/vim#4945

Managing vim internal variables

Using api functions

Much like options, internal variables have their own set of API functions:

Global variables (g:):
- vim.api.nvim_set_var()
- vim.api.nvim_get_var()
- vim.api.nvim_del_var()
Buffer variables (b:):
- vim.api.nvim_buf_set_var()
- vim.api.nvim_buf_get_var()
- vim.api.nvim_buf_del_var()
Window variables (w:):
- vim.api.nvim_win_set_var()
- vim.api.nvim_win_get_var()
- vim.api.nvim_win_del_var()
Tabpage variables (t:):
- vim.api.nvim_tabpage_set_var()
- vim.api.nvim_tabpage_get_var()
- vim.api.nvim_tabpage_del_var()
Predefined Vim variables (v:):
- vim.api.nvim_set_vvar()
- vim.api.nvim_get_vvar()

With the exception of predefined Vim variables, they can also be deleted (the :unlet command is the equivalent in Vimscript). Local variables (l:), script variables (s:) and function arguments (a:) cannot be manipulated as they only make sense in the context of a Vim script, Lua has its own scoping rules.

If you are unfamiliar with what these variables do, :help internal-variables describes them in detail.

These functions take a string containing the name of the variable to set/get/delete as well as the value you want to set it to.

vim.api.nvim_set_var('some_global_variable', { key1 = 'value', key2 = 300 })
print(vim.inspect(vim.api.nvim_get_var('some_global_variable'))) -- { key1 = "value", key2 = 300 }
vim.api.nvim_del_var('some_global_variable')

Variables that are scoped to a buffer, a window or a tabpage also receive a number (using 0 will set/get/delete the variable for the current buffer/window/tabpage):

vim.api.nvim_win_set_var(0, 'some_window_variable', 2500)
vim.api.nvim_tab_set_var(3, 'some_tabpage_variable', 'hello world')
print(vim.api.nvim_win_get_var(0, 'some_window_variable')) -- 2500
print(vim.api.nvim_buf_get_var(3, 'some_tabpage_variable')) -- 'hello world'
vim.api.nvim_win_del_var(0, 'some_window_variable')
vim.api.nvim_buf_del_var(3, 'some_tabpage_variable')

Using meta-accessors

Internal variables can be manipulated more intuitively using these meta-accessors:

vim.g.{name}: global variables
vim.b.{name}: buffer variables
vim.w.{name}: window variables
vim.t.{name}: tabpage variables
vim.v.{name}: predefined Vim variables

vim.g.some_global_variable = {
    key1 = 'value',
    key2 = 300
}

print(vim.inspect(vim.g.some_global_variable)) -- { key1 = "value", key2 = 300 }

To delete one of these variables, simply assign nil to it:

vim.g.some_global_variable = nil

Caveats

Unlike options meta-accessors, you cannot specify a number for buffer/window/tabpage-scoped variables.

Additionally, you cannot add/update/delete keys from a dictionary stored in one of these variables. For example, this snippet of Vimscript code does not work as expected:

let g:variable = {}
lua vim.g.variable.key = 'a'
echo g:variable
" {}

This is a known issue:

Issue #12544

Calling Vimscript functions

vim.call()

vim.call() calls a Vimscript function. This can either be a built-in Vim function or a user function. Again, data types are converted back and forth from Lua to Vimscript.

It takes in the name of the function followed by the arguments you want to pass to that function:

print(vim.call('printf', 'Hello from %s', 'Lua'))

local reversed_list = vim.call('reverse', { 'a', 'b', 'c' })
print(vim.inspect(reversed_list)) -- { "c", "b", "a" }

local function print_stdout(chan_id, data, name)
    print(data[1])
end

vim.call('jobstart', 'ls', { on_stdout = print_stdout })

vim.call('my#autoload#function')

See also:

:help vim.call()

vim.fn.{function}()

vim.fn does the exact same thing as vim.call(), but looks more like a native Lua function call:

print(vim.fn.printf('Hello from %s', 'Lua'))

local reversed_list = vim.fn.reverse({ 'a', 'b', 'c' })
print(vim.inspect(reversed_list)) -- { "c", "b", "a" }

local function print_stdout(chan_id, data, name)
    print(data[1])
end

vim.fn.jobstart('ls', { on_stdout = print_stdout })

Hashes # aren't valid characters for indentifiers in Lua, so autoload functions have to be called with this syntax:

vim.fn['my#autoload#function']()

See also:

:help vim.fn

Tips

Neovim has an extensive library of powerful built-in functions that are very useful for plugins. See :help vim-function for an alphabetical list and :help function-list for a list of functions grouped by topic.

Defining mappings

Neovim provides a list of API functions to set, get and delete mappings:

Global mappings:
- vim.api.nvim_set_keymap()
- vim.api.nvim_get_keymap()
- vim.api.nvim_del_keymap()
Buffer-local mappings:
- vim.api.nvim_buf_set_keymap()
- vim.api.nvim_buf_get_keymap()
- vim.api.nvim_buf_del_keymap()

Let's start with vim.api.nvim_set_keymap() and vim.api.nvim_buf_set_keymap()

The first argument passed to the function is a string containing the name of the mode for which the mapping will take effect:

String value	Help page	Affected modes	Vimscript equivalent
`''` (an empty string)	`mapmode-nvo`	Normal, Visual, Select, Operator-pending	`:map`
`'n'`	`mapmode-n`	Normal	`:nmap`
`'v'`	`mapmode-v`	Visual and Select	`:vmap`
`'s'`	`mapmode-s`	Select	`:smap`
`'x'`	`mapmode-x`	Visual	`:xmap`
`'o'`	`mapmode-o`	Operator-pending	`:omap`
`'!'`	`mapmode-ic`	Insert and Command-line	`:map!`
`'i'`	`mapmode-i`	Insert	`:imap`
`'l'`	`mapmode-l`	Insert, Command-line, Lang-Arg	`:lmap`
`'c'`	`mapmode-c`	Command-line	`:cmap`
`'t'`	`mapmode-t`	Terminal	`:tmap`

The second argument is a string containing the left-hand side of the mapping (the key or set of keys that trigger the command defined in the mapping). An empty string is equivalent to <Nop>, which disables a key.

The third argument is a string containing the right-hand side of the mapping (the command to execute).

The final argument is a table containing boolean options for the mapping as defined in :help :map-arguments (including noremap and excluding buffer).

Buffer-local mappings also take a buffer number as their first argument (0 sets the mapping for the current buffer).

vim.api.nvim_set_keymap('n', '<leader><Space>', ':set hlsearch!<CR>', { noremap = true, silent = true })
-- :nnoremap <silent> <leader><Space> :set hlsearch<CR>

vim.api.nvim_buf_set_keymap(0, '', 'cc', 'line(".") == 1 ? "cc" : "ggcc"', { noremap = true, expr = true })
-- :noremap <buffer> <expr> cc line('.') == 1 ? 'cc' : 'ggcc'

vim.api.nvim_get_keymap() takes a string containing the shortname of the mode for which you want the list of mappings (see table above). The return value is a table containing all global mappings for the mode.

print(vim.inspect(vim.api.nvim_get_keymap('n')))
-- :verbose nmap

vim.api.nvim_buf_get_keymap() takes an additional buffer number as its first argument (0 will get mapppings for the current bufffer)

print(vim.inspect(vim.api.nvim_buf_get_keymap(0, 'i')))
-- :verbose imap <buffer>

vim.api.nvim_del_keymap() takes a mode and the left-hand side of a mapping.

vim.api.nvim_del_keymap('n', '<leader><Space>')
-- :nunmap <leader><Space>

Again, vim.api.nvim_buf_del_keymap(), takes a buffer number as its first argument, with 0 representing the current buffer.

vim.api.nvim_buf_del_keymap(0, 'i', '<Tab>')
-- :iunmap <buffer> <Tab>

Defining user commands

There is currently no interface to create user commands in Lua. It is planned, though:

Pull request #11613

For the time being, you're probably better off creating commands in Vimscript.

Defining autocommands

Augroups and autocommands do not have an interface yet but it is being worked on:

Pull request #12378

In the meantime, you can either create autocommands in Vimscript or use this wrapper from norcalli/nvim_utils

Defining syntax/highlights

The syntax API is still a work in progress. Here are a couple of pointers:

Issue #9876
tjdevries/colorbuddy.vim, a library for creating colorschemes in Lua
:help lua-treesitter

General tips and recommendations

TODO:

vim.validate()?
Add stuff about unit tests? I know Neovim uses the busted framework, but I don't know how to use it for plugins
Best practices? I'm not a Lua wizard so I wouldn't know

27 KiB Raw Blame History

Getting started using Lua in Neovim

Introduction

Learning Lua

Existing tutorials for writing Lua in Neovim

Where to put Lua files

Caveats

Tips

Using Lua from Vimscript

:lua

Caveats

:luado

:luafile

luaeval()

v:lua

Caveats

The vim namespace

Tips

Using Vimscript from Lua

vim.api.nvim_eval()

Caveats

vim.api.nvim_exec()

vim.api.nvim_command()

Tips

Managing vim options

Using api functions

Using meta-accessors

Caveats

Managing vim internal variables

Using api functions

Using meta-accessors

Caveats

Calling Vimscript functions

vim.call()

vim.fn.{function}()

Tips

Defining mappings

Defining user commands

Defining autocommands

Defining syntax/highlights

General tips and recommendations

Miscellaneous

vim.loop

vim.lsp

vim.treesitter

27 KiB

Raw Blame History