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Getting started using Lua in Neovim

Translations

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 at least version 0.5 of Neovim.

Learning Lua

If you are not already familiar with the language, there are plenty of resources to get started:

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.

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.

Companion plugins

Where to put Lua files

init.lua

Neovim supports loading an init.lua file for configuration instead of the usual init.vim.

Note: init.lua is of course completely optional. Support for init.vim is not going away and is still a valid option for configuration. Do keep in mind that some features are not 100% exposed to Lua yet.

See also:

Modules

Lua modules are 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). You can require() files in this folder 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 having to specify the name of the file.

require('other_modules') -- loads other_modules/init.lua

Requiring a nonexistent module or a module which contains syntax errors aborts the currently executing script. pcall() may be used to prevent errors.

local ok, _ = pcall(require, 'module_with_error')
if not ok then
  -- not loaded
end

See also:

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

Runtime files

Much like Vimscript files, Lua files can be loaded automatically from special folders in your runtimepath. Currently, the following folders are supported:

Note: in a runtime directory, all *.vim files are sourced before *.lua files.

See also:

Tips

Since runtime files aren't based on the Lua module system, two plugins can have a plugin/main.lua file without it being an issue.

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

Note: each :lua command has its own scope and variables declared with the local keyword are not accessible outside of the command. This won't work:

:lua local foo = 1
:lua print(foo)
" prints 'nil' instead of '1'

Note 2: the print() function in Lua behaves similarly to the :echomsg command. Its output is saved in the message-history and can be suppressed by the :silent command.

See also:

: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:

Sourcing Lua files

Neovim provides 3 Ex commands to source Lua files

:luafile and :source are very similar:

:luafile ~/foo/bar/baz/myluafile.lua
:luafile %
:source ~/foo/bar/baz/myluafile.lua
:source %

:source also supports ranges, which can be useful to only execute part of a script:

:1,10source

:runtime is a little different: it uses the 'runtimepath' option to determine which files to source. See :help :runtime for more details.

See also:

Sourcing a lua file vs calling require():

You might be wondering what the difference between calling the require() function and sourcing a Lua file is and whether you should prefer one way over the other. They have different use cases:

Files sourced via :source, :runtime or automatically from runtime directories will also show up in :scriptnames and --startuptime

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()

" It is also possible to pass Lua functions as values to Vim functions
lua X = function(k, v) return string.format("%s:%s", k, v) end
echo map([1, 2, 3], luaeval("X"))

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:

v:lua

This global Vim variable allows you to call Lua functions in the global namespace (_G) 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'

" 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.api.nvim_win_get_cursor(0)[2]
    return (col == 0 or vim.api.nvim_get_current_line():sub(col, col):match('%s')) and true
end
EOF

inoremap <silent> <expr> <Tab>
    \ pumvisible() ? "\<C-N>" :
    \ v:lua.check_back_space() ? "\<Tab>" :
    \ completion#trigger_completion()

" Call a function from a Lua module by using single quotes and omitting parentheses:
call v:lua.require'module'.foo()

See also:

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)

Tips

You can get Lua syntax highlighting inside .vim files by putting let g:vimsyn_embed = 'l' in your configuration file. See :help g:vimsyn_embed for more on this option.

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:

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. API functions are documented under :help api-global.

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 (in Neovim 0.7.0+, this function is built-in, see :help vim.pretty_print()):

function _G.put(...)
  local objects = {}
  for i = 1, select('#', ...) do
    local v = select(i, ...)
    table.insert(objects, vim.inspect(v))
  end

  print(table.concat(objects, '\n'))
  return ...
end

You can then inspect the contents of an object very quickly in your code or from the command-line:

put({1, 2, 3})

:lua put(vim.loop)

Alternatively, you can use the :lua command to pretty-print a Lua expression by prefixing it with = (Neovim 0.7+ only):

:lua =vim.loop

Additionally, you may find that built-in Lua functions 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 s:mytext = 'hello world'

function! s:MyFunction(text)
    echo a:text
endfunction

call s:MyFunction(s:mytext)
]],
true)

print(result) -- 'hello world'

Caveats

nvim_exec does not support script-local variables (s:) prior to Neovim 0.6.0

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')

vim.cmd()

Alias for vim.api.nvim_exec(). Only the command argument is needed, output is always set to false.

vim.cmd('buffers')
vim.cmd([[
let g:multiline_list = [
            \ 1,
            \ 2,
            \ 3,
            \ ]

echo g:multiline_list
]])

Tips

Since you have to pass strings to these functions, you often end up having to escape backslashes:

vim.cmd('%s/\\Vfoo/bar/g')

Double bracketed strings are easier to use as they do not require escaping characters:

vim.cmd([[%s/\Vfoo/bar/g]])

vim.api.nvim_replace_termcodes()

This API function allows you to escape terminal codes and Vim keycodes.

You may have come across mappings like this one:

inoremap <expr> <Tab> pumvisible() ? "\<C-N>" : "\<Tab>"

Trying to do the same in Lua can prove to be a challenge. You might be tempted to do it like this:

function _G.smart_tab()
    return vim.fn.pumvisible() == 1 and [[\<C-N>]] or [[\<Tab>]]
end

vim.api.nvim_set_keymap('i', '<Tab>', 'v:lua.smart_tab()', {expr = true, noremap = true})

only to find out that the mapping inserts \<Tab> and \<C-N> literally...

Being able to escape keycodes is actually a Vimscript feature. Aside from the usual escape sequences like \r, \42 or \x10 that are common to many programming languages, Vimscript expr-quotes (strings surrounded with double quotes) allow you to escape the human-readable representation of Vim keycodes.

Lua doesn't have such a feature built-in. Fortunately, Neovim has an API function for escaping terminal codes and keycodes: nvim_replace_termcodes()

print(vim.api.nvim_replace_termcodes('<Tab>', true, true, true))

This is a little verbose. Making a reusable wrapper can help:

-- The function is called `t` for `termcodes`.
-- You don't have to call it that, but I find the terseness convenient
local function t(str)
    -- Adjust boolean arguments as needed
    return vim.api.nvim_replace_termcodes(str, true, true, true)
end

print(t'<Tab>')

Coming back to our earlier example, this should now work as expected:

local function t(str)
    return vim.api.nvim_replace_termcodes(str, true, true, true)
end

function _G.smart_tab()
    return vim.fn.pumvisible() == 1 and t'<C-N>' or t'<Tab>'
end

vim.api.nvim_set_keymap('i', '<Tab>', 'v:lua.smart_tab()', {expr = true, noremap = true})

This is not necessary with vim.keymap.set() as it automatically transforms vim keycodes returned by Lua functions in expr mappings by default:

vim.keymap.set('i', '<Tab>', function()
    return vim.fn.pumvisible() == 1 and '<C-N>' or '<Tab>'
end, {expr = true})

See also:

Managing vim options

Using api functions

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

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.smarttab = false -- let &smarttab = v:false
print(vim.o.smarttab) -- false
vim.o.isfname = vim.o.isfname .. ',@-@' -- on Linux: let &isfname = &isfname .. ',@-@'
print(vim.o.isfname) -- '@,48-57,/,.,-,_,+,,,#,$,%,~,=,@-@'

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)

These wrappers also have more sophisticated vim.opt* variants that provide convenient mechanisms for setting options in Lua. They're similar to what you might be used to in your init.vim:

vim.opt.smarttab = false
print(vim.opt.smarttab:get()) -- false

Some options can be set using Lua tables:

vim.opt.completeopt = {'menuone', 'noselect'}
print(vim.inspect(vim.opt.completeopt:get())) -- { "menuone", "noselect" }

Wrappers for list-like, map-like and set-like options also come with methods and metamethods that work similarly to their :set+=, :set^= and :set-= counterparts in Vimscript.

vim.opt.shortmess:append({ I = true })
-- alternative form:
vim.opt.shortmess = vim.opt.shortmess + { I = true }

vim.opt.whichwrap:remove({ 'b', 's' })
-- alternative form:
vim.opt.whichwrap = vim.opt.whichwrap - { 'b', 's' }

Be sure to look at :help vim.opt for more information.

See also:

Managing vim internal variables

Using api functions

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

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

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

-- target a specific buffer/window/tabpage (Neovim 0.6+)
vim.b[2].myvar = 1

Some variable names may contain characters that cannot be used for identifiers in Lua. You can still manipulate these variables by using this syntax: vim.g['my#variable'].

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

vim.g.some_global_variable = nil

See also:

Caveats

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
" {}

You can use a temporary variable as a workaround:

let g:variable = {}
lua << EOF
local tmp = vim.g.variable
tmp.key = 'a'
vim.g.variable = tmp
EOF
echo g:variable
" {'key': 'a'}

This is a known issue:

Calling Vimscript functions

vim.fn.{function}()

vim.fn can be used to call a Vimscript function. Data types are converted back and forth from Lua to Vimscript.

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 (#) are not valid characters for identifiers in Lua, so autoload functions have to be called with this syntax:

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

The functionality of vim.fn is identical to vim.call, but allows a more Lua-like syntax.

It is distinct from vim.api.nvim_call_function in that converting Vim/Lua objects is automatic: vim.api.nvim_call_function returns a table for floating point numbers and does not accept Lua closures while vim.fn handles these types transparently.

See also:

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.

Neovim API functions can be used directly through vim.api.{..}. See :help api for information.

Caveats

Some Vim functions that should return a boolean return 1 or 0 instead. This isn't a problem in Vimscript as 1 is truthy and 0 falsy, enabling constructs like these:

if has('nvim')
    " do something...
endif

In Lua however, only false and nil are considered falsy, numbers always evaluate to true no matter their value. You have to explicitly check for 1 or 0:

if vim.fn.has('nvim') == 1 then
    -- do something...
end

Defining mappings

API functions

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

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 valueHelp pageAffected modesVimscript equivalent
'' (an empty string)mapmode-nvoNormal, Visual, Select, Operator-pending:map
'n'mapmode-nNormal:nmap
'v'mapmode-vVisual and Select:vmap
's'mapmode-sSelect:smap
'x'mapmode-xVisual:xmap
'o'mapmode-oOperator-pending:omap
'!'mapmode-icInsert and Command-line:map!
'i'mapmode-iInsert:imap
'l'mapmode-lInsert, Command-line, Lang-Arg:lmap
'c'mapmode-cCommand-line:cmap
't'mapmode-tTerminal: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). Since Neovim 0.7.0, you can also pass a callback option to invoke a Lua function instead of the right-hand side when executing the mapping.

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_set_keymap('n', '<Leader>tegf',  [[<Cmd>lua require('telescope.builtin').git_files()<CR>]], { noremap = true, silent = true })
-- :nnoremap <silent> <Leader>tegf <Cmd>lua require('telescope.builtin').git_files()<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_set_keymap('n', '<Leader>ex', '', {
    noremap = true,
    callback = function()
        print('My example')
    end,
    -- Since Lua function don't have a useful string representation, you can use the "desc" option to document your mapping
    desc = 'Prints "My example" in the message area',
})

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>

vim.keymap

:warning: The functions discussed in this section are only available in Neovim 0.7.0+

Neovim provides two functions to set/del mappings:

These are similar to the above API functions with added syntactic sugar.

vim.keymap.set() takes a string as its first argument. It can also be a table of strings to define mappings for multiple modes at once:

vim.keymap.set('n', '<Leader>ex1', '<Cmd>lua vim.notify("Example 1")<CR>')
vim.keymap.set({'n', 'c'}, '<Leader>ex2', '<Cmd>lua vim.notify("Example 2")<CR>')

The second argument is the left-hand side of the mapping.

The third argument is the right-hand side of the mapping, which can either be a string or a Lua function:

vim.keymap.set('n', '<Leader>ex1', '<Cmd>echomsg "Example 1"<CR>')
vim.keymap.set('n', '<Leader>ex2', function() print("Example 2") end)
vim.keymap.set('n', '<Leader>pl1', require('plugin').plugin_action)
-- To avoid the startup cost of requiring the module, you can wrap it in a function to require it lazily when invoking the mapping:
vim.keymap.set('n', '<Leader>pl2', function() require('plugin').plugin_action() end)

The fourth (optional) argument is a table of options that correspond to the options passed to vim.api.nvim_set_keymap(), with a few additions (see :help vim.keymap.set() for the full list).

vim.keymap.set('n', '<Leader>ex1', '<Cmd>echomsg "Example 1"<CR>', {buffer = true})
vim.keymap.set('n', '<Leader>ex2', function() print('Example 2') end, {desc = 'Prints "Example 2" to the message area'})

Defining keymaps with a Lua function is different from using a string. The usual way to show information about a keymap like :nmap <Leader>ex1 will not output useful information (the string itself), but instead only show Lua function. It is recommended to add a desc key to describe the behavior of your keymap. This is especially important for documenting plugin mappings so users can understand the usage of the keymap more easily.

An interesting feature of this API is that it irons out some historical quirks of Vim mappings:

See also:

vim.keymap.del() works the same way but deletes mappings instead:

vim.keymap.del('n', '<Leader>ex1')
vim.keymap.del({'n', 'c'}, '<Leader>ex2', {buffer = true})

Defining user commands

:warning: The API functions discussed in this section are only available in Neovim 0.7.0+

Neovim provides API functions for user-defined commands:

Let's start with vim.api.nvim_create_user_command()

The first argument passed to this function is the name of the command (which must start with an uppercase letter).

The second argument is the code to execute when invoking said command. It can either be:

A string (in which case it will be executed as Vimscript). You can use escape sequences like <q-args>, <range>, etc. like you would with :command

vim.api.nvim_create_user_command('Upper', 'echo toupper(<q-args>)', { nargs = 1 })
-- :command! -nargs=1 Upper echo toupper(<q-args>)

vim.cmd('Upper hello world') -- prints "HELLO WORLD"

Or a Lua function. It receives a dictionary-like table that contains the data normally provided by escape sequences (see :help nvim_create_user_command() for a list of available keys)

vim.api.nvim_create_user_command(
    'Upper',
    function(opts)
        print(string.upper(opts.args))
    end,
    { nargs = 1 }
)

The third argument lets you pass command attributes as a table (see :help command-attributes). Since you can already define buffer-local user commands with vim.api.nvim_buf_create_user_command(), -buffer is not a valid attribute.

Two additional attributes are available:

The -complete attribute can take a Lua function in addition to the attributes listed in :help :command-complete.

vim.api.nvim_create_user_command('Upper', function() end, {
    nargs = 1,
    complete = function(ArgLead, CmdLine, CursorPos)
        -- return completion candidates as a list-like table
        return { 'foo', 'bar', 'baz' }
    end,
})

Buffer-local user commands also take a buffer number as their first argument. This is an advantage over -buffer which can only define a command for the current buffer.

vim.api.nvim_buf_create_user_command(4, 'Upper', function() end, {})

vim.api.nvim_del_user_command() takes a command name.

vim.api.nvim_del_user_command('Upper')
-- :delcommand Upper

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

vim.api.nvim_buf_del_user_command(4, 'Upper')

See also:

Caveats

The -complete=custom attribute automatically filters completion candidates and has built-in wildcard (:help wildcard) support:

function! s:completion_function(ArgLead, CmdLine, CursorPos) abort
    return join([
        \ 'strawberry',
        \ 'star',
        \ 'stellar',
        \ ], "\n")
endfunction

command! -nargs=1 -complete=custom,s:completion_function Test echo <q-args>
" Typing `:Test st[ae]<Tab>` returns "star" and "stellar"

Passing a Lua function to complete makes it behave like customlist which leaves filtering up to the user:

vim.api.nvim_create_user_command('Test', function() end, {
    nargs = 1,
    complete = function(ArgLead, CmdLine, CursorPos)
        return {
            'strawberry',
            'star',
            'stellar',
        }
    end,
})

-- Typing `:Test z<Tab>` returns all the completion results because the list was not filtered

Defining autocommands

(this section is a work in progress)

Neovim 0.7.0 has API functions for autocommands. See :help api-autocmd for details

Defining highlights

(this section is a work in progress)

Neovim 0.7.0 has API functions for highlight groups. See also:

General tips and recommendations

Reloading cached modules

In Lua, the require() function caches modules. This is a good thing for performance, but it can make working on plugins a bit cumbersome because modules are not updated on subsequent require() calls.

If you'd like to refresh the cache for a particular module, you have to modify the package.loaded global table:

package.loaded['modname'] = nil
require('modname') -- loads an updated version of module 'modname'

The nvim-lua/plenary.nvim plugin has a custom function that does this for you.

Don't pad Lua strings!

When using double bracketed strings, resist the temptation to pad them! While it is fine to do in contexts where spaces are ignored, it can cause hard to debug issues when whitespace is significant:

vim.api.nvim_set_keymap('n', '<Leader>f', [[ <Cmd>call foo()<CR> ]], {noremap = true})

In the above example, <Leader>f is mapped to <Space><Cmd>call foo()<CR><Space> instead of <Cmd>call foo()<CR>.

Notes about Vimscript <-> Lua type conversion

Converting a variable creates a copy:

You can't directly interact with the reference to a Vim object from Lua or a Lua object from Vimscript.
For example, the map() function in Vimscript modifies a variable in place:

let s:list = [1, 2, 3]
let s:newlist = map(s:list, {_, v -> v * 2})

echo s:list
" [2, 4, 6]
echo s:newlist
" [2, 4, 6]
echo s:list is# s:newlist
" 1

Using this function from Lua creates a copy instead:

local tbl = {1, 2, 3}
local newtbl = vim.fn.map(tbl, function(_, v) return v * 2 end)

print(vim.inspect(tbl)) -- { 1, 2, 3 }
print(vim.inspect(newtbl)) -- { 2, 4, 6 }
print(tbl == newtbl) -- false

Conversion is not always possible

This mostly affects functions and tables:

Lua tables that are a mix between a List and a Dictionary can't be converted:

print(vim.fn.count({1, 1, number = 1}, 1))
-- E5100: Cannot convert given lua table: table should either have a sequence of positive integer keys or contain only string keys

While you can call Vim functions in Lua with vim.fn, you can't hold references to them. This can cause surprising behaviors:

local FugitiveHead = vim.fn.funcref('FugitiveHead')
print(FugitiveHead) -- vim.NIL

vim.cmd("let g:test_dict = {'test_lambda': {-> 1}}")
print(vim.g.test_dict.test_lambda) -- nil
print(vim.inspect(vim.g.test_dict)) -- {}

Passing Lua functions to Vim functions is OK, storing them in Vim variables is not (fixed in Neovim 0.7.0+):

-- This works:
vim.fn.jobstart({'ls'}, {
    on_stdout = function(chan_id, data, name)
        print(vim.inspect(data))
    end
})

-- This doesn't:
vim.g.test_dict = {test_lambda = function() return 1 end} -- Error: Cannot convert given lua type

Note however that doing the same from Vimscript with luaeval() does work:

let g:test_dict = {'test_lambda': luaeval('function() return 1 end')}
echo g:test_dict
" {'test_lambda': function('<lambda>4714')}

Vim booleans

A common pattern in Vim scripts is to use 1 or 0 instead of proper booleans. Indeed, Vim did not have a separate boolean type until version 7.4.1154.

Lua booleans are converted to actual booleans in Vimscript, not numbers:

lua vim.g.lua_true = true
echo g:lua_true
" v:true
lua vim.g.lua_false = false
echo g:lua_false
" v:false

Setting up linters/language servers

If you're using linters and/or language servers to get diagnostics and autocompletion for Lua projects, you may have to configure Neovim-specific settings for them. Here are a few recommended settings for popular tools:

luacheck

You can get luacheck to recognize the vim global by putting this configuration in ~/.luacheckrc (or $XDG_CONFIG_HOME/luacheck/.luacheckrc):

globals = {
    "vim",
}

The Alloyed/lua-lsp language server uses luacheck to provide linting and reads the same file.

For more information on how to configure luacheck, please refer to its documentation

sumneko/lua-language-server

The nvim-lspconfig repository contains instructions to configure sumneko/lua-language-server (the example uses the built-in LSP client but the configuration should be identical for other LSP client implementations).

For more information on how to configure sumneko/lua-language-server see "Setting"

coc.nvim

The rafcamlet/coc-nvim-lua completion source for coc.nvim provides completion items for the Neovim stdlib.

Debugging Lua code

You can debug Lua code running in a separate Neovim instance with jbyuki/one-small-step-for-vimkind

The plugin uses the Debug Adapter Protocol. Connecting to a debug adapter requires a DAP client like mfussenegger/nvim-dap or puremourning/vimspector.

Debugging Lua mappings/commands/autocommands

The :verbose command allows you to see where a mapping/command/autocommand was defined:

:verbose map m

n  m_          * <Cmd>echo 'example'<CR>
        Last set from ~/.config/nvim/init.vim line 26

By default, this feature is disabled in Lua for performance reasons. You can enable it by starting Neovim with a verbose level greater than 0:

nvim -V1

See also:

Testing Lua code

Using Luarocks packages

wbthomason/packer.nvim supports Luarocks packages. Instructions for how to set this up are available in the README

Miscellaneous

vim.loop

vim.loop is the module that exposes the LibUV API. Some resources:

See also:

vim.lsp

vim.lsp is the module that controls the built-in LSP client. The neovim/nvim-lspconfig repository contains default configurations for popular language servers.

The behavior of the client can be configured using "lsp-handlers". For more information:

You may also want to take a look at plugins built around the LSP client

See also:

vim.treesitter

vim.treesitter is the module that controls the integration of the Tree-sitter library in Neovim. If you want to know more about Tree-sitter, you may be interested in this presentation (38:37).

The nvim-treesitter organisation hosts various plugins taking advantage of the library.

See also:

Transpilers

One advantage of using Lua is that you don't actually have to write Lua code! There is a multitude of transpilers available for the language.

Probably one of the most well-known transpilers for Lua. Adds a lots of convenient features like classes, list comprehensions or function literals. The svermeulen/nvim-moonmaker plugin allows you to write Neovim plugins and configuration directly in Moonscript.

A lisp that compiles to Lua. You can write configuration and plugins for Neovim in Fennel with the Olical/aniseed or the Hotpot plugin. Additionally, the Olical/conjure plugin provides an interactive development environment that supports Fennel (among other languages).

The name Teal comes from pronouncing TL (typed lua). This is exactly what it tries to do - add strong typing to lua while otherwise remaining close to standard lua syntax. The nvim-teal-maker plugin can be used to write Neovim plugins or configuration files directly in Teal

Other interesting projects: