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](https://github.com/neovim/neovim/releases/tag/nightly) 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.
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](https://learnxinyminutes.com/docs/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](https://www.youtube.com/watch?v=iMacxZQMPXs)
- The [lua-users wiki](http://lua-users.org/wiki/LuaDirectory) is full of useful information on all kinds of Lua-related topics
- The [official reference manual for Lua](https://www.lua.org/manual/5.1/) 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!
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](https://teukka.tech/luanvim.html)
- [2n.pl - How to write neovim plugins in Lua](https://www.2n.pl/blog/how-to-write-neovim-plugins-in-lua.md)
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.
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`:
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.
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 `return`ed 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`:
```vim
: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:
```vim
:luado if linenr % 2 == 0 then return line:upper() end
You might be wondering what the difference between `lua require()` and `luafile` is and whether you should use one over the other. They have different use cases:
-`require()`:
- is a built-in Lua function. It allows you to take advantage of Lua's module system
- searches for modules using the `package.path` variable (as noted earlier, you can `require()` Lua scripts located inside the `lua/` folder in your `runtimepath`)
- keeps track of what modules have been loaded and prevents a script from being parsed and executed a second time. If you change the file containing the code for a module and try to `require()` it a second time while Neovim is running, the module will not actually update
-`:luafile`:
- is an Ex command. It does not support modules
- takes a path that is either absolute or relative to the working directory of the current window
- executes the contents of a script regardless of whether it has been executed before
`:luafile` can also be useful if you want run a Lua file you are working on:
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).
```vim
" 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')
`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`:
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.
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:
```lua
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:
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.
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
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).
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:
**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.
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:
```lua
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:
```lua
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:
```lua
vim.o.expandtab = true
```
This time, you insert tabs when you first launch Neovim. Open another buffer and pressing `<Tab>` does what you expect.
**TODO**: Why does this happen? Do all buffer-local options behave this way? Might be related to [neovim/neovim#7658](https://github.com/neovim/neovim/issues/7658) and [vim/vim#2390](https://github.com/vim/vim/issues/2390). Also for window-local options: [neovim/neovim#11525](https://github.com/neovim/neovim/issues/11525) and [vim/vim#4945](https://github.com/vim/vim/issues/4945)
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.
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):
To delete one of these variables, simply assign `nil` to it:
```lua
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:
`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:
```lua
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" }
Hashes `#` aren't valid characters for indentifiers in Lua, so autoload functions have to be called with this syntax:
```lua
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.
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:
```vim
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`:
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_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.
```lua
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)
In the meantime, you can either create autocommands in Vimscript or use [this wrapper from norcalli/nvim_utils](https://github.com/norcalli/nvim_utils/blob/master/lua/nvim_utils.lua#L554-L567)
- Companion plugins like [bfredl/nvim-luadev](https://github.com/bfredl/nvim-luadev) and [rafcamlet/nvim-luapad](https://github.com/rafcamlet/nvim-luapad)
`vim.lsp` is the module that controls the built-in LSP client. The [neovim/nvim-lspconfig](https://github.com/neovim/nvim-lspconfig/) repository contains default configurations for popular language servers.
`vim.treesitter` is the module that controls the integration of the [Tree-sitter](https://tree-sitter.github.io/tree-sitter/) library in Neovim. If you want to know more about Tree-sitter, you may be interested in this [presentation (38:37)](https://www.youtube.com/watch?v=Jes3bD6P0To).
The [nvim-treesitter](https://github.com/nvim-treesitter/) organisation hosts various plugins taking advantage of the library.
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.
- [Moonscript](https://moonscript.org/)
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](https://github.com/svermeulen/nvim-moonmaker) plugin allows you to write Neovim plugins and configuration directly in Moonscript.
- [Fennel](https://fennel-lang.org/)
A lisp that compiles to Lua. You can write configuration and plugins for Neovim in Fennel with the [Olical/aniseed](https://github.com/Olical/aniseed) plugin. Additionally, the [Olical/conjure](https://github.com/Olical/conjure) plugin provides an interactive development environment that supports Fennel (among other languages).
