The [integration of Lua](https://www.youtube.com/watch?v=IP3J56sKtn0) as a [first-class language inside Neovim](https://github.com/neovim/neovim/wiki/FAQ#why-embed-lua-instead-of-x) 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.
- The [official reference manual for Lua](https://www.lua.org/manual/5.1/) should give you the most comprehensive tour of the language (exists as a Vimdoc plugin if you want to read it from the comfort of your editor: [wsdjeg/luarefvim](https://github.com/wsdjeg/luarefvim))
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](https://staff.fnwi.uva.nl/h.vandermeer/docs/lua/luajit/luajit_intro.html) 2.1.0, which maintains compatibility with Lua 5.1.
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)
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.
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.
Much like Vimscript files, Lua files can be loaded automatically from special folders in your `runtimepath`. Currently, the following folders are supported:
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:
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.
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
`:runtime` is a little different: it uses the `'runtimepath'` option to determine which files to source. See [`:help :runtime`](https://neovim.io/doc/user/repeat.html#:runtime) for more details.
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:
- 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
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 Lua functions in the global namespace ([`_G`](https://www.lua.org/manual/5.1/manual.html#pdf-_G)) directly from Vimscript. Again, Vim data types are converted to Lua types and vice versa.
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`](https://neovim.io/doc/user/syntax.html#g:vimsyn_embed) for more on this option.
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`](https://neovim.io/doc/user/lua.html#lua-stdlib) and [`:help lua-vim`](https://neovim.io/doc/user/lua.html#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`](https://neovim.io/doc/user/api.html#api-global).
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:
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).
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()`
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:
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`:
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.
```lua
vim.opt.shortmess:append({ I = true })
-- alternative form:
vim.opt.shortmess = vim.opt.shortmess + { I = true }
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`](https://neovim.io/doc/user/eval.html#internal-variables) describes them in detail.
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):
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']`.
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:
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.
Neovim has an extensive library of powerful built-in functions that are very useful for plugins. See [`:help vim-function`](https://neovim.io/doc/user/eval.html#vim-function) for an alphabetical list and [`:help function-list`](https://neovim.io/doc/user/usr_41.html#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`](https://neovim.io/doc/user/map.html#:map-arguments) (including `noremap` and excluding `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)
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.
require('modname') -- loads an updated version of module 'modname'
```
The [nvim-lua/plenary.nvim](https://github.com/nvim-lua/plenary.nvim) plugin has a [custom function](https://github.com/nvim-lua/plenary.nvim/blob/master/lua/plenary/reload.lua) that does this for you.
Passing Lua functions to Vim functions is OK, storing them in Vim variables is not:
```lua
-- 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:
```vim
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:
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](https://github.com/mpeterv/luacheck/) to recognize the `vim` global by putting this configuration in `~/.luacheckrc` (or `$XDG_CONFIG_HOME/luacheck/.luacheckrc`):
```lua
globals = {
"vim",
}
```
The [Alloyed/lua-lsp](https://github.com/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](https://luacheck.readthedocs.io/en/stable/config.html)
The [nvim-lspconfig](https://github.com/neovim/nvim-lspconfig/) repository contains [instructions to configure sumneko/lua-language-server](https://github.com/neovim/nvim-lspconfig/blob/master/CONFIG.md#sumneko_lua) (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](https://github.com/sumneko/lua-language-server/) see ["Setting without VSCode"](https://github.com/sumneko/lua-language-server/wiki/Setting-without-VSCode)
#### coc.nvim
The [rafcamlet/coc-nvim-lua](https://github.com/rafcamlet/coc-nvim-lua/) completion source for [coc.nvim](https://github.com/neoclide/coc.nvim/) provides completion items for the Neovim stdlib.
You can debug Lua code running in a separate Neovim instance with [jbyuki/one-small-step-for-vimkind](https://github.com/jbyuki/one-small-step-for-vimkind)
The plugin uses the [Debug Adapter Protocol](https://microsoft.github.io/debug-adapter-protocol/). Connecting to a debug adapter requires a DAP client like [mfussenegger/nvim-dap](https://github.com/mfussenegger/nvim-dap/) or [puremourning/vimspector](https://github.com/puremourning/vimspector/).
[wbthomason/packer.nvim](https://github.com/wbthomason/packer.nvim) supports Luarocks packages. Instructions for how to set this up are available in the [README](https://github.com/wbthomason/packer.nvim/#luarocks-support)
`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.
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) or the [Hotpot](https://github.com/rktjmp/hotpot.nvim) plugin. Additionally, the [Olical/conjure](https://github.com/Olical/conjure) plugin provides an interactive development environment that supports Fennel (among other languages).
