nvim-lua-guide/doc/nvim-lua-guide.txt

*nvim-lua-guide.txt*  Getting started using Lua in Neovim

==============================================================================
INTRODUCTION
                                                         *luaguide-introduction*

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.

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.

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:
https://learnxinyminutes.com/docs/lua/  should give you a quick overview
of the basics
-  This guide:
https://github.com/medwatt/Notes/blob/main/Lua/Lua_Quick_Guide.ipynb
is also a good resource for getting started quickly
- 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  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  with a few 5.2
extensions .

Existing tutorials for writing Lua in Neovim~

A few tutorials have already been written to help people write plugins
in Lua. Some of them helped quite a bit when writing this guide. Many
thanks to their authors.

-  teukka.tech - From init.vim to init.lua:
https://teukka.tech/luanvim.html
-  dev.to - How to write neovim plugins in Lua:
https://dev.to/2nit/how-to-write-neovim-plugins-in-lua-5cca
-  dev.to - How to make UI for neovim plugins in Lua:
https://dev.to/2nit/how-to-make-ui-for-neovim-plugins-in-lua-3b6e
-  ms-jpq - Neovim Async Tutorial:
https://ms-jpq.github.io/neovim-async-tutorial/
-  oroques.dev - Neovim 0.5 features and the switch to init.lua:
https://oroques.dev/notes/neovim-init/

Companion plugins~

-  Vimpeccable: https://github.com/svermeulen/vimpeccable  - Plugin to
help write your .vimrc in Lua
-  plenary.nvim: https://github.com/nvim-lua/plenary.nvim  - All the
lua functions I don't want to write twice
-  popup.nvim: https://github.com/nvim-lua/popup.nvim  - An implementation
of the Popup API from vim in Neovim
-  nvim_utils: https://github.com/norcalli/nvim_utils
-  nvim-luadev: https://github.com/bfredl/nvim-luadev  - REPL/debug
console for nvim lua plugins
-  nvim-luapad: https://github.com/rafcamlet/nvim-luapad  - Interactive
real time neovim scratchpad for embedded lua engine
-  nlua.nvim: https://github.com/tjdevries/nlua.nvim  - Lua Development
for Neovim
-  BetterLua.vim: https://github.com/euclidianAce/BetterLua.vim  -
Better Lua syntax highlighting in Vim/NeoVim

==============================================================================
WHERE TO PUT LUA FILES
                                               *luaguide-where-to-put-lua-files*

init.lua~

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

See also:
- |config|

Other 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). 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
having 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
special directories in your `runtimepath`. For example, Neovim can load
`plugin/foo.vim` automatically but not `plugin/foo.lua`.

See also:
-  Issue #12670: https://github.com/neovim/neovim/issues/12670

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
                                             *luaguide-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:

- |:lua|
- |:lua-heredoc|

: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 `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`:

    >
    :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:

- |: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:

- |:luafile|

luafile vs require():~

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 in `lua` folders 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:

    >
    :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()

    " 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:
- |luaeval()|

v:lua~

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.

    >
    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()
<

See also:
- |v:lua|
- |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)
<

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
                                                    *luaguide-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 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
                                             *luaguide-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	tasks: 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 mytext = 'hello world'

    function! MyFunction(text)
	echo a:text
    endfunction

    call MyFunction(mytext)
    ]],
    true)

    print(result) -- 'hello world'
<

	*Todo	tasks: The docs say that script-scope (`s:`) is supported,
	but running this snippet with a script-scoped variable throws
	an error. Why?

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

    >
    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]])
<

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})
<

See also:

- |keycodes|
- |expr-quote|
- |nvim_replace_termcodes()|

==============================================================================
MANAGING VIM OPTIONS
                                                 *luaguide-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.o.isfname = vim.o.isfname .. ',@-@' -- on Linux: set isfname+=@-@
    print(vim.o.listchars) -- '@,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)
<

See also:
- |lua-vim-options|

Caveats~

There is no equivalent to the `:set` command in Lua, you either set
an option globally or locally. If you're setting options from your
`init.lua`, some of them will require you to set both `vim.o.{option}`
and `vim.{wo/bo}.{option}` to work properly.

See also:
- |:setglobal|
- |global-local|
-  Pull request #13479: https://github.com/neovim/neovim/pull/13479

==============================================================================
MANAGING VIM INTERNAL VARIABLES
                                      *luaguide-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.env.{name}`: environment 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
<

See also:
- |lua-vim-variables|

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: https://github.com/neovim/neovim/issues/12544

==============================================================================
CALLING VIMSCRIPT FUNCTIONS
                                          *luaguide-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 })
<

Strings with invalid Lua names can be used with `vim.fn[variable]`.
For example, hashes (`#`) are not valid characters for indentifiers 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:
- |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.

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
                                                    *luaguide-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_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_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
                                               *luaguide-defining-user-commands*

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

-  Pull request #11613: https://github.com/neovim/neovim/pull/11613

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

==============================================================================
DEFINING AUTOCOMMANDS
                                                *luaguide-defining-autocommands*

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

-  Pull request #12378: https://github.com/neovim/neovim/pull/12378

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

==============================================================================
DEFINING SYNTAX/HIGHLIGHTS
                                           *luaguide-defining-syntax-highlights*

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

-  Issue #9876: https://github.com/neovim/neovim/issues/9876
-  tjdevries/colorbuddy.vim, a library for creating colorschemes in Lua:
https://github.com/tjdevries/colorbuddy.vim
- |lua-treesitter|

==============================================================================
GENERAL TIPS AND RECOMMENDATIONS
                                     *luaguide-general-tips-and-recommendations*

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]
<

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 }
<

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:

    >
    -- 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: https://github.com/mpeterv/luacheck/  to recognize
the `vim` global by putting this configuration in `~/.luacheckrc`  or
`$XDG_CONFIG_HOME/luacheck/.luacheckrc` :

    >
    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

sumneko/lua-language-server~

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.

Debugging Lua code~

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/ .

==============================================================================
MISCELLANEOUS
                                                        *luaguide-miscellaneous*

vim.loop~

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

-  Official documentation for LibUV: https://docs.libuv.org/en/v1.x/
-  Luv documentation: https://github.com/luvit/luv/blob/master/docs.md
-  teukka.tech - Using LibUV in Neovim:
https://teukka.tech/posts/2020-01-07-vimloop/

See also:
- |vim.loop|

vim.lsp~

`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.

The behavior of the client can be configured using "lsp-handlers". For
more information:
- |lsp-handler|
-  neovim/neovim#12655: https://github.com/neovim/neovim/pull/12655
-  How to migrate from diagnostic-nvim:
https://github.com/nvim-lua/diagnostic-nvim/issues/73#issue-737897078

You may also want to take a look at plugins built around the LSP client:
-  nvim-lua/completion-nvim: https://github.com/nvim-lua/completion-nvim
-  RishabhRD/nvim-lsputils: https://github.com/RishabhRD/nvim-lsputils

See also:
- |lsp|

vim.treesitter~

`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.

See also:
- |lua-treesitter|

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.

-  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 .

Other interesting projects:
-  TypeScriptToLua/TypeScriptToLua:
https://github.com/TypeScriptToLua/TypeScriptToLua
-  teal-language/tl: https://github.com/teal-language/tl
-  Haxe: https://haxe.org/
-  SwadicalRag/wasm2lua: https://github.com/SwadicalRag/wasm2lua
-  hengestone/lua-languages: https://github.com/hengestone/lua-languages

vim:tw=78:ts=8:noet:ft=help:norl: