NeoVim - Check if a Vim function exists from Lua

Question

I plan on using vim-plug with NeoVim. So, my init.lua file will have function calls such as

vim.fn['plug#begin'](vim.fn.stdpath('data') .. '/plugged')    
vim.fn['plug#']('hoob3rt/lualine.nvim')

However, I don't want to assume vim-plug is definitely installed. I want my init.lua file to degrade gracefully if vim-plug is not installed, rather than throwing an error

E5113: Error while calling lua chunk: Vim:E117: Unknown function: plug#begin
stack traceback:
        [C]: in function 'plug#begin'
        /Users/andy/.config/nvim/init.lua:8: in main chunk

How can I check if the vim-plug functions exist before attempting to call them?

I tried print(vim.fn['plug#begin']) but that for some reason prints a non-null value: function: 0x0104ba36f0, even though the function doesn't exist.

Luatic · Accepted Answer · 2022-07-03 21:48:19Z

3

I tried print(vim.fn['plug#begin']) but that for some reason prints a non-null value: function: 0x0104ba36f0, even though the function doesn't exist.

Presumably it's returning a function that throws the error you are getting. I would thus recommend using pcall:

local success, error = pcall(vim.fn['plug#begin'], vim.fn.stdpath('data') .. '/plugged')
if not success then --[[fail gracefully]] end

caveat: this will catch any error, so you'll probably want to perform some check like if error:find"Unknown function" then ... end to only catch this specific error.

answered Jul 3, 2022 at 21:48

Luatic

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3 Comments

Andy Carlson Over a year ago

Thanks for the workaround. I'm using this for now. I requested a cleaner method in an issue: github.com/neovim/neovim/issues/19271

Justin M. Keyes Over a year ago

why not use :help exists() ?

Andy Carlson Over a year ago

@JustinM.Keyes exists() actually won't work because vim-plug is autoloaded, so exists() will return false until you trigger something in NeoVim to look for the plugin and load it, such as calling vim.fn['plug#begin']. AFTER you do that, then exists()'s output will be accurate.

Martin · Accepted Answer · 2024-02-07 08:25:01Z

0

let data_dir = has('nvim') ? stdpath('config') : '~/.vim'
if empty(glob(data_dir . '/autoload/plug.vim'))
  silent execute '!curl -fLo '.data_dir.'/autoload/plug.vim --create-dirs  https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim'
  autocmd VimEnter * PlugInstall --sync | source $MYVIMRC
endif

answered Feb 7, 2024 at 8:25

Martin

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