when will the condition set for a plugin be fired?

[jdhao]

I am using the following config to load vim-fugitive conditionaly:

 use {'tpope/vim-fugitive', cond =
 function()
   local res = vim.fn.system('git rev-parse --is-inside-work-tree')
   if string.find(res, 'true') then
     return true
   else
     return false
   end
 end}

It only works when I first open nvim, i.e., fugitive will be loaded if the directory is a Git directory, otherwise fugitive will not be loaded.

It seems that the cond is only run when we firt enter Nvim? How can I make it also run when I change working directory inside Nvim?

[wbthomason]

Ah - yes, cond is only run when the compiled file is sourced (so, when you enter Neovim). The easiest way to do what you want is to load on the DirChanged event using the event key.

[jdhao]

If I use DirChanged event, I can not check if I am inside a Git repository (fugitive will be blindly loaded whenever I change current directory). Can I combine DirChanged with condition? I think what I want is as follows:

• If we open nvim inside a Git repository, then load fugitive.
• If we open nvim in a non-git repo and change the current working directory to a git repo, then load fugitive.

Can we achieve this with packer? I thought event and cond are exclusive, is it?

[wbthomason]

Fair point. You can achieve this, but not by simply using the event and cond keys.

• You can make an autocommand separate from packer that triggers on DirChanged and runs your "am I in a Git repository" function. Your function can then trigger a User autocommand, e.g. User InGitRepo.
• You can then load fugitive on event = User InGitRepo.

We could conceivably also make cond be checked on every attempted load of a plugin (i.e. it would run not just at startup). This wouldn't be hard to do, but I'd want to think about whether this would break other use cases. I think it wouldn't (one could always adapt their cond function to check for the original condition as well as a "have we already started", etc.). However, right now, this isn't how things work.

[jdhao]

Thanks for your kind mentor! Following your instruction, I have implemented the idea.

augroup git_repo_check
  autocmd!
  autocmd VimEnter,DirChanged * call utils#Inside_git_repo() 
augroup END

" inside ~/.config/nvim/autoload/utils.vim
" Check if we are inside a Git repo
function! utils#Inside_git_repo() abort
  let res = system('git rev-parse --is-inside-work-tree')
  if match(res, 'true') == -1
    return v:false
  else
    " Trigger a speical user autocmd
    doautocmd User InGitRepo
    return v:true
  endif
endfunction

The setting for packer:

use {'tpope/vim-fugitive', event = 'User InGitRepo'}

[WieeRd]

To anyone who stumbled upon this page while seeking for optimization,
The code above by @jdhao is now possible in pure Lua.

-- requires Neovim v0.7+
local vim = vim

local function check_git_repo()
  local cmd = "git rev-parse --is-inside-work-tree"
  if vim.fn.system(cmd) == "true\n" then
    vim.api.nvim_exec_autocmds("User", { pattern = "InGitRepo" })
    return true  -- removes autocmd after lazy loading git related plugins
  end
end

vim.api.nvim_create_autocmd(
  { "VimEnter", "DirChanged" },
  { callback = function() vim.schedule(check_git_repo) end }
)

vim.schedule is required if you want to benefit from lazy-loading and improve startup time.
Calling system() actually takes 6 times longer than loading vim-fugitive!
(at least it did on my PC, taking about 6ms and 1ms each)