Refusing to install while embedded in a git session

[jstrot]

If the GIT_DIR environment variable is set, then running git checkout can fail to install plugins but also corupt the Git repository GIT_DIR is pointing to.

---

Here's a script to reproduce the issue.

#!/bin/bash

set -eu

cd "$(dirname "$0")"

rm -Rf tmp-repro-dir

export XDG_CONFIG_HOME=$(pwd)/tmp-repro-dir/config
export XDG_DATA_HOME=$(pwd)/tmp-repro-dir/share
export GIT_EDITOR=nvim

mkdir -p tmp-repro-dir/config/nvim
cat > tmp-repro-dir/config/nvim/init.lua <<EOF

local lazypath = vim.fn.stdpath("data") .. "/lazy/lazy.nvim"
local uv = vim.uv or vim.loop
if not uv.fs_stat(lazypath) then
  -- bootstrap lazy.nvim
  -- stylua: ignore
  vim.fn.system({ "git", "clone", "--filter=blob:none", "https://github.com/folke/lazy.nvim.git", "--branch=stable", lazypath })
end
vim.opt.rtp:prepend(lazypath)

require('lazy').setup({
  {
    "nvim-treesitter/nvim-treesitter",
    opts = {
      auto_install = true,
    },
    config = function(_, opts)
      require('nvim-treesitter.install').prefer_git = true
      require('nvim-treesitter.configs').setup(opts)
    end,
  }
})

EOF

mkdir tmp-repro-dir/git-repo
cd tmp-repro-dir/git-repo
git init
export GIT_DIR=$(pwd)/.git

echo
echo "First nvim run to install plugins. Please :qa it."
echo -e "Press enter to continue." ; read
nvim

echo
echo "Next, performing a fake git commit to force treesitter to install the gitcommit parser."
echo "It is expected to fail."
echo -e "Press enter to continue." ; read
git commit --allow-empty

Save the above as "repro.sh", for example, and run it.

---

It creates a minimal Neovim configuration and an empty git repo. While doing a fake git commit, Treesitter will fail to install the gitcommit parser with the following message:

nvim-treesitter[gitcommit]: Error while checking out revision
fatal: reference is not a tree: aa5c279287f0895a7ebc76a06e55ac3e4b2df7c7

It can also corrupt the repo that GIT_DIR is pointing to, e.g.:

$ git status
error: invalid object 100644 8b79819533e4274f7b787580aa31461ba2aa67b7 for '.github/workflows/ci.yml'
fatal: unable to read ffb52abeccb5891893f58abc2f87944fc9760d00

This PR attempts to mitigate the issue by flat out refusing to install parsers while running within a Git session. The list of Git environments being used for detection is very broad: In my testing, setting GIT_DIR see ms to be a prerequisite to cause the issue but just unsetting it within Treesitter is not enough (although parser can install successfully) as it causes Git to set other variables such as GIT_INDEX_FILE and I suspect t hat may be the one doing the damage (corruption of the git repository).

[clason]

Duplicate of #6745. The actual resolution is deprecating prefer_git (which is no longer needed).

[clason]

(Although this is a cleaner fix than the closed PR.)

[clason]

Suggested change

	if luv.os_getenv(k) then
	if vim.uv.os_getenv(k) then

[clason]

Suggested change

local luv = vim.loop

[clason]

Suggested change

	-- Running `git clone` or `git checkout` while running under Git (such as
	-- editing a `git commit` message) will likely fail to install parsers
	-- (such as 'gitcommit') and can also corrupt the index file of the current
	-- Git repository.
	-- The check below will refuse to perform any risky action until a safe way
	-- is implemented.
	-- Running `git clone` or `git checkout` while running under Git (such as
	-- editing a `git commit` message) will likely fail to install parsers
	-- (such as 'gitcommit') and can also corrupt the index file of the current
	-- Git repository. Check for typical Git environment variables and abort.

[clason]

Please run stylua (from the repository root) on this file.

[clason]

(and please allow maintainers to push to your PR; you should always open PRs from your personal fork, not some other org.)

[clason]

superseded by #6960