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Programs invoked by git have libexec/git-core on $PATH

22 May 2020 in Blog

I discover a strange edge-case in my usage of git and vim together.

I posted very similar content on the git mailing list as well

I noticed something odd today—I was working in vim and spawned a new terminal with :terminal. My shell startup files, which use the location of the git binary to reconstruct paths to things like etc/bash_completion.d/git-prompt.sh and contrib/git-jump, suddenly choked. The location of the git program was suddenly different than usual!


A simple scenario where this might occur is in the following zsh code:

# zsh allows =cmd to expand to the path of the command, so echo =git is similar
# to which git or command -v git
path_to_git==git
# :h:h in an expansion is a lot like appending ../.. to go up two directories
path_to_git_jump="${git:h:h}/share/git-core/contrib/git-jump"
[[ -x "$path_to_git_jump"/git-jump ]] && path+=("$path_to_git_jump")

Here, I’m find the git executable location, moving up two directories, and then descending into share/git-core/contrib to find the git-jump script and add it to my path. This is somewhat more portable than assuming git-jump is always in the same place, and more convenient than copying that script into my own Dotfiles and managing updates for it.


After some debugging, I came to determine that this occurred, not because of vim, but because vim was launched from a git-invoked process (in this case, contrib/git-jump/git-jump). My own git-ed also suffers from this when invoked as git ed—most external git commands do not have this issue when run directly (e.g., git-ed).

The salient git code is setup_path() in exec-cmd.c and its call in git.c. They appear to coordinate to prepend the libexec directory to the environment variable PATH. This causes the location of the git binary to be (e.g.) /usr/local/libexec/git-core/git, and not (e.g.) /usr/local/bin/git.

Because subprocesses inherit environment variables from their parents, my vim process inherits the modifications to PATH from the above code. That means any shell that vim starts inherits the same modification! The net result is that if I run, say, git jump grep foo and then try to invoke :terminal or :shell, my shell complains—the git binary path is so different that it cannot properly find the git-jump script.

Unfortunately, this modification propagates to all child processes, as this simple test-case demonstrates:

# printf '%s\n' '#!/bin/sh' "printenv PATH | tr : '\n' | grep git-core" > git-show-env
# chmod u+x git-show-env
# PATH=.:$PATH git show-env
/usr/local/Cellar/git/2.26.2/libexec/git-core

While it would be nice if git didn’t modify PATH in such a way that it affected all subprocesses (i.e., if it was somehow scoped to only processes that need it), I suspect this is at best difficult and at worst highly-error prone or likely to break things.

In the (possibly eternal) interim, I would like to share some vimscript that “fixes” $PATH in vim when it detects this case. The easiest use is to drop the code in your vimrc file (usually ~/.vim/vimrc or ~/.vimrc). I’ve tried to keep it portable in terms of path separators and file paths, but I do not have a Windows box to test on.

Actually, it’s a little more aggressive than I suggested; it strips out all PATH entries ending in libexec/git-core, not just the first. But I never have libexec/git-core on my PATH anyway, so I’m not bothered by that. One could modify this function to only check the first entry (the one git would have prepended).

P.S. Does anyone know what the libexec/git-core equivalent is on Windows? This person alludes to libexec\git-core, which I think is handled by my code.

P.P.S. If your vim is old and does not have const, you can use let instead. You may need to change out the lambda {_, d -> ... } for a v:val string as well.

" When git starts up, it prepends it's libexec dir to PATH to allow it to find
" external commands.
"
" Thus, if vim is invoked via a git process (such as the contrib git-jump, my
" own git-ed, or any other usage of GIT_EDITOR/VISUAL/EDITOR in git commands, be
" they scripts or internals--with the exception of manually invoking the script
" yourself, without using git: sh .../git-jump), $PATH will contain something
" like libexec/git-core.
"
" We don't generally want it in vim's $PATH, though, as it is passed down to
" *all* subprocesses, including shells started with :terminal or :shell.
function s:fix_git_path() abort
  const slash = has('win32') ? '\' : '/'
  const git_core_base = printf('libexec%sgit-core', slash)
  " optimization: early return
  if $PATH !~# '.*'.git_core_base.'.*'
    return
  endif
  const path_sep = has('win32') ? ';' : ':'
  const path = split($PATH, path_sep)
  const path_sans_libexec_git_core = filter(path, {_, d -> d !~# '.*'.git_core_base})
  const new_path = join(path_sans_libexec_git_core, path_sep)
  let $PATH = new_path
endfunction

augroup fix_git_path
  autocmd!
  autocmd VimEnter * call s:fix_git_path()
augroup END

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