how to add a additional completion to the already defined git subcommand completion?

I was experimenting with custom git subcommand completion:

I am trying to extend the completion for git commit -m or git commit --message.

$HOME/.zsh/completions/_git-foo (this path is added to fpath fpath+=~/.zsh/completions)

#compdef git-foo

_git-foo() {
  _git-commit

  local -a commands
  commands=(
    'hello-git:our first autocompletion function.'
    'version:show the used gem version.'
  )

  if (( CURRENT == 3 )); then
    if [[ $words[2] == "--message" || $words[2] == "--message=" || $words[2] == "-m" ]]; then
      _describe -t commands 'commands' commands
    fi
  fi

  return 0
}

_git-foo

but the main objective is to add this additional completion to the already defined _git-commit completion without breaking the original completion function for git commit

I have tried to change the #compdef directive to #compdef git-commit and file name from _git-foo to _git-commit but it didn't work.

I was getting the following error:

_git-commit:1: maximum nested function level reached; increase FUNCNEST?
_git-commit:1: maximum nested function level reached; increase FUNCNEST?
_git-commit:1: maximum nested function level reached; increase FUNCNEST?

Creating your custom completion for a custom subcommand works fine, but how to extend the already defined git completions without breaking the original one?

Note that I'm not yet able to acheive what you're aiming to do. I am also fiddling with zsh custom autocompletion lately, hopefully what I found can help you out

In any case I'll be interested in your feedback as I'm discovering the ropes as well

Maximum nested function level error

Based on this answer from user 4015-alt:

You are attempting to define a function _git_commit which calls itself, thus creating a recursion. To prevent such mistakes from creating infinite loop, zsh will stop when the amount of nested function call reaches configured amount: FUNCNEST

Potential solution

Based on this answer from user Attila

You could save a reference to the original _git_commit completion function used natively by git, and redefine it as you need
Then use the reference you saved to call back the original completion function:

_git_commit_orig="$functions[_git_commit]"

_git_commit() {
  [...]
  _git_commit_orig "$@"
}

As mentioned by Attila:
> You wouldn't need to call compdef again, since it is already bound to that function, and you just changed the function definition.

Hope this helps