**ZSH Completion:**

Zsh completion are done with scripts usually located at `/usr/share/zsh/5.5/functions/Completion/Unix` (may differ depending on the distro) each command completion's script is named `_commandName`, Zsh include/handle those scripts with the environment variable `$fpath` similar to the variable `$PATH`, in this case the used script is `_git`, the location order on `$fpath` is important as Zsh use the first `_git` script that it find and ignore the others if present (also similar to `$PATH`).

**Scripting:**

Like explained on this [QA](https://unix.stackexchange.com/questions/543549/zsh-complete-relative-path-as-absolute) and **as an example**, the following function prepends `$PWD/` to any relative path before passing it to `_files`, which is the normal completion function for files.

```
_absolute_files () {
 local expansion=$PREFIX$SUFFIX; expansion=${(e)expansion}
 if [[ "${expansion%%/#}" != "${expansion:a}" ]]; then
 PREFIX="\$PWD/$PREFIX"
 fi
 _files "$@";
}
```

This works in many common cases, including recognizing paths starting with `~/` and such as absolute...

**Solution:**

The default `git` completion behavior does not include relative paths, we could edit its script and add a function like the one on the explanation above to add support for relative path **or** we could simply replace the default `git` completion with the completion plugin `gitfast` from [ohmyzsh](https://github.com/ohmyzsh/ohmyzsh) with the following steps:

Clone [ohmyzsh](https://github.com/ohmyzsh/ohmyzsh) to some location (let say `/location`):
 
 git clone https://github.com/ohmyzsh/ohmyzsh.git

Edit `~/.zshrc` and add at the bottom of the config file the following to include `gitfast`:

 fpath=( /location/ohmyzsh/plugins/gitfast $fpath ) 

The order is important as explained before and [here](https://stackoverflow.com/questions/17968024/zsh-disable-default-completion-for-make).

Update the completion cache by removing any `~/.zcompdump*` then run `compinit`.