zsh_completion: install as _hg not hg The contrib/zsh_completion file itself says to name it _hg. With a name like `hg`, if the user has a line like `autoload ${^fpath}/*(N-.:t)` in their zshrc, it will create a shell function named `hg` that will hide the actual hg command and make hg unusable. Separately from that though, the underscore prefix makes it actually work. The zsh man page states: The convention for autoloaded functions used in completion is that they start with an underscore This does not seem to just be a "convention", though. With the ill-advised line removed from my zshrc and the file named `/usr/local/share/zsh/site-functions/hg` (without the underscore), these completions did not seem to get loaded and the ones from the zsh installation were loaded instead. If I renamed them to be `/usr/local/share/zsh/site-functions/_hg`, however, they were loaded. I manually tested the above statement by starting a new zsh instance with the file in `/usr/local/share/zsh/site-functions` with the following names: - As `hg`, `which _hg_labels` did not show anything - As `_hg`, `which _hg_labels` showed the expected function.