How to bash complete an alias as the command

I have an alias

alias gi=git

Unlike git, gi cannot complete on subcommands, paths, branches.

How can I tell bash to "complete X as if it were Y"?

Answer

You'll probably want to add this to your .bashrc or .bash_aliases.

# load git completions
_completion_loader git

# assign git's completion function _git to gi
complete -o bashdefault -o default -o nospace -F _git gi

Alternatively you can use the following (which is pretty much equivalent):

# load git completions
. /usr/share/bash-completion/completions/git

# assign git's completion function _git to gi
__git_complete gi _git

Note, you can skip the first line (of either of the aforementioned examples) if dynamic completions are not enabled. You should probably assume it is enabled though.