Git aliases – command line autocompletion of branch names

If I run a regular git command such as git checkout I get helpful autocompletion of branch names when hitting the tab key.

I have a few git aliases which take branch names as parameters, and I’m wondering if there’s a way of getting the branch name autocompletion to work with them?

Edit:

Just to provide some clarification from the discussion in the comments, aliases with a direct mapping work fine, i.e.:

ci = commit
co = checkout

It’s ones that are a bit more involved and use $1 as a parameter that don’t, for example:

tagarchive = !f() { git tag archive/$1 origin/$1 && git push origin :$1 && git push origin archive/$1 && git branch -d $1; }; f

Answer

For git aliases, the autocomplete function for the git command (__git()) uses a call to git config --get "alias.$1" to determine that equivalent autocomplete function. This works for simple mappings but will choke on more complex aliases.

To get around this, define an autocomplete function with a name that matches your alias, i.e. _git_tagarchive(). The autocomplete function for git should pick that up and use it for autocompletion.

For example:

[me@home]$ git tagarchive <TAB><TAB>
AUTHORS             gentleSelect/       .gitignore          LICENSE             test_multiple.html  
cron/               .git/               index.html          README.md  
[me@home]$ _git_tagarchive() {
> _git_branch  # reuse that of git branch
> }
[me@home]$ git tagarchive  <TAB><TAB>
enable_multiple          master                   origin/gh-pages          v0.1                     v0.1.3 
FETCH_HEAD               ORIG_HEAD                origin/HEAD              v0.1.1                   v0.1.3.1 
HEAD                     origin/enable_multiple   origin/master            v0.1.2 

For a more permanent solution simply add the function definition to your bashrc file. Eg:

_git_tagarchive() 
{
    _git_branch
}

Note that I’ve simply reused the autocomplete function for git branch; you may wish to change this to something more suitable or write your own.

More info

This solution was identified based on an exploration of /etc/bash_completion.d/git.

Typically, aliased git commands are handled by the __git_aliased_commands() function which parses the output of git config --get "alias.$1" to decide on the autocomplete function to use. Using a more complex shell command as the alias target would understandably foil this approach.

Looking further, it appears the autocomplete function for git (_git()) chains in autocomplete function for subcommands by simple prepending the function with _git_ (with dashes (-) in the command replaced by underscores). This is done before __git_aliased_command() is checked so this is something we could use.

_git ()
{ 
   # .....
   local completion_func="_git_${command//-/_}"
   declare -f $completion_func >/dev/null && $completion_func && return

   local expansion=$(__git_aliased_command "$command")
   if [ -n "$expansion" ]; then
       completion_func="_git_${expansion//-/_}"
       declare -f $completion_func >/dev/null && $completion_func
   fi

}

The approach I’ve gone for is therefore to ensure that a function that matches your alias exists, i.e. _git_tagarchive().