Zsh completion for custom git "bang" alias - Git branch name

Question

I have a Git alias update that I would like to outfit with branch-name completion. The alias is defined like so:

[alias]
        update = "!f() { git push . origin/$1:$1; }; f"

(It updates a local tracking branch with its upstream version, without having to check out the branch. Not really important to the specific question, though.)

I would like the command to tab-complete existing branch names for its $1 argument. I know I can define a function called _git-update to control completion, but I'm missing some pieces to get it to work:

_git-update ()
{
  ***some-function-here*** "$(__git_branch_names)"
}

I am using the completions installed on OS X by brew install zsh-completions, which is the set at https://github.com/zsh-users/zsh-completions .

(This question is directly analogous to https://stackoverflow.com/a/41307951/169947, but for Zsh instead of Bash.)

Answer 1

May be a bit preemptive, but this is working:

# provides completion options similar to git branch/rebase/log
_complete_like_git_branch() {
  __gitcomp_nl_append "FETCH_HEAD"
  __gitcomp_nl_append "HEAD"
  __gitcomp_nl_append "ORIG_HEAD"
  __gitcomp_nl_append "$(__git_heads)"
  __gitcomp_nl_append "$(__git_remote_heads)"
  __gitcomp_nl_append "$(__git_tags)"
  __gitcomp_nl_append "$(__git_complete_refs)"
}

_git_rebase_chain() { _complete_like_git_branch }

# my git "bang" alias of git log
_git_lgk() { _complete_like_git_branch }

reference: contrib/completion/git-completion.bash

Possible improvements:

• Is the above canonically correct? i.e. Using global shell functions in ~/.zshrc?
• Choices are super-similar to git rebase and git log, but are they the same?

Answer 2

i use this function to append the working branch to my PS1:

    parse_git_branch() {
        git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/(\1)/'
    }

Answer 3

If you want the same completions as another existing git subcommand (that the completion system knows about), easiest is like this:

[alias]
    update = "!f() { : git branch ; git push . origin/$1:$1; }; f"

The null command (:) followed by the git subcommand (e.g. git branch) tells the git completion system to complete your alias using the completions from the subcommand.

This functionality is built-in to the git alias system and using it means you don't have to worry about shell differences.

Answer 4

It looks like the completions in Git sources are different from those actually used by zsh, at least for the zsh Debian package. This package installs /usr/share/zsh/functions/Completion/Unix/_git which explains how to customize the completions in a comment near the beginning and with it's just a matter of defining the following function:

_git-update() { __git_branch_names }

(which can/should be made autoloaded, of course).

FWIW I wanted to avoid completing the current branch name in my own alias and I couldn't see how to exclude it when using __git_branch_names, so I ended up doing this instead:

_git-my-alias () {
        head=$(git symbolic-ref HEAD)
        for b in $(ls -1 $(git rev-parse --git-dir)/refs/heads)
        do
                if [[ "refs/heads/$b" != $head ]]
                then
                        compadd $b
                fi
        done
}