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The first positional argument to git switch can be a branch, e.g. git switch <branch> and it tab completes nicely.

  1. How can I make my own command with an argument that can tab complete into a git branch?

    For git banana [--optional-option] <branch> to tab complete, it does not seem to be enough to bash builtin complete -F as that would not necessarily include "banana". And also I want to amend the completions for git, not overwrite it.

  2. Does git have some subcommand or shell functions to help with this?

    I found __gitcomp but not sure how to use it

    • together with an alias
    • specifically to trigger for the 1st positional argument
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1 Answer 1

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5

The standard bash-completion module shipped with Git automatically determines all available subcommands (see [1]). If you make an alias.banana, bash-completion will recognize it. If you create a git-banana script in your usual $PATH, Git itself will recognize it as a subcommand, and so will bash-completion.

For each subcommand, the bash-completion script (see [2]) checks whether a function named _git_<subcommand> is defined in the shell (not necessarily in the file but in the "live" environment). The same file has plenty of examples – you'll want to look at the definition of _git_switch, which uses __git_complete_refs to suggest completions.

~/.bashrc

_git_banana() {
    __git_complete_refs --mode=heads
}

(Specifically for aliases, if a specific _git_<name> function does not exist, then bash-completion will actually look up the alias and will apply completion of whichever "real" Git subcommand the alias points to.)

[1] See __git_compute_all_commands in /usr/share/bash-completion/completions/git, which uses git --list-cmds=main,others,alias,nohelpers

[2] See __git_complete_command in the same file.

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8 Comments

Thanks, how can I troubleshoot this if the autocompletion doesn't kick in? I got an executable git-review visible from my path (I can complete git revi<TAB>) but I just get regular file completion when typing git review <TAB> even though I have this function declare: _git_review() { __git_complete_refs --mode=heads; }
If you run (set -x; __git_complete_command review) do you see it calling _git_review?
I get __git_complete_command: command not found, so maybe I don't have git completions fully set up?
However declaring _git_review() { __gitcomp "a b"; } does make git review <TAB> to suggest a and b.
After doing source /usr/share/bash-completion/completions/git it works to autocomplete git review <TAB>, Thanks! :) Is it also possible to support git-review<TAB>?
They are supposed to be auto-loaded by the bash-completion framework when trying to tab-complete git something<TAB>, I don't know when exactly it triggers. (It has so many completion modules that it can't really pre-load all of them upfront, it uses a lazy-load system.) I suppose you could manually source a few individual ones that you know you'll be needing, like /usr/share/bash-completion/completions/git, from your ~/.bashrc.
(Setting PS4="+\\e[34m\${BASH_SOURCE:--}:\\e[1m\$LINENO\\e[m:\${FUNCNAME:+\\e[33m\$FUNCNAME\\e[m} " might make the -x trace output more readable.)
For standalone commands like git-review, I think you could just bind the completion function using Bash's regular complete, just pre-load (i.e. manually source from your .bashrc) the Git completion module so that all of the __git_complete* helpers will be available.

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