Re: [PATCH v2 1/1] completion: load completion file for external subcommand

["SZEDER Gábor" <szeder.dev@gmail.com>]

On Tue, Apr 10, 2018 at 10:28 PM, Florian Gamböck <mail@floga.de> wrote:
> Adding external subcommands to Git is as easy as to put an executable
> file git-foo into PATH. Packaging such subcommands for a Linux
> distribution can be achieved by unpacking the executable into /usr/bin
> of the user's system. Adding system-wide completion scripts for new
> subcommands, however, can be a bit tricky.
>
> Since bash-completion started to use dynamical loading of completion
> scripts since v1.90 (preview of v2.0),

I believe the main bash-completion repository can be found at:

  https://github.com/scop/bash-completion.git

This repository still contains the branch 'dynamic-loading'; for the
record it points to 3b029892f6f9db3b7210a7f66d636be3e5ec5fa2.

Two commits on that branch are worth mentioning:

  20c05b43 (Load completions in separate files dynamically, get rid of
            have()., 2011-10-12)
  5baebf81 (Add _xfunc for loading and calling functions on demand,
            use it in apt-get, cvsps, rsync, and sshfs., 2011-10-13)

> it is no longer sufficient to
> drop a completion script of a subcommand into the standard completions
> path, /usr/share/bash-completion/completions, since this script will not
> be loaded if called as a git subcommand.
>
> For example, look at https://bugs.gentoo.org/544722. To give a short
> summary: The popular git-flow subcommand provides a completion script,
> which gets installed as /usr/share/bash-completion/completions/git-flow.
>
> If you now type into a Bash shell:
>
>     git flow <TAB>
>
> You will not get any completions, because bash-completion only loads
> completions for git and git has no idea that git-flow is defined in
> another file. You have to load this script manually or trigger the
> dynamic loader with:
>
>     git-flow <TAB> # Please notice the dash instead of whitespace
>
> This will not complete anything either, because it only defines a Bash
> function, without generating completions. But now the correct completion
> script has been loaded and the first command can use the completions.
>
> So, the goal is now to teach the git completion script to consider the
> possibility of external completion scripts for subcommands, but of
> course without breaking current workflows.
>
> I think the easiest method is to use a function that is defined by
> bash-completion v2.0+, namely __load_completion.

This is wrong, __load_completion() was introduced in cad3abfc
(__load_completion: New function, use in _completion_loader and
_xfunc, 2015-07-15), and the first release tag containg it is '2.2'
from 2016-03-03.

The release tags '1.90' and '2.0' are from 2011-11-03 and 2012-06-17,
respectively.  This leaves a couple of years long hole where
completions were already loaded dynamically but there was no
__load_completion() function.

Would it be possible to use _xfunc() instead to plug that hole?  It
seems the be tricky, because that function not only sources but also
_calls_ the completion function.

> It will take care of
> loading the correct script if present. Afterwards, the git completion
> script behaves as usual.
>
> This way we can leverage bash-completion's dynamic loading for git
> subcommands and make it easier for developers to distribute custom
> completion scripts.
>
> Signed-off-by: Florian Gamböck <mail@floga.de>
> ---
>  contrib/completion/git-completion.bash | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
> index b09c8a236..09a820990 100644
> --- a/contrib/completion/git-completion.bash
> +++ b/contrib/completion/git-completion.bash
> @@ -3096,12 +3096,22 @@ __git_main ()
>         fi
>
>         local completion_func="_git_${command//-/_}"
> +       if ! declare -f $completion_func >/dev/null 2>/dev/null &&
> +               declare -f __load_completion >/dev/null 2>/dev/null
> +       then
> +               __load_completion "git-$command"
> +       fi
>         declare -f $completion_func >/dev/null 2>/dev/null && $completion_func && return
>
>         local expansion=$(__git_aliased_command "$command")
>         if [ -n "$expansion" ]; then
>                 words[1]=$expansion
>                 completion_func="_git_${expansion//-/_}"
> +               if ! declare -f $completion_func >/dev/null 2>/dev/null &&
> +                       declare -f __load_completion >/dev/null 2>/dev/null
> +               then
> +                       __load_completion "git-$expansion"
> +               fi
>                 declare -f $completion_func >/dev/null 2>/dev/null && $completion_func
>         fi
>  }
> --
> 2.16.1
>