Re: [PATCH v4 2/3] completion: complete tracked paths for 'git diff'

On Thu, Aug 6, 2026 at 6:38 PM Junio C Hamano <[email protected]> wrote:
>
> When completing arguments for 'git diff', _git_diff() delegates to
> __git_complete_revlist_file(), which only completes revision
> references.  This is good [*], as mixing both revisions and paths in a
> single list for the user to pick from is simply too confusing.
>
> If no reference matches, or if '--' is given, however, _git_diff()
> leaves COMPREPLY empty.  Bash then falls back to default filename
> completion in $PWD.  This fails when 'git -C <path>' is used because
> $PWD is not the target repository.
>
> Update _git_diff() to use __git_complete_index_file() when '--' is
> present, or when revision reference completion yields no matching
> candidates, so that tracked paths are offered as candidates.
>
> This changes behavior even in the case where '-C <there>' is not
> used.  The new behavior omits untracked paths from suggestions when
> no revs match the prefix but matching tracked paths exist, which is
> more useful in the context of 'git diff'.

I'm looking forward to using this.  :-)

[...]
> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
> index ccd3b2a372..845fd19f70 100644
> --- a/contrib/completion/git-completion.bash
> +++ b/contrib/completion/git-completion.bash
> @@ -1981,6 +1981,10 @@ _git_diff ()
>                 esac
>                 __git_complete_revlist_file
>         fi
> +
> +       if [ ${#COMPREPLY[@]} -eq 0 ]; then
> +               __git_complete_index_file
> +       fi
>  }

Curious; __git_complete_index_file() is documented as "requires 1
argument", but you pass none here.  As far as I can tell, it works
anyway, but feels like an accident:

1.   __git_complete_index_file CALLS
      __git_index_files "$1" ...
      (Here, "$1" == "")
2.   __git_index_files "$1" ... CALLS
      __git_ls_files_helper "$root" "$1" ...
      (Here, "$1" == "", again)
3.   __git_ls_files_helper "$root" "$1" CALLS
      __git -C "$1" -c core.quotePath=false ls-files
--exclude-standard $2 -- ...
      (Note that $2 is unquoted, and since it's empty, it disappears)

It seems like it'd be better to pass an explicit "" to
__git_complete_index_file than to implicitly get it.

[...]
The rest looks good.