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

> On Thu, Aug 6, 2026 at 6:38 PM Junio C Hamano <gitster@pobox.com> 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.