Re: [PATCH 1/2] submodule: port subcommand 'set-branch' from shell to C

> For those who lack the context, during the conversion of the script
> Shourya faced an issue where the '--branch' argument did not work as
> expected. He described the issue in a private e-mail where Christian
> pointed out the following (quoting his reply hoping he doesn't mind):
>
>> On Tue, May 12, 2020 at 5:55 PM Christian Couder
> <christian.couder@gmail.com> wrote:
>>>
>>> In your commit (in submodule.sh line 781) there is:
>>>
>>>         `git ${wt_prefix:+-C "$wt_prefix"} ${prefix:+--super-prefix
>>> "$prefix"} submodule--helper set-branch ${GIT_QUIET:+--quiet}
>>> ${branch:+--branch} ${default:+--default} -- "$@"`
>>
>> Actually the issue might come from the above. I think it should use 
> ${branch:+--branch $branch} instead of ${branch:+--branch}.
>>
>> See: https://www.tldp.org/LDP/abs/html/parameter-substitution.html
>
> That's why Shourya mentions the '$branch' as extra. Of course, that's
> how it is supposed to be in the first place :)