Re: [PATCHv2 5/6] submodule update: add super-reference flag

[Junio C Hamano <gitster@pobox.com>]

Stefan Beller <sbeller@google.com> writes:

> When we have a another clone of a superproject, we may want to
> mirror the submodules using alternates. Introduce an option
> `--super-reference` that let's a user point to another superproject,
> which is assumed to have the same structure as the one they are
> running the "submodule update" command from and has all submodules
> checked out to borrow the submodule objects from within the other
> superprojects git directory.

That's much better than the previous round.

I however have trouble with the "checked out", though.  Isn't it
that it merely has to be "init"ed?  For that matter, as long as
super.git has $GIT_DIR/modules/ populated fully, it does not matter
it has checkout, and more interestingly and importantly, the
superproject mirror can even be a bare repository!

> +--super-reference <superproject repository>::
> +	This option is only valid for the update command. When update needs
> +	to clone a repository, a reference will be passed to the clone command
> +	that points at the submodule path inside the reference superproject.

"points at the submodule path inside" sounds as if we would look at

    /var/cache/super/libs/xyzzy

in the scenario in <xmqqoa57vvzl.fsf@gitster.mtv.corp.google.com>, 
when you give us "--super-reference=/var/cache/super".  Can we
clarify to avoid such a misread?

> +superreference=

Please don't name a multiple_word field "multipleword".

>  cached=
>  recursive=
>  init=
> @@ -520,6 +521,14 @@ cmd_update()
>  		--reference=*)
>  			reference="$1"
>  			;;
> +		--super-reference)
> +			case "$2" in '') usage ;; esac
> +			superreference="--super-reference=$2"
> +			shift
> +			;;
> +		--super-reference=*)
> +			superreference="$1"
> +			;;
>  		-m|--merge)
>  			update="merge"
>  			;;
> @@ -576,6 +585,7 @@ cmd_update()
>  		${prefix:+--recursive-prefix "$prefix"} \
>  		${update:+--update "$update"} \
>  		${reference:+"$reference"} \
> +		${superreference:+"$superreference"} \
>  		${depth:+--depth "$depth"} \
>  		${recommend_shallow:+"$recommend_shallow"} \
>  		${jobs:+$jobs} \