Re: [RFC PATCH 3/3] filter-branch: support --submodule-filter

Thomas Rast [off-list ref] writes:

Subject: TOY PATCH: filter-branch --split-submodule

Sometimes it makes sense to split out a path not as a subdirectory
(that would be merged by subtree-merge), but as a submodule.  Since
git objects are just shaped in the right way, this is actually quite
easy to do in a way that maintains the correct history relations:

The patch from a cursory look feels sane.

Just a style, but I find

	if test -n "$split_submodule"
        then
        	sub_differs= sub_parents= sub_commit=

easier to read.  Not a biggie, as the neighbourhood in the script already
is infested in the other style, but I thought I'd mention it.

+		submodule="$(git rev-parse --verify $commit:$split_submodule 2>/dev/null)"

Do we need double quotes around it?

+		if test -z "$parents"; then
+			if test -n "$submodule"; then
+				sub_differs=t
+			fi
+		fi

	if test -z "$parents" && test -n "$submodule"
        then
        	sub_differs=t
	fi

+		for parent in $parents; do
+			if ! test "$(git rev-parse --verify $parent:$split_submodule 2>/dev/null)" = "$submodule"; then
+				sub_differs=t
+			fi

If even one of the parents is different, we say "differs"...

+		if test -n "$sub_differs"; then
+			sub_commit="$(sed -e '1,/^$/d' <../commit |
+				      git commit-tree $submodule $sub_parents)" || exit
+		else
+			for parent in $parents; do
+				sub_commit="$(git rev-parse --verify "$(map "$parent")":$split_submodule 2>/dev/null)"
+				break

... so we can just pick from the first parent and know all of them are the
same (could be empty which also is fine).  Good.