subtree: validate --prefix against commit in split

git subtree split currently validates --prefix against the working tree.
This breaks when splitting an older commit or when the working tree does
not contain the subtree, even though the commit does.

For example:

  git subtree split --prefix=pkg <commit>

fails if pkg was removed later, even though it exists in <commit>.

Fix this by validating the prefix against the specified commit using
git cat-file instead of the working tree.

Add a test to ensure this behavior does not regress.

Signed-off-by: Pushkar Singh <pushkarkumarsingh1970@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index 17106d1a72..d7f9121f2f 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -257,6 +257,9 @@ main () {
 		test -e "$arg_prefix" &&
 			die "fatal: prefix '$arg_prefix' already exists."
 		;;
+	split)
+		# checked later against the commit, not the working tree
+		;;
 	*)
 		test -e "$arg_prefix" ||
 			die "fatal: '$arg_prefix' does not exist; use 'git subtree add'"
@@ -966,6 +969,12 @@ cmd_split () {
 	else
 		die "fatal: you must provide exactly one revision, and optionally a repository.  Got: '$*'"
 	fi
+
+	# Now validate prefix against the commit, not the working tree
+	if ! git cat-file -e "$rev:$dir" 2>/dev/null
+	then
+		die "fatal: '$dir' does not exist; use 'git subtree add'"
+	fi
 	repository=""
 	if test "$#" = 2
 	then