Merge branch 'ij/subtree-reject-v2-config' into jch

The shell script implementation of 'git subtree' has been updated to
check for the presence of the configuration file of the new Rust
implementation, preventing users from accidentally running the old
script on repositories already managed by the new tool.

* ij/subtree-reject-v2-config:
  git-subtree: Bail out if we find output from Rust rewrite (test)
  git-subtree: Bail out if we find output from Rust rewrite

contrib/subtree/git-subtree.sh

@@ -278,6 +278,20 @@ main () {
 	"cmd_$arg_command" "$@"
 }
 
+# Usage: reject_if_v2_config REV
+#
+# Bails if we find .git-subtree/config.  This file is used by the RIIR
+# git-subtree, which can read data from this script, but which generates
+# data that this script cannot cope with.  So if we find that the user's
+# project has already been processed with the new tool, we stop, to
+# avoid generating broken output.
+reject_if_v2_config () {
+	local config=.git-subtree/config
+	if git rev-parse --verify -q "$rev:$config"; then
+		die "fatal: tree contains $config: has been processed with new standalone (Rust) git-subtree; use that tool instead of this one.  See https://codeberg.org/diziet/git-subtree https://crates.io/crates/git-subtree"
+	fi
+}
+
 # Usage: cache_setup
 cache_setup () {
 	assert test $# = 0
@@ -846,6 +860,7 @@ process_split_commit () {
 #    Or: cmd_add REPOSITORY REF
 cmd_add () {
 
+	reject_if_v2_config HEAD
 	ensure_clean
 
 	if test $# -eq 1
@@ -934,6 +949,8 @@ cmd_split () {
 		die "fatal: you must provide exactly one revision, and optionally a repository.  Got: '$*'"
 	fi
 
+	reject_if_v2_config "$rev"
+
 	# Now validate prefix against the commit, not the working tree
 	if ! git cat-file -e "$rev:$dir" 2>/dev/null
 	then
@@ -1034,6 +1051,7 @@ cmd_merge () {
 	then
 		repository="$2"
 	fi
+	reject_if_v2_config HEAD
 	ensure_clean
 
 	if test -n "$arg_addmerge_squash"

contrib/subtree/t/t7900-subtree.sh

@@ -439,6 +439,24 @@ test_expect_success 'split sub dir/ with --rejoin' '
 	)
 '
 
+test_expect_success 'split fail on RIIR git subtree data' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree add --prefix="sub dir" FETCH_HEAD &&
+		# simulate RIIR git-subtree generated data
+		mkdir .git-subtree &&
+		echo "# sabotage" >.git-subtree/config &&
+		git add .git-subtree/config &&
+		git commit -m sabotage &&
+		test_must_fail git subtree split -P "sub dir" HEAD
+	)
+'
+
 # Tests that commits from other subtrees are not processed as
 # part of a split.
 #