merge: detect delete/modechange conflict

If one side deletes a file and the other changes its
content, we notice and report a conflict. However, if
instead of changing the content, we change only the mode,
the merge does not notice (and the mode change is silently
dropped).

The trivial index merge notices the problem and correctly
leaves the conflict in the index, but both merge-recursive
and merge-one-file will silently resolve this in favor of
the deletion.  In many cases that is a sane resolution, but
we should be punting to the user whenever there is any
question. So let's detect and treat this as a conflict (in
both strategies).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-merge-one-file.sh

@@ -38,6 +38,14 @@ case "${1:-.}${2:-.}${3:-.}" in
 # Deleted in both or deleted in one and unchanged in the other
 #
 "$1.." | "$1.$1" | "$1$1.")
+	if { test -z "$6" && test "$5" != "$7"; } ||
+	   { test -z "$7" && test "$5" != "$6"; }
+	then
+		echo "ERROR: File $4 deleted on one branch but had its" >&2
+		echo "ERROR: permissions changed on the other." >&2
+		exit 1
+	fi
+
 	if test -n "$2"
 	then
 		echo "Removing $4"

merge-recursive.c

@@ -1535,13 +1535,17 @@ static int read_sha1_strbuf(const unsigned char *sha1, struct strbuf *dst)
 }
 
 static int blob_unchanged(const unsigned char *o_sha,
+			  unsigned o_mode,
 			  const unsigned char *a_sha,
+			  unsigned a_mode,
 			  int renormalize, const char *path)
 {
 	struct strbuf o = STRBUF_INIT;
 	struct strbuf a = STRBUF_INIT;
 	int ret = 0; /* assume changed for safety */
 
+	if (a_mode != o_mode)
+		return 0;
 	if (sha_eq(o_sha, a_sha))
 		return 1;
 	if (!renormalize)
@@ -1727,8 +1731,8 @@ static int process_entry(struct merge_options *o,
 	} else if (o_sha && (!a_sha || !b_sha)) {
 		/* Case A: Deleted in one */
 		if ((!a_sha && !b_sha) ||
-		    (!b_sha && blob_unchanged(o_sha, a_sha, normalize, path)) ||
-		    (!a_sha && blob_unchanged(o_sha, b_sha, normalize, path))) {
+		    (!b_sha && blob_unchanged(o_sha, o_mode, a_sha, a_mode, normalize, path)) ||
+		    (!a_sha && blob_unchanged(o_sha, o_mode, b_sha, b_mode, normalize, path))) {
 			/* Deleted in both or deleted in one and
 			 * unchanged in the other */
 			if (a_sha)

t/t6031-merge-filemode.sh

@@ -74,4 +74,27 @@ do_both_modes () {
 do_both_modes recursive
 do_both_modes resolve
 
+test_expect_success 'set up delete/modechange scenario' '
+	git reset --hard &&
+	git checkout -b deletion master &&
+	git rm file1 &&
+	git commit -m deletion
+'
+
+do_delete_modechange () {
+	strategy=$1
+	us=$2
+	them=$3
+	test_expect_success "detect delete/modechange conflict ($strategy, $us)" '
+		git reset --hard &&
+		git checkout $us &&
+		test_must_fail git merge -s $strategy $them
+	'
+}
+
+do_delete_modechange recursive b1 deletion
+do_delete_modechange recursive deletion b1
+do_delete_modechange resolve b1 deletion
+do_delete_modechange resolve deletion b1
+
 test_done