[PATCH] replace: fix replacing object with itself

[Manzur Mukhitdinov <manzurmm@gmail.com>]

When object is replaced with itself git shows unhelpful messages like(git log):
    "fatal: replace depth too high for object <SHA1>"

Prevents user from replacing object with itself(with test for checking
this case).

Signed-off-by: Manzur Mukhitdinov <manzurmm@gmail.com>
---
 builtin/replace.c  |  8 +++-----
 t/t6050-replace.sh | 11 +++++++++--
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/builtin/replace.c b/builtin/replace.c
index 294b61b..628377a 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -157,6 +157,9 @@ static int replace_object_sha1(const char *object_ref,
 	char ref[PATH_MAX];
 	struct ref_lock *lock;
 
+	if (!hashcmp(object, repl))
+		return error("new object is the same as the old one: '%s'", sha1_to_hex(object));
+
 	obj_type = sha1_object_info(object, NULL);
 	repl_type = sha1_object_info(repl, NULL);
 	if (!force && obj_type != repl_type)
@@ -295,9 +298,6 @@ static int edit_and_replace(const char *object_ref, int force, int raw)
 
 	free(tmpfile);
 
-	if (!hashcmp(old, new))
-		return error("new object is the same as the old one: '%s'", sha1_to_hex(old));
-
 	return replace_object_sha1(object_ref, old, "replacement", new, force);
 }
 
@@ -406,8 +406,6 @@ static int create_graft(int argc, const char **argv, int force)
 
 	strbuf_release(&buf);
 
-	if (!hashcmp(old, new))
-		return error("new commit is the same as the old one: '%s'", sha1_to_hex(old));
 
 	return replace_object_sha1(old_ref, old, "replacement", new, force);
 }
diff --git a/t/t6050-replace.sh b/t/t6050-replace.sh
index 4d5a25e..5f96374 100755
--- a/t/t6050-replace.sh
+++ b/t/t6050-replace.sh
@@ -369,9 +369,8 @@ test_expect_success '--edit with and without already replaced object' '
 	git cat-file commit "$PARA3" | grep "A fake Thor"
 '
 
-test_expect_success '--edit and change nothing or command failed' '
+test_expect_success '--edit with failed editor' '
 	git replace -d "$PARA3" &&
-	test_must_fail env GIT_EDITOR=true git replace --edit "$PARA3" &&
 	test_must_fail env GIT_EDITOR="./fakeeditor;false" git replace --edit "$PARA3" &&
 	GIT_EDITOR=./fakeeditor git replace --edit "$PARA3" &&
 	git replace -l | grep "$PARA3" &&
@@ -440,4 +439,12 @@ test_expect_success GPG '--graft on a commit with a mergetag' '
 	git replace -d $HASH10
 '
 
+test_expect_success 'replacing object with itself must fail' '
+    test_must_fail git replace $HASH1 $HASH1 &&
+    HASH8=$(git rev-parse --verify HEAD) &&
+    test_must_fail git replace HEAD $HASH8 &&
+    test_must_fail git replace --graft HEAD HEAD^ &&
+    test_must_fail env GIT_EDITOR=true git replace --edit HEAD
+'
+
 test_done
-- 
1.9.1