[PATCH 1/4] git-merge: test octopus with redundant parents

[Junio C Hamano <gitster@pobox.com>]

From: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>

This happens when git merge is run to merge multiple commits that are
descendants of current HEAD (or are HEAD).  We've hit this while updating
master to origin/master but accidentaly we called (while being on master):

	$ git merge master origin/master

Here is a minimal testcase:

	$ git init a && cd a
	$ echo a >a && git add a
	$ git commit -minitial
	$ echo b >a && git add a
	$ git commit -msecond
	$ git checkout master^

	$ git merge master master
	Fast-forwarding to: master
	Already up-to-date with master
	Merge made by the 'octopus' strategy.
	 a |    2 +-
	  1 files changed, 1 insertions(+), 1 deletions(-)

	$ git cat-file commit HEAD
	tree eebfed94e75e7760540d1485c740902590a00332
	parent bd679e85202280b263e20a57639a142fa14c2c64
	author Michał Kiedrowicz <michal.kiedrowicz@gmail.com> 1329132996 +0100
	committer Michał Kiedrowicz <michal.kiedrowicz@gmail.com> 1329132996 +0100

	Merge branches 'master' and 'master' into HEAD

Signed-off-by: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t6028-merge-up-to-date.sh |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/t/t6028-merge-up-to-date.sh b/t/t6028-merge-up-to-date.sh
index a91644e..824fca5 100755
--- a/t/t6028-merge-up-to-date.sh
+++ b/t/t6028-merge-up-to-date.sh
@@ -16,7 +16,12 @@ test_expect_success setup '
 	test_tick &&
 	git commit -m second &&
 	git tag c1 &&
-	git branch test
+	git branch test &&
+	echo third >file &&
+	git add file &&
+	test_tick &&
+	git commit -m third &&
+	git tag c2
 '
 
 test_expect_success 'merge -s recursive up-to-date' '
@@ -74,4 +79,14 @@ test_expect_success 'merge -s subtree up-to-date' '
 
 '
 
+test_expect_failure 'merge fast-forward octopus' '
+
+	git reset --hard c0 &&
+	test_tick &&
+	git merge c1 c2
+	expect=$(git rev-parse c2) &&
+	current=$(git rev-parse HEAD) &&
+	test "$expect" = "$current"
+'
+
 test_done
-- 
1.7.10.332.g1863c