bug in rebase--interactive with squash and conflicts

[Johannes Sixt <J.Sixt@eudaptics.com>]

Hi,

There's a problem with rebase--interactive where I want to squash two
commits and the one to squash is the first in the original series. In
particular, I change the commit list from

	pick 1
	pick 2
	pick 3
to
	pick 3
	squash 1
	pick 2

In this case, the edits of commit 3 are lost. There are conflicts when
commits 3 and 1 are cherry-picked.

You can simulate the problematic case by applying this patch:

index 40d6799..861ece1 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -252,3 +252,4 @@ 'interrupted squash works as expected' '
 		echo $n >> conflict &&
-		git add conflict &&
+		echo $n > $n
+		git add conflict $n &&
 		git commit -m $n
@@ -256,3 +257,3 @@ 'interrupted squash works as expected' '
 	one=$(git rev-parse HEAD~3) &&
-	! FAKE_LINES="1 squash 3 2" git rebase -i HEAD~3 &&
+	! FAKE_LINES="3 squash 1 2" git rebase -i HEAD~3 &&
 	(echo one; echo two; echo four) > conflict &&


The test fails now, because git rebase --continue did not fail although
it should have. Run

   gitk HEAD to-be-rebased@{1}

Note that the rebase was completed, i.e. there are now 2 commits instead
of the original 3. But the file 'four' is missing and the final contents
of the file 'conflict' is

one
two
three

i.e. as if commit 3 had never taken place.

-- Hannes