rebase -i: demonstrate incorrect behavior of post-rewrite

The 'exec' command is sending the current commit to stopped-sha, which is
supposed to contain the original commit (before rebase). As a result, if
an 'exec' command fails, the next 'git rebase --continue' will send the
current commit as <old-sha1> to the post-rewrite hook.

The test currently fails with :

  --- expected.data       2015-05-21 17:55:29.000000000 +0000
  +++ [...]post-rewrite.data      2015-05-21 17:55:29.000000000 +0000
  @@ -1,2 +1,3 @@
   2362ae8e1b1b865e6161e6f0e165ffb974abf018 488028e9fac0b598b70cbeb594258a917e3f6fab
  +488028e9fac0b598b70cbeb594258a917e3f6fab 488028e9fac0b598b70cbeb594258a917e3f6fab
   babc8a4c7470895886fc129f1a015c486d05a351 8edffcc4e69a4e696a1d4bab047df450caf99507

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5407-post-rewrite-hook.sh

@@ -212,4 +212,21 @@ EOF
 	verify_hook_input
 '
 
+test_expect_failure 'git rebase -i (exec)' '
+	git reset --hard D &&
+	clear_hook_input &&
+	FAKE_LINES="edit 1 exec_false 2" git rebase -i B &&
+	echo something >bar &&
+	git add bar &&
+	# Fails because of exec false
+	test_must_fail git rebase --continue &&
+	git rebase --continue &&
+	echo rebase >expected.args &&
+	cat >expected.data <<EOF &&
+$(git rev-parse C) $(git rev-parse HEAD^)
+$(git rev-parse D) $(git rev-parse HEAD)
+EOF
+	verify_hook_input
+'
+
 test_done