builtin/rebase.c: make sure the active branch isn't moved when autostashing

Consider the following scenario:
    git checkout not-the-master
    work work work
    git rebase --autostash upstream master

Here 'rebase --autostash <upstream> <branch>' incorrectly moves the
active branch (not-the-master) to master (before the rebase).

The expected behavior: (58794775:/git-rebase.sh:526)
    AUTOSTASH=$(git stash create autostash)
    git reset --hard
    git checkout master
    git rebase upstream
    git stash apply $AUTOSTASH

The actual behavior: (6defce2b:/builtin/rebase.c:1062)
    AUTOSTASH=$(git stash create autostash)
    git reset --hard master
    git checkout master
    git rebase upstream
    git stash apply $AUTOSTASH

This commit reinstates the 'legacy script' behavior as introduced with
58794775: rebase: implement --[no-]autostash and rebase.autostash

Signed-off-by: Ben Wijen <ben@wijen.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/t/t3420-rebase-autostash.sh b/t/t3420-rebase-autostash.sh
index b8f4d03467..1131e0016a 100755
--- a/t/t3420-rebase-autostash.sh
+++ b/t/t3420-rebase-autostash.sh
@@ -306,4 +306,12 @@ test_expect_success 'branch is left alone when possible' '
 	test unchanged-branch = "$(git rev-parse --abbrev-ref HEAD)"
 '
 
+test_expect_success 'never change active branch' '
+	git checkout -b not-the-feature-branch unrelated-onto-branch &&
+	test_when_finished "git reset --hard && git checkout master" &&
+	echo changed >file0 &&
+	git rebase --autostash not-the-feature-branch feature-branch &&
+	test_cmp_rev not-the-feature-branch unrelated-onto-branch
+'
+
 test_done