Merge branch 'js/rebase-autostash-detach-fix'

"git rebase --autostash" did not correctly re-attach the HEAD at times.

* js/rebase-autostash-detach-fix:
  built-in rebase --autostash: leave the current branch alone if possible
  built-in rebase: demonstrate regression with --autostash

builtin/rebase.c

@@ -613,7 +613,8 @@ static int reset_head(struct object_id *oid, const char *action,
 		reflog_head = msg.buf;
 	}
 	if (!switch_to_branch)
-		ret = update_ref(reflog_head, "HEAD", oid, orig, REF_NO_DEREF,
+		ret = update_ref(reflog_head, "HEAD", oid, orig,
+				 detach_head ? REF_NO_DEREF : 0,
 				 UPDATE_REFS_MSG_ON_ERR);
 	else {
 		ret = create_symref("HEAD", switch_to_branch, msg.buf);

t/t3420-rebase-autostash.sh

@@ -361,4 +361,12 @@ test_expect_success 'autostash with dirty submodules' '
 	git rebase -i --autostash HEAD
 '
+test_expect_success 'branch is left alone when possible' '
+	git checkout -b unchanged-branch &&
+	echo changed >file0 &&
+	git rebase --autostash unchanged-branch &&
+	test changed = "$(cat file0)" &&
+	test unchanged-branch = "$(git rev-parse --abbrev-ref HEAD)"
+'
+
 test_done