add tests for rebasing root

Signed-off-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3421-rebase-topology-linear.sh

@@ -218,4 +218,133 @@ test_run_rebase failure -m
 test_run_rebase failure -i
 test_run_rebase failure -p
 
+#       m
+#      /
+# a---b---c---g
+#
+# x---y---B
+#
+# uppercase = cherry-picked
+# m = reverted b
+#
+# Reverted patches are there for tests to be able to check if a commit
+# that introduced the same change as another commit is
+# dropped. Without reverted commits, we could get false positives
+# because applying the patch succeeds, but simply results in no
+# changes.
+test_expect_success 'setup of linear history for test involving root' '
+	git checkout b &&
+	revert m b &&
+	git checkout --orphan disjoint &&
+	git rm -rf . &&
+	test_commit x &&
+	test_commit y &&
+	cherry_pick B b
+'
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* --onto --root" "
+		reset_rebase &&
+		git rebase $* --onto c --root y &&
+		test_cmp_rev c HEAD~2 &&
+		test_linear_range 'x y' c..
+	"
+}
+test_run_rebase success ''
+test_run_rebase failure -m
+test_run_rebase success -i
+test_run_rebase success -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* without --onto --root with disjoint history" "
+		reset_rebase &&
+		git rebase $* c y &&
+		test_cmp_rev c HEAD~2 &&
+		test_linear_range 'x y' c..
+	"
+}
+test_run_rebase success ''
+test_run_rebase failure -m
+test_run_rebase success -i
+test_run_rebase failure -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* --onto --root drops patch in onto" "
+		reset_rebase &&
+		git rebase $* --onto m --root B &&
+		test_cmp_rev m HEAD~2 &&
+		test_linear_range 'x y' m..
+	"
+}
+test_run_rebase success ''
+test_run_rebase failure -m
+test_run_rebase success -i
+test_run_rebase success -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* --onto --root with merge-base does not go to root" "
+		reset_rebase &&
+		git rebase $* --onto m --root g &&
+		test_cmp_rev m HEAD~2 &&
+		test_linear_range 'c g' m..
+	"
+}
+
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
+test_run_rebase failure -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* without --onto --root with disjoint history drops patch in onto" "
+		reset_rebase &&
+		git rebase $* m B &&
+		test_cmp_rev m HEAD~2 &&
+		test_linear_range 'x y' m..
+	"
+}
+test_run_rebase success ''
+test_run_rebase failure -m
+test_run_rebase success -i
+test_run_rebase failure -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* --root on linear history is a no-op" "
+		reset_rebase &&
+		git rebase $* --root c &&
+		test_cmp_rev c HEAD
+	"
+}
+test_run_rebase failure ''
+test_run_rebase failure -m
+test_run_rebase failure -i
+test_run_rebase failure -p
+
+test_run_rebase () {
+	result=$1
+	shift
+	test_expect_$result "rebase $* -f --root on linear history causes re-write" "
+		reset_rebase &&
+		git rebase $* -f --root c &&
+		! test_cmp_rev a HEAD~2 &&
+		test_linear_range 'a b c' HEAD
+	"
+}
+test_run_rebase success ''
+test_run_rebase success -m
+test_run_rebase success -i
+test_run_rebase success -p
+
 test_done