Merge branch 'bw/rebase-merge-entire-branch'

"git rebase -m" could be asked to rebase an entire branch starting
from the root, but failed by assuming that there always is a parent
commit to the first commit on the branch.

* bw/rebase-merge-entire-branch:
  git-rebase--merge: don't include absent parent as a base

git-rebase--merge.sh

@@ -67,7 +67,9 @@ call_merge () {
 		GIT_MERGE_VERBOSITY=1 && export GIT_MERGE_VERBOSITY
 	fi
 	test -z "$strategy" && strategy=recursive
-	eval 'git-merge-$strategy' $strategy_opts '"$cmt^" -- "$hd" "$cmt"'
+	# If cmt doesn't have a parent, don't include it as a base
+	base=$(git rev-parse --verify --quiet $cmt^)
+	eval 'git-merge-$strategy' $strategy_opts $base ' -- "$hd" "$cmt"'
 	rv=$?
 	case "$rv" in
 	0)

t/t3402-rebase-merge.sh

@@ -85,6 +85,15 @@ test_expect_success 'rebase -Xtheirs' '
 	! grep 11 original
 '
 
+test_expect_success 'rebase -Xtheirs from orphan' '
+	git checkout --orphan orphan-conflicting master~2 &&
+	echo "AB $T" >> original &&
+	git commit -morphan-conflicting original &&
+	git rebase -Xtheirs master &&
+	grep AB original &&
+	! grep 11 original
+'
+
 test_expect_success 'merge and rebase should match' '
 	git diff-tree -r test-rebase test-merge >difference &&
 	if test -s difference

t/t3421-rebase-topology-linear.sh

@@ -253,7 +253,7 @@ test_run_rebase () {
 	"
 }
 test_run_rebase success ''
-test_run_rebase failure -m
+test_run_rebase success -m
 test_run_rebase success -i
 test_run_rebase success -p
 
@@ -268,7 +268,7 @@ test_run_rebase () {
 	"
 }
 test_run_rebase success ''
-test_run_rebase failure -m
+test_run_rebase success -m
 test_run_rebase success -i
 test_run_rebase failure -p