merge-recursive: demonstrate an incorrect conflict with submodule

When one side of a merge turns a directory into a submodule, and the other
side does not touch that directory (but has other non-conflicting changes),
then a merge should succeed. But currently, it does not; it rather fails
with a file/directory conflict.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3030-merge-recursive.sh

@@ -22,6 +22,7 @@ test_expect_success 'setup 1' '
 	git branch df-2 &&
 	git branch df-3 &&
 	git branch remove &&
+	git branch submod &&
 
 	echo hello >>a &&
 	cp a d/e &&
@@ -236,6 +237,17 @@ test_expect_success 'setup 6' '
 	test_cmp expected actual
 '
 
+test_expect_success 'setup 7' '
+
+	git checkout submod &&
+	git rm d/e &&
+	test_tick &&
+	git commit -m "remove d/e" &&
+	git update-index --add --cacheinfo 160000 $c1 d &&
+	test_tick &&
+	git commit -m "make d/ a submodule"
+'
+
 test_expect_success 'merge-recursive simple' '
 
 	rm -fr [abcd] &&
@@ -551,4 +563,21 @@ test_expect_success 'merge removes empty directories' '
 	test_must_fail test -d d
 '
 
+test_expect_failure 'merge-recursive simple w/submodule' '
+
+	git checkout submod &&
+	git merge remove
+'
+
+test_expect_failure 'merge-recursive simple w/submodule result' '
+
+	git ls-files -s >actual &&
+	(
+		echo "100644 $o5 0	a"
+		echo "100644 $o0 0	c"
+		echo "160000 $c1 0	d"
+	) >expected &&
+	test_cmp expected actual
+'
+
 test_done