t6036: criss-cross + rename/rename(1to2)/add-source + modify/modify

This is another challenging testcase trying to exercise the virtual merge
base creation in the rename/rename(1to2) code.  A testcase is added that
we should be able to merge cleanly, but which requires a virtual merge
base to be created that is aware of rename/rename(1to2)/add-source
conflicts and can handle those.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6036-recursive-corner-cases.sh

@@ -644,4 +644,81 @@ test_expect_failure 'handle rename/rename(1to2)/modify followed by what looks li
 	test $(git rev-parse HEAD:newname) = $(git rev-parse E:newname)
 '
 
+#
+# criss-cross with rename/rename(1to2)/add-source + resolvable modify/modify:
+#
+#      B   D
+#      o---o
+#     / \ / \
+#  A o   X   ? F
+#     \ / \ /
+#      o---o
+#      C   E
+#
+#   Commit A: new file: a
+#   Commit B: rename a->b
+#   Commit C: rename a->c, add different a
+#   Commit D: merge B&C, keeping b&c and (new) a modified at beginning
+#   Commit E: merge B&C, keeping b&c and (new) a modified at end
+#
+# Merging commits D & E should result in no conflict; doing so correctly
+# requires getting the virtual merge base (from merging B&C) right, handling
+# renaming carefully (both in the virtual merge base and later), and getting
+# content merge handled.
+
+test_expect_success 'setup criss-cross + rename/rename/add + modify/modify' '
+	git rm -rf . &&
+	git clean -fdqx &&
+	rm -rf .git &&
+	git init &&
+
+	printf "lots\nof\nwords\nand\ncontent\n" >a &&
+	git add a &&
+	git commit -m A &&
+	git tag A &&
+
+	git checkout -b B A &&
+	git mv a b &&
+	git commit -m B &&
+
+	git checkout -b C A &&
+	git mv a c &&
+	printf "2\n3\n4\n5\n6\n7\n" >a &&
+	git add a &&
+	git commit -m C &&
+
+	git checkout B^0 &&
+	git merge --no-commit -s ours C^0 &&
+	git checkout C -- a c &&
+	mv a old_a &&
+	echo 1 >a &&
+	cat old_a >>a &&
+	rm old_a &&
+	git add -u &&
+	git commit -m "Merge commit C^0 into HEAD" &&
+	git tag D &&
+
+	git checkout C^0 &&
+	git merge --no-commit -s ours B^0 &&
+	git checkout B -- b &&
+	echo 8 >>a &&
+	git add -u &&
+	git commit -m "Merge commit B^0 into HEAD" &&
+	git tag E
+'
+
+test_expect_failure 'detect rename/rename/add-source for virtual merge-base' '
+	git checkout D^0 &&
+
+	git merge -s recursive E^0 &&
+
+	test 3 -eq $(git ls-files -s | wc -l) &&
+	test 0 -eq $(git ls-files -u | wc -l) &&
+	test 0 -eq $(git ls-files -o | wc -l) &&
+
+	test $(git rev-parse HEAD:b) = $(git rev-parse A:a) &&
+	test $(git rev-parse HEAD:c) = $(git rev-parse A:a) &&
+	test "$(cat a)" = "$(printf "1\n2\n3\n4\n5\n6\n7\n8\n")"
+'
+
 test_done