t3509: Add rename + D/F conflict testcase that recursive strategy fails

When one side of a file rename matches a directory name on the other side,
the recursive merge strategy will fail.  This is true even if the merge is
trivially resolvable.

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

t/t3509-cherry-pick-merge-df.sh

@@ -32,4 +32,70 @@ test_expect_success SYMLINKS 'Cherry-pick succeeds with rename across D/F confli
 	git cherry-pick branch
 '
 
+test_expect_success 'Setup rename with file on one side matching directory name on other' '
+	git checkout --orphan nick-testcase &&
+	git rm -rf . &&
+
+	>empty &&
+	git add empty &&
+	git commit -m "Empty file" &&
+
+	git checkout -b simple &&
+	mv empty file &&
+	mkdir empty &&
+	mv file empty &&
+	git add empty/file &&
+	git commit -m "Empty file under empty dir" &&
+
+	echo content >newfile &&
+	git add newfile &&
+	git commit -m "New file"
+'
+
+test_expect_success 'Cherry-pick succeeds with was_a_dir/file -> was_a_dir (resolve)' '
+	git reset --hard &&
+	git checkout -q nick-testcase^0 &&
+	git cherry-pick --strategy=resolve simple
+'
+
+test_expect_failure 'Cherry-pick succeeds with was_a_dir/file -> was_a_dir (recursive)' '
+	git reset --hard &&
+	git checkout -q nick-testcase^0 &&
+	git cherry-pick --strategy=recursive simple
+'
+
+test_expect_success 'Setup rename with file on one side matching different dirname on other' '
+	git reset --hard &&
+	git checkout --orphan mergeme &&
+	git rm -rf . &&
+
+	mkdir sub &&
+	mkdir othersub &&
+	echo content > sub/file &&
+	echo foo > othersub/whatever &&
+	git add -A &&
+	git commit -m "Common commmit" &&
+
+	git rm -rf othersub &&
+	git mv sub/file othersub &&
+	git commit -m "Commit to merge" &&
+
+	git checkout -b newhead mergeme~1 &&
+	>independent-change &&
+	git add independent-change &&
+	git commit -m "Completely unrelated change"
+'
+
+test_expect_success 'Cherry-pick with rename to different D/F conflict succeeds (resolve)' '
+	git reset --hard &&
+	git checkout -q newhead^0 &&
+	git cherry-pick --strategy=resolve mergeme
+'
+
+test_expect_failure 'Cherry-pick with rename to different D/F conflict succeeds (recursive)' '
+	git reset --hard &&
+	git checkout -q newhead^0 &&
+	git cherry-pick --strategy=recursive mergeme
+'
+
 test_done