Demonstrate bugs when a directory is replaced with a symlink

This test creates two directories, a/b and a/b-2, then replaces a/b with
a symlink to a/b-2, then merges that change into the 'baseline' commit,
which contains an unrelated change.

There are two bugs:
1. 'git checkout' incorrectly deletes work tree file a/b-2/d.
2. 'git merge' incorrectly deletes work tree file a/b-2/d.

The test goes on to create another branch in which a/b-2 is replaced
with a symlink to a/b (i.e., the reverse of what was done the first
time), and merge it into the 'baseline' commit.

There is a different bug:
3. The merge should be clean, but git reports a conflict.

Signed-off-by: James Pickens <james.e.pickens@intel.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6035-merge-dir-to-symlink.sh

@@ -0,0 +1,87 @@
+#!/bin/sh
+
+test_description='merging when a directory was replaced with a symlink'
+. ./test-lib.sh
+
+test_expect_success 'create a commit where dir a/b changed to symlink' '
+	mkdir -p a/b/c a/b-2/c &&
+	> a/b/c/d &&
+	> a/b-2/c/d &&
+	> a/x &&
+	git add -A &&
+	git commit -m base &&
+	git tag start &&
+	rm -rf a/b &&
+	ln -s b-2 a/b &&
+	git add -A &&
+	git commit -m "dir to symlink"
+'
+
+test_expect_failure 'keep a/b-2/c/d across checkout' '
+	git checkout HEAD^0 &&
+	git reset --hard master &&
+	git rm --cached a/b &&
+	git commit -m "untracked symlink remains" &&
+	 git checkout start^0 &&
+	 test -f a/b-2/c/d
+'
+
+test_expect_failure 'checkout should not have deleted a/b-2/c/d' '
+	git checkout HEAD^0 &&
+	git reset --hard master &&
+	 git checkout start^0 &&
+	 test -f a/b-2/c/d
+'
+
+test_expect_success 'setup for merge test' '
+	git reset --hard &&
+	test -f a/b-2/c/d &&
+	echo x > a/x &&
+	git add a/x &&
+	git commit -m x &&
+	git tag baseline
+'
+
+test_expect_success 'do not lose a/b-2/c/d in merge (resolve)' '
+	git reset --hard &&
+	git checkout baseline^0 &&
+	git merge -s resolve master &&
+	test -h a/b &&
+	test -f a/b-2/c/d
+'
+
+test_expect_failure 'do not lose a/b-2/c/d in merge (recursive)' '
+	git reset --hard &&
+	git checkout baseline^0 &&
+	git merge -s recursive master &&
+	test -h a/b &&
+	test -f a/b-2/c/d
+'
+
+test_expect_success 'setup a merge where dir a/b-2 changed to symlink' '
+	git reset --hard &&
+	git checkout start^0 &&
+	rm -rf a/b-2 &&
+	ln -s b a/b-2 &&
+	git add -A &&
+	git commit -m "dir a/b-2 to symlink" &&
+	git tag test2
+'
+
+test_expect_failure 'merge should not have conflicts (resolve)' '
+	git reset --hard &&
+	git checkout baseline^0 &&
+	git merge -s resolve test2 &&
+	test -h a/b-2 &&
+	test -f a/b/c/d
+'
+
+test_expect_failure 'merge should not have conflicts (recursive)' '
+	git reset --hard &&
+	git checkout baseline^0 &&
+	git merge -s recursive test2 &&
+	test -h a/b-2 &&
+	test -f a/b/c/d
+'
+
+test_done