t7607: add leading-path tests

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7607-merge-overwrite.sh

@@ -12,6 +12,12 @@ test_expect_success 'setup' '
 	test_commit c1a c1.c "c1 a" &&
 	git reset --hard c0 &&
 	test_commit c2 c2.c &&
+	git reset --hard c0 &&
+	mkdir sub &&
+	echo "sub/f" > sub/f &&
+	git add sub/f &&
+	git commit -m sub &&
+	git tag sub &&
 	echo "VERY IMPORTANT CHANGES" > important
 '
 
@@ -23,6 +29,14 @@ test_expect_success 'will not overwrite untracked file' '
 	test_cmp important c2.c
 '
 
+test_expect_success 'will overwrite tracked file' '
+	git reset --hard c1 &&
+	cp important c2.c &&
+	git add c2.c &&
+	git commit -m important &&
+	git checkout c2
+'
+
 test_expect_success 'will not overwrite new file' '
 	git reset --hard c1 &&
 	cp important c2.c &&
@@ -76,6 +90,43 @@ test_expect_success 'will not overwrite removed file with staged changes' '
 	test_cmp important c1.c
 '
 
+test_expect_success 'will not overwrite untracked subtree' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	mkdir -p sub/f &&
+	cp important sub/f/important &&
+	test_must_fail git merge sub &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important sub/f/important
+'
+
+test_expect_failure 'will not overwrite untracked file in leading path' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	cp important sub &&
+	test_must_fail git merge sub &&
+	test_path_is_missing .git/MERGE_HEAD &&
+	test_cmp important sub
+'
+
+test_expect_failure SYMLINKS 'will not overwrite untracked symlink in leading path' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	mkdir sub2 &&
+	ln -s sub2 sub &&
+	test_must_fail git merge sub &&
+	test_path_is_missing .git/MERGE_HEAD
+'
+
+test_expect_success SYMLINKS 'will not be confused by symlink in leading path' '
+	git reset --hard c0 &&
+	rm -rf sub &&
+	ln -s sub2 sub &&
+	git add sub &&
+	git commit -m ln &&
+	git checkout sub
+'
+
 cat >expect <<\EOF
 error: Untracked working tree file 'c0.c' would be overwritten by merge.
 fatal: read-tree failed