t7450: test verify_path() handling of gitmodules

Commit 10ecfa7 (verify_path: disallow symlinks in .gitmodules,
2018-05-04) made it impossible to load a symlink .gitmodules file into
the index. However, there are no tests of this behavior. Let's make sure
this case is covered. We can easily reuse the test setup created by
the matching b7b1fca (fsck: complain when .gitmodules is a symlink,
2018-05-04).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7450-bad-git-dotfiles.sh

@@ -139,7 +139,7 @@ test_expect_success 'index-pack --strict works for non-repo pack' '
 	grep gitmodulesName output
 '
 
-test_expect_success 'fsck detects symlinked .gitmodules file' '
+test_expect_success 'set up repo with symlinked .gitmodules file' '
 	git init symlink &&
 	(
 		cd symlink &&
@@ -155,8 +155,14 @@ test_expect_success 'fsck detects symlinked .gitmodules file' '
 		{
 			printf "100644 blob $content\t$tricky\n" &&
 			printf "120000 blob $target\t.gitmodules\n"
-		} >bad-tree &&
-		tree=$(git mktree <bad-tree) &&
+		} >bad-tree
+	) &&
+	tree=$(git -C symlink mktree <symlink/bad-tree)
+'
+
+test_expect_success 'fsck detects symlinked .gitmodules file' '
+	(
+		cd symlink &&
 
 		# Check not only that we fail, but that it is due to the
 		# symlink detector
@@ -165,6 +171,13 @@ test_expect_success 'fsck detects symlinked .gitmodules file' '
 	)
 '
 
+test_expect_success 'refuse to load symlinked .gitmodules into index' '
+	test_must_fail git -C symlink read-tree $tree 2>err &&
+	grep "invalid path.*gitmodules" err &&
+	git -C symlink ls-files >out &&
+	test_must_be_empty out
+'
+
 test_expect_success 'fsck detects non-blob .gitmodules' '
 	git init non-blob &&
 	(