win32: tests around handling forbidden paths

Introduce a repository that contains some paths that were illegal
on PC-DOS circa 1981 (like `aux`, `con`, `com1`) and that in a
bizarre fit of retrocomputing, remain illegal on some "modern"
computers, despite being "new technology".

Introduce some aspirational tests that suggest that we should be
able to cope with trees and indexes that contain paths that
would be illegal on the filesystem, so that we can at least diff
them.  Further ensure that checkout will not write a repository
with forbidden paths.

tests/resources/win32-forbidden/.gitted/HEAD

+ref: refs/heads/master

tests/resources/win32-forbidden/.gitted/config

+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = false
+	logallrefupdates = true
+	ignorecase = true
+	precomposeunicode = true

tests/resources/win32-forbidden/.gitted/info/exclude

+# git ls-files --others --exclude-from=.git/info/exclude
+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~

tests/resources/win32-forbidden/.gitted/refs/heads/master

+3496991d72d500af36edef68bbfcccd1661d88db

tests/win32/forbidden.c

+#include "clar_libgit2.h"
+
+#include "repository.h"
+#include "buffer.h"
+#include "submodule.h"
+
+static const char *repo_name = "win32-forbidden";
+static git_repository *repo;
+
+void test_win32_forbidden__initialize(void)
+{
+	repo = cl_git_sandbox_init(repo_name);
+}
+
+void test_win32_forbidden__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+void test_win32_forbidden__can_open_index(void)
+{
+	git_index *index;
+	cl_git_pass(git_repository_index(&index, repo));
+	cl_assert_equal_i(7, git_index_entrycount(index));
+
+	/* ensure we can even write the unmodified index */
+	cl_git_pass(git_index_write(index));
+
+	git_index_free(index);
+}
+
+void test_win32_forbidden__can_add_forbidden_filename_with_entry(void)
+{
+	git_index *index;
+	git_index_entry entry = {{0}};
+
+	cl_git_pass(git_repository_index(&index, repo));
+
+	entry.path = "aux";
+	entry.mode = GIT_FILEMODE_BLOB;
+	git_oid_fromstr(&entry.id, "da623abd956bb2fd8052c708c7ed43f05d192d37");
+
+	cl_git_pass(git_index_add(index, &entry));
+
+	git_index_free(index);
+}
+
+void test_win32_forbidden__cannot_add_dot_git_even_with_entry(void)
+{
+	git_index *index;
+	git_index_entry entry = {{0}};
+
+	cl_git_pass(git_repository_index(&index, repo));
+
+	entry.path = "foo/.git";
+	entry.mode = GIT_FILEMODE_BLOB;
+	git_oid_fromstr(&entry.id, "da623abd956bb2fd8052c708c7ed43f05d192d37");
+
+	cl_git_fail(git_index_add(index, &entry));
+
+	git_index_free(index);
+}
+
+void test_win32_forbidden__cannot_add_forbidden_filename_from_filesystem(void)
+{
+	git_index *index;
+
+	/* since our function calls are very low-level, we can create `aux.`,
+	 * but we should not be able to add it to the index
+	 */
+	cl_git_pass(git_repository_index(&index, repo));
+	cl_git_write2file("win32-forbidden/aux.", "foo\n", 4, O_RDWR | O_CREAT, 0666);
+
+#ifdef GIT_WIN32
+	cl_git_fail(git_index_add_bypath(index, "aux."));
+#else
+	cl_git_pass(git_index_add_bypath(index, "aux."));
+#endif
+
+	cl_must_pass(p_unlink("win32-forbidden/aux."));
+	git_index_free(index);
+}
+
+static int dummy_submodule_cb(
+	git_submodule *sm, const char *name, void *payload)
+{
+	GIT_UNUSED(sm);
+	GIT_UNUSED(name);
+	GIT_UNUSED(payload);
+	return 0;
+}
+
+void test_win32_forbidden__can_diff_tree_to_index(void)
+{
+	git_diff *diff;
+	git_tree *tree;
+
+	cl_git_pass(git_repository_head_tree(&tree, repo));
+	cl_git_pass(git_diff_tree_to_index(&diff, repo, tree, NULL, NULL));
+	cl_assert_equal_i(0, git_diff_num_deltas(diff));
+	git_diff_free(diff);
+	git_tree_free(tree);
+}
+
+void test_win32_forbidden__can_diff_tree_to_tree(void)
+{
+	git_diff *diff;
+	git_tree *tree;
+
+	cl_git_pass(git_repository_head_tree(&tree, repo));
+	cl_git_pass(git_diff_tree_to_tree(&diff, repo, tree, tree, NULL));
+	cl_assert_equal_i(0, git_diff_num_deltas(diff));
+	git_diff_free(diff);
+	git_tree_free(tree);
+}
+
+void test_win32_forbidden__can_diff_index_to_workdir(void)
+{
+	git_index *index;
+	git_diff *diff;
+	const git_diff_delta *delta;
+	git_tree *tree;
+	size_t i;
+
+	cl_git_pass(git_repository_index(&index, repo));
+	cl_git_pass(git_repository_head_tree(&tree, repo));
+	cl_git_pass(git_diff_index_to_workdir(&diff, repo, index, NULL));
+
+	for (i = 0; i < git_diff_num_deltas(diff); i++) {
+		delta = git_diff_get_delta(diff, i);
+		cl_assert_equal_i(GIT_DELTA_DELETED, delta->status);
+	}
+
+	git_diff_free(diff);
+	git_tree_free(tree);
+	git_index_free(index);
+}
+
+void test_win32_forbidden__checking_out_forbidden_index_fails(void)
+{
+#ifdef GIT_WIN32
+	git_index *index;
+	git_checkout_options opts = GIT_CHECKOUT_OPTIONS_INIT;
+	git_diff *diff;
+	const git_diff_delta *delta;
+	git_tree *tree;
+	size_t num_deltas, i;
+
+	opts.checkout_strategy = GIT_CHECKOUT_FORCE;
+
+	cl_git_pass(git_repository_index(&index, repo));
+	cl_git_fail(git_checkout_index(repo, index, &opts));
+
+	cl_git_pass(git_repository_head_tree(&tree, repo));
+	cl_git_pass(git_diff_index_to_workdir(&diff, repo, index, NULL));
+
+	num_deltas = git_diff_num_deltas(diff);
+
+	cl_assert(num_deltas > 0);
+
+	for (i = 0; i < num_deltas; i++) {
+		delta = git_diff_get_delta(diff, i);
+		cl_assert_equal_i(GIT_DELTA_DELETED, delta->status);
+	}
+
+	git_diff_free(diff);
+	git_tree_free(tree);
+	git_index_free(index);
+#endif
+}
+
+void test_win32_forbidden__can_query_submodules(void)
+{
+	cl_git_pass(git_submodule_foreach(repo, dummy_submodule_cb, NULL));
+}
+
+void test_win32_forbidden__can_blame_file(void)
+{
+	git_blame *blame;
+
+	cl_git_pass(git_blame_file(&blame, repo, "aux", NULL));
+	git_blame_free(blame);
+}