apply: test `git_apply` application to a workdir

Introduce a standard test applying a diff to a working directory with no
complications.

tests/apply/workdir.c

+#include "clar_libgit2.h"
+#include "../merge/merge_helpers.h"
+
+static git_repository *repo;
+
+#define TEST_REPO_PATH "merge-recursive"
+
+void test_apply_workdir__initialize(void)
+{
+	repo = cl_git_sandbox_init(TEST_REPO_PATH);
+}
+
+void test_apply_workdir__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+struct iterator_compare_data {
+	struct merge_index_entry *expected;
+	size_t cnt;
+	size_t idx;
+};
+
+static int iterator_compare(const git_index_entry **entries, void *_data)
+{
+	const git_index_entry *head_entry = entries[0];
+	const git_index_entry *index_entry = entries[1];
+	const git_index_entry *workdir_entry = entries[2];
+	git_oid expected_id;
+	struct iterator_compare_data *data = (struct iterator_compare_data *)_data;
+
+	cl_assert_equal_i(GIT_IDXENTRY_STAGE(head_entry), GIT_IDXENTRY_STAGE(index_entry));
+	cl_assert_equal_oid(&head_entry->id, &index_entry->id);
+	cl_assert_equal_i(head_entry->mode, index_entry->mode);
+	cl_assert_equal_s(head_entry->path, index_entry->path);
+
+	cl_assert_equal_i(GIT_IDXENTRY_STAGE(workdir_entry), data->expected[data->idx].stage);
+	cl_git_pass(git_oid_fromstr(&expected_id, data->expected[data->idx].oid_str));
+	cl_assert_equal_oid(&workdir_entry->id, &expected_id);
+	cl_assert_equal_i(workdir_entry->mode, data->expected[data->idx].mode);
+	cl_assert_equal_s(workdir_entry->path, data->expected[data->idx].path);
+
+	if (data->idx >= data->cnt)
+		return -1;
+
+	data->idx++;
+	return 0;
+}
+
+static void validate_apply_workdir(
+	git_repository *repo,
+	struct merge_index_entry *entries,
+	size_t cnt)
+{
+	git_tree *head;
+	git_index *repo_index;
+	git_iterator *head_iterator, *index_iterator, *workdir_iterator, *iterators[3];
+	git_iterator_options workdir_opts = GIT_ITERATOR_OPTIONS_INIT;
+
+	struct iterator_compare_data data = { entries, cnt };
+
+	workdir_opts.flags |= GIT_ITERATOR_INCLUDE_HASH;
+
+	cl_git_pass(git_repository_head_tree(&head, repo));
+	cl_git_pass(git_repository_index(&repo_index, repo));
+
+	cl_git_pass(git_iterator_for_tree(&head_iterator, head, NULL));
+	cl_git_pass(git_iterator_for_index(&index_iterator, repo, repo_index, NULL));
+	cl_git_pass(git_iterator_for_workdir(&workdir_iterator, repo, repo_index, NULL, &workdir_opts));
+
+	iterators[0] = head_iterator;
+	iterators[1] = index_iterator;
+	iterators[2] = workdir_iterator;
+
+	cl_git_pass(git_iterator_walk(iterators, 3, iterator_compare, &data));
+	cl_assert_equal_i(data.idx, data.cnt);
+
+	git_iterator_free(head_iterator);
+	git_iterator_free(index_iterator);
+	git_iterator_free(workdir_iterator);
+	git_index_free(repo_index);
+	git_tree_free(head);
+}
+
+void test_apply_workdir__generated_diff(void)
+{
+	git_oid a_oid, b_oid;
+	git_commit *a_commit, *b_commit;
+	git_tree *a_tree, *b_tree;
+	git_diff *diff;
+	git_diff_options opts = GIT_DIFF_OPTIONS_INIT;
+
+	struct merge_index_entry expected[] = {
+		{ 0100644, "ffb36e513f5fdf8a6ba850a20142676a2ac4807d", 0, "asparagus.txt" },
+		{ 0100644, "68f6182f4c85d39e1309d97c7e456156dc9c0096", 0, "beef.txt" },
+		{ 0100644, "4b7c5650008b2e747fe1809eeb5a1dde0e80850a", 0, "bouilli.txt" },
+		{ 0100644, "c4e6cca3ec6ae0148ed231f97257df8c311e015f", 0, "gravy.txt" },
+		{ 0100644, "68af1fc7407fd9addf1701a87eb1c95c7494c598", 0, "oyster.txt" },
+		{ 0100644, "a7b066537e6be7109abfe4ff97b675d4e077da20", 0, "veal.txt" },
+	};
+	size_t expected_cnt = sizeof(expected) / sizeof(struct merge_index_entry);
+
+	git_oid_fromstr(&a_oid, "539bd011c4822c560c1d17cab095006b7a10f707");
+	git_oid_fromstr(&b_oid, "7c7bf85e978f1d18c0566f702d2cb7766b9c8d4f");
+
+	cl_git_pass(git_commit_lookup(&a_commit, repo, &a_oid));
+	cl_git_pass(git_commit_lookup(&b_commit, repo, &b_oid));
+
+	cl_git_pass(git_commit_tree(&a_tree, a_commit));
+	cl_git_pass(git_commit_tree(&b_tree, b_commit));
+
+	cl_git_pass(git_diff_tree_to_tree(&diff, repo, a_tree, b_tree, &opts));
+
+    cl_git_pass(git_reset(repo, (git_object *)a_commit, GIT_RESET_HARD, NULL));
+	cl_git_pass(git_apply(repo, diff, NULL));
+
+	validate_apply_workdir(repo, expected, expected_cnt);
+
+	git_diff_free(diff);
+	git_tree_free(a_tree);
+	git_tree_free(b_tree);
+	git_commit_free(a_commit);
+	git_commit_free(b_commit);
+}