Initial implementation of diff rename detection

This implements the basis for diff rename and copy detection,
although it is based on simple SHA comparison right now instead
of using a matching algortihm.  Just as `git_diff_merge` can be
used as a post-pass on diffs to emulate certain command line
behaviors, there is a new API `git_diff_detect` which will
update a diff list in-place, adjusting some deltas to RENAMED
or COPIED state (and also, eventually, splitting MODIFIED deltas
where the change is too large into DELETED/ADDED pairs).

This also adds a new test repo that will hold rename/copy/split
scenarios.  Right now, it just has exact-match rename and copy,
but the tests are written to use tree diffs, so we should be able
to add new test scenarios easily without breaking tests.

1 files changed, 105 insertions, 0 deletions

diff --git a/tests-clar/diff/rename.c b/tests-clar/diff/rename.c
new file mode 100644
index 000000000..8a50fd5ea
--- /dev/null
+++ b/tests-clar/diff/rename.c
@@ -0,0 +1,105 @@
+#include "clar_libgit2.h"
+#include "diff_helpers.h"
+
+static git_repository *g_repo = NULL;
+
+void test_diff_rename__initialize(void)
+{
+	g_repo = cl_git_sandbox_init("renames");
+}
+
+void test_diff_rename__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+/*
+ * Renames repo has:
+ *
+ * commit 31e47d8c1fa36d7f8d537b96158e3f024de0a9f2 -
+ *   serving.txt     (25 lines)
+ *   sevencities.txt (50 lines)
+ * commit 2bc7f351d20b53f1c72c16c4b036e491c478c49a -
+ *   serving.txt     -> sixserving.txt  (rename, no change, 100% match)
+ *   sevencities.txt -> sevencities.txt (no change)
+ *   sevencities.txt -> songofseven.txt (copy, no change, 100% match)
+ *
+ * TODO: add commits with various % changes of copy / rename
+ */
+
+void test_diff_rename__match_oid(void)
+{
+	const char *old_sha = "31e47d8c1fa36d7f8d537b96158e3f024de0a9f2";
+	const char *new_sha = "2bc7f351d20b53f1c72c16c4b036e491c478c49a";
+	git_tree *old_tree, *new_tree;
+	git_diff_list *diff;
+	git_diff_options diffopts = {0};
+	git_diff_detect_options opts;
+	diff_expects exp;
+
+	old_tree = resolve_commit_oid_to_tree(g_repo, old_sha);
+	new_tree = resolve_commit_oid_to_tree(g_repo, new_sha);
+
+	/* Must pass GIT_DIFF_INCLUDE_UNMODIFIED if you expect to emulate
+	 * --find-copies-harder during rename detection...
+	 */
+	memset(&diffopts, 0, sizeof(diffopts));
+	diffopts.flags |= GIT_DIFF_INCLUDE_UNMODIFIED;
+
+	cl_git_pass(git_diff_tree_to_tree(
+		g_repo, &diffopts, old_tree, new_tree, &diff));
+
+	/* git diff --no-renames \
+	 *          31e47d8c1fa36d7f8d537b96158e3f024de0a9f2 \
+	 *          2bc7f351d20b53f1c72c16c4b036e491c478c49a
+	 */
+	memset(&exp, 0, sizeof(exp));
+	cl_git_pass(git_diff_foreach(
+		diff, &exp, diff_file_fn, diff_hunk_fn, diff_line_fn));
+
+	cl_assert_equal_i(4, exp.files);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_UNMODIFIED]);
+	cl_assert_equal_i(2, exp.file_status[GIT_DELTA_ADDED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_DELETED]);
+
+	/* git diff 31e47d8c1fa36d7f8d537b96158e3f024de0a9f2 \
+	 *          2bc7f351d20b53f1c72c16c4b036e491c478c49a
+	 */
+	cl_git_pass(git_diff_detect(diff, NULL));
+
+	memset(&exp, 0, sizeof(exp));
+	cl_git_pass(git_diff_foreach(
+		diff, &exp, diff_file_fn, diff_hunk_fn, diff_line_fn));
+
+	cl_assert_equal_i(3, exp.files);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_UNMODIFIED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_ADDED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_RENAMED]);
+
+	git_diff_list_free(diff);
+
+	cl_git_pass(git_diff_tree_to_tree(
+		g_repo, &diffopts, old_tree, new_tree, &diff));
+
+	/* git diff --find-copies-harder \
+	 *          31e47d8c1fa36d7f8d537b96158e3f024de0a9f2 \
+	 *          2bc7f351d20b53f1c72c16c4b036e491c478c49a
+	 */
+	memset(&opts, 0, sizeof(opts));
+	opts.flags = GIT_DIFF_DETECT_COPIES_FROM_UNMODIFIED;
+	cl_git_pass(git_diff_detect(diff, &opts));
+
+	memset(&exp, 0, sizeof(exp));
+	cl_git_pass(git_diff_foreach(
+		diff, &exp, diff_file_fn, diff_hunk_fn, diff_line_fn));
+
+	cl_assert_equal_i(3, exp.files);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_UNMODIFIED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_COPIED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_RENAMED]);
+
+	git_diff_list_free(diff);
+
+	git_tree_free(old_tree);
+	git_tree_free(new_tree);
+}