patch: show copy information for identical copies

When showing copy information because we are duplicating contents,
for example, when performing a `diff --find-copies-harder -M100 -B100`,
then show copy from/to lines in a patch, and do not show context.
Ensure that we can also parse such patches.

4 files changed, 98 insertions, 13 deletions

diff --git a/tests/diff/diff_helpers.c b/tests/diff/diff_helpers.c
index 8fa8e3eb5..50752b203 100644
--- a/tests/diff/diff_helpers.c
+++ b/tests/diff/diff_helpers.c
@@ -242,18 +242,44 @@ void diff_print_raw(FILE *fp, git_diff *diff)
 			git_diff_print_callback__to_file_handle, fp ? fp : stderr));
 }
 
+static size_t num_modified_deltas(git_diff *diff)
+{
+	const git_diff_delta *delta;
+	size_t i, cnt = 0;
+
+	for (i = 0; i < git_diff_num_deltas(diff); i++) {
+		delta = git_diff_get_delta(diff, i);
+
+		if (delta->status != GIT_DELTA_UNMODIFIED)
+			cnt++;
+	}
+
+	return cnt;
+}
+
 void diff_assert_equal(git_diff *a, git_diff *b)
 {
 	const git_diff_delta *ad, *bd;
-	size_t i;
+	size_t i, j;
 
 	assert(a && b);
 
-	cl_assert_equal_i(git_diff_num_deltas(a), git_diff_num_deltas(b));
+	cl_assert_equal_i(num_modified_deltas(a), num_modified_deltas(b));
+
+	for (i = 0, j = 0;
+		i < git_diff_num_deltas(a) && j < git_diff_num_deltas(b); ) {
 
-	for (i = 0; i < git_diff_num_deltas(a); i++) {
 		ad = git_diff_get_delta(a, i);
-		bd = git_diff_get_delta(b, i);
+		bd = git_diff_get_delta(b, j);
+
+		if (ad->status == GIT_DELTA_UNMODIFIED) {
+			i++;
+			continue;
+		}
+		if (bd->status == GIT_DELTA_UNMODIFIED) {
+			j++;
+			continue;
+		}
 
 		cl_assert_equal_i(ad->status, bd->status);
 		cl_assert_equal_i(ad->flags, bd->flags);
@@ -265,15 +291,26 @@ void diff_assert_equal(git_diff *a, git_diff *b)
 		 * computed deltas will have flags of `VALID_ID` and
 		 * `EXISTS` (parsed deltas will not query the ODB.)
 		 */
-		cl_assert_equal_oid(&ad->old_file.id, &bd->old_file.id);
-		cl_assert_equal_i(ad->old_file.id_abbrev, bd->old_file.id_abbrev);
+
+		/* an empty id indicates that it wasn't presented, because
+		 * the diff was identical.  (eg, pure rename, mode change only, etc)
+		 */
+		if (ad->old_file.id_abbrev && bd->old_file.id_abbrev) {
+			cl_assert_equal_i(ad->old_file.id_abbrev, bd->old_file.id_abbrev);
+			cl_assert_equal_oid(&ad->old_file.id, &bd->old_file.id);
+			cl_assert_equal_i(ad->old_file.mode, bd->old_file.mode);
+		}
 		cl_assert_equal_s(ad->old_file.path, bd->old_file.path);
-		cl_assert_equal_i(ad->old_file.mode, bd->old_file.mode);
 
-		cl_assert_equal_oid(&ad->new_file.id, &bd->new_file.id);
-		cl_assert_equal_i(ad->new_file.id_abbrev, bd->new_file.id_abbrev);
+		if (ad->new_file.id_abbrev && bd->new_file.id_abbrev) {
+			cl_assert_equal_oid(&ad->new_file.id, &bd->new_file.id);
+			cl_assert_equal_i(ad->new_file.id_abbrev, bd->new_file.id_abbrev);
+			cl_assert_equal_i(ad->new_file.mode, bd->new_file.mode);
+		}
 		cl_assert_equal_s(ad->new_file.path, bd->new_file.path);
-		cl_assert_equal_i(ad->new_file.mode, bd->new_file.mode);
+
+		i++;
+		j++;
 	}
 }
 
diff --git a/tests/diff/format_email.c b/tests/diff/format_email.c
index 2e6d0368e..9f8fe3142 100644
--- a/tests/diff/format_email.c
+++ b/tests/diff/format_email.c
@@ -351,9 +351,6 @@ void test_diff_format_email__mode_change(void)
 	"diff --git a/file1.txt.renamed b/file1.txt.renamed\n" \
 	"old mode 100644\n" \
 	"new mode 100755\n" \
-	"index a97157a..a97157a\n" \
-	"--- a/file1.txt.renamed\n" \
-	"+++ b/file1.txt.renamed\n" \
 	"--\n" \
 	"libgit2 " LIBGIT2_VERSION "\n" \
 	"\n";
diff --git a/tests/diff/parse.c b/tests/diff/parse.c
index 56b98903b..83000a92d 100644
--- a/tests/diff/parse.c
+++ b/tests/diff/parse.c
@@ -143,6 +143,11 @@ void test_diff_parse__can_parse_generated_diff(void)
 		"31e47d8c1fa36d7f8d537b96158e3f024de0a9f2",
 		"2bc7f351d20b53f1c72c16c4b036e491c478c49a",
 		GIT_DIFF_INCLUDE_UNMODIFIED,
+		0);
+	test_tree_to_tree_computed_to_parsed("renames",
+		"31e47d8c1fa36d7f8d537b96158e3f024de0a9f2",
+		"2bc7f351d20b53f1c72c16c4b036e491c478c49a",
+		GIT_DIFF_INCLUDE_UNMODIFIED,
 		GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED | GIT_DIFF_FIND_EXACT_MATCH_ONLY);
 }
 
diff --git a/tests/diff/rename.c b/tests/diff/rename.c
index 5cfd8e235..c1cd25239 100644
--- a/tests/diff/rename.c
+++ b/tests/diff/rename.c
@@ -1702,3 +1702,49 @@ void test_diff_rename__blank_files_not_renamed_when_not_ignoring_whitespace(void
 	expect_files_not_renamed("", "\n\n\n\n",  GIT_DIFF_FIND_DONT_IGNORE_WHITESPACE);
 	expect_files_not_renamed("\n\n\n\n", "\r\n\r\n\r\n",  GIT_DIFF_FIND_DONT_IGNORE_WHITESPACE);
 }
+
+/* test that 100% renames and copies emit the correct patch file
+ * git diff --find-copies-harder -M100 -B100 \
+ *          31e47d8c1fa36d7f8d537b96158e3f024de0a9f2 \
+ *          2bc7f351d20b53f1c72c16c4b036e491c478c49a
+ */
+void test_diff_rename__identical(void)
+{
+	const char *old_sha = "31e47d8c1fa36d7f8d537b96158e3f024de0a9f2";
+	const char *new_sha = "2bc7f351d20b53f1c72c16c4b036e491c478c49a";
+	git_tree *old_tree, *new_tree;
+    git_diff *diff;
+	git_diff_options diff_opts = GIT_DIFF_OPTIONS_INIT;
+	git_diff_find_options find_opts = GIT_DIFF_FIND_OPTIONS_INIT;
+	git_buf diff_buf = GIT_BUF_INIT;
+	const char *expected =
+		"diff --git a/serving.txt b/sixserving.txt\n"
+		"similarity index 100%\n"
+		"rename from serving.txt\n"
+		"rename to sixserving.txt\n"
+		"diff --git a/sevencities.txt b/songofseven.txt\n"
+		"similarity index 100%\n"
+		"copy from sevencities.txt\n"
+		"copy to songofseven.txt\n";
+
+	old_tree = resolve_commit_oid_to_tree(g_repo, old_sha);
+	new_tree = resolve_commit_oid_to_tree(g_repo, new_sha);
+
+	diff_opts.flags |= GIT_DIFF_INCLUDE_UNMODIFIED;
+	find_opts.flags = GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED |
+		GIT_DIFF_FIND_EXACT_MATCH_ONLY;
+
+	cl_git_pass(git_diff_tree_to_tree(&diff,
+		g_repo, old_tree, new_tree, &diff_opts));
+	cl_git_pass(git_diff_find_similar(diff, &find_opts));
+
+	cl_git_pass(git_diff_to_buf(&diff_buf, diff, GIT_DIFF_FORMAT_PATCH));
+
+	cl_assert_equal_s(expected, diff_buf.ptr);
+
+	git_buf_free(&diff_buf);
+	git_diff_free(diff);
+	git_tree_free(old_tree);
+	git_tree_free(new_tree);
+}
+